Listeriosis Cases and Genetic Diversity of Their L. monocytogenes Isolates in China, 2008-2019

Prevalence, Genotypic Characteristics, and Antibiotic Resistance of Listeria monocytogenes From Retail Foods in Huzhou, China

Listeria monocytogenes are considered to be the major foodborne pathogen worldwide. To understand the prevalence and potential risk of L. monocytogenes in retail foods, a total of 1243 retail foods in 12 food categories were sampled and screened for L. monocytogenes from 2020 to 2022 in Huzhou, China. A total of 46 out of 1234 samples were confirmed to be L. monocytogenes positive with a total rate of 3.7%. The contamination rate of seasoned raw meat (15.2%) was the highest, followed by raw poultry meat and raw livestock meat (9.9%) and salmon sashimi (9.5%). The L. monocytogenes isolates belonged to four serotypes, 1/2a,1/2b, 1/2c, and 4b, with the most prevalent serotype being 1/2a (47.9%). All isolates were grouped into 15 sequence types (STs) belonging to 14 clonal complexes (CCs) via multilocus sequence typing (MLST). The most prevalent ST was ST9/CC9 (23.9%), followed by ST3/CC3 (19.6%) and ST121/CC121 (17.4%). Notably, 11 STs were detected from ready-to-eat (RTE) foods, some of them have been verified to be strongly associated with clinical origin listeriosis cases, such as ST3, ST2, ST5, ST8, and ST87. Listeria pathogenicity islands 1 (LIPI-1) and LIPI-2 were detected in approximately all L. monocytogenes isolates, whereas the distribution of both LIPI-3 genes and LIPI-4 genes exhibited association with specific ST, with LIPI-3 in ST3 and ST288, and LIPI-4 in ST87. The strains carrying LIPI-3 and LIPI-4 virulence genes in this study were all isolated from RTE foods. Antimicrobial susceptibility tests showed that >90% of isolates were susceptible to PEN, AMP, ERY, CIP, SXT, VAN, CHL, and GEN, indicating the antibiotic treatment might be still efficient for most of the L. monocytogenes strains. However, for the three clinical first-line antibiotics (PEN, AMP, and GEN), we also observed three and four strains showing MIC values greater than the susceptibility standards for PEN and AMP, respectively, and one strain showing resistance to GEN.

Listeria monocytogenes from Food Products and Food Associated Environments: Antimicrobial Resistance, Genetic Clustering and Biofilm Insights

Listeria monocytogenes, a foodborne pathogen, exhibits high adaptability to adverse environmental conditions and is common in the food industry, especially in ready-to-eat foods. L. monocytogenes strains pose food safety challenges due to their ability to form biofilms, increased resistance to disinfectants, and long-term persistence in the environment. The aim of this study was to evaluate the presence and genetic diversity of L. monocytogenes in food and related environmental products collected from 2014 to 2022 and assess antibiotic susceptibility and biofilm formation abilities. L. monocytogenes was identified in 13 out of the 227 (6%) of samples, 7 from food products (meat preparation, cheeses, and raw milk) and 6 from food-processing environments (slaughterhouse-floor and catering establishments). All isolates exhibited high biofilm-forming capacity and antibiotic susceptibility testing showed resistance to several classes of antibiotics, especially trimethoprim-sulfamethoxazole and erythromycin. Genotyping and core-genome clustering identified eight sequence types and a cluster of three very closely related ST3 isolates (all from food), suggesting a common contamination source. Whole-genome sequencing (WGS) analysis revealed resistance genes conferring resistance to fosfomycin (fosX), lincosamides (lin), fluoroquinolones (norB), and tetracycline (tetM). In addition, the qacJ gene was also detected, conferring resistance to disinfecting agents and antiseptics. Virulence gene profiling revealed the presence of 92 associated genes associated with pathogenicity, adherence, and persistence. These findings underscore the presence of L. monocytogenes strains in food products and food-associated environments, demonstrating a high virulence of these strains associated with resistance genes to antibiotics, but also to disinfectants and antiseptics. Moreover, they emphasize the need for continuous surveillance, effective risk assessment, and rigorous control measures to minimize the public health risks associated to severe infections, particularly listeriosis outbreaks. A better understanding of the complex dynamics of pathogens in food products and their associated environments can help improve overall food safety and develop more effective strategies to prevent severe health consequences and economic losses.

