Characterization of Listeria monocytogenes isolates from human listeriosis cases in Italy

Virulence and Antimicrobial Resistance of Listeria monocytogenes Isolated from Ready-to-Eat Food Products in Romania

Listeria monocytogenes (L. monocytogenes) poses a significant threat to food safety due to its ability to cause severe human illness and its resistance to various antibiotics and environmental conditions. This study investigated the prevalence, serotype distribution, virulence gene profiles, and antimicrobial resistance patterns of L. monocytogenes in ready-to-eat (RTE) food products from Romania. A total of 8151 samples were analyzed, including various processed dairy, bovine, poultry, pork, and fish products. Bacterial isolation was conducted using the classical standard method, followed by confirmation through biochemical and molecular testing. Among the isolated strains, serotypes 1/2a, 1/2b, and 1/2c were identified, with a prevalence of 75% for serotype 1/2a. Additionally, virulence genes specific to listeriolysin O (hlyA) and regulatory factor A (prfA) were detected in all isolates. Antimicrobial susceptibility testing revealed varying resistance patterns among the L. monocytogenes strains. Trimethoprim-sulfamethoxazole and oxacillin showed the highest prevalence of resistance at 26.92% and 23.07%, respectively. However, all strains remained susceptible to ciprofloxacin, levofloxacin, and moxifloxacin. Notably, 23.07% of the isolates exhibited multidrug resistance, with the most common pattern being resistance to oxacillin, penicillin, and tetracycline. Analysis of antimicrobial resistance genes identified tetracycline resistance genes, particularly tet(C), tet(M), and tet(K), in a significant proportion of isolates. The presence of ampC and dfrD genes was also notable, indicating potential mechanisms of resistance. These results emphasize the necessity for ongoing surveillance of L. monocytogenes in RTE foods and emphasize the importance of thorough monitoring of antimicrobial resistance to guide public health strategies within the European Union.

Classification and prediction of Klebsiella pneumoniae strains with different MLST allelic profiles via SERS spectral analysis

The Gram-negative non-motile Klebsiella pneuomoniae is currently a major cause of hospital-acquired (HA) and community-acquired (CA) infections, leading to great public health concern globally, while rapid identification and accurate tracing of the pathogenic bacterium is essential in facilitating monitoring and controlling of K. pneumoniae outbreak and dissemination. Multi-locus sequence typing (MLST) is a commonly used typing approach with low cost that is able to distinguish bacterial isolates based on the allelic profiles of several housekeeping genes, despite low resolution and labor intensity of the method. Core-genome MLST scheme (cgMLST) is recently proposed to sub-type and monitor outbreaks of bacterial strains with high resolution and reliability, which uses hundreds or thousands of genes conserved in all or most members of the species. However, the method is complex and requires whole genome sequencing of bacterial strains with high costs. Therefore, it is urgently needed to develop novel methods with high resolution and low cost for bacterial typing. Surface enhanced Raman spectroscopy (SERS) is a rapid, sensitive and cheap method for bacterial identification. Previous studies confirmed that classification and prediction of bacterial strains via SERS spectral analysis correlated well with MLST typing results. However, there is currently no similar comparative analysis in K. pneumoniae strains. In this pilot study, 16 K. pneumoniae strains with different sequencing typings (STs) were selected and a phylogenetic tree was constructed based on core genome analysis. SERS spectra (N = 45/each strain) were generated for all the K. pneumoniae strains, which were then comparatively classified and predicted via six representative machine learning (ML) algorithms. According to the results, SERS technique coupled with the ML algorithm support vector machine (SVM) could achieve the highest accuracy (5-Fold Cross Validation = 100%) in terms of differentiating and predicting all the K. pneumoniae strains that were consistent to corresponding MLSTs. In sum, we show in this pilot study that the SERS-SVM based method is able to accurately predict K. pneumoniae MLST types, which has the application potential in clinical settings for tracing dissemination and controlling outbreak of K. pneumoniae in hospitals and communities with low costs and high rapidity.

Inhibition Activity of Plantaricin Q7 Produced by Lactobacillus plantarum Q7 against Listeria monocytogenes and Its Biofilm

Plantaricin Q7 is a broad-spectrum antimicrobial peptide produced by Lactobacillus plantarum Q7. The effects of plantaricin Q7 on Listeria monocytogenes and its biofilm were investigated. The results showed that plantaricin Q7 changed the cell membrane permeability and integrity of Listeria monocytogenes significantly. The extracellular lactate dehydrogenase activity increased from 156.74 U/L to 497.62 U/L, and the K+ concentration was increased rapidly from 0.02 g/L to 0.09 g/L. Furthermore, the flagellum motility of Listeria monocytogenes reduced and the relative adhesion rate decreased about 30% after treatment with plantaricin Q7. Meanwhile, the morphology and structure of Listeria monocytogenes cell and biofilm were damaged. These findings suggested that plantaricin Q7 exhibited significant inhibitory effects on not only Listeria monocytogenes cell but also its biofilm, which might be used as a natural and effective biological preservative for food storage.

Genomic Characterization of Clinical Listeria monocytogenes Isolates in Beijing, China

Listeria monocytogenes is a foodborne human pathogen that affects public health worldwide. Whole-genome sequencing (WGS) can classify L. monocytogenes isolates and identify virulence islands and resistance genes potentially influencing infectivity. Herein, WGS was used to assess 151 L. monocytogenes isolates from 120 cases of clinical infection in Beijing, China, between 2014 and 2018. Most isolates were either serogroup 1/2a,3a or serogroup 1/2b,3b,7, with 25 multilocus sequence typing (MLST) types (STs) represented, of which ST8, ST87, and ST5 were the most common. Core-genome MLST (cgMLST) grouped the 151 isolates into 116 cgMLST types. The discriminatory power of cgMLST was greater than other subtypes, revealing that isolates from the same patient were highly related (only differing at one allele). Eighty-six isolates formed 30 complexes with ≤ 7 cgMLST alleles between neighboring isolates, suggesting possible outbreaks. Compared with isolates in the United States, ST8, ST121, ST619, ST87, and ST155 isolates were grouped into unified clades. All 151 isolates were positive for common virulence-associated loci, and 26 lineage I isolates harbored the pathogenicity island 3 (LIPI-3) locus, while 42 lineage I isolates harbored the complete LIPI-4 locus. Eleven ST619 isolates had both LIPI-3 and LIPI-4. Among the 151 isolates, 13 were resistant to at least one antibiotic, and no multidrug-resistant isolates were identified. Resistance phenotypes correlated with genotypes, apart from two meropenem resistance isolates. The findings provided insight into the nature of L. monocytogenes strains currently causing clinical disease in Beijing, and WGS analysis indicated possible outbreaks.

