Maternal bacteremia caused by Listeria monocytogenes ST87: A case report

Abstract

Pregnant women are at a high risk of contracting listeriosis; however, there have been only a few clinical reports of maternal bacteremia occurring before 20 weeks of gestation in China. In this case report, a 28-year-old pregnant woman at 16 weeks and 4 days of gestation was admitted to our hospital suffering from fever for four days. The patient was initially diagnosed with an upper respiratory tract infection at the local community hospital; nevertheless, the cause of the infection was unknown. In our hospital, she was diagnosed with Listeria monocytogenes (L. monocytogenes) infection by the blood culture system. Before the results of blood culture were obtained, ceftriaxone and cefazolin were given for three days respectively based on clinical experience. However, the fever didn't reduce until she was treated with ampicillin. This pathogen was further identified as L. monocytogenes ST87 by serotyping, multilocus sequence typing (MLST), and virulence gene amplification. Finally, a healthy baby boy was born in our hospital, and the neonate was developing well at the 6-week postnatal follow-up visit. This case report suggests that patients with L. monocytogenes ST87-caused maternal listeriosis can have a good prognosis; however, more clinical information and molecular experiments are needed to confirm our hypothesis.

1. Introduction

Listeria monocytogenes (L. monocytogenes) is a typical foodborne pathogen with high genetic heterogeneity. Multilocus sequence typing (MLST) has indicated that L. monocytogenes has a distinct and frequent sequence types (STs) or clonal complexes (CCs) in clinical infections and food products. Differences in the strength of a clone's association with human listeriosis could be causally linked to the high heterogeneity of virulence factors [1]. For instance, Listeria pathogenicity island 4 (LIPI-4)–confirmed to exist in strains CC4, ST619, and ST87–has high clinical relevance, especially in central nervous system and maternal neonate infections [2]. L. monocytogenes ST87 (ST87) is one of the most common ST strains isolated from food products, food-associated environments, and samples from patients with sporadic listeriosis in China [[3], [4], [5]]. However, the disease phenotypes of clinical ST87 infection remain poorly understood at the epidemiological, clinical, and mechanistic levels [6,7].

Maternal neonatal listeriosis accounts for approximately 8–17% of listeriosis cases [8,9], with maternal infection rarely occurring before 20 weeks of gestation [10]. Patients with fetal disseminated infections have a poor prognosis with a high risk of stillbirth, miscarriage, or fetal death [11,12]. Herein, we present a case of ST87 bacteremia in a pregnant woman at 16 weeks of gestation who had a healthy pregnancy outcome. This pathogen was confirmed by serotyping, MLST, and virulence gene amplification methods. Up to now, many studies have reported about L. monocytogenes clinical cases and molecular mechanisms [[13], [14], [15]]; however, only a few studies have focused on ST87. This report suggests that patients with ST87-caused maternal listeriosis can have a good prognosis; however, more clinical information and molecular experiments are needed to confirm our hypothesis.

2. Case presentation

A 28-year-old gestation 2 and parturition 0 (G2P0) pregnant woman was admitted to our hospital at 16 weeks and 4 days gestation due to suffering from fever for four days. Four days ago, she had visited the local community hospital's emergency department for some checks due to a fever (38.5 °C). The results of physical examination, cervical and fetal examination were normal except for the temperature. The white blood cell (WBC), C-reactive protein (CRP), and procalcitonin (PCT) values were 7.17 × 10⁹ cells/L (Neu 67.6%, Ly 20.6%, and Mo 11.6%), 36.7 mg/L, and 0.27 ng/mL, respectively. Furthermore, an influenza test result was also negative. No blood cultures or vaginal swabs were obtained and examined. She was diagnosed as an upper respiratory tract infection and discharged from the local community hospital. However, the fever persisted along with general weakness and appetite loss, therefore she came to our hospital.