Genomic epidemiology of hypervirulent Listeria monocytogenes CC619: Population structure, phylodynamics and virulence

Listeria monocytogenes is a ubiquitous foodborne pathogen causing human and animal listeriosis with high mortality. Neurological and maternal-neonatal listeriosis outbreaks in Europe and the United States were frequently associated with clonal complexes CC1, CC2 and CC6 harboring Listeria Pathogenicity Island-1 (LIPI-1), as well as CC4 carrying both LIPI-1 and LIPI-4. However, human listeriosis in China was predominantly linked to CC87 and CC619 from serotype 1/2b. To understand the genetic evolution and distribution patterns of CC619, we characterized the epidemic history, population structure, and transmission feature of CC619 strains through analysis of 49,421 L. monocytogenes genomes globally. We found that CC619 was uniquely distributed in China, and closely related with perinatal infection. As CC619 strains were being mainly isolated from livestock and poultry products, we hypothesized that pigs and live chicken were the reservoirs of CC619. Importantly, all CC619 strains not only harbored the intact LIPI-1 and LIPI-4, but these also carried LIPI-3 that could facilitate host colonization and invasion. The deficiency of LIPI-3 or LIPI-4 markedly decreased L. monocytogenes colonization capacity in a model of intragastric infection in the mouse. Altogether, our findings suggest that the hypervirulent CC619 harboring three pathogenicity islands LIPI-1, LIPI-3 and LIPI-4 is a putatively persistent population in various foods, environment, and human population, warranting the further research for deciphering its pathogenicity and strengthening epidemiological surveillance.

A novel multiplex PCR based method for the detection of Listeria monocytogenes clonal complex 8

Listeria monocytogenes is an important foodborne pathogen worldwide, which could cause listeriosis with a 20-30 % fatality rate in immunocompromised individuals. Listeria monocytogenes MLST clonal complex (CC) 8 strain is a common clone in food and clinical cases. The aim of this study was to develop multiplex PCR (mPCR) and high-resolution melting (HRM) qPCR to simultaneously detect L. monocytogenes CC8 and the other L. monocytogenes strains based on pan-genome analysis. A novel multiplex PCR and HRM qPCR targeted for the genes LM5578_1180 (specific for CC8) and LM5578_2262 (for L. monocytogenes) were developed. The specificity of this multiplex PCR and HRM qPCR were verified with other CCs of L. monocytogenes and other species strains. The detection limit of this multiplex PCR and HRM qPCR is 2.1 × 103 CFU/mL and 2.1 × 100 CFU/mL, respectively. This multiplex PCR and HRM qPCR could accurately detect CC8 strains with the interference of different ratios of L. monocytogenes CC9, CC87, CC121, CC155, and L. innocua strains. Subsequently, the detection ability of mPCR and HRM qPCR were also evaluated in spiked samples. The mPCR method could successfully detect 6.2 × 103 CFU/mL of CC8 L. monocytogenes after 6 h enrichment while the multiplex HRM qPCR method could successfully detect 6.2 × 104 CFU/mL of CC8 L. monocytogenes after 3 h enrichment. The feasibility of these methods were satisfactory in terms of sensitivity, specificity, and efficiency after evaluating 12 mushroom samples and was consistent with that of the National Standard Detection Method (GB4789.30-2016). In conclusion, the developed assays could be applied for rapid screening and detection of L. monocytogenes CC8 strains both in food and food production environments, providing accurate results to adopt monitoring measures to improve microbiological safety.

DegU-mediated suppression of carbohydrate uptake in Listeria monocytogenes increases adaptation to oxidative stress

The foodborne bacterial pathogen Listeria monocytogenes exhibits remarkable survival capabilities under challenging conditions, severely threatening food safety and human health. The orphan regulator DegU is a pleiotropic regulator required for bacterial environmental adaptation. However, the specific mechanism of how DegU participates in oxidative stress tolerance remains unknown in L. monocytogenes. In this study, we demonstrate that DegU suppresses carbohydrate uptake under stress conditions by altering global transcriptional profiles, particularly by modulating the transcription of the phosphoenolpyruvate-carbohydrate phosphotransferase system (PTS)-related genes, such as ptsH, ptsI, and hprK. Specifically, in the absence of degU, the transcripts of ptsI are significantly upregulated and those of hprK are significantly downregulated in response to copper ion-induced stress. Overexpression of ptsI significantly increases bacterial growth in vitro, while overexpression of hprK leads to a decrease in growth. We further demonstrate that DegU directly senses oxidative stress, downregulates ptsI transcription, and upregulates hprK transcription. Additionally, through an electrophoretic mobility shift assay, we demonstrate that DegU directly regulates the transcription of ptsI and hprK by binding to specific regions within their respective promoter sequences. Notably, the putative pivotal DegU binding sequence for ptsI is located from 38 to 68 base pairs upstream of the ptsH transcription start site (TSS), whereas for hprK, it is mapped from 36 to 124 base pairs upstream of the hprK TSS. In summary, we elucidate that DegU plays a significant role in suppressing carbohydrate uptake in response to oxidative stress through the direct regulation of ptsI and hprK.ImportanceUnderstanding the adaptive mechanisms employed by Listeria monocytogenes in harsh environments is of great significance. This study focuses on investigating the role of DegU in response to oxidative stress by examining global transcriptional profiles. The results highlight the noteworthy involvement of DegU in this stress response. Specifically, DegU acts as a direct sensor of oxidative stress, leading to the modulation of gene transcription. It downregulates ptsI transcription while it upregulates hprK transcription through direct binding to their promoters. Consequently, these regulatory actions impede bacterial growth, providing a defense mechanism against stress-induced damage. These findings gained from this study may have broader implications, serving as a reference for studying adaptive mechanisms in other pathogenic bacteria and aiding in the development of targeted strategies to control L. monocytogenes and ensure food safety.