The first isolation and detection of Ornithobacterium rhinotracheale from swollen head syndrome-infected broiler flocks in Iraq

Background and Aim:

The swollen head syndrome (SHS) makes up complex diseases that infect the upper respiratory tract in poultry and causes several economic losses. Furthermore, this syndrome is considered one of the multifactorial etiological agents. Therefore, this study isolated and molecularly detected Ornithobacterium rhinotracheale (ORT) in poultry.

Materials and Methods:

This study was conducted at 67 broiler farms that had birds observed to be infected with the SHS from September 2018 until August 2019. Subsequently, swabs were collected from their trachea, infraorbital sinuses, and lungs, after which obtained samples were treated through two methods: (a) The direct method, by uploading samples on FTA cards, and the indirect method using a transport media. Afterward, reverse transcription-polymerase chain reaction (RT-PCR) was used to analyze the directly treated samples; howeverAQ1, the culture method, followed by PCR, was used to analyze the indirectly treated samples. Next, a partial 16S RNA gene was isolated using four positive PCR products, after which the effect of 16 antibiotics was studied on the seven local ORT strains isolated.

Results:

The quantity of ORT isolated using the direct method was 28 (41.7%) samples, which were all positive for the strain. Identification was by direct molecular identification (RT-PCR) from samples loaded on FTA cards. Alternatively, 7 (10.4%) ORTs were detected from the indirect method, as obtained using the culture method and biochemical tests. Then, PCR was subsequently used to confirm the results. As observed, 784 bp bands were shown for all seven ORT isolates. Furthermore, results revealed a significant difference in the detection of ORT strains between direct and indirect methods, with p-value (<0.05) and standard deviation of the error±0.038 for the direct, then ±0.061 for the indirect method. For further analysis on the strain types, four 784 bp PCR products were taken, then partial 16S ribosomal sequence typing was conducted. All these four strains were found to be recorded in NCBI for the 1^st time as a local Iraqi strain, with accession numbers (MN931657, MN931656, MN931655, and MN931654). Notably, results also showed that all isolated strains were multidrug-resistant.

Conclusion:

From the results, ORT is proposed to be implicated as one of the etiological factors that cause SHSs in poultry. Phylogenetic analysis of the current ORT bacterial strains also showed that they are closely related to the Egyptian isolates.

Detection of virulence genes and antimicrobial susceptibility profile of Listeria monocytogenes isolates recovered from artisanal cheese produced in the Southern region of Brazil

Listeria monocytogenes is an opportunistic pathogen that causes listeriosis, a foodborne disease with low incidence but with high mortality rate in humans. This microorganism has been recovered from several dairy products, especially those produced with raw milk. The objective of this work was to investigate the presence of virulence genes, and also to define the antimicrobial susceptibility profile of L. monocytogenes isolates recovered from serrano artisanal cheese produced in Southern region of Brazil. Nine strains of L. monocytogenes (serotypes 1/2b and 4b) were evaluated through PCR to detect the presence of the virulence genes hly, inlA, inlC, inlJ, actA, plcB and iap, while antimicrobial susceptibility profile was determined via disk diffusion method. All strains exhibited the presence of the genes hly and plcB, whereas the other genes (iap, actA, inlA, inlC and inlJ) were only detected in eight strains. We verified that all strains were resistant to at least one antimicrobial agent and three of them showed multidrug resistance. These findings demonstrated the serrano artisanal cheese offers risks to consumers' health and point to a need of adaptations and monitoring of manufacturing process of this food, in order to prevent the dissemination of L. monocytogenes.

Occurrence, antimicrobial resistance, serotyping and virulence genes of Listeria monocytogenes isolated from foods

Listeria monocytogenes is a pathogen contaminated food, it is the cause of listeriosis worldwide. The aims of this study were to investigate the occurrence, antimicrobial resistance, serotyping and virulence genes of L. monocytogenes isolated from foods in Meknes city of Morocco. From June 2017 to May 2018, 520 food samples were randomly collected from a traditional market and two overcrowded popular neighborhoods (Lahdim and Hamria) and subjected to the detection of L. monocytogenes. Then, the antimicrobial susceptibility of the isolated strains were evaluated using the standard disk diffusion method and the determination of serotypes and virulence genes was performed by PCR. The results showed the detection of L. monocytogenes in fifteen (2.9%) of 520 samples, including three (5.7%) isolates in traditional whey, raw minced meat and raw sausage, two (3.8%) in raw milk and one (1.9%) in smen (traditional butter), raw bovine meat, raw poultry meat and raw fish, while salads and rayeb (traditional coagulated milk) were not contaminated. Among the fifteen isolated L. monocytogenes, nine (60%) belonged to the serogroup (1/2a, 1/2c, 3a and 3c), two (13.3%) belonged to the serogroup (1/2b, 3b, 4b and 4d) and four (26.6%) do not belong to any studied serogroup. Furthermore, fifteen (100%) isolates showed the presence of actA gene, fourteen (93.3%) harbored hlyA, prfA and plcB genes, thirteen (86.7%) carried inlA and inlC genes and twelve (80%) showed inlJ gene. The antimicrobial susceptibility analysis showed that the isolated strains were more resistant to amoxicillin/clavulanic acid (67.0%), erythromycin (60.0%), sulphamethoxazole (40.0%), ampicillin and sulphamethoxazole/trimethoprim (33.0%) and tetracycline (20.0%). Furthermore, 66.7% (10/15) were multidrug-resistant. From this study, we can conclude that foods marketed in Meknes city were contaminated by multidrug-resistant strains of L. monocytogenes harboring virulence genes, which may cause a serious risk to public health.

