Correlation analysis between clinical characteristics of adult patients with Mycoplasma pneumoniae pneumonia and 23S rRNA A2063 gene in alveolar lavage fluid

Abstract

Background

To investigate the clinical features and laboratory and imaging characteristics of patients with mutations in the 23S rRNA A2063G drug resistance gene in the alveolar lavage fluid of adults with MPP.

Methods

Sixty-one cases of adult MPP were retrospectively analyzed. Based on the detection of the 23S rRNA A2063G resistance gene, the patients were classified into drug resistance gene-positivity (resistance group) and drug resistance gene-negative (sensitivity group) groups. The patients' general information, clinical manifestations, and relevant laboratory and chest High-Resolution Computed Tomography (chest HRCT) data were collected. The data were analyzed by t tests, rank-sum tests, chi-square tests, multifactor logistic regression analyses and other statistical methods.

Results

Among 61 patients, 44 (72.1%) were in the resistance group, and 17 (27.9%) were in the sensitivity group. The fever rate, duration of fever and incidence of extrapulmonary complications were significantly greater in the resistance group than in the sensitivity group (P < 0.05). Fibrinogen content was significantly higher in the resistant group than in the sensitivity group (P < 0.05). Forty-two patients (95.5%) in the resistance group had imaging manifestations of centrilobular distribution, tree-in-bud sign, ground-glass opacity, and thickening of the bronchial wall, which were significantly greater than those in the sensitivity group. The difference was statistically significant (P < 0.05). Logistic regression analysis demonstrated that these imaging manifestations had a significant positive effect on the drug resistance gene-positive group.

Conclusion

Adults with MPP with 23S rRNA A2063G drug resistance gene mutation have more severe clinical presentations, higher serum fibrinogen levels and a greater incidence of extrapulmonary complications. Serum fibrinogen levels and imaging signs of infectious bronchiolitis are informative for the early identification of drug-resistant Mycoplasma pneumoniae in adults.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12890-025-03704-y.

Introduction

Mycoplasma pneumoniae (MP) is a common pathogen that causes community-acquired pneumonia [1] through acute upper and lower respiratory tract inflammation and extrapulmonary complications through adhesion to host cells and direct cytotoxic effects. In China, Mycoplasma pneumoniae pneumonia (MPP) accounts for 20.65% and 2.78% of community-acquired pneumonia in adolescents and adults, respectively [2]. Furthermore, its prevalence continues to surge, as highlighted by recent research [3]. Macrolide antibiotics are the primary therapeutic agents for addressing Mycoplasma pneumoniae pneumonia (MPP). However, an increasing number of cases of refractory Mycoplasma pneumoniae pneumonia (RMPP) have been reported, which is closely related to the increased resistance of Mycoplasma pneumoniae to macrolide antibiotics. Therefore, early identification of macrolide-resistant Mycoplasma pneumoniae (MRMP) is a positive guide for clinical treatment and disease prevention. Globally, the incidence of macrolide-resistant Mycoplasma pneumoniae (MRMP) infections surged from 18.2% in 2000 to 76.5% in 2019, with 96.8% of these cases linked to the A2063G mutation in the ribosomal 23S rRNA V region, as revealed by Kim et al. in 2022 [4]. In contrast to patients infected with macrolide-sensitive Mycoplasma pneumoniae (MSMP), patients infected with MRMP have a prolonged duration of illness, exacerbation of clinical symptoms, and an increased incidence of extrapulmonary complications [5]. Currently, there is a scarcity of clinical investigations concerning MRMP infection; in particular, data on MPP in adults are even more scarce. The specific clinical symptoms, laboratory test results and imaging manifestations of changes associated with MRMP infection are still controversial, impeding the early identification of this pathogen. Therefore, in this study, we analyzed the relationship between 23S rRNA V region A2063G drug resistance gene mutations in the alveolar lavage fluid of adult patients with MPP and clinical symptoms, laboratory data and imaging alterations to explore the feasibility of early recognition of MRMP infection in the diagnosis and treatment of this disease and to provide references and bases for the treatment of clinical MPP.

Materials and methods

Research subjects

This study was a retrospective analysis. Clinical data of 61 hospitalized patients who were diagnosed with adult Mycoplasma pneumoniae pneumonia and underwent alveolar lavage from July 2023 to February 2024 in the Department of Respiratory Medicine of the Third Affiliated Hospital of Southern Medical University were collected. According to the presence or absence of a mutation at the A2063G gene locus of the Mycoplasma pneumoniae resistance gene 23S rRNA in bronchoalveolar lavage fluid (BALF), the patients were grouped into a group with resistance gene positivity (resistance group) and a group with resistance gene negativity (sensitivity group). The clinical symptoms and imaging manifestations of the patients included in the study were consistent with the indications for electron bronchoscopic alveolar lavage, and the study was approved by the Medical Ethics Committee of the hospital (approval number: to be determined) with the informed consent of the patients or their guardians.