Clinical Features and Antibiotic Treatment of Neonatal Listeriosis: A Hospital-Based Study

Purpose

To determine the clinical features, laboratory findings, antibiotic treatment, and outcomes of neonatal listeriosis in a specialized tertiary hospital in Wuhan, China.

Patients and Methods

We retrospectively analyzed the medical records of patients diagnosed with neonatal listeriosis at Maternal and Child Health Hospital of Hubei Province from January 2015 to December 2022. Listeriosis was indicated by positive culture for Listeria monocytogenes (LM).

Results

A total of 11 cases were included in our study. The incidence rate of neonatal listeriosis was 2.06 per 100,000 live births. Seventy-three percent of the cases were born prematurely, caused early onset sepsis. Respiratory distress (100%) was the most common and earliest symptom, followed by fever (64%) and rashes (27%). The levels of C-reactive protein (CRP) and procalcitonin (PCT) were elevated in 100% of the cases. The median time-to-positivity (TTP) of the culture was 15 hours (range 9-28hours). Of the 11 neonates, 6 were cured, 2 showed improvement, and 3 died, with a mortality rate of 27%. There were statistically significant differences in Apgar score at 5 minutes (p=0.037) and CRP (p=0.025) between the survival group and fatality group. Ampicillin was sensitive to LM isolates and effective for therapy if initiated early.

Conclusion

Neonatal listeriosis is a rare but severe infection with a high mortality rate. Early identification and appropriate use of effective antibiotics are particularly critical for achieving positive outcomes. Apgar score and CRP are relevant indices for prognosis. Ampicillin is the first-line therapy and can be empirically administered to neonates suspected of having listeriosis.

Carbapenem-resistant Citrobacter freundii harboring blaKPC-2 and blaNDM-1: a study on their transferability and potential dissemination via generating a transferrable hybrid plasmid mediated by IS6100

Introduction

The increase in clinical Enterobacteriaceae with dual carbapenemase has become a serious healthcare concern. It is essential to characterize the transferability and potential dissemination of blaKPC-2- and blaNDM-1-coharboring carbapenem-resistant Citrobacter freundii (CRCF).

Methods

Four blaKPC-2- and blaNDM-1-coharboring CRCF strains were collected from our surveillance of the prevalence of carbapenem-resistant Enterobacteriaceae. The isolates were assessed using species identification, antimicrobial susceptibility testing, conjugation assays, whole-genome sequencing, plasmid stability, and fitness costs. Clonality, genome, plasmidome, and phylogeny were analyzed to reveal potential dissemination.

Results

Three ST523 blaKPC-2- and blaNDM-1-coharboring CRCF strains, collected from the same hospital within 1 month, exhibited high homology (both identity and coverage >99%), implying clonal dissemination and a small-scale outbreak. Moreover, the blaKPC-2 and blaNDM-1 genes were coharbored on an IncR plasmid, probably generated by a blaKPC-2-harboring plasmid acquiring blaNDM-1, in these three strains. Importantly, the IncR plasmid may form a transferable hybrid plasmid, mediated by IS6100 via transposition, with another IncFII plasmid included in the same C. freundii strain. Furthermore, the blaKPC-2 and blaNDM-1 of the fourth CRCF strain are located on two different non-transferable plasmids lacking complete transfer elements. Additionally, throughout the course of the 10-day continuous passage, the genetic surroundings of blaNDM-1 in four CRCF strains were gradually excised from their plasmids after the 8th day, whereas they maintained 100% retention for blaKPC-2. Genome and plasmidome analyses revealed that blaKPC-2- or blaNDM-1-harboring C. freundii were divergent, and these plasmids have high homology to plasmids of other Enterobacteriaceae.

Conclusion

Clonal dissemination of ST523 blaKPC-2- and blaNDM-1-coharboring CRCF strains was detected, and we first reported blaKPC-2 and blaNDM-1 concomitantly located on one plasmid, which could be transferred with mediation by IS6100 via transposition. Continued surveillance should urgently be implemented.