Nosocomial cross-infection of hypervirulent Listeria monocytogenes sequence type 87 in China

Background

To investigate the epidemiological and phenotypic characteristics and molecular relatedness of L. monocytogenes, which were cultured from the blood and cerebrospinal fluid (CSF) samples isolated from two neonates.

Methods

In the present case study, two infected neonates were interviewed and epidemiological investigation performed. The phenotypic characteristics and molecular relatedness of L. monocytogenes was characterized by serotyping, pulsed-field gel electrophoresis and whole-genome sequencing (WGS).

Results

The field investigation found that the two neonates were born in the same hospital (Hospital B) and admitted to the neonatal department through different channels within half an hour by different nurses, where they were weighed and placed in different but adjacent incubators. Then they were cared for by the same group of nurses that evening. It is worth noting that there was no record of sanitation of the neonatal incubator of neonate-1. The serotype of the two isolated L. monocytogenes were 1/2b, with an indistinguishable pulsotypes and were sequence type (ST) 87. WGS showed that there were no core SNP differences identified. In order to explore the genomic traits associated with L. monocytogenes virulence genes, we identified the Listeria pathogenicity island 4 and found that the genome was devoid of any stress islands. There are no positive results from the environmental samples. Considering the genomic data together with epidemiological evidence and clinical symptoms, insufficient surface cleaning along with the nursing staff caring for these neonates was considered as cross-infection factors.

Conclusions

To our knowledge, this is the first report of a nosocomial cross-infection of L. monocytogenes ST87 between two neonates, which carries the recently identified gene cluster expressing the cellobiose-family phosphotransferase system (PTS-LIPI-4) between two neonates. The test results of environmental samples in the hospital indicate that strict sterilization and patient isolation measures cannot be emphasized enough in neonatal nursing.

Prevalence, Pathogenicity, Virulence, Antibiotic Resistance, and Phylogenetic Analysis of Biofilm-Producing Listeria monocytogenes Isolated from Different Ecological Niches in Egypt: Food, Humans, Animals, and Environment

Serious outbreaks of foodborne disease have been caused by Listeria monocytogenes found in retail delicatessens and the severity of disease is significant, with high hospitalization and mortality rates. Little is understood about the formidable public health threat of L. monocytogenes in all four niches, humans, animals, food, and environment, in Egypt. This study analyzed the presence of L. monocytogenes collected from the four environmental niches and bioinformatics analysis was implemented to analyze and compare the data. PCR was used to detect virulence genes encoded by pathogenicity island (LIPI-1). prfA amino acid substation that causes constitutive expression of virulence was common in 77.7% of isolates. BLAST analysis did not match other isolates in the NCBI database, suggesting this may be a characteristic of the region associated with these isolates. A second group included the NH1 isolate originating in China, and BLAST analysis showed this prfA allele was shared with isolates from other global locations, such as Europe and North America. Identification of possible links and transmission pathways between the four niches helps to decrease the risk of disease in humans, to take more specific control measures in the context of disease prevention, to limit economic losses associated with food recalls, and highlights the need for treatment options.

Isolation and Characterization of Clinical Listeria monocytogenes in Beijing, China, 2014-2016

Listeria monocytogenes is an important foodborne pathogen with a significant impact on public health worldwide. A great number of outbreaks caused by L. monocytogenes has been reported, especially in the United States, and European countries. However, listeriosis has not yet been included in notifiable disease in China, and thus information on this infection has been scarce among the Chinese population. In this study, we described a 3-year surveillance of listeriosis in Beijing, China. Fifty-six L. monocytogenes strains isolated from 49 clinical infectious cases (27 pregnancy-associated infections and 22 non-pregnancy-associated infections) were analyzed by serotyping, pulsed field gel electrophoresis (PFGE), multilocus sequence typing (MLST), and antimicrobial susceptibility testing between 2014 and 2016 in Beijing. The predominant serogroups were 1/2a,3a and 1/2b,3b,7 which accounted for 92% of the overall isolates. Four strains were serogroup 4b,4d,4e, isolated from patients with pregnancy-associated infections. Based on PFGE, these isolates were divided into 32 pulsotypes (PTs) and 3 clusters associated with serogroups. Ten PTs were represented by more than one isolate with PT09 containing the most number of isolates. MLST differentiated the isolates into 18 STs, without new ST designated. The three most common STs were ST8 (18.4%), ST5 (16.3%), and ST87 (12.2%), accounting for 46.9% of the isolates. STs prevalent in other parts of the world were also present in China such as ST1, ST2, ST5, ST8, and ST9 which caused maternal fetal infections or outbreaks. However, the STs and serogroup distribution of clinical L. monocytogenes in Beijing, China was different from those in other countries. Strains of ST1 and ST2 were isolated from patients with pregnancy-associated infection, whereas none of ST155 isolates caused pregnancy-associated cases. Surveillance of molecular characterization will provide important information for prevention of listeriosis. This study also enhances our understanding of genetic diversity of clinical L. monocytogenes in China.

Characterization of Listeria monocytogenes from encephalitis cases of small ruminants from different geographical regions, in Greece

AIMS

The aim of this study was to evaluate the genetic diversity and resistance phenotypes of Listeria monocytogenes strains isolated from clinical encephalitis cases, and compare this population to isolates derived from tank milk of healthy animals.