The patient was admitted to our obstetrics and gynecology clinic. Her vital signs were normal when admitted, except for an axillary temperature >38.7 °C. The WBC, CRP, and PCT values were 8.06 × 10⁹ cells/L (Neu 78.1%, Ly 14.0%, and Mo 7.7%), 11.5 mg/L, and 0.22 ng/mL, respectively. The functions of urine and liver were found to be normal. Vaginal swabs and blood cultures were obtained before empirical antimicrobial therapy with intravenous ceftriaxone (2 g/day) for three days; however, a mild fever (37.6 °C) persisted. No pathogens were detected from vaginal swabs; however, L. monocytogenes was detected from the blood culture bottles and confirmed using matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry. Due to a lack of experience in treating with L. monocytogenes, the patient's therapy was replaced with intravenous cefazolin (2 g every 12 h) for another three days, which resulted in body temperature fluctuations between 36.4 °C and 37.2 °C. Cefazolin was discontinued on day 7, and her body temperature rose to 37.8 °C. After consulting clinical laboratory experts, ampicillin was recommended and administered intravenously (1.2 g every 8 h) for seven days until the results of blood culture became negative. She was discharged from our hospital and continued oral ampicillin for additional week. Subsequently, she underwent routine prenatal examination at our hospital. Eventually, the patient gave birth to a eutrophic boy via vaginal delivery at 40 weeks of gestation, and the infant's clinical examination and placental macroscopic assessments were normal. No blood cultures were obtained from the infant; however, the CRP levels of the mother and the newborn were normal in a clinical examination during the 3-day postpartum observation. The infant developed well without any neurological damage at the 6-week follow-up assessment.

The strain isolated from the patient was kept in our laboratory. Serotyping, MLST, and virulence gene amplification methods were used to determine the genotype of this strain. Firstly, ten virulence genes (rrn, hlyA, actA, prfA, inlA, inlB, iap, plcA, plcB, and mpl) of L. monocytogenes were amplified to determine it was L. monocytogenes (Fig. 1) [16]. Secondly, serotyping was performed to identify PCR serogroups of L. monocytogenes strains by amplifying four marker genes (lmo0737, lmo1118, ORF2819, and ORF2110), with prs serving as a positive control [17]. This strain was identified as serovars 1/2b, 3b, and 7, for only ORF2819 was amplified (Fig. 2) [17]. Lastly, MLST analysis was performed to determine the genotype of this strain, according to the Pasteur Institute Protocol (https://bigsdb.pasteur.fr/listeria/). The internal fragments of seven L. monocytogenes housekeeping genes (acbZ, bglA, cat, dapE, dat, ldh, and lhkA) were amplified and sequenced using an Applied Biosystems 3730XL DNA Analyzer to assess similarity and compatibility. As only ST87 was found, the strain was finally identified as L. monocytogenes ST87 (Fig. 3A and B; MLST sequencing results are available in the Supplementary Materials) [18]. Based on these results, we concluded that the isolated strain from this patient was a virulent strain of L. monocytogenes ST87. The primers used in this study are listed in Table 1.

Fig. 1.

Ten virulence genes of L. monocytogenes were amplified by PCR.

Fig. 2.

Serotyping was performed by amplifying four marker genes: lmo0737, lmo1118, ORF2819, and ORF2110, with prs served as a positive control.

Fig. 3.

MLST analysis was performed based on the sequencing of internal fragments of seven L. monocytogenes housekeeping genes: acbZ, bglA, cat, dapE, dat, ldh, and lhkA. Results of (A) PCR amplification and (B) MLST comparison revealed that this strain was ST87.

Table 1.

PCR and sequencing primers used in this study.

