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. 2021 May 31;14:1989–2001. doi: 10.2147/IDR.S306632

A 5-Year Retrospective Analysis of Raoultella planticola Bacteriuria

Sai Vikram Alampoondi Venkataramanan 1, Lovin George 1, Kamal Kant Sahu 1,✉, George M Abraham 1,1
PMCID: PMC8178696  PMID: 34103946

Abstract

Introduction

Raoultella planticola is an aerobic gram-negative rod predominantly found in soil and aquatic environments. The typical reservoirs of Raoultella spp. include the gastrointestinal tract and the upper respiratory tract. It usually causes pneumonia, biliary tract infections, and bacteremia. Urinary tract infection (UTI) secondary to R. planticola is an uncommon entity. Less than 10 cases of R. planticola-associated UTIs in adults have been published in the literature to date.

Objective

This is a single institution retrospective study undertaken to identify the epidemiology, patient characteristics, clinical spectrum, predisposing risk factors and the outcome of patients with UTI caused by R. planticola.

Results

A total of 37 R. planticola isolates were identified in urine samples over a 5-year study period. The mean age of the patient population was 77 years. The most common comorbidity was diabetes mellitus, which was present in 16 patients. Only 3 patients had a history of steroid use, an immunosuppressive condition, or were on chemotherapy. The most common presenting complaint was altered mental status followed by fever. Resistance to ampicillin was found in 35 isolates which seems to be an intrinsic characteristic of Raoultella spp. and 2 isolates were multidrug-resistant, but still susceptible to ciprofloxacin. The average length of stay was 3 days, and the average duration of antibiotic administration was 8 days. Ciprofloxacin was the most frequently prescribed antibiotic (9 patients). The severity of infection ranged from simple cystitis in 15 patients to urosepsis in 2 patients and septic shock in 2 patients. There were no mortalities in our cohort.

Conclusion

Our study revealed that patients with R. planticola UTI had higher proportion of diabetes mellitus, renal failure compared to the general population. Our study also confirms the intrinsic resistance to ampicillin of Raoultella spp., which has been documented previously in the literature.

Keywords: infection, antibiotics, Raoultella, urinary tract infection, bacteriuria

Introduction

Infections related to rare pathogens are very challenging to treat due to lack of enough data in the medical literature.1,2 Raoultella planticola is a ubiquitous, non-motile, aerobic gram-negative bacteria. It belongs to the genus Raoultella under the Enterobacteriaceae family. Two species are clinically important: [1] Raoultella planticola and [2] Raoultella ornithinolytica. The microbiological identification of R. planticola remains a challenge even after 30 years of its identification.3,4 This is because the conventional phenotypic assessments often misidentify it as Klebsiella spp., which is its remarkably close relative in the Enterobacteriaceae family. This might be one of the many reasons that the incidence of infections caused by R. planticola is underreported.

The gastrointestinal tract and the upper respiratory tract are the typical reservoirs of R. planticola.5 It commonly causes pneumonia, biliary tract infections, and bacteremia.6–9 Only a handful of cases of urinary tract infection (UTI) caused by R. planticola in adults have thus far been published in the literature.10–16 Most of the UTIs have been reported in immunocompromised adults, in patients with urinary tract procedures or instrumentation.11–13,15

The recent emergence of extended-spectrum β-lactamase (ESBL) producing and carbapenem-resistant nosocomial R. planticola infections is a matter of concern. These strains can act as a reservoir for these resistance genes.17

Except for a few case reports/series, there has been no published comprehensive review or original study on R. planticola-associated UTIs. We conducted a retrospective study to better understand the characteristics of the organism, risk factors for acquisition of infection and to analyze the outcomes associated with UTI caused by R. planticola.

Materials and Methods

Search Strategy

This was a retrospective study conducted at a community-based teaching hospital in Massachusetts, United States. The study included data from January 2015 to September 2020 and included all urine cultures positive for R. planticola at our institution. The study was approved by our institutional review board (IRB #2020 −142).

Selection and Inclusion Criteria

All adult patients (>18 years) who had a urine culture growing R. planticola were included in the study. Primary identification and sensitivities of colonies were done with VITEK® 2 compact automated system and confirmation was done with API 20-E, both from BioMérieux.