METHODS AND RESULTS

A total of 57 L. monocytogenes strains isolated from ruminant's listeriosis cases (n = 31) and from tank milk of healthy ruminants (n = 26) were characterized by species PCR, molecular serotyping, PCR detection of virulence genes, pulsed-field gel electrophoresis and antimicrobial susceptibility testing. All strains possessed inlA, inlC, inlJ, plcA, actA, hlyA and iap virulence-associated genes while serotyping analysis revealed that they were mainly assigned into IVb group. Genotyping revealed 50 pulsotypes among the 57 strains assigned into seven clusters while indistinguishable pulsotypes between clinical and milk strains were not identified. Resistance of L. monocytogenes isolates to 14-16 antimicrobial agents tested was observed and 23 antimicrobial resistance profiles (ARPs) were defined while no apparent predominant ARP type was observed among isolates.

CONCLUSIONS

Small ruminants are exposed to a broad range of antimicrobial-resistant as well as genetically diverse strains of L. monocytogenes carrying virulence-associated genes but not all of them associated with the disease. Pulsed-field gel electrophoresis analysis suggests that pulsotypes associated with encephalitis are found in farms only in association with listeriosis.

SIGNIFICANCE AND IMPACT OF THE STUDY

These findings are valuable in understanding the ecology of this important food-borne pathogen and creating awareness for the emerging antimicrobial resistance.

The investigation of molecular characterization of presumptive Listeria monocytogenes isolates from a food-processing environment

BACKGROUND

Listeria is a Gram-positive, non-spore forming, facultative anaerobic intracellular bacterium. The most important pathogens in mammals include Listeria monocytogenes and Listeria ivanovii. The former generally causes disease and death in both humans and animals while the latter performs sporadically and primarily causes illness in ruminants.

AIMS

The aim of this project was to use conventional and molecular techniques to determine whether the provided samples were L. monocytogenes, and whether they were genetically similar or different.

METHODS

The provided presumptive Listeria cultures isolated from industrial processed food are conventionally assumed to be L. monocytogenes. All samples were cultured on brain heart infusion agar and broth first and then on blood agar. Later, hly gene amplification was applied.

RESULTS

The provided culture phenotypically resembled L. monocytogenes as it caused haemolysis on blood agar plates; however, the absence of the hly gene revealed that they were genotypically different. 16S rRNA confirmed three species of Listeria species including L. grayi, L. welshimeri and L. ivanovii. The results from 16S rRNA sequencing confirmed the results obtained from hly gene amplification.

CONCLUSION

Enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC PCR) confirmed that all bacterial cultures were isolated from different sources depending on their ERIC PCR profile variation.

Listeriosis in two twin pregnancies after in vitro fertilization with differential outcome and literature review

PURPOSE

In vitro fertilization (IVF) has become a very common procedure in the infertility practice due to its accessibility. The study is aiming at presenting two twin pregnancy-related infections caused by Listeria monocytogenes and reviewing the reported cases of listeriosis in multiple pregnancies.

MATERIALS AND METHODS

Two listeriosis cases with twin pregnancy after IVF were described and the literature on pregnancy-associated listeriosis was reviewed.

RESULTS

The risk of listeriosis should be underscored in pregnant women after IVF, and timely diagnosis and rational treatment might result in a better outcome.

CONCLUSIONS

The current study highlights that the infections due to L. monocytogenes should be noted in multiple pregnancies after IVF.

Listeria monocytogenes in raw milk, milking equipment and dairy workers: Molecular characterization and antimicrobial resistance patterns

OBJECTIVES

The aim of this study was to evaluate the genetic relatedness and patterns of antimicrobial resistance amongst L. monocytogenes isolated from raw milk, milking equipment, and hand swabs from workers in dairy farms.

METHODS

A total of 300 samples of raw milk, milking equipment, and hand swabs were collected from four dairy farms to examine the presence of Listeria species. Suspected isolates were further identified by VITEK-2 system and Polymerase Chain Reaction (PCR). Antimicrobial susceptibility of the L. monocytogenes isolates was determined, and genotyping analysis was performed by enterobacterial repetitive intergenic consensus-polymerase chain reaction (ERIC-PCR).

RESULTS

Listeria spp. was isolated from 79 (26.3%) of the 300 samples, including 29 (36.7%), 32 (40.5%), and 18 (22.8%) isolates found in raw milk, milking equipment, and hand swabs, respectively. L. monocytogenes was the most common isolated (87.3%) species, while the remaining Listeria isolates were L. innocua (12.7%). Among the 69 L. monocytogenes isolates, 42 (60.8%) showed the mutual presence of hlyA, prfA, inlA, and inlB virulence-associated genes. L. monocytogenes isolates from raw milk, milking equipment, and hand swabs showed high genetic relatedness. The potentially virulent L. monocytogenes isolates were most frequently resistance to tetracycline and clindamycin (81%, each) followed by rifampicin (71.4%), whereas, antimicrobial susceptibility was most frequently observed for ampicillin, levofloxacin, moxifloxacin, linezolid, and tigecycline (100%, each). Furthermore, 88% of L. monocytogenes isolates showed multidrug-resistance.

CONCLUSIONS

The findings of this study show that the contamination of dairy farms with L. monocytogenes is relatively high, and highlight the emergence of multi-drug resistant L. monocytogenes in dairy farms. However, ampicillin is a good choice for treatment of listeriosis in the study area.

Genetic Characterization of Listeria monocytogenes Isolates from Industrial and Retail Ready-to-Eat Meat-Based Foods and Their Relationship with Clinical Strains from Human Listeriosis in Portugal

Listeria monocytogenes isolates (n = 81) recovered from ready-to-eat meat-based food products (RTEMP) collected in industrial processing plants and retail establishments were genetically characterized for comparison with those from human clinical cases of listeriosis (n = 49). The aim was to assess RTEMP as a possible food source for human infection. L. monocytogenes was detected in 12.5% of the RTEMP samples, and in some cases, counts were above the European food safety criteria. All isolates were assessed by multiplex PCR for serogroup determination and detection of virulence-associated genes inlA, inlB, inlC, inlJ, plcA, hlyA, actA, and iap. Serogroups IIb and IVb dominated in RTEMP and human isolates, and all were positive for the assessed virulence genes. Antibiotic susceptibility testing by the disk diffusion method revealed a low level of resistance among the isolates. Pulsed-field gel electrophoresis (PFGE) of L. monocytogenes isolates, using restriction enzymes ApaI and AscI, revealed genetic variability and differentiated the isolates in five clusters. Although some pulsed-field gel electrophoresis profiles of particular RTEMP and human isolates seemed to be highly related, exhibiting more than 90% similarity, which suggests a possible common source, in most cases the strains were not genetically or temporally matched. The close genetic relatedness of RTEMP and human listeriosis strains stressed the importance of preventive measure implementation throughout the food chain.

