Antimicrobial susceptibility and serotyping of Listeria monocytogenes isolated from ready-to-eat seafood and food processing environments in Korea

Listeria monocytogenes in the seafood industry: Exploring contamination sources, outbreaks, antibiotic susceptibility and genetic diversity

Fish and seafood are rich sources of protein, vitamins, and minerals, significantly contributing to individual health. A global increase in consumption has been observed. Listeria monocytogenes is a known problem in food processing environments and is found in various seafood forms, including raw, smoked, salted, and ready-to-eat. Without heat treatment and given L. monocytogenes' ability to multiply under refrigerated conditions, consuming seafood poses a substantial health hazard, particularly to immunocompromised individuals. Numerous global outbreaks of listeriosis have been linked to various fish products, underscoring the importance of studying L. monocytogenes. Different strains exhibit varying disease-causing abilities, making it crucial to understand and monitor the organism's virulence and resistance aspects for food safety. This paper aims to highlight the genetic diversity of L. monocytogenes found in fish products globally and to enhance understanding of contamination routes from raw fish to the final product.

Genetic diversity of Listeria monocytogenes from seafood products, its processing environment, and clinical origin in the Western Cape, South Africa using whole genome sequencing

Listeria monocytogenes is a concern in seafood and its food processing environment (FPE). Several outbreaks globally have been linked to various types of seafood. Genetic profiling of L. monocytogenes is valuable to track bacterial contamination throughout the FPE and in understanding persistence mechanisms, with limited studies from South Africa. Forty-six L. monocytogenes isolates from origins: Fish/seafood products (n = 32) (salmon, smoked trout, fresh hake, oysters), the FPE (n = 6), and clinical (n = 8) were included in this study. Lineage typing, antibiotic susceptibility testing, and screening for two genes (bcrABC and emrC) conferring sanitizer tolerance was conducted. The seafood and FPE isolates originated from seven different factories processing various seafood products with undetermined origin. All clinical isolates were categorized as lineage I, and seafood and FPE isolates were mostly categorized into lineage II (p < 0.01). Seafood and FPE isolates (53%) carried the bcrABC gene cassette and one fish isolate, the emrC gene. A subset, n = 24, was grouped into serotypes, sequence types (STs), and clonal complexes (CCs) with whole genome sequencing (WGS). Eight CCs and ten STs were identified. All clinical isolates belonged to serogroup 4b, hypervirulent CC1. CC121 was the most prevalent in isolates from food and the FPE. All isolates carried Listeria pathogenicity islands (LIPI) 1 and 2. LIPI-3 and LIPI-4 were found in certain isolates. We identified genetic determinants linked to enhanced survival in the FPE, including stress survival islets (SSI) and genes conferring tolerance to sanitizers. SSI-1 was found in 44% isolates from seafood and the FPE. SSI-2 was found in all the ST121 seafood isolates. Isolates (42%) harbored transposon Tn1688_qac (ermC), conferring tolerance to quaternary ammonium compounds. Five plasmids were identified in 13 isolates from seafood and the FPE. This is the first One Health study reporting on L. monocytogenes genetic diversity, virulence and resistance profiles from various types of seafood and its FPE in South Africa.

Antimicrobial Resistance of Listeria monocytogenes Strains Isolated in Food and Food-Processing Environments in Italy

Listeria monocytogenes, along with various other pathogenic bacteria, may show resistance against a broad spectrum of antibiotics. Evaluating the extent of resistance in harmful microorganisms like Listeria monocytogenes holds significant importance in crafting novel therapeutic strategies to mitigate or combat the rise of infections stemming from antibiotic-resistant bacteria. The present work aims to investigate the occurrence of antimicrobial resistance among Listeria monocytogenes strains in meat products (n = 173), seafood (n = 54), dairy products (n = 19), sauces (n = 2), confectionary products (n = 1), ready-to-eat rice dishes (n = 1), and food-processing environments (n = 19). A total of 269 Listeria monocytogenes strains belonging to eight different serovars were tested against 10 antimicrobials. In the classes of antibiotics, most of the strains were resistant antibiotics belonging to the family of β-lactams (92.94%). High proportions of L. monocytogenes isolates were resistant to oxacillin (88.48%), followed by fosfomycin (85.87%) and flumenique (78.44%). The lowest level of resistance was observed against gentamycin (1.49%). A total of 235 strains (n = 87.36%) showed a profile of multidrug resistance. In conclusion, a high occurrence of resistant and multidrug-resistant strains of Listeria monocytogenes was observed among the examined serotypes isolated from different food sources. This understanding enables the adoption of suitable measures to avert contamination and the spread of resistant bacteria via food.