Molecular Characteristics of an NDM-4 and OXA-181 Co-Producing K51-ST16 Carbapenem-Resistant Klebsiella pneumoniae: Study of Its Potential Dissemination Mediated by Conjugative Plasmids and Insertion Sequences

The carbapenem-resistant Klebsiella pneumoniae (CRKP) strain GX34 was recovered from the respiratory tract of an elderly male with severe pneumonia, and only susceptible to amikacin, tigecycline, and colistin. Complete genome suggested that it belonged to K51-ST16 and harbored plasmid-encoded NDM-4 and OXA-181, located on IncFIB plasmid GX34p1_NDM-4 and ColKP3/IncX3 plasmid GX34p4_OXA-181, respectively. A series of transconjugants generated in the plasmid conjugation assays, including Escherichia coli J53-N1 (harboring a self-transmissible and bla_NDM-1-producing plasmid Eco-N-1-p), J53-N2 (harboring a bla_NDM-4-producing plasmid and a helper plasmid GX34p5), and J53-O (harboring a bla_OXA-181-producing plasmid), could be stably inherited after 10 days of serial passage and no significant biological fitness costs were detected. Furthermore, we first reported the bla_NDM-1 gene, derived from bla_NDM-4 mutation (460C>A) under meropenem pressure, could be in vitro transferred into a self-conjugative, recombined plasmid Eco-N-1-p of J53-N1. Eco-N-1-p was mainly recombined by GX34p4_OXA-181 (40,449 bp, 75.16%) and GX34p1_NDM-4 (8,553 bp, 15.89%), in which IS26 and IS5-like probably played a major role. Eco-N-1-p could be transferred into the conjugation recipient K. pneumoniae KP54 and make the latter sacrifice fitness. The retention rates of bla_NDM-1 remained high stability (>80% after 200 generations). The comparative genomic analysis of GX34 and those carrying bla_NDM-4 or bla_OXA-181 genes retrieved from the NCBI RefSeq database showed all bla_NDM-4 (26/26, 100.00%) and bla_OXA-181 (13/13, 100.00%) were surrounded by IS26. The immediate environment of bla_NDM-4 and bla_OXA-181 in GX34 and some retrieved strains shared identical features, hinting at their possible dissemination. Effective measures should be taken to monitor the spread of this clone.

Analysis of Clinical and Microbiological Features of Listeria monocytogenes Infection

Introduction

To analyze the demographics and clinical features of 59 cases of Listeria monocytogenes, and determine the predisposing conditions for severe meningitis infections for reference.

Materials and methods

A total of 59 cases isolated L. monocytogenes from 2009 to 2020 were enrolled. Electronic medical record data were used to determine the epidemiological and clinical characteristics of L. monocytogenes infection. Univariate and multifactorial logistic regression analyses were performed to predict risk factors for Listeria meningitis.

Results

A total of 59 cases (median age of 52 years, 30 females and 29 males) were enrolled. Twenty-five patients (42.37%) developed a neuroinvasive infection. The indexes of interleukin-6 (IL-6), CD3+T, CD4+T, and CD8+T cells in the study group were higher than those in the control group (P<0.05). In univariate analysis, the use of hormone drugs (odds ratio=3.21, P=0.000) and immunosuppressive agents (odds ratio=3.06, P=0.000) were relevant predictors of severe meningitis. 47 patients (79.66%) were treated with ampicillin (27.12%), carbapenems (18.64%), quinolones (11.86%), and β-lactamase inhibitors (11.86%) as the primary agents of antimicrobial therapy. Thirty-four patients (57.63%) showed clinical improvement, five patients (8.47%) had a poor prognosis, and two patients (3.39%) died.

Conclusion

Infection with Listeria changed the levels of IL-6, CD3+T, CD4+T, and CD8+T cells, and these analyzing items were significantly different between L. monocytogenes and other bacterial infections. Long-term use of immunosuppressants and hormones may be risk factors for severe adult forms of Listeria-related infections. Sensitive antibiotics, such as penicillins and carbapenems, should be added or replaced in the early empiric treatment of L. monocytogenes.