Data Extraction

Records of selected patients were reviewed and information including the demographics, clinical symptoms, physical examination findings, laboratory data, radiological parameters and microbiological data were extracted. Further details on hospitalization including the severity of the illness, antibiotics administered, hospital course and outcomes were also obtained. The data extracted was verified by two independent researchers. The data was then entered into a spreadsheet.

Data Analysis

All categorical data were expressed as counts, whereas continuous data were expressed as a mean. The data was analyzed using Google sheets®. No statistical analysis was performed given the small sample size.

Results

Demographic Details

A total of 37 patients had a positive urine culture for R. planticola. The demographics of the patients are listed in Table 1. The mean age of our cohort was 77 years (47 years - 91 years). There were 28 females and 9 males in total. Out of our 37 patients, 9 were residents of nursing homes or group homes, and 28 presented from home. The body mass index (BMI) was measured to be <19 kg/m2 in 3 patients, between 19kg/m2 to 25 kg/m2 in 15 patients, between 25 kg/m2 to 30 kg/m2 in 10 patients and more than 30 kg/m2 in 9 patients. The mean BMI was 26.64 kg/m2.

Table 1.

Patient Demographics and Predisposing Factors

Case No. Age Sex BMI Living Condition History of Diabetes Steroid Use or on Chemotherapy Renal Failure Alcohol Use Smoking Past Urological Surgery or Procedure Renal Structural Abnormalities
1 86 F 18.29 Home No No No No Never No None
2 73 M 24.37 Home Yes No No No Never No None
3 65 F 19.1 Home No No No Yes Never No None
4 71 F 29.2 Home Yes No No No Never No None
5 85 F 21.3 NH No No Chronic No Never No None
6 90 F 20.5 Home No No Chronic No Former No None
7 64 F 19.6 NH No No No No Former No None
8 83 F 29.3 Home No No Chronic Yes Never No None
9 76 F 32.6 Home No No No No Former No None
10 91 F 27.9 Home No No No Yes Former No None
11 63 M 36.6 NH No No No No Never No None
12 70 M 21.70 Home No No Acute on chronic No Never No None
13 59 M 21.24 Home Yes No No No Never Yes None
14 61 F 35.4 Home No Yes Chronic No Former Yes None
15 47 M 34.4 Home No No No No Never Yes None
16 74 F 37.6 Home Yes Yes Chronic Yes Former No None
17 90 F 19.53 Home No No Chronic No Never Yes None
18 85 F 22.8 Home Yes No Chronic Yes Never No None
19 85 F 23.17 Home Yes No Acute on Chronic No Never No None
20 68 M 17.85 Home Yes No No No Never No None
21 83 M 23.2 Home No No Acute on Chronic No Never No None
22 81 M 28.4 Home No No Acute on Chronic No Never Yes None
23 88 F 19.01 Home No No No No Former No Bladder outlet obstruction
24 89 F 17.33 Home No No No No Former No Abnormal urethra
25 89 F 28.33 NH Yes No Chronic No Former No None
26 89 F 27.44 NH Yes No Chronic No Former No Renal cystic disease
27 89 F 26.8 NH Yes No Chronic No Former No Renal cystic disease
28 89 F 27.1 NH No No No No Former No Renal cystic disease
29 83 F 44.14 Home Yes o No No Former No None
30 50 F 34.46 Home Yes No No No Former No None
31 66 M 37 Home Yes No No No Never No None
32 81 F 26.9 NH No Yes Chronic No Never No Renal cystic disease
33 89 F 22.4 Home Yes No Chronic No Never No None
34 81 F 32.01 Home Yes No Chronic No Former No None
35 82 F 29.94 Home Yes No Acute on chronic No Former No None
36 82 F 24.61 Home No No No No Former No None
37 83 F 24.22 Home No No No No Never No None
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Abbreviation: NH, nursing home.

Risk Factors

We studied the systemic and genitourinary factors in our population that were associated and/or have prognostic significance to our patients with R. planticola-associated UTIs (Table 1).

Systemic Characteristics

Alcohol consumption was reported by 5 patients while 32 patients denied it. None of the patients was active smokers with 17 endorsing prior tobacco use. Amongst the 37 patients, 16 patients had a history of diabetes mellitus. Liver dysfunction was present in 7 patients. Chronic corticosteroid and immunosuppressant use were reported by 1 patient each, and chemotherapy by 2 patients.