Whole-genome sequencing of Listeria monocytogenes isolated from the first listeriosis foodborne outbreak in South Korea

Listeria monocytogenes is a foodborne pathogen that causes listeriosis in humans with severe symptoms. In South Korea, listeriosis had only been reported sporadically among hospitalized patients until the first foodborne outbreak occurred in 2018. In this study, a L. monocytogenes strain responsible for this outbreak (FSCNU0110) was characterized via whole genome sequencing and compared with publicly available L. monocytogenes genomes of the same clonal complex (CC). Strain FSCNU0110 belonged to multilocus sequence typing (MLST)-based sequence type 224 and CC224, and core genome MLST-based sublineage 6,178. The strain harbored tetracycline resistance gene tetM, four other antibiotic resistance genes, and 64 virulence genes, including Listeria pathogenicity island 1 (LIPI-1) and LIPI-3. Interestingly, llsX in LIPI-3 exhibited a characteristic SNP (deletion of A in position 4, resulting in a premature stop codon) that was missing among all CC224 strains isolated overseas but was conserved among those from South Korea. In addition, the tetM gene was also detected only in a subset of CC224 strains from South Korea. These findings will provide an essential basis for assessing the characteristics of CC224 strains in South Korea that have shown a potential to cause listeriosis outbreaks.

Antibiotic Resistance in Selected Emerging Bacterial Foodborne Pathogens-An Issue of Concern?

Antibiotic resistance (AR) and multidrug resistance (MDR) have been confirmed for all major foodborne pathogens: Campylobacter spp., Salmonella spp., Escherichia coli and Listeria monocytogenes. Of great concern to scientists and physicians are also reports of antibiotic-resistant emerging food pathogens-microorganisms that have not previously been linked to food contamination or were considered epidemiologically insignificant. Since the properties of foodborne pathogens are not always sufficiently recognized, the consequences of the infections are often not easily predictable, and the control of their activity is difficult. The bacteria most commonly identified as emerging foodborne pathogens include Aliarcobacter spp., Aeromonas spp., Cronobacter spp., Vibrio spp., Clostridioides difficile, Escherichia coli, Mycobacterium paratuberculosis, Salmonella enterica, Streptocccus suis, Campylobacter jejuni, Helicobacter pylori, Listeria monocytogenes and Yersinia enterocolitica. The results of our analysis confirm antibiotic resistance and multidrug resistance among the mentioned species. Among the antibiotics whose effectiveness is steadily declining due to expanding resistance among bacteria isolated from food are β-lactams, sulfonamides, tetracyclines and fluoroquinolones. Continuous and thorough monitoring of strains isolated from food is necessary to characterize the existing mechanisms of resistance. In our opinion, this review shows the scale of the problem of microbes related to health, which should not be underestimated.

Phenotypic and genotypic characterization of Listeria monocytogenes in clinical ruminant cases in Korea

Listeria monocytogenes, a foodborne human and veterinary pathogen, is associated with high mortality rates in ruminants. However, no studies have investigated the antimicrobial resistance of L. monocytogenes isolates from clinical ruminant cases. This study aimed to determine the phenotypic and genotypic characteristics of L. monocytogenes isolates from clinical cases of Korean ruminants. We collected 24 L. monocytogenes isolates from aborted bovine fetuses and goats presenting with listeriosis-related symptoms. The isolates were subjected to PCR serogrouping, conventional serotyping, virulence gene detection, and antimicrobial susceptibility testing. Furthermore, pulsed-field gel electrophoresis and multilocus sequence typing were used to classify and compare genetic diversity among the isolates, including human L. monocytogenes isolates. The most prevalent L. monocytogenes serotypes were 4b (Ⅳ_b), 1/2a (Ⅱ_a; Ⅱ_c), and 1/2b (Ⅱ_b). All isolates harbored the virulence genes; however, llsX-encoding listeriolysin were identified only in serotypes 4b and 1/2b. All isolates, including two found in humans, formed three genetically diverse pulsed-field gel electrophoresis clusters according to serotype, lineage, and sequence type. The most prevalent sequence type was ST1, followed by ST365 and ST91. The isolates from ruminants with listeriosis were resistant to oxacillin and ceftriaxone and showed diverse lineage, serotype (serogroup), and sequence type characteristics. Considering that the atypical sequence types exhibited clinical manifestations and histopathological lesions, further study is needed to elucidate the pathogenicity of genetically diverse ruminant L. monocytogenes isolates. Furthermore, continuous monitoring of antimicrobial resistance is required to prevent the emergence of L. monocytogenes strains resistant to common antimicrobials.