Inclusion and exclusion criteria

Inclusion criteria for patients were as follows: With reference to the diagnostic criteria for community-acquired pneumonia in the Chinese Guidelines for the Diagnosis and Treatment of Community-Acquired Pneumonia in Adults (2016 edition) [6] and the Chinese Expert Consensus on Bronchoalveolar Lavage Pathogen Testing for Infectious Diseases of the Lung (2017 edition) [7], community-acquired pneumonia was diagnosed and was compatible with the indications for performing bronchoalveolar lavage pathogen testing. If the alveolar lavage specimen was positive for Mycoplasma pneumoniae nucleic acid testing, the diagnosis was Mycoplasma pneumoniae pneumonia.

Exclusion criteria for patients were as follows: (1) under 18 years of age; (2) with congenital heart disease or concomitant immunodeficiency diseases; (3) unable to cooperate with the completion of bronchoalveolar lavage; (4) only positive MP serologic antibodies and negative nucleic acid tests of lavage fluid; (5) cases with incomplete clinical data.

General information

Clinical data were collected from 61 patients, and relevant laboratory and imaging tests were performed within 24 h before and 24 h after hospital admission. The information collected included age, sex, underlying disease, history of smoking, mixed pathogen infections, days of hospitalization, presence of fever, peak fever, duration of fever, cough, hemoptysis, hypoxemia, extrapulmonary complications, arterial partial pressure of oxygen, blood counts, hs-CRP, procalcitoninogen, amyloid, interleukin-6, lactate dehydrogenase, phosphokinase isoforms, D-dimer, fibrinogen levels, serum albumin, and chest HRCT. The drugs used in each group included macrolides, quinolones, tetracyclines and cephalosporins supplemented with oxygen and surface hormones if necessary.

Alveolar lavage fluid collection and 23S rRNA A2063G resistance gene detection

Bronchoalveolar lavage was performed using sterile saline at 37 °C, and negative pressure suction was used to obtain the lavage fluid; mid-section samples were collected, promptly stored in a −80°C freezer and sent for testing. Targeted sequencing of respiratory pathogens (tNGS) was performed by Guangzhou Goldcorp Medical Laboratory Center.

Statistical analysis

All the data were statistically analyzed using SPSS 25.0. Count data are expressed as percentages, and comparisons between groups were made using the chi-square test; for a total number of patients < 40, a theoretical frequency < 1, or when $P\approx \alpha$, four-cell table information was calculated using Fisher's exact probability method. Measurement data were subjected to normality tests and chi-square tests, and those conforming to a normal distribution are expressed as the mean ± standard deviation.$(\overline{x}\pm s)$ The differences between groups were tested by the independent sample information $t$ test; nonnormally distributed data are expressed as medians (interquartile spacing)$(M\left(P_{25},,,P_{75}\right))$ and medians (interquartile spacing); and the rank-sum test was used. p < 0.05 was considered to indicate a statistically significant difference. Logistic regression analysis was performed for significantly different independent variables.

Results

General information

Age and sex

A total of 61 patients with MMP were included in this study—26 (42.6%) male patients and 35 (57.4%) female patients. The patients were categorized into 44 patients (72.1%) in the drug resistance gene-positive group and 17 patients (27.9%) in the drug resistance gene-negative group according to whether they had the drug resistance gene 23S rRNA A2063G. The age of the individuals in the resistance gene-positive group was 34.00 years (26.25, 42.50), and the age of the individuals in the resistance gene-negative group was 34.00 years (28.50, 56.00). There was no statistically significant difference between the two groups in terms of age or sex (P > 0.05) (Table 1).

Table 1.

Comparison of age and sex between the drug resistance gene-positive group and the drug resistance gene-negative group

	Sex[cases(%)]		Age[M, (P25,P75), y]	Total
	Male	Female
Resistance group	18(40.9%)	26(59.1%)	34.00 (26.25, 42.50)	44
Sensitivity group	8(47.1%)	9(52.9%)	34.00 (28.50, 56.00)	17
Z/X2	0.190		−0.676
P value	0.663		0.499

Underlying disease, history of smoking, and mixed pathogen infections

Twenty-eight (63.6%) patients in the drug resistance gene-positive group had underlying disease, including 4 cases(9.1%) of structural lung disease, and 7 (15.9%) had a history of smoking; 11 (64.7%) patients in the drug resistance gene-negative group had underlying disease, including 5 cases(29.4%) of structural lung disease, and 3 (17.6%) had a history of smoking. The differences between the two groups were not statistically significant (P > 0.05). Mixed pathogen infections were present in 19 (43.2%) cases in the resistant group and 12 (70.6%) cases in the sensitive group, with no statistically significant difference between the two groups (p > 0.05). The mixed pathogens detected included Gram-positive bacteria, Gram-negative bacteria, fungi, chlamydia and tuberculosis, DNA viruses and RNA viruses. When the infection rate of different pathogens in the two groups was analysed, it was found that the infection rate of Gram-negative bacteria in the drug-resistant group was significantly lower than that in the sensitive group, and there was a statistically significant difference between the infection rates of Gram-negative bacteria in the two groups (P < 0.05) (Table 2).