Genitourinary Characteristics

A history of chronic kidney disease was present in 18 patients. Out of these 18 patients, 5 had an acute on chronic kidney injury. There was a history of a urological procedure or genitourinary instrumentation in 4 patients, with 2 having the procedure within a month of their UTI. An underlying structural abnormality of the genitourinary tract was present in 9 patients as depicted in Figure 1. A history of renal transplantation was present in 1 patient.

Figure 1.

Figure 1

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Underlying structural abnormality of the genitourinary tract.

Clinical Features

As shown in Table 2, most of the patients were asymptomatic at the time of presentation. The symptomatic patients presented with the following symptoms altered mental status (6 patients), generalized fatigue (5 patients), fever (4 patients), dysuria (2 patients), flank pain (1 patient), the combination of fever, suprapubic pain, and increased frequency (1 patient), flank pain and turbid urine (1 patient), and altered mental status and increased urinary frequency (1 patient).

Table 2.

Clinical Features of Patients with R. planticola-Associated UTIs

Symptom Number of Patients (Total:37) Percentage
Asymptomatic Bacteriuria 16 43.24%
Altered sensorium 7 18.92%
Fatigue 5 13.51%
Fever 5 13.51%
Dysuria 2 5.41%
Flank pain 2 5.41%
Increased frequency 2 5.41%
Suprapubic pain 2 5.41%
Turbid urine 1 2.7%
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Four patients were bradycardic, and 8 patients were tachycardic at the time of presentation. Only 8 patients were febrile (>100.4O F) at the time of presentation. Hypotension was present in 1 patient and the rest of the patients had systolic blood pressure greater than 90 mm Hg.

Laboratory Data

The laboratory results of the patients are depicted in Table 3. The mean white blood cell count was 8.96 x 109/L (2.3 × 109/L - 20.5 × 109/L), platelet count was 246 x109/L (52 × 109/L - 599 × 109/L), glucose was 152 mg/dL (49 mg/dl - 684 mg/dL), creatinine was 1.31 mg/dL (0.53 mg/dl - 6.3 mg/dL), and GFR was 56.87 mL/min (5.7 mL/min - 111.6 mL/min). A glycated hemoglobin level was measured only in 12 patients and the mean was 8.39% (5.3%- 13.7%). An elevated lactate level was present in 3 patients.

Table 3.

Laboratory Results

Case No. WBC (Cells/mL) Platelets
(Cells/µL)		 Hemoglobin A1C
(%)		 Blood Sugar at Presentation (mg/dl) Creatinine (mg/dl) Glomerular Filtrataion Rate (mL/min) Lactic Acid (mmol/L)
1 11.7 430 Not done 110 0.84 63.4 1.2
2 14.4 231 6.5 171 0.87 85.6 1.4
3 12.7 599 Not done 116 0.6 95.7 1.8
4 7.7 277 8.5 213 1.07 52.6 Not done
5 6.5 285 Not done 99 0.81 66.7 Not done
6 10.2 199 5.9 96 1.38 33.6 Not done
7 4.6 87 Not done 106 0.53 100.3 Not done
8 8.2 269 Not done 49 1.16 43.5 Not done
9 18.9 567 Not done 93 1.35 44.1 Not done
10 12.7 253 Not done 119 1.73 29.6 1.8
11 5.6 118 5.3 111 0.98 81.7 0.8
12 12.8 330 Not done 126 1.63 42.1 1.5
13 6.6 184 9 156 111.6 1 2.5
14 10.6 259 7.2 95 1.55 36.1 2.1
15 2.3 257 Not done 117 1.13 77 Not done
16 8.3 400 8.8 216 1.32 39.6 1.2
17 7 240 Not done 95 1.08 45.2 Not done
18 9 52 6.2 235 1.23 46.3 Not done
19 9.9 88 Not done 285 3.36 11.9 Not done
20 7.3 270 13.7 684 0.81 92 1.8
21 20.5 147 Not done 121 1.98 30.6 1.4
22 19.5 199 Not done 123 1.57 40.7 2.3
23 8 182 Not done 122 0.86 59.1 Not done
24 6.4 183 Not done 115 0.84 60.3 Not done
25 7.7 200 5.4 131 1.32 35.7 Not done
26 7.1 214 Not done 225 1.35 34.7 1.9
27 8.7 201 Not done 123 1.42 38.5 1.5
28 8.2 321 Not done 148 0.54 84.3 0.7
29 5.8 109 Not done 176 0.63 83.5 Not done
30 5.4 168 Not done 142 0.72 98.3 Not done
31 6.2 225 Not done 129 1.01 77.1 Not done
32 6.2 61 Not done 85 6.3 5.7 0.5
33 3.3 75 Not done 124 1.75 25.4 Not done
34 8.3 227 11.1 117 1.27 39.5 Not done
35 12.1 243 13.2 251 1.83 25.2 Not done
36 6.3 451 Not done 98 0.68 81.5 Not done
37 5 503 Not done 104 0.59 85.4 Not done
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Culture, Coexisting Organism, and Antibiotic Sensitivity