Genomic Surveillance of Listeria monocytogenes in Taiwan, 2014 to 2019

Listeria monocytogenes is a life-threatening foodborne pathogen. Here, we report the genomic characterization of a nationwide dataset of 411 clinical and 82 food isolates collected in Taiwan between 2014 and 2019. The observed incidence of listeriosis increased from 0.83 to 7 cases per million population upon implementation of mandatory notification in 2018. Pregnancy-associated cases accounted for 2.8% of human listeriosis and all-cause 7-day mortality was of 11.9% in nonmaternal-neonatal listeriosis. L. monocytogenes was isolated from 90% of raw pork and 34% of chicken products collected in supermarkets. Sublineages SL87, SL5, and SL378 accounted for the majority (65%) of clinical cases. SL87 and SL378 were also predominant (57%) in food products. Five cgMLST clusters accounted for 57% clinical cases, suggesting unnoticed outbreaks spanning up to 6 years. Mandatory notification allowed identifying the magnitude of listeriosis in Taiwan. Continuous real-time genomic surveillance will allow reducing contaminating sources and disease burden. IMPORTANCE Understanding the phylogenetic relationship between clinical and food isolates is important to identify the transmission routes of foodborne diseases. Here, we performed a nationwide study between 2014 and 2019 of both clinical and food Listeria monocytogenes isolates and sequenced their genomes. We show a 9-fold increase in listeriosis reporting upon implementation of mandatory notification. We found that sublineages SL87 and SL378 predominated among both clinical (50%) and food (57%) isolates, and identified five cgMLST clusters accounting for 57% of clinical cases, suggestive of potential protracted sources of contamination over up to 6 years in Taiwan. These findings highlight that mandatory declaration is critical in identifying the burden of listeriosis, and the importance of genome sequencing for a detailed characterization of the pathogenic L. monocytogenes genotypes circulating in Asia.

Genomic Characterization of a Clinical Listeria monocytogenes ST1 Isolate Recovered from the Blood Sample of a Woman with Third Trimester Stillbirth

Background

Listeria monocytogenes is a foodborne gram-positive bacterium which causes adverse pregnancy outcomes. Here, the genomic and phylogenetic characteristics of a L. monocytogenes isolate obtained from blood sample of a third trimester pregnant woman with stillbirth are investigated.

Methods

Whole genome DNA of L. monocytogenes ST1 was sequenced with HiSeq X Ten platform. The NCBI Prokaryotic Genome Annotation Pipeline was used to annotate the genome sequence. The sequence type (ST) and antimicrobial resistance genes were then identified. The core genome multilocus sequence typing (cgMLST) analysis with other closely related L. monocytogenes stored in the NCBI GenBank database was performed using BacWGSTdb 2.0.

Results

The complete genome sequence of L. monocytogenes ST1 is made up of 20 contigs totaling 2,914,725 bp, with 2886 protein-coding sequences and a GC content of 37.9%. Fosfomycin [fosX], Lincosamide antibiotic [lin] and peptide antibiotic [mprF] were discovered as antimicrobial resistance genes. In silico serogroup typing prediction revealed that L. monocytogenes ST1 belonged to serotype IVb. The closest relative of L. monocytogenes ST1, obtained from Poland in 2015, differs by only 15 cgMLST alleles.

Conclusion

We identified a L. monocytogenes ST1 strain from blood sample of a woman with third trimester stillbirth in China. These discoveries would aid in our understanding of the genomic characteristics, mechanisms of antimicrobial resistance, and epidemiological features of this pathogen.

A comprehensive analysis of listeriosis in 13 pregnant women and 27 newborns in Xi'an from 2011 to 2020

BACKGROUND

Listeriosis is a severe foodborne infection associated with high mortality. Pregnant women and newborns are at a particularly high risk of infection. However, the data on epidemiology of maternal-neonatal listeriosis in Xi'an are little known. The aim of this study was to investigate the epidemiological and clinical features of maternal-neonatal listeriosis in Xi'an.

METHODS

A total of 40 cases of listeriosis confirmed by positive cultures [blood or cerebrospinal fluid (CSF)] and admitted to the Northwest Women's and Children's Hospital (NWCH) from 2011 to 2020 were enrolled. Data from all patients were collected from the hospital's electronic medical records. Data analysis and epidemiological investigation were carried out by demographic information, time of onset, clinical and laboratory characteristics. Descriptive statistical indicators were obtained using SPSS21.0 and were expressed as median, mean, standard deviation and interquartile range.

RESULTS

The incidence of maternal and neonatal listeriosis in NWCH over the last decade was 5/100,000 and 10.4/100,000 respectively and Listeriosis was more likely to occur in spring and summer. The most common symptom was as follows: (I) maternal: fever (85%), abdominal pain (77%), vaginal fluid or colporrhagia (46%); (II) neonatal: respiratory distress (52%), fever (33%). Laboratary results were as follows: (I) maternal: elevated C-reactive protein (CRP) (100%), white blood cells (WBC) or neutrophil (NEUT#) (85%), and monocyte counts (MONO#) (77%); (II) neonatal: increased WBC (81%), MONO# (81%), CRP (78%), NEUT# and lymphocytes (73%); and elevated protein (PRO) (95%) and WBC count (86%) in CSF while decreased in glucose (GLU) (73%). Compared to neonatal group, the ratio of neutrophils to lymphocytes in maternal group raise to a higher level (92% to 42%). The outcomes of maternal were favorable and 54% of them suffered acute chorioamnionitism. Yet neonatal deaths account for up to 33%.