Table 2.

Comparison of underlying disease and mixed pathogen infections

	Resistance group	Sensitivity group	X2	P value
Mixed pathogens[cases(%)]	19 (43.2%)	12 (70.6%)	3.685	0.055
Gram-positive bacteria[cases(%)]	8 (18.2%)	6 (35.3%)	1.178	0.278
Gram-negative bacteria[cases(%)]	5 (11.4%)	6 (35.3%)	4.340	0.037
Chlamydia/Tuberculosis [cases(%)]	1 (2.3%)	0 (0%)	-	1.000
Fungi[cases(%)]	5 (11.4%)	2 (11.8%)	0.002	0.965
DNA viruses[cases(%)]	6 (13.6%)	2 (11.8%)	0.038	0.845
RNA viruses[cases(%)]	4 (9.1%)	5 (29.4%)	3.642	0.056
Structural lung disease[cases(%)]	4 (9.1%)	5 (29.4%)	3.642	0.056

Comparison of clinical characteristics between drug resistance gene-positive and drug resistance gene-negative groups

Among the 61 patients, 38 (86.4%) had fever in the drug resistance gene-positive group and 10 (62.5%) in the drug resistance gene-negative group; the mean duration of fever was significantly greater in the drug resistance gene-positive group than in the drug resistance gene-negative group, and the differences in the number of fever cases and the duration of fever were also statistically significant (P < 0.05)(Table 3, Fig. 1).

Table 3.

Comparison of clinical characteristics between the drug resistance gene-positive and drug resistance gene-negative groups

	Resistance group	Sensitivity group	t/Z/X2	P value
Hospitalization days $[d,(M\left(P_{25},,,P_{75}\right)]$	7.00(6.00,7.75)	6.00(5.00,7.50)	−1.323	0.186
Fever[cases(%)]	38 (86.4%)	10 (62.5%)	4.176	0.041
Peak fever ${[}^{\circ }\mathrm{C},(M\left(P_{25},,,P_{75}\right)]$	39.00 (38.50,39.80)	39.55 (38.73,40.00)	−0.778	0.436
Duration of fever[d, $\overline{x}\pm s$]	7.37 ± 3.06	4.89 ± 2.03	−2.303	0.026
Hemoptysis [cases(%)]	3(6.8%)	2(11.8%)	0.012	0.912
Hypoxaemia[cases(%)]	14(32.6%)	4(23.5%)	0.473	0.492
Extrapulmonary complications[cases(%)]	43(97.7%)	11(74.7%)	10.112	0.001

Fig. 1.

Comparison of clinical symptoms and imaging findings between the two groups

The incidence of extrapulmonary complications was significantly greater in the drug resistance gene-positive group (97.8% of 43 patients) than in the drug resistance gene-negative group (64.7% of 11 patients), and the difference in incidence rates between the two groups was statistically significant (P < 0.05) (Table 3). Extrapulmonary complications mainly included skin rash, elevated liver enzymes, myoenzyme abnormalities, ionic disorders, coagulation abnormalities, and acute kidney damage. The incidence of coagulation abnormalities (32 patients, 72.7%) was the highest in the drug resistance gene-positive group, followed by ionic disorders (26 patients, 59.1%). In the drug resistance gene-negative group, the prevalence of myoenzyme abnormalities (8 patients, 47.1%) and ionic disorders (8 patients, 47.1%) was the highest, but the differences in skin rash, elevated liver enzymes, muscle enzyme abnormalities, ionic disorders, coagulation abnormalities, and acute kidney damage between the two groups were not statistically significant (P > 0.05) (Table 4). The sensitivity of identifying positive resistance genes was 92.5%, and the specificity was 33.3% when calculating the total incidence of extrapulmonary complications subject operating characteristic (ROC) curves, the area under the curve (AUC), and the optimal cutoff value (Table 8).

Table 4.