Ongoing outbreak of invasive listeriosis due to serotype 1/2a Listeria monocytogenes, Ancona province, Italy, January 2015 to February 2016

In the first seven weeks of 2016, five serotype 1/2a Listeria monocytogenes isolates were collected from patients with invasive listeriosis in Ancona province in Italy. These strains and six 1/2a isolates identified in 2015 in the same area were typed by ERIC-PCR and PFGE. A clonal relationship, documented between the two sets of isolates, suggested a listeriosis outbreak in Ancona that started most probably in 2015. Investigation into the source of infection is still ongoing.

Analysis of Multilocus Sequence Typing and Virulence Characterization of Listeria monocytogenes Isolates from Chinese Retail Ready-to-Eat Food

Eighty Listeria monocytogenes isolates were obtained from Chinese retail ready-to-eat (RTE) food and were previously characterized with serotyping and antibiotic susceptibility tests. The aim of this study was to characterize the subtype and virulence potential of these L. monocytogenes isolates by multilocus sequence typing (MLST), virulence-associate genes, epidemic clones (ECs), and sequence analysis of the important virulence factor: internalin A (inlA). The result of MLST revealed that these L. monocytogenes isolates belonged to 14 different sequence types (STs). With the exception of four new STs (ST804, ST805, ST806, and ST807), all other STs observed in this study have been associated with human listeriosis and outbreaks to varying extents. Six virulence-associate genes (inlA, inlB, inlC, inlJ, hly, and llsX) were selected and their presence was investigated using PCR. All strains carried inlA, inlB, inlC, inlJ, and hly, whereas 38.8% (31/80) of strains harbored the listeriolysin S genes (llsX). A multiplex PCR assay was used to evaluate the presence of markers specific to epidemic clones of L. monocytogenes and identified 26.3% (21/80) of ECI in the 4b-4d-4e strains. Further study of inlA sequencing revealed that most strains contained the full-length InlA required for host cell invasion, whereas three mutations lead to premature stop codons (PMSC) within a novel PMSCs at position 326 (GAA → TAA). MLST and inlA sequence analysis results were concordant, and different virulence potentials within isolates were observed. These findings suggest that L. monocytogenes isolates from RTE food in China could be virulent and be capable of causing human illness. Furthermore, the STs and virulence profiles of L. monocytogenes isolates have significant implications for epidemiological and public health studies of this pathogen.

Listeria monocytogenes Prevalence and Characteristics in Retail Raw Foods in China

The prevalence and levels of Listeria monocytogenes in retail raw foods covering most provincial capitals in China were studied with testing of 1036 samples of vegetables, edible mushrooms, raw meat, aquatic products and quick-frozen products from September 2012 to January 2014. The total prevalence of Listeria monocytogenes was 20.0% (207/1036), and the most probable number (MPN) values of 65.7% of the positive samples ranged from 0.3 to 110 MPN/g. Geographical differences were observed in this survey, and the results of both qualitative and quantitative methods indicated that the levels in the samples from North China were higher than those in the samples from South China. A total of 248 isolates were analyzed, of which approximately half belonged to molecular serogroup 1/2a-3a (45.2%), followed by 1/2b-3b-7 (30.6%), 1/2c-3c (16.1%), 4b-4d-4e (5.2%) and 4a-4c (2.8%). Most of the isolates carried hly (100%), inlB (98.8%), inlA (99.6%), inlC (98.0%) and inlJ (99.2%), and 44.8% of the isolates were llsX-positive. Seventeen epidemic clones (ECs) were detected, with 7 strains belonging to ECI (2.8%) and 10 belonging to ECIII (4.03%). Resistance to clindamycin (46.8%) was commonly observed, and 59 strains (23.8%) were susceptible to all 14 tested antibiotics, whereas 84 (33.9%) showed an intermediate level of resistance or were resistant to two or more antibiotics, including 7 multi-resistant strains that exhibited resistance to more than 10 antibiotics. The data obtained in the present study provides useful information for assessment of the possible risk posed to Chinese consumers, and this information will have a significant public health impact in China. Furthermore, the presence of virulence markers, epidemic clones, as well as the antibiotic resistance amongst the isolates strongly implies that many of these strains might be capable of causing listeriosis, and more accurate treatment of human listeriosis with effective antibiotics should be considered. This research represents a more full-scale and systematical investigation of the prevalence of L. monocytogenes in retail raw foods in China, and it provides baseline information for Chinese regulatory authorities that will aid in the formulation of a regulatory framework for controlling L. monocytogenes with the aim of improving the microbiological safety of raw foods.