The microbiological data are detailed in Table 4. Resistance to ampicillin was found in 35 isolates, which seems to be an intrinsic character of the Raoultella spp., and 2 isolates were multidrug-resistant, but still susceptible to ciprofloxacin. Concomitant growth of other organisms was found in 9 urine culture samples; namely, Escherichia coli (5 cultures), carbapenem-resistant Pseudomonas aeruginosa (1 culture), Enterococcus sp. (1 culture), Group B Streptococcus (1 culture), and mixed gram-positive organisms (1 culture). None of the patients had positive blood cultures.

Table 4.

Microbiological Characteristics

Case No. Antibiotic Sensitivity Profile* Blood Cultures Mode of Urine Collection Other Organisms#
1 Resistant to ampicillin Negative Clean catch None
2 Resistant to ampicillin Not done Clean catch None
3 Resistant to ampicillin Not done Clean catch <50,000 Group B Streptococcus
4 Resistant to ampicillin Not done Clean catch None
5 Resistant to ampicillin, cefazolin, ceftazidime, gentamicin. Intermediate sensitivity to tobramycin. Not done Clean catch Escherichia coli
6 Resistant to ampicillin. Not done Clean catch None
7 Resistant to ampicillin Negative Clean catch Escherichia coli
8 Resistant to ampicillin Not done Clean catch Escherichia coli, 50,000–100,000 CFU mixed gram positive orgnisms
9 Resistant to ampicillin Not done Clean catch None
10 Resistant to ampicillin Not done Clean catch None
11 Resistant to ampicillin Not done Clean catch None
12 Resistant to ampicillin Not done Nephrostomy tube Enterococcus fecalis
13 Resistant to ampicillin, cefazolin, ceftazidime, cefoxitin, gentamicin, trimethoprim-sulfamethoxazole, aztreonam, meropenem, piperacillin-tazobactam. Intermediate sensitivity to tobramycin; Negative Foley catheter CRE Pseudomonas aeurogenosa.
14 Resistant to ampicillin Negative Clean catch None
15 Resistant to ampicillin Negative Clean catch Escherichia coli
16 Resistant to ampicillin Not done Foley catheter Escherichia coli
17 Resistant to ampicillin Not done Clean catch None
18 Resistant to ampicillin Not done Straight catheterization None
19 Resistant to ampicillin Not done Clean catch None
20 Resistant to ampicillin Negative Clean catch None
21 Resistant to ampicillin Negative Straight catheterization None
22 Resistant to ampicillin Negative Clean catch 50,000–100,000 CFU
Mixed gram positive and gram negative.
23 Resistant to ampicillin Not done Clean catch None
24 Resistant to ampicillin Not done Clean catch None
25 Resistant to ampicillin Negative Clean catch None
26 Resistant to ampicillin Not done Clean catch None
27 Resistant to ampicillin Not done Foley catheter None
28 Resistant to ampicillin Not done Clean catch None
29 Resistant to ampicillin Not done Straight catheterization None
30 Resistant to ampicillin Not done Clean catch None
31 Resistant to ampicillin Not done Foley catheter None
32 Resistant to ampicillin Negative Clean catch None
33 Resistant to ampicillin Negative Clean catch None
34 Resistant to ampicillin Not done Clean catch None
35 Resistant to ampicillin Negative Foley catheter None
36 Resistant to ampicillin Not done Clean catch None
37 Resistant to ampicillin Not done Clean catch None
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Notes: *The antibiotics for which the sensitivities were analyzed were ampicillin, cefoxitin, cefazolin, ceftazidime, gentamicin, ciprofloxacin, nitrofurantoin, trimethoprim-sulfamethoxazole (Bactrim), aztreonam, meropenem, piperacillin-tazobactam. Due to lack of space, only the resistance pattern has been documented in the table It is implied that the isolate was sensitive to other antibiotics mentioned above. #All the organisms in the urine culture were greater than 105 colony forming units unless specified.