Comparison of various extrapulmonary complications between the drug resistance gene-positive and drug resistance gene-negative groups

Extrapulmonary complications	Resistance group	Sensitivity group	X2	P value
Rash[cases(%)]	1 (2.2%)	1 (5.9%)		0.483
Elevated liver enzymes[cases(%)]	16 (36.4%)	6 (35.3%)	0.006	0.938
Abnormal muscle enzymes[cases(%)]	13 (29.5%)	8 (47.1%)	1.666	0.197
Electrolyte disorders[cases(%)]	26(59.1%)	8 (47.1%)	0.72	0.396
Coagulation abnormality[cases(%)]	32(72.7%)	8 (47.1%)	3.579	0.059
Acute kidney injury[cases(%)]	3(6.8%)	1 (5.9%)	< 0.001	1.000

Table 8.

Assessment of extrapulmonary complications, fibrinogen content, imaging manifestations, and predictive modeling for the diagnosis of drug-resistant Mycoplasma pneumoniae with reference to significance

	Specificity	Sensitivity	Youden index	AUC	Cut-off point	P value
Fibrinogen	60.0%	81.0%	0.41	0.710	4.64	0.017
Extrapulmonary complications	26.7%	97.6%	0.243	0.621	0.50	0.166
Centrilobular distribution, Tree-in-bud Sign, ground-glass opacity, thickening of bronchial wall	33.3%	92.5%	0.286	0.643	0.50	0.103
Predictive model	80.0%	83.3%	0.633	0.797	0.78	0.001

The differences in the number of days of hospitalization and peak fever, hemoptysis, cough, or hypoxemia were not statistically significant (P > 0.05) (Table 3).

Comparison of laboratory tests between patients in the drug resistance gene-positive and drug resistance gene-negative groups

The median and mean fibrinogen contents of the drug resistance gene-positive group were significantly greater than those of the drug resistance gene-negative group (P < 0.05). The differences in blood leukocyte, lymphocyte, neutrophil, platelet, hs-C-reactive protein, calcitoninogen, interleukin 6, lactate dehydrogenase, calculated phosphate isoenzyme, D-dimer, and serum albumin were not statistically significant between the two groups (P > 0.05) (Table 5).

Table 5.

Comparison of laboratory test results between the drug resistance gene-positive group and the drug resistance gene-negative group

	Resistance group	Sensitivity group	t/Z/X2	P value
Leukocytes $\left[\times ,{10}^9,/,L,,,,\left(M,(,P_{25},,,P_{75}\right)\right]$	7.76 ± 2.470	7.07 ± 2.089	−0.99	0.326
Lymphocytes $\left[\times ,{10}^9,/,L,,,,\left(M,(,P_{25},,,P_{75}\right)\right]$	1.37(1.00,1.64)	1.45(0.93,1.85)	−0.016	0.987
Neutrophils $\left[\times ,{10}^9,/,L,,,,\overline{x},\pm ,s\right]$	5.49 ± 2.33	4.54 ± 2.05	−1.468	0.148
Platelets $\left[\times ,{10}^9,/,L,,,,\left(M,(,P_{25},,,P_{75}\right)\right]$	231.0 (191.0,288.0)	213.0 (174.5,301.5)	−0.569	0.569
hs-CRP $\left[m,g,/,L,,,,\left(M,(,P_{25},,,P_{75}\right)\right]$	51.98(17.17, 72.79)	42.84(4.27, 81.62)	−0.664	0.506
LDH $\left[U,/,L,,,,\left(M,(,P_{25},,,P_{75}\right)\right]$	193.00 (167.25,217.50)	210.00 (172.00,240.00)	−0.57	0.569
Creatine kinase isoenzyme $\left[U,/,L,,,,\left(M,(,P_{25},,,P_{75}\right)\right]$	10.00(8.00,12.00)	11.00 (8.00,14.00)	−0.804	0.422
D-dimer $\left[\mu ,g,/,L,,,,\left(M,(,P_{25},,,P_{75}\right)\right]$	215.00(118.00,467.75)	200.00(89.50,356.25)	−0.783	0.434
Fibrinogen content $\left[g,/,L,,,,\left(M,(,P_{25},,,P_{75}\right)\right]$	4.94(4.68,5.58)	4.56(3.60,5.12)	−2.939	0.017
Serum Albumin $\left[g,/,L,,,,\left(M,(,P_{25},,,P_{75}\right)\right]$	40.11 ± 3.39	41.21 ± 3.71	1.046	0.3

The work characteristics (ROC) curves, area under the curve (AUC), and optimal cutoff value for fibrinogen content in subjects were calculated (Fig. 2), and the optimal cutoff value for fibrinogen content was 4.64 g/L, with 81% sensitivity and 60% specificity for identifying drug resistance genes (Table 8).

Fig. 2.