CONCLUSIONS

Listeriosis is a rare disease with extremely variable clinical characteristics in Xi'an. Our data indicated that unexplained fever, abdominal pain, signs of premature and respiratory symptoms accompanied by a progressive increase in WBC, CRP, NEUT#, MONO# even include WBC and PRO in CSF while GLU decreased, the possibility of an LM infection should be considered.

Surveillance and examination of microbial contamination in ice cream in China

This study investigated the microbial contamination of ice cream in China. A total of 2,887 ice cream samples were collected from different regions of China. Contamination by the aerobic plate count (APC), coliforms, and three foodborne pathogens, such as Listeria monocytogenes, Staphylococcus aureus, and Salmonella spp., was detected in the samples. L. monocytogenes isolates were further analyzed for antibiotic susceptibility and multi-locus sequence typing (MLST). The results showed that APC was more than 10 5 CFU/g in 6.10% (176/2887) and coliform was more than 10 2 CFU/g in 15.69% (453/2887) of all samples. The positive rates of S. aureus, L. monocytogenes, and Salmonella spp. were 0.66%, 0.62%, and 0.10%, respectively. Of these, S. aureus contamination was more than 10 2 CFU/g in two samples, and L. monocytogenes in the positive sample was in the range of 0.3–240 MPN/g, with a median of 4.3 MPN/g. The hygienic status of the packaged samples was much better than that of the bulk samples (P &lt; 0.05). Catered samples were more frequently and heavily contaminated than samples from retail and wholesale outlets (P &lt; 0.05). No significant differences were observed in samples bought from urban and rural areas (P &gt;0.05). For 18 L. monocytogenes strains isolated from ice cream, the resistance rate of nine antibiotics was 5.56% (1/18). By MLST, the L. monocytogenes strains were classified into 9 sequence types (STs), of which ST8 was most common (6 isolates). These above results indicate that a potential health risk to the public may be caused by ice cream, particularly susceptible populations.

Dissecting Listeria monocytogenes Persistent Contamination in a Retail Market Using Whole-Genome Sequencing

Listeria monocytogenes is a foodborne pathogen that can cause invasive disease with high mortality in immunocompromised individuals and can survive in a variety of food-associated environments for a long time. L. monocytogenes clonal complex (CC) 87 is composed of ST87 and three other STs and has been identified as the most common subgroup associated with both foods and human clinical infections in China. Therefore, the persistence of CC87 L. monocytogenes in food-associated environments poses a significant concern for food safety. In this study, 83 draft genomes of CC87 L. monocytogenes, including 60 newly sequenced genomes, were analyzed with all isolates from our previous surveillance in Zigong, Sichuang, China. Sixty-eight of the studied isolates were isolated from one retail market (M1 market), while the others were from seven other markets (M2–M8 markets) in the same city. Whole-genome multilocus sequence typing (wg-MLST) and the whole-genome single nucleotide polymorphism (wg-SNP) analysis were performed. Three persistent contamination routes were identified in the M1 market, caused by 2 clusters (A and B) and a wgST31 type. Cluster A isolates were associated with the persistent contamination in a raw meat stall (M1-S77), while Cluster B isolates caused a persistent contamination in aquatic foods stalls. Five wgST31 isolates caused persistent contamination in a single aquatic stall (M1-S65). A pLM1686-like plasmid was found in all Cluster A isolates. A novel plasmid, pLM1692, a truncated pLM1686 plasmid without the cadmium, and other heavy metal resistance genes were conserved in all wgST31 isolates. By comparing persistent and putative non-persistent isolates, four genes that were all located in the prophage comK might be associated with persistence. These findings enhanced our understanding of the underlying mechanisms of contamination and assist in formulating targeted strategies for the prevention and control of L. monocytogenes transmission from the food processing chain to humans.

IMPORTANCE Contamination of food by Listeria monocytogenes at retail level leads to potential consumption of contaminated food with high risk of human infection. Our previous study found persistent contamination of CC87 L. monocytogenes from a retail market in China through pulsed-field gel electrophoresis and multilocus sequence typing. In this study, whole-genome sequencing was used to obtain the highest resolution inference of the source and reasons for persistent contamination; meat grinders and minced meat were the major reservoir of persistent contamination in meat stalls, whereas fishponds were the major reservoir in seafood stalls, with different L. monocytogenes isolates involved. These isolates carried different properties such as plasmids and prophages, which may have contributed to their ability to survive or adapt to the different environments. Our findings suggest that whole-genome sequencing will be an effective surveillance tool to detect persistent L. monocytogenes contamination in retail food markets and to design new control strategies to improve food safety.