Prevalence, Antibiogram and Biofilm Production of Listeria Monocytogenes from Faeces and Foetuses of Slaughtered Pregnant Cows: Environmental and Public Health Implications

The indiscriminate slaughter of pregnant animals which characterizes most developing countries poses increasing environmental and public health risks from Listeria monocytogenes infections which are endemic in such settings. The available reports show increasing trends of Listeria monocytogenes infections in both humans and animals in Nigeria. This study examined the prevalence, antibiogram and biofilm production of L. monocytogenes from faeces and foetuses of slaughtered pregnant cows in Ibadan Central Abattoir, Nigeria. Faecal (n = 118) and foetal (n = 118) swabs were cultured and isolates tested for antibiotic susceptibility by Kirby-Bauer assay, while biofilm production was quantified following the standard procedures. The data were analysed using the Chi Square and Student’s t-test at P < 0.05. Listeria monocytogenes were isolated from five (4.2 %) and three (2.5 %) faeces and foetus swabs, respectively, without significant association with sample type (P = 0.50). The isolates were resistant to all the antibiotics tested except gentamicin; with significantly higher production of biofilm by those from foetal samples (P = 0.012). The detection of widespread antibiotic-resistant L. monocytogenes from faeces and foetuses has important environmental and public health implications, given the risk of contamination through faecal shedding and foetal handling. The biofilm production by the pathogen connotes its ability to persist in the environment, suggestive of the challenging effects to its control. Campaigns against indiscriminate slaughter of pregnant animals, and proper hygiene are advocated to ultimately safeguard human and animal health.

Prevalence and antimicrobial resistance of Listeria species and molecular characterization of Listeria monocytogenes isolated from retail ready-to-eat foods

A wide variety of foods can be contaminated with Listeria species, especially L. monocytogenes. Ready-to-eat (RTE) foods are predominantly associated with human listeriosis caused by L. monocytogenes. Therefore, this study aimed to assess the presence of Listeria species in RTE foods and to characterize L. monocytogenes isolates by means of detection of virulence markers, serotypes and genetic relatedness. Of the 300 RTE food samples, 59 (19.7%) were positive for Listeria species: L. innocua (13.3%), L. monocytogenes (5%), L. welshimerii (2.3%), L. grayi subsp. murrayi (1.3%), L. grayi (1%), L. ivanovii (1%) and L. ivanovi subsp. londoniensis (0.3%). All L. monocytogenes isolates identified were positive for the actA, iap, inlA, inlB, inlC, inlJ, plcA and prfA virulence genes and biofilm. The isolates were serotyped as 1/2c (33.3%), 4b (26.7%), 1/2a (26.7%), 1/2b (6.7%) and 3c (6.7%) by the multiplex-PCR and agglutination methods. PCR-restriction fragment length polymorphism with AluI and MluCI resulted in three and two profiles, respectively. Pulsed-field gel electrophoresis differentiated the L. monocytogenes isolates into 15 ApaI and 12 AscI patterns. Antimicrobial resistance of all Listeria isolates was determined by the disk diffusion method. Most L. monocytogenes isolates were sensitive to antimicrobials used in the treatment of listeriosis. This study shows the presence of potential pathogenic and antimicrobial-resistant L. monocytogenes in RTE foods that may lead to consumer health risks.

Isolation and Characterization of Fengycins Produced by Bacillus amyloliquefaciens JFL21 and Its Broad-Spectrum Antimicrobial Potential Against Multidrug-Resistant Foodborne Pathogens

The continuing emergence and development of pathogenic microorganisms that are resistant to antibiotics constitute an increasing global concern, and the effort in new antimicrobials discovery will remain relevant until a lasting solution is found. A new bacterial strain, designated JFL21, was isolated from seafood and identified as B. amyloliquefaciens. The antimicrobial substance produced by B. amyloliquefaciens JFL21 showed low toxicity to most probiotics but exhibited strong antimicrobial activities against multidrug-resistant foodborne pathogens. The partially purified antimicrobial substance, Anti-JFL21, was characterized to be a multiple lipopeptides mixture comprising the families of surfactin, fengycin, and iturin. Compared with commercially available polymyxin B and Nisin, Anti-JFL21 not only could exhibit a wider and stronger antibacterial activity toward Gram-positive pathogens but also inhibit the growth of a majority of fungal pathogens. After further separation through gel filtration chromatography (GFC), the family of surfactin, fengycin, and iturin were obtained, respectively. The results of the antimicrobial test pointed out that only fengycin family presented marked antimicrobial properties against the indicators of L. monocytogenes, A. hydrophila, and C. gloeosporioides, which demonstrated that fengycins might play a major role in the antibacterial and antifungal activity of Anti-JFL21. Additionally, the current study also showed that the fengycins produced by B. amyloliquefaciens JFL21 not only maintained stable anti-Listeria activity over a broad pH and temperature range, but also remained active after treatment with ultraviolet sterilization, chemical reagents, and proteolytic enzymes. Therefore, the results of this study suggest the new strain and its antimicrobials are potentially useful in food preservation for the biological control of the multidrug-resistant foodborne pathogens.