ROC curves for extrapulmonary complications, fibrinogen content, imaging manifestations, and prediction models

Comparison of imaging findings between the drug resistance gene-positive and drug resistance gene-negative groups

Among the 61 patients, 42 (95.5%) in the drug resistance gene-positive group had centrilobular distribution, tree-in-bud signs, ground-glass opacity, and thickening of the bronchial wall on imaging, whereas 11 (64.7%) in the drug resistance gene-positive group had significantly different findings (P < 0.05). In the drug resistance gene-positive cohort, 13 patients (29.5%) had predominantly upper lung field lesions, and 36 patients (81.8%) had lesions involving the middle and lower lobes of the lungs. 18 patients (40.9%) had bilobar changes, 34 patients (77.3%) had solid lesions in the lung lobe segments with or without cavities or necrosis, 4 patients (9.1%) had pleural effusions, 4 patients (23.5%) had predominantly upper lung field lesions, 14 patients (82.4%) had lesions in the middle and lower lobes of the lungs, 5 patients (29.4%) had bilobar changes, 13 patients (76.5%) had solid lesions in the lobar segments of the lungs with or without cavitation and necrosis, and 1 patient (5.9%) had pleural effusion; the differences between the two groups were not statistically significant (P > 0.05) (Table 6) (Fig. 1).

Table 6.

Comparison of imaging findings between the drug resistance gene-positive and drug resistance gene-negative groups

	B	P value	OR	95% CI
Extrapulmonary complications	−6.033	0.008	0.002	0.679 ~ 94.218
Fibrinogen	0.698	0.059	2.011	0.975 ~ 4.145
Centrilobular distribution, Tree-in-bud Sign, ground-glass opacity, thickening of bronchial wall	2.290	0.021	9.871	1.423 ~ 68.484
Constants	1.030	0.001	2.800

The sensitivity of identifying positive resistance genes was 92.5%, and the specificity was 33.3% according to the calculation of leaflet-centered nodules, tree bud signs, ground-glass opacities, and bronchial wall thickening imaging signs, which were used to determine the subjects'work characteristics (ROC) curves and area under the curve (AUC) (Table 8) (Fig. 2).

Multivariate logistic regression analysis, correlation analysis and predictive modeling

Logistic regression analysis of the clinical features, laboratory indices and imaging findings revealed that the imaging manifestations of centrilobular nodules, tree bud signs, ground glass shadows, and bronchial wall thickening had significant positive effects on the prognosis of drug-resistant patients (Table 7) (Fig. 3). The prediction model for drug resistance gene positivity was logit (P) = 1.030 + 2.290* for imaging signs of infectious bronchiolitis, with an overall prediction accuracy of 78.9%. Analysis of the ROC curve revealed that the predictive model had an AUC of 0.797 (P < 0.05), an optimal cutoff value of 0.78, a sensitivity of 83.3%, and a specificity of 80.0% (Table 8).

Table 7.

Logistic regression analysis of drug resistance gene positivity with extrapulmonary complications, fibrinogen content and imaging manifestations

	B	P value	OR	95% CI
Extrapulmonary complications	−6.033	0.008	0.002	0.679 ~ 94.218
Fibrinogen	0.698	0.059	2.011	0.975 ~ 4.145
Centrilobular distribution, Tree-in-bud Sign, ground-glass opacity, thickening of bronchial wall	2.290	0.021	9.871	1.423 ~ 68.484
Constants	1.030	0.001	2.800

Fig. 3.

Forest plot for logistic regression analysis

Spearman correlation analysis of resistance genes and fibrinogen content revealed a statistically significant correlation coefficient (r = 0.320; P = 0.015 < 0.05).

Discussion

MP infection can cause atypical clinical symptoms such as dry cough and fever. The peak of MPP often follows MRMP infection [8]. Patients with MRMP infections tend to have a long duration of illness, severe disease, and an increased incidence of various complications, increasing the risk of developing RMPP [9]. These patients are at high risk for RMPP (Tong, Huang, Zheng, Zhang, & Chen, 2022). The clinical symptoms of these patients are diverse and atypical, increasing susceptibility to underdiagnosis and delayed treatment, which may contribute to the progression of the disease and be detrimental to patient prognosis (Waites, Xiao, Liu, & Chen, 2022) [10]. The patient's prognosis is unfavorable. Therefore, it is imperative to summarize the characteristics of MRMP infection by analyzing various examination indices and clinical symptoms to identify MRMP infection at an early stage, which is important for predicting the severity of the disease and disease prevention in the community.

Tenson T et al. showed that macrolides inhibit bacterial protein synthesis by shortening the tunnel diameter and blocking the passage of nascent peptides, mainly by targeting the nascent peptide exit tunnel NPET of the ribosomal 50S subunit (Tenson T, Lovmar & Ehrenberg, 2003) [11]. Mutations in the 23S RNA A2063 gene result in enzyme-catalyzed methylation of the adenylate at the ribosome-binding site of macrolide antibiotics, rendering macrolide antibiotics useless for antimicrobial activity [12].