PCR	Target genes	Primer sequences (5′–3′)	Product size (bp)
Virulence genes [16]	rrn-F	CAGCAGCCGCGGTAATAC	938
	rrn-R	CTCCATAAAGGTGACCCT
	hlyA-F	CCTAAGACGCCAATCGAA	702
	hlyA-R	AAGCGCTTGCAACTGCTC
	actA-F	GACGAAAATCCCGAAGTGAA	268/385
	actA-R	CTAGCGAAGGTGCTGTTTCC
	prfA-F	CTGTTGGAGCTCTTCTTGGTGAAGCAATCG	1060
	prfA-R	AGCAACCTCGGAACCATATACTAACTC
	inlA-F	CCTAGCAGGTCTAACCGCAC	255
	inlA-R	TCGCTAATTIGGTTATGCCC
	inlB-F	AAAGCACGATTTCATGGGAG	146
	inlB-R	ACATAGCCTTGTTTGGICGG
	iap-F	ACAAGCTGCACCTGTTGCAG	131
	iap-R	TGACAGCGTGTGTAGTAGCA
	plcA-F	CGAGCAAAACAGCAACGATA	129
	plcA-R	CCGCGGACATCTTTTAATGT
	plcB-F	GGGAAATTTGACACAGCGTT	261
	plcB-R	ATTTTCGGGTAGTCCGCTTT
	mpl-F	TTGTTCTGGAATTGAGGATG	502
	mpl-R	TTAAAAAGGAGCGGTGAAAT
Serotyping [17]	lmo0737-F	AGGGCTTCAAGGACTTACCC	691
	lmo0737-R	ACGATTTCTGCTTGCCATTC
	lmo1118-F	AGGGGTCTTAAATCCTGGAA	906
	lmo1118-R	CGGCTTGTTCGGCATACTTA
	ORF2819-F	AGCAAAATGCCAAAACTCGT	471
	ORF2819-R	CATCACTAAAGCCTCCCATTG
	ORF2110-F	AGTGGACAATTGATTGGTGAA	597
	ORF2110-R	CATCCATCCCTTACTTTGGAC
	prs-F	GCTGAAGAGATTGCGAAAGAAG	370
	prs-R	CAAAGAAACCTTGGATTTGCGG
MLST [18]	abcZ-F	GTTTTCCCAGTCACGACGTTGTATCGCTGCTGCCACTTTTATCCA	537
	abcZ-R	TTGTGAGCGGATAACAATTTCTCAAGGTCGCCGTTTAGAG
	bglA-F	GTTTTCCCAGTCACGACGTTGTAGCCGACTTTTTATGGGGTGGAG	399
	bglA-R	TTGTGAGCGGATAACAATTTCCGATTAAATACGGTGCGGACATA
	cat-F	GTTTTCCCAGTCACGACGTTGTAATTGGCGCATTTTGATAGAGA	486
	cat-R	TTGTGAGCGGATAACAATTTCAGATTGACGATTCCTGCTTTTG
	dapE-F	GTTTTCCCAGTCACGACGTTGTACGACTAATGGGCATGAAGAACAAG	462
	dapE-R	TTGTGAGCGGATAACAATTTCATCGAACTATGGGCATTTTTACC
	dat-F	GTTTTCCCAGTCACGACGTTGTAGAAAGAGAAGATGCCACAGTTGA	471
	dat-R	TTGTGAGCGGATAACAATTTCTGCGTCCATAATACACCATCTTT
	ldh-F	GTTTTCCCAGTCACGACGTTGTAGTATGATTGACATAGATAAAGA	453
	ldh-R	TTGTGAGCGGATAACAATTTCTATAAATGTCGTTCATACCAT
	lhkA-F	GTTTTCCCAGTCACGACGTTGTAAGAATGCCAACGACGAAACC	480
	lhkA-R	TTGTGAGCGGATAACAATTTCTGGGAAACATCAGCAATAAAC