Pregnancy - associated human listeriosis: Virulence and genotypic analysis of Listeria monocytogenes from clinical samples

Listeria monocytogenes, a life-threatening pathogen, poses severe risk during pregnancy, may cause abortion, fetal death or neonatal morbidity in terms of septicemia and meningitis. The present study aimed at characterizing L. monocytogenes isolated from pregnant women based on serotyping, antibiotic susceptibility, virulence genes, in vivo pathogenicity test and ERIC- and REP-PCR fingerprint analyses. The results revealed that out of 3700 human clinical samples, a total of 30 (0.81%) isolates [12 (0.80%) from placental bit (1500), 18 (0.81%) from vaginal swab (2200)] were positive for L. monocytogenes. All the isolates belonged to serogroup 4b, and were + ve for virulence genes tested i.e. inlA, inlC, inlJ, plcA, prfA, actA, hlyA, and iap. Based on the mice inoculation tests, 20 isolates showed 100% and 4 isolates 60% relative virulence while 6 isolates were non-pathogenic. Moreover, 2 and 10 isolates were resistant to ciprofloxacin and cefoxitin, respectively, while the rest susceptible to other antibiotics used in this study. ERIC- and REP-PCR collectively depicted that the isolates from placental bit and vaginal swab had distinct PCR fingerprints except a few isolates with identical patterns. This study demonstrates prevalence of pathogenic strains mostly resistant to cefoxitin and/or ciprofloxacin. The results indicate the importance of isolating and characterizing the pathogen from human clinical samples as the pre-requisite for accurate epidemiological investigations.

Prevalence, antimicrobial susceptibility and virulotyping of Listeria species and Listeria monocytogenes isolated from open-air fish markets

BACKGROUND

The aim of this study was to investigate the prevalence and characterization of Listeria species and Listeria monocytogenes isolated from raw fish and open-air fish market environments. Eight hundred and sixty two samples including raw fish and fish market environments (samples from workers' hands, workers' knives, containers and work surface) were collected from the open-air fish markets in the Northern region of Iran.

RESULTS

Listeria spp. was isolated from 104/488 (21.3%) raw fish and 29/374 (7.8%) of samples from open-air fish market environment. The isolates of Listeria spp. included L. innocua (35.3%), L. monocytogenes (32.3%), L. seeligeri (18%), and L. ivanovii (14.3%). Of the 43 L. monocytogenes isolates, 31 (72.1%), 10 (23.3%) and 2 (4.7%) belonged to serovars 1/2a, 4b, and 1/2b, respectively. The inlA, inlB, inlC, inlJ, actA, hlyA, iap, plcA, and prfA virulence-associated genes were detected in almost all of the L. monocytogenes isolates. The Listeria spp. isolates showed high resistance against tetracycline (23.3%), penicillin G, and cephalothin (each 16.5%). Besides, we observed significant resistance level to tetracycline (27.9%), ampicillin (20.9%), cephalothin, penicillin G, and streptomycin (each 16.3%) in the L. monocytogenes isolates. All of the isolates were susceptible to cefotaxime, gentamicin, kanamycin, and pefloxacin. We found that tetM (25.6%), tetA (23.3%), ampC (14%), and penA (11.6%) were the most prevalent antibiotic resistance genes in the L. monocytogenes isolates.

CONCLUSIONS

Recovery of potentially pathogenic L. monocytogenes from raw fish and environment of open-air fish market samples in this study is a convincing evidence for the zoonotic potential of listeriosis.

Prevalence, antimicrobial susceptibility and virulotyping of Listeria species and Listeria monocytogenes isolated from open-air fish markets

BACKGROUND

The aim of this study was to investigate the prevalence and characterization of Listeria species and Listeria monocytogenes isolated from raw fish and open-air fish market environments. Eight hundred and sixty two samples including raw fish and fish market environments (samples from workers' hands, workers' knives, containers and work surface) were collected from the open-air fish markets in the Northern region of Iran.

RESULTS

Listeria spp. was isolated from 104/488 (21.3%) raw fish and 29/374 (7.8%) of samples from open-air fish market environment. The isolates of Listeria spp. included L. innocua (35.3%), L. monocytogenes (32.3%), L. seeligeri (18%), and L. ivanovii (14.3%). Of the 43 L. monocytogenes isolates, 31 (72.1%), 10 (23.3%) and 2 (4.7%) belonged to serovars 1/2a, 4b, and 1/2b, respectively. The inlA, inlB, inlC, inlJ, actA, hlyA, iap, plcA, and prfA virulence-associated genes were detected in almost all of the L. monocytogenes isolates. The Listeria spp. isolates showed high resistance against tetracycline (23.3%), penicillin G, and cephalothin (each 16.5%). Besides, we observed significant resistance level to tetracycline (27.9%), ampicillin (20.9%), cephalothin, penicillin G, and streptomycin (each 16.3%) in the L. monocytogenes isolates. All of the isolates were susceptible to cefotaxime, gentamicin, kanamycin, and pefloxacin. We found that tetM (25.6%), tetA (23.3%), ampC (14%), and penA (11.6%) were the most prevalent antibiotic resistance genes in the L. monocytogenes isolates.

CONCLUSIONS

Recovery of potentially pathogenic L. monocytogenes from raw fish and environment of open-air fish market samples in this study is a convincing evidence for the zoonotic potential of listeriosis.

Characterization of Listeria monocytogenes from three countries and antibiotic resistance differences among countries and Listeria monocytogenes serogroups

A total of 104 Listeria monocytogenes isolates from 330 fish samples from three countries were characterized by multiplex PCR for serogrouping and virulence markers determination and tested for antibiotics resistance. A 53·8% of the isolates belonged to serogroup 1/2a, 3a; 32% belonged to 1/2b, 3b, 7; 14·4% belonged to 4b, 4d, 4e and 1% belonged to 1/2c, 3c. All isolates exhibited resistance to at least one antibiotic but the resistance rates varied among countries. The isolates exhibited high resistance to penicillin, rifampicin, clindamycin, erythromycin and tetracycline, but low resistance to amoxicillin-clavulanic acid, streptomycin, sulfamethoxazole-trimethoprim, gentamicin, chloramphenicol and kanamycin. When comparing countries, the resistance rate for rifampicin, clindamycin, erythromycin, tetracycline, amoxicillin-clavulanic acid varied among countries. When comparing serogroup, 1/2a, 3a exhibited the highest resistance to clindamycin, erythromycin, tetracycline and vancomycin while serogroup 4b, 4d, 4e exhibited the highest resistance to amoxicillin-clavulanic acid. All isolates carried inlA, inlC, inlJ and lmo2672. Listeriolysin S was carried by 42 and 30% of 4b and 1/2b isolates respectively. Significance and impact of the study: This is one of few studies to correlate antibiotic resistance with Listeria monocytogenes serogroups. The study also compared the antibiotic resistance and serogroups of L. monocytogenes isolates from three countries in one single study. The findings of this study will be helpful in improving data on the antibiotics resistance of L. monocytogenes in developing countries and enriches the epidemiological and public health studies of L. monocytogenes.