The expression of the 23S rRNA A2063G drug resistance gene in alveolar lavage and sputum specimens was detected in two groups of study subjects in this study: the drug resistance gene-positive (resistance group) and drug resistance gene-negative (sensitivity group) groups. A statistically significant difference was not found between the two groups in terms of age, sex, history of smoking, incidence of underlying disease, incidence of mixed pathogen infection (P > 0.05). However, we observed that the infection rate of mixed pathogens in the resistant group (43.2%) was significantly lower than that in the sensitive group (70.6%), and it was found that the infection rate of gram-negative bacilli in the resistant group was significantly lower than that in the sensitive group (P < 0.05). These findings suggest that there may be an association between drug-resistant gene-negativity and an increased risk of mixed infections, especially gram-negative bacilli. There is an absence of direct evidence that drug-resistant gene-negativity increases the risk of mixed pathogen infections [13], which may be related to the body's immune response [14], differences in antibiotic treatment program and the interaction between drug-resistant strains and other pathogens [15]. Jorge L. Medina et al. reported [16] that Mycoplasma pneumoniae can produce an ADP-ribosylating and vacuolating toxin termed the community-acquired respiratory distress syndrome (CARDS) toxin, suggesting that drug-resistant bacteria may deliver virulence factors to host cells via EVs, induce inflammatory responses and epithelial damage, and inhibit the growth of co-infecting pathogens and reduce flora diversity. Furthermore, in this study, within the resistant group, 18 patients (40.9%) expressed a preference for combination regimens, incorporating β-lactams in conjunction with macrolides or quinolone antibiotic regimens. In contrast, a mere 2 patients (11.8%) in the sensitive group demonstrated a preference for combination regimens, a figure that was significantly lower than that observed in the resistant group. It was hypothesised that this was due to a greater proportion of patients in the resistant group preferring potent or broad-spectrum antibiotics, which could simultaneously cover other mixed pathogens, including Gram-positive and Gram-negative bacilli. In contrast, the sensitive group was biased towards conventional macrolides, which failed to cover other pathogens, resulting in a relatively high rate of mixed-pathogen infections. This suggests the necessity of using potent or broad-spectrum antibiotics as early as possible in the clinic for inpatients and the Rationality. However, the results of most current studies suggest that Mycoplasma pneumoniae-resistant patients are more likely to have mixed pathogen infections, which contradicts the statistical results of the present study, and cannot be ruled out due to the insufficient sample size and the presence of multiple confounding factors in the present study, and further prospective studies are still needed.

Comparing the clinical characteristics of the two groups, there was no statistically significant difference in the number of days of hospitalization and peak fever, hemoptysis, cough, and hypoxaemia (P > 0.05). In the resistance group, the incidence of fever, duration of fever and incidence of extrapulmonary complications were significantly greater than those in the sensitivity group (P < 0.05), which was the same as the results of other studies [17, 18]. The mechanism of extrapulmonary complications caused by MRMP infection has not been fully clarified. This difference may be related to the following aspects: (1) The C-terminal regions of the P1 and P30 proteins in Mycoplasma pneumoniae are highly homologous to host troponins, cytoskeletal proteins and fibronectin. After Mycoplasma pneumoniae infects an organism, the surface antigen of the pathogen can cross-react with its own tissues, and the resulting antigen–antibody immune complex can cause extrapulmonary multiorgan damage, such as thrombocytopenic purpura and renal failure. [19, 20]. The Mycoplasma pneumoniae DNA load has been reported to be significantly greater in MRMP-infected patients than in MSMP-infected patients after treatment with macrolides [5]. High Mycoplasma pneumoniae DNA loads may induce stronger and more persistent immune responses, especially immune modulation mediated by IL-18, which enhances the toxic effects of T lymphocytes and exacerbates severe damage to extrapulmonary tissues [21, 22]. The high proportion of MRMP-infected patients with fever and prolonged duration of fever may also be associated with this difference. (2) Mycoplasma pneumoniae can encode a variety of virulence factors, such as the HapE enzyme [23], lipoproteins, CARDS toxins [24], and podocarp polysaccharides [23]. These virulence factors can affect various transduction pathways, such as the NF-κB pathway and the Toll-like receptor signaling pathway, contributing to the imbalance of cytokines in the body and inducing the onset of inflammatory responses, which in turn can cause damage to distant extrapulmonary tissues [25]. (3) Mycoplasma pneumoniae can enter the circulatory system through the gaps between damaged epithelial cells in the lungs, transfer to various parts of the body by adhering to blood cells, and directly act on other organs to cause various extrapulmonary complications. In this study, the extrapulmonary complications of skin rash, liver injury, muscle enzyme abnormalities, ionic disorders, coagulation abnormalities and acute kidney injury were analyzed separately, and in both groups, there was no significant difference in the incidence of any type of extrapulmonary complication (P > 0.05), which may be due to factors such as insufficient observation time and a small sample size.

