The genus
Listeria
is currently comprised of 17 species, including 9
Listeria
species newly described since 2009. Genomic and phenotypic data clearly define a distinct group of six species (
Listeria
...sensu strictu) that share common phenotypic characteristics (e.g., ability to grow at low temperature, flagellar motility); this group includes the pathogen
Listeria monocytogenes
. The other 11 species (
Listeria
sensu lato) represent three distinct monophyletic groups, which may warrant recognition as separate genera. These three proposed genera do not contain pathogens, are non-motile (except for
Listeria grayi
), are able to reduce nitrate (except for
Listeria floridensis
), and are negative for the Voges-Proskauer test (except for
L. grayi
). Unlike all other
Listeria
species, species in the proposed new genus
Mesolisteria
are not able to grow below 7 °C. While most new
Listeria
species have only been identified in a few countries, the availability of molecular tools for rapid characterization of putative
Listeria
isolates will likely lead to future identification of isolates representing these new species from different sources. Identification of
Listeria
sensu lato isolates has not only allowed for a better understanding of the evolution of
Listeria
and virulence characteristics in
Listeria
but also has practical implications as detection of
Listeria
species is often used by the food industry as a marker to detect conditions that allow for presence, growth, and persistence of
L. monocytogenes
. This review will provide a comprehensive critical summary of our current understanding of the characteristics and distribution of the new
Listeria
species with a focus on
Listeria
sensu lato.
Fresh produce may be contaminated by bacterial pathogens, including Listeria monocytogenes, during harvesting, packaging, or transporting. A low-intensity cavitation process with air being injected ...into water was studied to determine the microbubbles' efficiency when detaching L. monocytogenes from stainless steel and the surface of fresh cucumber and avocado. Stainless steel coupons (1″ × 2″), cucumber, and avocado surfaces were inoculated with L. monocytogenes (LCDC strain). After 1, 24 or 48 h, loosely attached cells were washed off, and inoculated areas were targeted by microbubbles (~0.1-0.5 mm dia.) through a bubble diffuser (1.0 L air/min) for 1, 2, 5, or 10 min. For steel, L. monocytogenes (48 h drying) detachment peaked at 2.95 mean log reduction after 10 min of microbubbles when compared to a no-bubble treatment. After 48 h pathogen drying, cucumbers treated for 10 min showed a 1.78 mean log reduction of L. monocytogenes. For avocados, L. monocytogenes (24 h drying) detachment peaked at 1.65 log reduction after 10 min of microbubbles. Microbubble applications may be an effective, economical, and environmentally friendly way to remove L. monocytogenes, and possibly other bacterial pathogens, from food contact surfaces and the surfaces of whole, intact fresh produce.
Postprocessing contamination in processing plants has historically been a significant source of Listeria monocytogenes in ready-to-eat delicatessen meats, and therefore a major cause of human ...listeriosis cases and outbreaks. Recent risk assessments suggest that a majority of human listeriosis cases linked to consumption of contaminated deli meats may be due to L. monocytogenes contamination that occurs at the retail level. To better understand the ecology and transmission of Listeria spp. in retail delicatessens, food and nonfood contact surfaces were tested for L. monocytogenes and other Listeria spp. in a longitudinal study conducted in 30 retail delis in three U.S. states. In phase I of the study, seven sponge samples were collected monthly for 3 months in 15 delis (5 delis per state) prior to start of daily operation; in phase II, 28 food contact and nonfood contact sites were sampled in each of 30 delis during daily operation for 6 months. Among the 314 samples collected during phase I, 6.8% were positive for L. monocytogenes. Among 4,503 samples collected during phase II, 9.5% were positive for L. monocytogenes; 9 of 30 delis showed low L. monocytogenes prevalence (<1%) for all surfaces. A total of 245 Listeria spp. isolates, including 184 Listeria innocua, 48 Listeria seeligeri, and 13 Listeria welshimeri were characterized. Pulsed-field gel electrophoresis (PFGE) was used to characterize 446 L. monocytogenes isolates. PFGE showed that for 12 of 30 delis, one or more PFGE types were isolated on at least three separate occasions, providing evidence for persistence of a given L. monocytogenes subtype in the delis. For some delis, PFGE patterns for isolates from nonfood contact surfaces were distinct from patterns for occasional food contact surface isolates, suggesting limited cross-contamination between these sites in some delis. This study provides longitudinal data on L. monocytogenes contamination patterns in retail delis, which should facilitate further development of control strategies in retail delis.