Occurrence and Characteristics of Listeria monocytogenes in Ready-to-Eat Meat Products in Poland

ABSTRACT

Listeria monocytogenes is a potential hazard for food safety and therefore for public health. The aim of the present study was to determine the prevalence and characteristics of L. monocytogenes in Polish ready-to-eat (RTE) meat products for retail sale. Among the 184,439 food samples collected within the framework of a national official control and monitoring program, only 0.3% were positive for L. monocytogenes. A significant group of products that did not meet the criteria were RTE meat products. This group accounted for 40% of all noncompliant samples. Seventy L. monocytogenes isolates from these RTE meat products (meat, sausages, and delicatessen products with meat) were examined. The majority of the tested isolates (51%) belonged to serogroup 1/2a-3a followed by 1/2c-3c (21%), 1/2b-3b-7 (14%), and 4ab-4b-4d-4e (13%). Serogroup 4a-4c was not present among the tested isolates. All L. monocytogenes isolates harbored the virulence-associated genes inlA, inlC, inlJ, and lmo2672. The llsX marker was detected in 12 (17%) of the 70 isolates. Ampicillin resistance was the most common resistance phenotype and was identified in 83% of the L. monocytogenes isolates. A low incidence of resistance to amoxicillin-clavulanic acid (6% of isolates) was also detected. All L. monocytogenes isolates were susceptible to chloramphenicol, gentamicin, ciprofloxacin, meropenem, sulfamethoxazole-trimethoprim, tetracycline, and erythromycin. This work provides useful information regarding contamination of RTE meat products with L. monocytogenes, which may have implications for food safety risks.

HIGHLIGHTS

A systematic review and meta-analysis on the prevalence of antibiotic-resistant Listeria species in food, animal and human specimens in Iran

The aim of this study was to determine the antimicrobial resistance characteristics of Listeria species isolated from foods and food processing environments, animal and human specimens in Iran. A systematic review of the papers published in Persian and English languages up to 20th May 2019 and indexed in the Scientific Information Database, PubMed, Scopus and Google Scholar databases using related keywords was conducted. Eligible articles were selected based on the predefined inclusion and exclusion criteria, followed by data extraction and meta-analysis using random-effects or fixed-effects models. A total of 27 articles were found reporting antibiotic resistance patterns of different Listeria species using disk diffusion method. Among Listeria species, Listeria monocytogenes resistance to commonly used antibiotics i.e. penicillin, ampicillin and gentamicin was as follows: 34.5%, 26.4%, 8.9% in isolates from foods and food processing environments, 47.1%, 29.5%, 9.2% in isolates from animal specimens and 56.8%, 29.5%, 32.4% in human strains, respectively. A high prevalence of L. monocytogenes strains resistant to penicillin, ampicillin and gentamicin was observed in Iran. Our findings suggested that trimethoprim/sulfamethoxazole, vancomycin and ciprofloxacin can be used as alternatives in the treatment of human listeriosis in Iran due to their low resistance rates.

Emergence of Antibiotic Resistance in Listeria monocytogenes Isolated from Food Products: A Comprehensive Review

Listeria monocytogenes is an opportunistic pathogen that has been involved in several deadly illness outbreaks. Future outbreaks may be more difficult to manage because of the emergence of antibiotic resistance among L. monocytogenes strains isolated from food products. The present review summarizes the available evidence on the emergence of antibiotic resistance among L. monocytogenes strains isolated from food products and the possible ways this resistance has developed. Furthermore, the resistance of food L. monocytogenes isolates to antibiotics currently used in the treatment of human listeriosis such as penicillin, ampicillin, tetracycline, and gentamicin, has been documented. Acquisition of movable genetic elements is considered the major mechanism of antibiotic resistance development in L. monocytogenes. Efflux pumps have also been linked with resistance of L. monocytogenes to some antibiotics including fluoroquinolones. Some L. monocytogenes strains isolated from food products are intrinsically resistant to several antibiotics. However, factors in food processing chains and environments (from farm to table) including extensive or sub-inhibitory antibiotics use, horizontal gene transfer, exposure to environmental stresses, biofilm formation, and presence of persister cells play crucial roles in the development of antibiotic resistance by L. monocytogenes.