Ruminant rhombencephalitis-associated Listeria monocytogenes strains constitute a genetically homogeneous group related to human outbreak strains

Listeriosis is a disease that causes significant economic losses at the farm level because of high morbidity and mortality in ruminants. This study was performed to investigate the role of ruminants in the epidemiology of listeriosis in northern Italy and the possible association of animal-adapted strains of Listeria monocytogenes with strains associated with human disease. Twenty ruminant rhombencephalitis isolates previously confirmed as L. monocytogenes by bacteriology and PCR were characterized by serotyping, pulsed-field gel electrophoresis, multi-virulence-locus sequence typing (MVLST), and multiplex single nucleotide polymorphism (mSNP) typing for the detection of epidemic clones. Subtyping results were subsequently compared with those obtained from human, food, and environmental isolates of L. monocytogenes, including 311 isolates from the University of Turin, Grugliasco, Italy, and 165 isolates representing major human listeriosis outbreaks worldwide, in addition to other unrelated isolates. Both mSNP typing and MVLST showed that 60% of the isolates analyzed belonged to epidemic clone I (ECI), which has been epidemiologically linked to several human outbreaks of listeriosis. In particular, the 1981 Canada outbreak was linked to the use of sheep manure and the 1985 California outbreak was linked to the use of raw cow's milk. In our study, ECI isolates were collected from different ruminant species on geographically and temporally distinct occasions for the last 13 years. Our results support the hypothesis that ruminants represent possible natural reservoirs of L. monocytogenes strains capable of causing epidemics of listeriosis in humans.

Enhanced surveillance of invasive listeriosis in the Lombardy region, Italy, in the years 2006-2010 reveals major clones and an increase in serotype 1/2a

BACKGROUND

Invasive listeriosis is a rare, life-threatening foodborne disease. Lombardy, an Italian region accounting for 16% of the total population, reported 55% of all listeriosis cases in the years 2006-2010. The aim of our study was to provide a snapshot of listeriosis epidemiology in this region after the implementation of a voluntary laboratory-based surveillance system.

METHODS

We characterized by serotyping, pulsed-field gel electrophoresis, multilocus sequence typing and detection of epidemic clone markers, 134 isolates from 132 listeriosis cases, including 15 pregnancy-related cases, occurring in the years 2006-2010 in Lombardy. Demographic and clinical characteristics of cases have also been described.

RESULTS

The mean age of non pregnancy-associated cases was 64.7 years, with 55.9% of cases being older than 65 years. Cases having no underlying medical conditions accounted for 11.6%. The all-cause fatality rate of 83 cases with a known survival outcome was 25.3%.Serotypes 1/2a and 4b comprised 52.2% and 38.8% of isolates, respectively. Seventy-three AscI pulsotypes and 25 sequence types assigned to 23 clonal complexes were recognized. Moreover, 53 (39.5%) isolates tested positive for the epidemic clone markers. Twelve molecular subtype clusters including at least three isolates were detected, with cluster 11 (1/2a/ST38) including 31 isolates identified during the entire study period. No outbreaks were notified to public health authorities during this period.

CONCLUSIONS

The findings of our study proved that epidemiology of listeriosis in Lombardy is characterized by a high prevalence of major clones and the increasing role of serotype 1/2a. Molecular subtyping is an essential tool in the epidemiology and surveillance of listeriosis. Rapid molecular cluster detection could alert about putative outbreaks, thus increasing the chance of detecting and inactivating routes of transmission.

An internalin a probe-based genosensor for Listeria monocytogenes detection and differentiation

Internalin A (InlA), a protein required for Listeria monocytogenes virulence, is encoded by the inlA gene, which is only found in pathogenic strains of this genus. One of the best ways to detect and confirm the pathogenicity of the strain is the detection of one of the virulence factors produced by the microorganism. This paper focuses on the design of an electrochemical genosensor used to detect the inlA gene in Listeria strains without labelling the target DNA. The electrochemical sensor was obtained by immobilising an inlA gene probe (single-stranded oligonucleotide) on the surfaces of screen-printed gold electrodes (Au-SPEs) by means of a mercaptan-activated self-assembled monolayer (SAM). The hybridisation reaction occurring on the electrode surface was electrochemically transduced by differential pulse voltammetry (DPV) using methylene blue (MB) as an indicator. The covalently immobilised single-stranded DNA was able to selectively hybridise to its complementary DNA sequences in solution to form double-stranded DNA on the gold surface. A significant decrease of the peak current of the voltammogram (DPV) upon hybridisation of immobilised ssDNA was recorded. Whole DNA samples of L. monocytogenes strains could be discriminated from other nonpathogenic Listeria species DNA with the inlA gene DNA probe genosensor.

Molecular subtyping and virulence gene analysis of Listeria monocytogenes isolates from food

A total of 67 Listeria monocytogenes isolates from 698 raw meat samples were characterized for molecular serogroup identification and antimicrobial susceptibility. Approximately one third (32.8%) of the isolates belonged to molecular serogroup 1/2a, 3a, followed by 1/2c, 3c (26.9%), 1/2b, 3b, 7 (22.4%), 4b, 4d, 4e (16.4%) and 4a, 4c (1.5%). Most of the L. monocytogenes isolates were susceptible to 14 antimicrobials tested but several were resistant to tetracycline, ciprofloxacin and nitrofurantoin. An additional 30 L. monocytogenes isolates from chicken and produce in our collection were also included to determine the presence of significant virulence markers. All 97 isolates carried inlC and inlJ except for a lineage III isolate 110-1. Most Listeriolysin S (LLS)-carrying isolates (11/12) belonged to lineage I, whereas the remaining one isolate belonged to lineage III. Five 4b, 4d, 4e isolates including two from turkey and three from produce belonged to Epidemic Clone I (ECI). Four molecular serogroup associated mutation types that lead to premature stop codons (PMSCs) in inlA were identified. PFGE and inlA sequence analysis results were concordant, and different virulence potential within 1/2a, 3a and 4b, 4d, 4e isolates were observed. The study revealed that a subset of isolates from meat and produce belonged to ECI, harbored inlC, inlJ and LLS, and produced full length InlA, suggesting that they be capable of causing human illness.