Current studies have demonstrated that patients infected with MRMP have a prolonged duration of hospitalisation [26] and an elevated risk of hypoxaemia [27] in comparison to those infected with MSMP. Nevertheless, the present study revealed no statistically significant discrepancy in the duration of hospitalisation and the incidence of hypoxaemia between the two groups (P > 0.05). Concomitant with earlier studies, the efficacy and promptness of treatment for adult patients with Mycoplasma pneumoniae may have diminished the incidence of hypoxaemia and ameliorated clinical symptoms in patients with MRMP infections. Karl Hagman et al. researchers [28] observed that administration of macrolides (mainly erythromycin) or fluoroquinolones was associated with a more protracted duration of hypoxemia and lengthier duration of stay in comparison to tetracyclines. Furthermore, macrolide treatment has been shown to be associated with a significantly prolonged duration of fever. In contrast, the present study observed that 98% of patients within the resistant group were treated with broad-spectrum quinolone or tetracycline antibiotics, and 10 patients (23%) were treated with oxygen therapy and respiratory support. This finding suggests that, in clinical practice, the aggressive treatment of patients with MRMP infection, the replacement of broad-spectrum and potent antibiotics, and the provision of respiratory support can have a positive effect on alleviating clinical symptoms and reducing the incidence of critical emergencies in patients with MRMP infection. The presence of a greater number of mixed pathogen infections and underlying lung diseases, such as bronchiectasis, COPD, interstitial lung disease and emphysema, in the sensitive group compared to the resistant group, increased the risk of hypoxaemia in patients and may have contributed to the lack of statistically significant differences. In patients with Mycoplasma pneumoniae and underlying lung disease, particularly those with structural lung disease, heightened clinical vigilance is imperative for the identification of disease progression.

In this study, nonspecific laboratory indicators commonly used in clinical practice were analyzed. Fibrinogen concentrations were significantly greater in the resistance group than in the sensitivity group (P < 0.05). ROC curves, area under the curve (AUC), etc., were used to determine the optimal fibrinogen concentration cutoff value of 4.64 g/L; the sensitivity of identifying drug resistance gene positivity was 81% and the specificity was 60%. Logistic regression analysis revealed that the 95% confidence interval (CI) of the association between the fibrinogen concentration and drug resistance gene was 0.975 ~ 4.145, and Spearman correlation analysis yielded a correlation coefficient of 0.032 (P < 0.05). Taken together, these findings indicate that the association between drug resistance genes and fibrinogen is general and that there is still uncertainty about this association, which needs additional research. Fibrinogen is an acute response protein synthesized by the liver and is directly involved in the coagulation process mainly as coagulation factor I [29]. Conditions such as smoking, obesity, shock, infection, pregnancy, and tumors can cause elevated fibrinogen. Previously, it was believed that elevated fibrinogen levels increase blood viscosity, contribute to the development of atherosclerosis and hematogenous metastasis of tumors and are among the most important risk factors for various types of cardiovascular and cerebrovascular diseases [30]. It is also one of the most important risk factors for cardiovascular diseases (Ernst, 1990). However, Jecko Thachil suggested that when the body is in a state of novel coronavirus pneumonia or other inflammatory conditions, in contrast to its role as a risk factor for developing thrombotic disease, fibrinogen may be an acutee-phase reactant that protects the body. During significant coagulation activation and widespread thrombus formation, D-dimer levels begin to increase, and fibrinogen levels begin to decrease in the later stages of disease [31]. Flick MJ et al. reported that fibrinogen is an associated ligand for Mac-1, an important adhesion receptor on the surface of leukocytes, and has an important function in regulating immune cell resistance to pathogens and coagulation, thus limiting the spread of pathogens in the body [32]. Since patients with MRMP infections tend to have an intense inflammatory response, more severe clinical symptoms, and more extrapulmonary complications, it is hypothesized that fibrinogen may be elevated during disease progression as a protective factor that regulates the host inflammatory response; therefore, increased fibrinogen levels may be informative in identifying MRMP infections. However, since the protective role of fibrinogen is still unclear and because the correlation between fibrinogen levels and drug resistance genes is unclear, additional research is needed to support this hypothesis.