3. Discussion

L. monocytogenes is an opportunistic foodborne pathogen that can cause severe human listeriosis in immunocompromised individuals. Although rare, this pathogen contributes significantly to the global burden of foodborne diseases. In fact, almost 1600 cases of listeriosis are reported each year in the United States, resulting in 260 deaths [19]. Mortality from listeriosis ranges between 20 and 30% in several European regions [20]. There has been a recent increase in human listeriosis in China, with mortality reaching up to 26% [21,22]. Considering the low morbidity and high mortality associated with human listeriosis, effective surveillance of L. monocytogenes is urgently required in China. This involves extensive investigation of the population distribution and molecular characterization of isolates from clinical and food sources. L. monocytogenes can be divided into at least four phylogenetic lineages [[23], [24], [25]], thirteen serotypes and four PCR serogroups [17]. MLST allows further classification of L. monocytogenes populations into STs or CCs. The relative distribution of clones, ascribed to isolates from both clinical and food samples, is highly uneven across countries. In Western countries, CC1, CC2, CC4, and CC6 are strongly associated with clinical infections, whereas CC121 and CC9 are the most frequent types responsible for food contamination [26]. ST87 is the most common ST isolated from human listeriosis in China and has been detected in various food sources [[3], [4], [5]]. Notably, a previous study revealed that ST87 is predominantly found in fresh vegetable samples, accounting for 36.7% of the total L. monocytogenes population, followed by ST8 (26.7%), ST9 (13.3%), and ST3 (6.7%) [27].

In China, vegetables, such as lettuce, cabbage, tomato, carrot, cucumber, and corn are heavily contaminated with L. monocytogenes. The highest contamination rates have been reported for lettuce, tomato, and cucumber (7.78%, 4.90%, and 4.88%, respectively) [27]. Hence, the vegetable salad was considered the probable cause of listeriosis, although the source tracing has not been well conducted. Nevertheless, ST87 is associated with foodborne infections in China [6]. Genomes of ST87 isolates from food and clinical sources were analyzed, showing that Chinese ST87 clones have essentially conserved core and accessory genomes. This finding demonstrates that these ST87 isolates from both sources were closely related clones.

Clinically, listeriosis most commonly occurs during the third trimester of pregnancy [10]. Maternal listeriosis is usually mild or asymptomatic, but fetal or neonatal infection can lead to miscarriage, stillbirth, neonatal sepsis, and meningitis [28], with an overall mortality rate exceeding 50% [29]. Gestational age at the beginning of infection is an important prognostic indicator of fetal survival [9]. Specifically, maternal neonatal listeriosis in the first trimester of pregnancy is characterized by a poor prognosis, with a high risk of miscarriage (up to 65%) and a poor prognosis; however, second or third-trimester infections have a relatively low risk of miscarriage, stillbirth, or fetal death (26%) [12]. Notably, in this case report, despite the pregnant patient experiencing an earlier misdiagnosis and a delay in antibiotic therapy, she achieved a good outcome with no fetal or neonatal infection. Moreover, a human listeriosis surveillance study in Beijing discovered that fetuses in pregnancy-associated cases caused by the ST87 strain survived, whereas those caused by the ST5 strain died [3]. Interestingly, ST87-caused maternal listeriosis did not affect pregnancy outcomes, implying that patients with ST87-caused maternal listeriosis may have a good prognosis. However, in this case report, clinical empirical medication must also be considered. Despite the fact that L. monocytogenes was detected in the blood culture on day 3, cefazolin was administered for another three days before consulting a clinical laboratory specialist. In fact, the fever significantly reduced until ampicillin was prescribed and administered intravenously. Given the potential for miscommunication between physicians and clinical laboratory experts, we hope that the present case report can be used as a wake-up call to both. While this case had a positive outcome, there are still insufficient data to confidently predict the outcome of maternal and neonatal listeriosis caused by the ST87 strains. To improve the surveillance of this infection, future study should focus on more clinical and molecular mechanisms, such as whole-genome sequencing and animal studies.

4. Conclusions

This case report describes the incidence of a 28-year-old pregnant woman diagnosed with listeriosis at 16 weeks and 4 days of gestation who delivered a healthy baby after treatment. Serotyping, MLST, and virulence gene amplification confirmed that the isolated strain was L. monocytogenes ST87. In conclusion, we found a favorable prognosis for patients with maternal L. monocytogenes ST87. However, more clinical information and molecular experiments are needed to confirm the hypothesis.

Author contribution statement

All authors listed have significantly contributed to the investigation, development and writing of this article.

Funding statement

Associate Professor Yaya Pian was supported by Beijing Natural Science Foundation [5222034].

Data availability statement

No data was used for the research described in the article.

Appendix A. Supplementary data

The following is the Supplementary data to this article:

Fig. S1.