Characterization and antimicrobial resistance of Listeria monocytogenes isolated from retail beef meat in Poland

Four hundred seventeen retail beef meat samples purchased in the eastern part of Poland during October 2009 to January 2011 were tested for the presence of Listeria monocytogenes. It was found that 81 (19.4%) of them were positive for this microorganism as identified by the culture and polymerase chain reaction (PCR) methods. Molecular serotyping performed by PCR revealed that the majority of the isolates (50 strains; 61.7%) were of 1/2a serotype. Furthermore, 26 (32.1%) L. monocytogenes strains were classified as 1/2c serotype, and only five strains belonged to serotypes 1/2b or 4b (four and one isolates, respectively). All the isolates were positive for the inlA, inlC, inlJ, and lmo2672 sequences, whereas two L. monocytogenes (both of 4b serotype) had another virulence marker gene--llsX. The results of the antimicrobial resistance revealed that the strains were sensitive to most of the antimicrobials used in the study except oxacillin (62.7% resistant strains). Several isolates (17.3%) were also resistant to ceftriaxone. Our results indicate that L. monocytogenes identified in raw beef meat possessed virulence markers that make them potentially pathogenic for humans. Therefore, this kind of food may create a public health concern.

[Microbiological characterisation of Listeria monocytogenes isolates from human cases in Andalusia]

OBJECTIVE

The aim of this study was to perform a retrospective study by genotyping 154 isolates from human listeriosis cases occurred in the region of Andalusia (southern Spain) in the period 2005-2009.

MATERIAL AND METHODS

Serotyping was performed for 1 and 4 somatic antigens using commercial Listeria antisera, and by multiplex-PCR serogrouping according to the method described by Doumith et al. (2004). The antimicrobial susceptibility was performed by Epsilon test and interpreted by CLSI criteria. PFGE was performed according to the PulseNet protocol with the ApaI enzyme. The similarity of PFGE profiles was evaluated using the Bionumerics software. The multiplex PCR protocol described by Chen and Knabel (2007) was used for the identification of isolates belonging to L. monocytogenes ECI, ECII, and ECIII epidemic clones.

RESULTS

The 154 isolates were grouped into four serotypes: 4b [94 (61%)] strains, 1/2b [30 (19%)] strains, 1/2a [27 (18%)] strains, and 1/2c [3 (2%)] strains, with 100% of susceptibility to ampicillin and cotrimoxazole. A further sixty-two ApaI distinct pulsotypes were recognized. Thirty-seven isolates (24%) showed unique ApaI pulsotypes, and the remaining 117 strains (76%) were assigned to 25 ApaI clusters (60% in clusters of more than two isolates). The EC markers were found in 62 (40.3%) of the L. monocytogenes isolates tested. The ECI marker was present in 43 (46.2%) 4b serotype isolates, ECII in 10 (10.7%) 4b serotype isolates, and ECIII in 9 (33,3%) 1/2a serotype isolates.

DISCUSSION

A large proportion of the human listeriosis cases under investigation could be grouped into molecular subtype clusters, and our cases could be related to international food-borne outbreaks.

Prevalence, characterization, and antimicrobial resistance of Listeria monocytogenes isolates from bovine hides and carcasses

Listeria monocytogenes isolates from bovine hides and carcasses (n = 812) were mainly of serogroup 1/2a. All strains were positive for internalin genes. Several isolates were resistant to oxacillin (72.2%) or clindamycin (37.0%). These findings indicate that L. monocytogenes of beef origin can be considered a public health concern.

Genotypic characterization of Listeria monocytogenes isolated from humans in India

Listeria monocytogenes is a foodborne pathogen associated with severe diseases in humans and animals. The genotypic analysis of 17 L. monocytogenes isolates recovered from humans in India during 2006-2009 using multiplex serotyping PCR allowing serovar predictions, conventional serology and by pulsed field gel electrophoresis (PFGE) is presented. The isolates were recovered from patients exhibiting various clinical conditions. A multiplex-PCR based serotyping assay revealed 88·24% (15/17) of the strains belonging to the serovar group 4b, 4d, 4e and 11·76% (2/17) to the serovar group 1/2b, 3b. Conventional serology indicated that 13 (76·47%) L. monocytogenes isolates to be of serotype 4b, 2 (11·76%) serotype 4d, and 2 (11·76%) serotype 1/2b. Ten ApaI and nine AscI pulsotypes were recognized among the 17 human isolates. PFGE analysis allowed discrimination among isolates of the same serotype and among isolates from the same sampling areas or those isolated from different areas. Thus, PFGE together with multiplex-PCR serotyping allows rapid discrimination of L. monocytogenes strains. In addition, the predominance of L. monocytogenes serotype 4b is of concern, as this serotype has been most frequently associated with human listeriosis outbreaks.

Novel multiplex single nucleotide polymorphism-based method for identifying epidemic clones of Listeria monocytogenes

A novel primer extension-based, multiplex minisequencing assay targeting six highly informative single nucleotide polymorphisms (SNPs) in four virulence genes correctly identified and differentiated all four epidemic clones (ECs) of Listeria monocytogenes and 9 other strains initially misclassified as non-ECs. This assay allows rapid, accurate, and high-throughput screening for all known ECs of L. monocytogenes.