Functional Genomics Identified Novel Genes Involved in Growth at Low Temperatures in Listeria monocytogenes

Listeria monocytogenes (Lm) is a foodborne pathogen that can cause severe human illness. Standard control measures for restricting bacterial growth, such as refrigeration, are often inadequate as Lm grows well at low temperatures. To identify genes involved in growth at low temperatures, a powerful functional genomics method Tn-seq was performed in this study. This genome-wide screening comprehensively identified the known and novel genetic determinants involved in low-temperature growth. A novel gene lmo1366, encoding rRNA methyltransferase, was identified to play an essential role in Lm growth at 16°C. In contrast, the inactivation of lmo2301, a gene encoding the terminase of phage A118, significantly enhanced the growth of Lm at 16°C. The deletion of lmo1366 or lmo2301 resulted in cell morphology alterations and impaired the growth rate in milk and other conditions at low temperatures. Transcriptomic analysis revealed that the Δlmo1366 and Δlmo2301 mutants exhibited altered transcriptional patterns compared to the wild-type strain at 16°C with significant differences in genes involved in ribosome structural stability and function, and membrane biogenesis, respectively. This work uncovered novel genetic determinants involved in Lm growth at 16°C, which could lead to a better understanding of how bacteria survive and multiply at low temperatures. Furthermore, these findings could potentially contribute to developing novel antibacterial strategies under low-temperature conditions.

IMPORTANCEListeria monocytogenes is a Gram-positive pathogen that contributes to foodborne outbreaks due to its ability to survive at low temperatures. However, the genetic determinants of Lm involved in growth at low temperatures have not been fully defined. Here, the genetic determinants involved in the low-temperature growth of Lm were comprehensively identified on a genome-wide scale by Tn-seq. The gene lmo1366, encoding rRNA methyltransferase, was identified essential for growth under low-temperature conditions. On the other hand, the gene lmo2301, encoding terminase of phage A118, plays a negative role in bacterial growth at low temperatures. The transcriptomic analysis revealed the potential mechanisms. These findings lead to a better understanding of how bacteria survive and multiply at low temperatures and could provide unique targets for novel antibacterial strategies under low-temperature conditions.

Frozen Vegetable Processing Plants Can Harbour Diverse Listeria monocytogenes Populations: Identification of Critical Operations by WGS

Frozen vegetables have emerged as a concern due to their association with foodborne outbreaks such as the multi-country outbreak of Listeria monocytogenes serogroup IVb linked to frozen corn. The capacity of L. monocytogenes to colonize food-processing environments is well-known, making the bacteria a real problem for consumers. However, the significance of the processing environment in the contamination of frozen foods is not well established. This study aimed to identify potential contamination niches of L. monocytogenes in a frozen processing plant and characterize the recovered isolates. A frozen vegetable processing plant was monitored before cleaning activities. A total of 78 points were sampled, including frozen vegetables. Environmental samples belonged to food-contact surfaces (FCS); and non-food-contact surfaces (n-FCS). Positive L. monocytogenes samples were found in FCS (n = 4), n-FCS (n = 9), and the final product (n = 1). A whole-genome sequencing (WGS) analysis revealed two clusters belonging to serotypes 1/2a-3a and 1/2b-3b). The genetic characterization revealed the presence of four different sequence types previously detected in the food industry. The isolate obtained from the final product was the same as one isolate found in n-FCS. A multi-virulence-locus sequence typing (MVLST) analysis showed four different virulence types (VT). The results obtained highlight the relevant role that n-FCS such as floors and drains can play in spreading L. monocytogenes contamination to the final product.

Epidemiology and Antimicrobial Resistance Profiles of the Nocardia Species in China, 2009 to 2021

The genus Nocardia includes ubiquitous environmental saprophytes and the most frequently isolated aerobic actinomycete human pathogen responsible for localized or disseminated infection. Herein, the species distribution and antimicrobial susceptibility profiles of 441 nonrepetitive Nocardia strains are reported, collected from 21 provinces/cities in China over 13 years (from 2009 to 2021). These isolates were identified to species level by mass spectrometry or targeted DNA sequencing. The susceptibility profiles of Nocardia species for 15 antibiotics were determined by the broth microdilution method. Among these Nocardia isolates, Nocardia farcinica was the most commonly isolated species (39.9%, 176 of 441), followed by Nocardia cyriacigeorgica (28.6%, 126), Nocardia abscessus (6.6%, 29), and Nocardia otitidiscaviarum (5.9%, 26). Furthermore, 361 Nocardia strains (81.9%) were collected from lower respiratory tract (sputum, lung tissue, and bronchoalveolar lavage fluid), 50 (11.3%) were collected from skin and soft tissues, 9 were collected from blood, 9 were collected from eye, 4 were collected from cerebrospinal fluid and brain abscesses, and 2 were collected from pleural effusion. All of the Nocardia strains were susceptible to linezolid, followed by amikacin (99.3%) and trimethoprim-sulfamethoxazole (TMP-SMX) (99.1%). The antibiotic resistance profiles of other antibiotics varied tremendously among different Nocardia species. This demonstrated that accurate species identification and/or antibiotic susceptibility testing should be performed before the usage of these antibiotics. In summary, this is the largest study on the species and antibiotic resistance profiles of the genus Nocardia circulating in China, and our data will contribute to a better understanding of clinical nocardiosis.