Four isolates (FSL S4-120(T), FSL S4-696, FSL S4-710, and FSL S4-965) of Gram-positive, motile, facultatively anaerobic, non-spore-forming bacilli that were phenotypically similar to species of the ...genus Listeria were isolated from soil, standing water and flowing water samples obtained from the natural environment in the Finger Lakes National Forest, New York, USA. The four isolates were closely related to one another and were determined to be the same species by whole genome DNA-DNA hybridization studies (>82 % relatedness at 55 degrees C and >76 % relatedness at 70 degrees C with 0.0-0.5 % divergence). 16S rRNA gene sequence analysis confirmed their close phylogenetic relatedness to Listeria monocytogenes and Listeria innocua and more distant relatedness to Listeria welshimeri, L. seeligeri, L. ivanovii and L. grayi. Phylogenetic analysis of partial sequences for sigB, gap, and prs showed that these isolates form a well-supported sistergroup to L. monocytogenes. The four isolates were sufficiently different from L. monocytogenes and L. innocua by DNA-DNA hybridization to warrant their designation as a new species of the genus Listeria. The four isolates yielded positive reactions in the AccuProbe test that is purported to be specific for L. monocytogenes, did not ferment L-rhamnose, were non-haemolytic on blood agar media, and did not contain a homologue of the L. monocytogenes virulence gene island. On the basis of their phenotypic characteristics and their genotypic distinctiveness from L. monocytogenes and L. innocua, the four isolates should be classified as a new species within the genus Listeria, for which the name Listeria marthii sp. nov. is proposed. The type strain of L. marthii is FSL S4-120(T) (=ATCC BAA-1595(T) =BEIR NR 9579(T) =CCUG 56148(T)). L. marthii has not been associated with human or animal disease at this time.
is considered a nonpathogenic
species. Natural atypical hemolytic
isolates have been reported but have not been characterized in detail. Here, we report the genomic and functional characterization of ...representative isolates from the two known natural hemolytic
clades. Whole-genome sequencing confirmed the presence of
pathogenicity islands (LIPI) characteristic of
species. Functional assays showed that LIPI-1 and
genes are transcribed, and the corresponding gene products are expressed and functional. Using
and
assays, we show that atypical hemolytic
is virulent, can actively cross the intestinal epithelium, and spreads systemically to the liver and spleen, albeit to a lesser degree than the reference
EGDe strain. Although human exposure to hemolytic
is likely rare, these findings are important for food safety and public health. The presence of virulence traits in some
clades supports the existence of a common virulent ancestor of
and
.
The global coconut water market is projected to grow in the upcoming years, attributed to its numerous health benefits. However, due to its susceptibility to microbial contamination and the ...limitations of non-thermal decontamination methods, thermal treatments remain the primary approach to ensure the shelf-life stability and the microbiological safety of the product. In this study, the thermal inactivation of Listeria innocua, a Listeria monocytogenes surrogate, was evaluated in coconut water and in tryptone soy broth (TSB) under both isothermal (50–60 °C) and dynamic conditions (from 30 to 60 °C, with temperature increases of 0.5, 1 and 5 °C/min). Mathematical models were used to analyse the inactivation data. The Geeraerd model effectively described the thermal inactivation of L. innocua in both TSB and coconut water under isothermal conditions, with close agreement between experimental data and model fits. Parameter estimates and analysis revealed that acidified TSB is a suitable surrogate medium for studying the thermal inactivation of L. innocua in coconut water, despite minor differences observed in the shoulder length of inactivation curves, likely attributed to the media composition. The models fitted to the data obtained at isothermal conditions fail to predict L. innocua responses under dynamic conditions. This is attributed to the stress acclimation phenomenon that takes place under dynamic conditions, where bacterial cells adapt to initial sub-lethal treatment stages, leading to increased thermal resistance. Fitting the Bigelow model directly to dynamic data with fixed z-values reveals a three-fold increase in D-values with lower heating rates, supporting the role of stress acclimation. The findings of this study aid in designing pasteurization treatments targeting L. innocua in coconut water and enable the establishment of safe, mild heat treatments for refrigerated, high-quality coconut water.