Ting-ting Jiang et al. reported that the differences in leukocyte, platelet, and phosphocreatine isoenzyme levels between the MRMP group and the MSMP group were not significant (P > 0.05), which is consistent with the results of the present study. LDH and D-dimer levels were significantly greater in patients infected with MRMP than in those infected with MSMP (P < 0.05), indicating that MRMP-infected patients had a severe degree of disease and a long treatment duration. It was not statistically significant to distinguish the two groups on the basis of CRP levels, but there was a significant trend toward increased CRP in the MRMP group [33]. In the MRMP group, CRP levels were significantly greater (Jiang et al., 2023). In contrast, there was no statistically significant difference in hs-CRP, LDH, or D-dimer between the two groups in this study (P > 0.05). The possible reasons for this difference are as follows: ① Adolescents and adults have a more mature immune system than children, with a milder inflammatory response after MRMP infection and a lower risk of infection. ② Quinolone and tetracycline antibiotics have good therapeutic effects on MRMP infection, suggesting that when epidemiologic investigations suggest a higher rate of MRMP infection, perhaps an early switch to quinolone or tetracycline antibiotics could be considered.

According to the analysis of the imaging results, 42 patients (95.5%) and 11 patients (64.7%) had centrilobular distribution, tree-in-bud sign, ground-glass opacity, and thickening of the bronchial wall in the resistance group and the sensitivity group, respectively, and the difference between the two groups was statistically significant (P < 0.05). These findings suggest that, compared with MSMP infection, MRMP infection is more likely to involve fine bronchioles and small airways below the bronchioles and small airways, and exuded inflammatory substances cause the lumen to be blocked and dilated and the wall to thicken, resulting in the development of infectious fine bronchiolitis. Xiao-Wen Zhan et al. reported that the incidence of sputum embolus and mucosal congestion and edema in patients with drug resistance gene positivity was significantly greater than that in patients with negative results, which further confirmed the results of the present study through bronchoscopy.

In this study, by plotting the ROC curve, the sensitivity of identifying drug resistance genes in fine bronchitis-related imaging manifestations, such as centrilobular distribution, tree-in-bud sign, ground-glass opacity, and thickening of the bronchial wall, was found to be 92.5%, and multifactorial logistic regression analysis revealed that this gene was an independent predictor of drug resistance. The high sensitivity and specificity of this model suggest the reliability and feasibility of combining imaging findings to improve the ability to discriminate MRMP infections in the clinic, which can help guide the clinical adjustment of the diagnosis and planning of treatment, such as prolonging the course of anti-infective therapy and switching to quinolone or tetracycline antibiotics in adults, to minimize the risk of the disease progressing to occlusive fine bronchitis and to improve the prognosis and quality of life.

This study has several limitations. The first limitation is that this was a retrospective study, and the completeness of the data collected for several related indices, such as amyloid A concentration, calcitoninogen concentration, and interleukin 6 concentration, was insufficient. Additionally, it was difficult to clarify the causal associations in retrospective studies, and the reliability of predicting positive results for drug-resistant mutations was not as good as that for prospective studies. Second, there were 61 study subjects in this study, which is a relatively small sample size and impacts the accuracy of the results. In view of this, the results of the study could be further supplemented in the future by expanding the sample size based on this study and improving the completeness of the data collection.

In conclusion, patients with mutations in the A2063G gene in the V region of ribosomal 23S rRNA had a high number of fever cases, prolonged duration of fever, high incidence of extrapulmonary complications, and significant increase in fibrinogen content. Imaging signs of infectious bronchiolitis, such as centrilobular distribution, tree-in-bud signs, ground-glass opacity, and thickening of the bronchial wall, correlate with the occurrence of drug resistance gene positivity, which is an independent predictor of early MR-MPP disease. Earlier use of broad-spectrum or potent antibiotics such as quinolones or tetracyclines may be considered in adult patients with Mycoplasma pneumoniae, which may have a beneficial effect in reducing the risk of developing mixed pathogen infections and shortening the duration of the patient's illness. The above results can be used as a reference for adult patients with Mycoplasma pneumoniae pneumonia, further illustrating the importance of early recognition of drug-resistant Mycoplasma pneumoniae infections and timely action.

Authors’ contributions

Yuexun Huang wrote the main manuscript text and analyzed data. Haolin Wen prepared figures.Zhenyang Fu, Sicheng Chen and Dacheng Zhang managed and coordinated the research activity planning and execution. All authors reviewed the manuscript and made substantial contributions to the design of the work and original draft.

Funding

The authors declare that no funds, grants, or other support was received during the preparation of this manuscript.

Data availability

The data that supports the findings of this study are available from the corresponding author upon reasonable request.

Declarations

Ethics approval and consent to participate

This study was performed in accordance with the principles of the Declaration of Helsinki. All individuals provided informed consent to participate in this study, and approval was provided by the Medical Research Ethics Committee of The Third Affiliated Hospital of Southern Medical University (Approval No. 2024-ER-040). As this was not a clinical trial, a clinical trial number is not applicable.

Consent for publication

Not Applicable.

Competing interests

The authors declare no competing interests.