Abbreviation: CFU, colony forming units.

Clinical Course, Hospital Management, and Outcome

The severity of illness varied widely ranging from asymptomatic bacteriuria to septic shock as depicted in Table 5. Antibiotics were administered to 24 patients while 13 patients did not receive any antibiotics. The mean duration of antibiotic administration was 7.54 days. Ciprofloxacin was the most commonly used antibiotic and was administered to 9 patients. Ceftazidime/avibactam was used in the UTI caused by drug-resistant isolates. All patients responded to treatment. The mean length of stay was 3.18 days.

Table 5.

The Clinical Course of the Patients with R. planticola-Associated UTIs

Case No. Severity of Illness Antibiotic Administered Length of Stay Duration of Antibiotics Outcome
1 Acute cystitis Ciprofloxacin 2 7 Discharged home
2 Acute cystitis Ciprofloxacin 3 7 Discharged home
3 Asymptomatic bacteriuria None 4 – Discharged home
4 Asymptomatic bacteriuria None 2 – Discharged home
5 Asymptomatic bacteriuria None 5 – Discharged back to NH.
6 Acute cystitis Ciprofloxacin 3 5 Discharged home
7 Acute cystitis Ciprofloxacin 5 7 Discharged back to NH.
8 Acute cystitis Ciprofloxacin 5 5 Discharged home
9 Asymptomatic bacteriuria Nitrofurantoin 6 10 Discharged home
10 Acute cystitis Levofloxacin, Cefdinir 4 1 Discharged home
11 Acute cystitis Cephalexin 0 Left against medical advice from the ED.
12 Asymptomatic bacteriuria Ampicillin 7 3 Discharged home
13 Septic shock Ceftazidime/Avibactam 8 14 Discharged home
14 Asymptomatic bacteriuria Ampicillin + ceftazidime 4 3 Discharged home
15 Asymptomatic bacteriuria None Discharged home
16 Acute cystitis Ciprofloxacin 4 10 Discharged home.
17 Acute cystitis None 0 Left against medical advice from the ED.
18 Asymptomatic bacteriuria None 0 Discharged home from the ED
19 Asymptomatic bacteriuria None 4 0 Discharged home
20 Sepsis Ceftriaxone 3 7 Discharged home
21 Sepsis Ceftazidime 6 14 Discharged home
22 Acute cystitis Ceftazidime for 3 days then ciprofloxacin. 3 10 Discharged to short term rehab
23 Asymptomatic bacteriuria None 2 0 Discharged home
24 Asymptomatic bacteriuria None 0 (ED) 0 Discharged home
25 Acute cystitis Ceftazidime for 3 days then cefpodoxime 4 7 Discharged back to NH
26 Acute cystitis Nitrofurantoin 0 (ED) 7 Discharged back to NH
27 Acute cystitis Ceftazidime for 3 days then cefpodoxime 3 10 Discharged back to NH
28 Asymptomatic bacteriuria Ciprofloxacin 4 5 Discharged back to NH
29 Acute cystitis Ceftazidime for 4 days then cefpodoxime 5 10 Discharged to short term rehab.
30 Acute cystitis Ciprofloxacin 0(ED) 7 Discharged home
31 Asymptomatic bacteriuria None 2 0 Discharged to short term rehab.
32 Septic shock Ceftazidime 4 7 Discharged back to NH.
33 Asymptomatic bacteriuria None 4 0 Discharged home.
34 Asymptomatic bacteriuria None 3 0 Discharged home.
35 Acute cystitis Ceftazidime for 3 days then cefpodoxime. 3 7 Discharged home.
36 Asymptomatic bacteriuria None 2 0 Discharged home.
37 Acute cystitis Cefpodoxime 4 7 Discharged home.
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Abbreviations: NH, nursing home; ED, emergency department.

Discussion

Urinary tract infections can range from simple asymptomatic bacteriuria to complicated ascending tract infections leading to bacteremia and sepsis.18 The risk of complications is more pronounced in diabetics, elderly people with indwelling catheters, and immunocompromised individuals.19–21 Raoultella planticola has been rarely reported to be significantly associated with UTI. To the best of our knowledge, this is the first review of the clinical characteristics of R. planticola-associated UTIs.