IMPORTANCE The genus Nocardia has the potential to cause nocardiosis, which might be underrecognized and underdiagnosed. Herein, the demographical features of 441 nonrepetitive nocardiosis cases and species distribution of their Nocardia strains in China, 2009 to 2021, are summarized. The susceptibility profiles for 15 antibiotics against all of the above Nocardia strains were also determined by the broth microdilution method. To date, this is the largest study on the genus Nocardia contributing to nocardiosis in China. Our study will be helpful for understanding the species diversity of Nocardia isolates distributed in China and for decision-making in the context of nocardiosis diagnosis and treatment.

Clinical and Laboratory Characteristics of Patients infected by Listeria monocytogenes at a Tertiary Hospital in Hefei City, China

Background

Human listeriosis is a severe foodborne infection caused by Listeria monocytogenes and the data of patients with this infection are largely limited for the Hefei population.

Purpose

This is a retrospective study that evaluated the clinical and laboratory data of patients with listeriosis at a tertiary hospital in Hefei City.

Patients and Methods

A total of 24 listeriosis patients were admitted to the First Affiliated Hospital of Anhui Medical University from January 2003 to July 2021. Data from all patients were collected from the hospital’s electronic medical records.

Results

The most common symptom of all patients was fever (91.7%), followed by altered consciousness (50.0%), rashes (45.8%), respiratory distress symptoms (37.5%), nuchal rigidity (29.2%), and headaches (20.8%). Laboratory results also indicated elevated C-reactive protein (CRP) (79.1%), hypoproteinemia (75.0%), anemia (62.5%), leukocytosis (45.8%), and neutrophilia (45.8%). The mean value of 5.1 μg/mL (SD, 3.8) for D‐dimer (D‐D) was significantly higher than the normal value ((0.00–0.50) μg/mL), while both altered consciousness (6 vs 4, P = 0.034) and headaches (4 vs 1, P = 0.036) occurred more frequently in the neurolisteriosis group compared with the bacteremia one. Additionally, the mean maximal body temperature (°C) (40.5 ± 0.7) as well as white blood cell (WBC) (15.3 vs 7.5 ×10⁹/L, P = 0.014) and neutrophil (NEUT#) (13.2 vs 6.1 ×10⁹/L, P = 0.026) counts of neurolisteriosis patients were higher than those of bacteremia (39.4 ± 0.4) (P = 0.001). Of all patients, four (50%) from the maternal-neonatal group remained uncured.

Conclusion

Listeriosis is a rare disease with extremely variable clinical characteristics in Hefei City. Our data indicated that unexplained fever, altered consciousness, hypoproteinemia, anemia, elevated CRP and DD should be considered to assist diagnosis of listeriosis for early treatment interventions.

An Update Review on Listeria Infection in Pregnancy

Listeria monocytogenes (LM) is an intracellular, aerobic and facultative anaerobic, Gram-positive bacterium, which is primarily transmitted to humans orally via food. LM could occur in asymptomatic pregnant women; however, fetal infection is a serious condition, entailing premature birth, abortion, sepsis, central nervous system (CNS) involvement, or even death. If a pregnant woman exhibits symptoms, the performance is almost like influenza, such as fever, headache, diarrhea, myalgia, or other digestive-related symptoms. This review collected clinical and empirical results regarding the mechanism, clinical manifestations, obstetrical outcome, diagnosis, treatment, vertical transmission, neonatal infection, and prevention of listeriosi according to articles published in PubMed from January 1, 1980, to March 20, 2021. The early detection and diagnosis of pregnancy-associated listeriosis are significant since sensitive antibiotics are effective at enhancing the prognosis of newborns. Listeriosis can be diagnosed using positive cultures from maternal or neonatal blood, neonatal cerebrospinal fluid (CSF), amniotic fluid, intrauterine mucosa, or the placenta. Two weeks of high-dose intravenous amoxicillin (more than 6 g/day) is recommended for LM pregnant women without allergy. Terminating the pregnancy to save the mother’s life should be considered if maternal and fetal conditions aggravate. Neonatal Listeria infection is primarily transmitted through the placenta, which is a critical illness associated with a high mortality rate. The necessary dietary guidance for pregnant women can reduce the incidence rate of pregnancy-related listeriosis.