Listeria monocytogenes biofilms are ubiquitous in the food-processing environment, where they frequently show resistance against treatment with disinfectants such as peracetic acid (PAA) due to ...sub-lethal damage resulting in biofilm persistence or the formation of secondary biofilms. L. monocytogenes serovar ½a EGD-e biofilms were cultivated under continuous flow conditions at 10 °C, 22 °C, and 37 °C and exposed to industrially relevant PAA concentrations. The effect of PAA on biofilm metabolic activity and biomass was monitored in real-time using the CEMS-BioSpec system, in addition to daily measurement of biofilm-derived planktonic cell production. Biofilm-derived planktonic cell yields proved to be consistent with high yields during biofilm establishment (≥10sup.6 CFU.mLsup.−1). The exposure of biofilms to the minimum inhibitory PAA concentration (0.16%) resulted in only a brief disruption in whole-biofilm metabolic activity and biofilm biomass accumulation. The recovered biofilm accumulated more biomass and greater activity, but cell yields remained similar. Increasing concentrations of PAA (0.50%, 1.5%, and 4.0%) had a longer-lasting inhibitory effect. Only the maximum dose resulted in a lasting inhibition of biofilm activity and biomass-a factor that needs due consideration in view of dilution in industrial settings. Better disinfection monitoring tools and protocols are required to adequately address the problem of Listeria biofilms in the food-processing environment, and more emphasis should be placed on biofilms serving as a "factory" for cell proliferation rather than only a survival mechanism.
Background. We analyzed clinical characteristics, treatment, genetic diversity, and outcome of 92 adults with Listeria monocytogenes meningitis included in 2 prospective nationwide cohort studies. ...Methods. Episodes of community-acquired listerial meningitis confirmed by cerebrospinal fluid culture were included from 1998 to 2002 and 2006 to 2012. We compared patients and pathogen characteristics between cohorts and identified predictors for an unfavorable outcome according to the Glasgow Outcome Scale. Results. Thirty episodes were included from 1998 to 2002 and 62 from 2006 to 2012; clinical and laboratory characteristics on admission were similar between cohorts. However, the rate of unfavorable outcome increased from 27% in the 1998–2002 cohort to 61% in the 2006–2012 cohort (P = .002). Differences between cohorts were increased use of adjunctive dexamethasone therapy (0% in 1998–2002 vs 53% in 2006–2012; P < .001) and emergence of infection by L. monocytogenes genotype sequence type 6 (ST6; 4% in 1998–2002 vs 29% in 2006–2012; P = .009). Multivariate regression analysis identified infection with L. monocytogenes ST6 as the sole predictor of unfavorable outcome (odds ratio, 3.77; 95% confidence interval, 1.07–13.33). Patients infected with genotypes other than ST6 also had an increased rate of unfavorable outcome over time (P = .03). Conclusions. The rate of unfavorable outcome among adults with listerial meningitis has increased over a 14year period, from 27% to 61%. The emerging L. monocytogenes genotype ST6 was identified as the main factor leading to poorer prognosis. Adjunctive dexamethasone may be discontinued if L. monocytogenes is identified, as there is no proven benefit in Listeria meningitis.
ABSTRACT
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.
Listeria monocytogenes which harbor virulence factors linked to the pathogenesis and serotypes associated with listeriosis in ready-to-eat foods pose a health risk for consumers, particularly susceptible individuals.
Aims
An extensive source investigation was conducted on a dairy farm with neurolisteriosis and subclinical mastitis cases to identify infection source and potential transmission routes of Listeria ...monocytogenes.
Methods and Results
A total of 36 L. monocytogenes isolates were obtained from animal clinical cases (neurolisteriosis and udder infection) and the farm environment (silage, faeces, water). Isolates were typed using pulsed‐field gel electrophoresis (PFGE) and whole‐genome sequencing (WGS). Their virulence potential was assessed using the gentamicin protection assay and WGS‐based identification of virulence genes. PFGE and WGS revealed a high genetic diversity of L. monocytogenes. An epidemiological link was confirmed for isolates from (i) several subclinical mastitis cases, (ii) silage and subclinical mastitis cases and (iii) different water sources. The neurolisteriosis isolate belonged to clonal complex (CC) 1, but infection source was not identified. A high occurrence (9/47 cows; 19·1%) of subclinical mastitis was observed with isolates belonging to CC2, CC4 and CC11.
Conclusions
The dairy farm environment was contaminated with diverse L. monocytogenes strains, including genotypes associated with human disease. Several isolates harboured genetic determinants associated with increased infectious potential in humans.
Significance and Impact of the Study
Results suggest that subclinical listerial mastitis should not be neglected as a potential source of milk contamination. The presence of hypervirulent CCs in subclinical mastitis cases calls for the implementation of improved mastitis detection.
PDF