R. planticola UTI seems to occur approximately three times more common in females in our study population, which mirrors the gender distribution for UTIs with other organisms.22

Advanced age, immunocompromised condition like cancer, diabetes mellitus and impaired renal function were noted to be significant risk factors for developing R. planticola UTI, similar to the risk factors in UTIs due to other organisms.23,42 The mean age of our study population was 77 years. A diagnosis of diabetes mellitus was present in 43.24% (16/37) of the patients and 21% (8/37) had a glycated hemoglobin (HbA1C) >6%.

A BMI of greater than 25 kg/m2 was present in 51.35% (19/37) of patients and the mean BMI of this cohort was 26.64 kg/m2. Our study was underpowered to determine if obesity was an independent risk factor.

A large study of UTI in diabetics, done in Germany, has suggested that a GFR of less than 60 mL/min increases the risk of UTI.23 However, it is unclear if chronic renal insufficiency is a risk independent of age and diabetes mellitus.24 Twenty-three patients (including one patient who was post-renal transplant) in our study population had chronic kidney disease (GFR < 60 mL/min). In the subset of patients with chronic renal insufficiency, 52% (12/23) did not have a diagnosis of diabetes mellitus. Therefore, it is likely that impaired renal function increases the risk of R. planticola-associated UTIs. However, our study was not powered to make that determination.

In our study, the most common presentation was asymptomatic bacteriuria (16/37, 43.24%). However, 4 patients (10.81%) in the study population fulfilled the SIRS criteria for sepsis. Of those, 2 patients (5.4%) went into septic shock requiring aggressive intravenous fluid therapy and/or pressor support. Levy et al found that approximately 9–31% of all cases of sepsis can be attributed to urinary tract infection (depending on the geographical region).25 Based on studies, Klebsiella spp. is responsible for 15% of all cases of urosepsis.26,27 Due to its close similarity to Klebsiella spp., it is possible that many of those could have been due to R. planticola and may have been misdiagnosed in the past. There have been a few case reports of Raoultella bacteremia.6–9,28,29 No cases of bacteremia secondary to UTI were observed in our study. With the increasing use of techniques such as Matrix-Assisted Desorption Ionization–Time of Flight Mass Spectrometry (MALDI-TOF MS), R. planticola is being detected more frequently than in the past.28,29

Multiple studies have demonstrated that UTIs present differently in the elderly.30,31 A study performed by D’Agata et al in-nursing home residents showed that altered mental status is by far the commonest presentation (approximately 40%). The classical UTI symptoms of dysuria (3.8%), costovertebral tenderness (2.3%), urinary frequency (1.5%), urgency (0%) and suprapubic pain (0%) are much less common in adults greater than 65 years.30 Our study demonstrated similar findings.

As mentioned above, due to phylogenetic similarities, it is difficult to differentiate between Klebsiella spp. and Raoultella spp. by microscopy. The biochemical tests to differentiate Raoultella spp. from Klebsiella spp. such as ornithine decarboxylase activity, histamine or D-melezitose utilization, is not routinely available in commercial test kits.26,27 MALDI-TOF MS has emerged, in recent years, as a faster technique to identify Raoultella spp. and its reliability has been proven by multiple studies.5,32–34 It essentially involves taking a sample from a bacterial colony, absorbing the lysed bacterial proteins onto a matrix, followed by ionizing and desorbing it with a laser. The resultant plume is analyzed through mass spectrometry to detect the signature pattern that identifies the bacteria. An additional advantage is the rapid detection of resistant strains. This technique is very effective in gram-negative bacteria, even with microcolonies.35 One limitation is the need for pure colonies; mixed colonies can lead to erroneous results.

In our laboratory, we used the VITEK® 2 compact automated system microbial identification (ID) and antibiotic susceptibility testing (AST) card for identification of organisms. The VITEK® 2 compact automated system uses 47 biochemical tests on a compact card specifically designed to identify gram-negative bacilli and their sensitivity. This technique usually identifies the organisms within 10 hours.36 A frequently encountered problem with the system is the misidentification of Raoultella spp. as Klebsiella spp.32 To avoid such errors, Analytical Profile Index-20E (API-20E) was used to differentiate between members of the Enterobacteriaceae family in our laboratory. This technique uses a miniaturized version of 20 biochemical tests. The positive and negative results are compiled to obtain a unique profile code used to identify the organism. The sensitivity for identification of Raoultella spp. is 93.3% in VITEK® 2 compact automated system, and 97.4% in the MALDI-TOF MS method. Though MALDI-TOF is better than VITEK® 2 compact automated system in terms of sensitivity, both systems detect Raoultella spp. with a high degree of accuracy and the high initial cost of the MALDI-TOF system has restricted its use mostly to higher centres.

R. planticola is intrinsically resistant to ampicillin due to the over-expression of chromosomally encoded class-A β-lactamase.31,32 The other two major groups of resistance genes seen in Raoultella spp. are extended-spectrum β-lactamase (ESBL) and carbapenemase genes. Due to the ubiquitous nature of Raoultella spp, there is a very high risk of them acting as environmental reservoirs for resistance genes, such as carbapenemase.37,38 An analysis of sewage water from a tertiary centre in Spain revealed the presence of multiple carbapenemases producing Raoultella spp.39 These resistance genes can then be carried on mobile genetic elements like transposons and plasmids which are capable of transforming naive bacteria. In our study population, 2 patients had multidrug-resistant R. planticola-associated UTI. Both of these strains were resistant to ceftazidime which is routinely used in our institution to cover urinary gram-negative bacteria as per our hospital antibiogram. Though not reported, we can assume that this isolate probably had ESBL resistance gene/genes. Out of these two patients, one had a hospital-acquired catheter-associated UTI with a coexisting carbapenem-resistant Pseudomonas aeruginosa. The other patient had a coexisting Escherichia coli infection.

In addition to this, another 9 patients had a concomitant growth of a second organism found on urine culture. This is particularly concerning as mobile genetic elements, especially plasmids (chiefly IncF, IncI, IncA/C, IncL, IncN, and IncH plasmids) can transmit resistance genes between Enterobacteriaceae.40,41

Limitations of the Study

Due to the low prevalence of R. planticola-associated UTIs in general, the sample size was small in our study. We were not able to establish the statistical significance of our findings as a result of the small sample size. As this was a retrospective study, we encountered missing data. For example, not all patients had glycated hemoglobin levels analyzed during their hospitalization. Information on whether a urinary catheter was placed during the current hospitalization or whether it was chronic was not documented in many patient’s charts. This left us unable to determine whether some of the UTIs were true infections or colonization that was discovered incidentally. Similarly, details on the structural abnormalities of the genitourinary tract and outpatient urological procedures were missing sometimes. The samples were analyzed by VITEK® 2 compact automated system microbial identification (ID) and antibiotic susceptibility testing (AST) card which is less accurate than a MALDI-TOF MS.

Conclusion

Our study revealed that patients with R. planticola UTI had higher proportion of diabetes mellitus, renal failure compared to the general population. Unlike prior case reports, most of the infections occurred in immunocompetent patients. Our study also confirms the intrinsic resistance to ampicillin of R. species, which has been documented previously in the literature. Surprisingly, Escherichia coli seems to coexist with Raoultella spp. in a significant number of cultures. A worrying finding was the presence of multidrug-resistant isolates, one of which was associated with multidrug-resistant Pseudomonas aeruginosa, which raises concern for the transmission of resistance genes. This raises concern for the transmission of resistance genes. As our study was limited by relatively small sample size and the retrospective nature of the analysis, larger studies would help us further define the observations noted in this study.

Funding Statement

No funding used.

Ethical Statement

The article doesn’t contain the participation of any human being and animal. As per our IRB, we did not require to take patient consent for the retrospective study for the electronic chart review. The study team ensured to maintain the patient data confidentiality and also was compliant with the Declaration of Helsinki.

Institutional Approval

IRB approval taken for this project from our hospital research approval team (MetroWest Medical Centre Institutional Review Board, IRB #2020 −142).

Author Contributions

All authors made substantial contributions to conception and design, acquisition of data, or analysis and interpretation of data; took part in drafting the article or revising it critically for important intellectual content; agreed to submit to the current journal; gave final approval of the version to be published; and agreed to be accountable for all aspects of the work.

Disclosure

Authors have no conflicts of interest to declare.

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