Genetic Carriers and Genomic Distribution of cadA6—A Novel Variant of a Cadmium Resistance Determinant Identified in Listeria spp.

Listeria monocytogenes is a pathogen responsible for severe cases of food poisoning. Listeria spp. strains occurring in soil and water environments may serve as a reservoir of resistance determinants for pathogenic L. monocytogenes strains. A large collection of Listeria spp. strains (155) isolated from natural, agricultural, and urban areas was screened for resistance to heavy metals and metalloids, and the presence of resistance determinants and extrachromosomal replicons. Of the tested strains, 35% were resistant to cadmium and 17% to arsenic. Sequence analysis of resistance plasmids isolated from strains of Listeria seeligeri and Listeria ivanovii, and the chromosome of L. seeligeri strain Sr73, identified a novel variant of the cadAC cadmium resistance efflux system, cadA6, that was functional in L. monocytogenes cells. The cadA6 cassette was detected in four Listeria species, including strains of L. monocytogenes, isolated from various countries and sources—environmental, food-associated, and clinical samples. This resistance cassette is harbored by four novel composite or non-composite transposons, which increases its potential for horizontal transmission. Since some cadAC cassettes may influence virulence and biofilm formation, it is important to monitor their presence in Listeria spp. strains inhabiting different environments.

Comparison of biofilm formation between non-pathogenic Listeria strains under different stress conditions

Micro-organisms can attach to food surfaces and develop biofilms which present a concern in food and environmental safety. The main goal of the current study was to investigate the biofilm formation of six non-pathogenic Listeria strains under different stress conditions using a microplate assay. The effect of the weak biofilm-forming non-pathogenic Listeria strains on the biofilm formation of a strong biofilm-forming pathogenic Listeria strain (Listeria monocytogenes #8) was also examined. Listeria innocua CCM4030, Listeria innocua 2885 and Listeria seeligeri/welshimeri 292 showed the same patterns of biofilm formation with increasing NaCl concentrations from 0.05 to 15%, but all the other strains showed a continuously decreasing trend of OD595 in the same conditions. This study showed that in the case of non-pathogenic Listeria strains, higher concentrations of NaCl do not present a stress condition that enhances biofilm formation. Decrease in pH inhibited biofilm formation for all the non-pathogenic Listeria strains. The weak biofilm forming non-pathogenic Listeria strains (Listeria innocua 2885 and Listeria innocua CCM4030) overgrew the strong biofilm-forming Listeria strain (Listeria monocytogenes #8) during biofilm formation. This phenomenon could be beneficial and potentially be used as a novel control strategy to prevent the colonization of the pathogenic Listeria at food processing facilities such as in meat industry.

A phage-encoded anti-CRISPR enables complete evasion of type VI-A CRISPR-Cas immunity

The CRISPR RNA (crRNA)–guided nuclease Cas13 recognizes complementary viral transcripts to trigger the degradation of both host and viral RNA during the type VI CRISPR-Cas antiviral response. However, how viruses can counteract this immunity is not known. We describe a listeriaphage (ϕLS46) encoding an anti-CRISPR protein (AcrVIA1) that inactivates the type VI-A CRISPR system of Listeria seeligeri. Using genetics, biochemistry, and structural biology, we found that AcrVIA1 interacts with the guide-exposed face of Cas13a, preventing access to the target RNA and the conformational changes required for nuclease activation. Unlike inhibitors of DNA-cleaving Cas nucleases, which cause limited immunosuppression and require multiple infections to bypass CRISPR defenses, a single dose of AcrVIA1 delivered by an individual virion completely dismantles type VI-A CRISPR-mediated immunity.

Surveillance for Contamination of Salad with Listeria Monocytogenes in Some of Baghdad Restaurants

Background: Listeria monocytogenes, a member of the genus Listeria, is widely distributed in agricultural environments, such as soil, manure and water. The genus of Listeria bacteria is about 15-17 species. It is a pathogenic bacterium that can cause a rare but dangerous infection called listeriosis. Objectives: Studying the rate of salads contaminated with Listeria bacteria. and Listeria monocytogenes according to International, Arabic and Iraqi specifications and finding the correlation between commitments of restaurants to standard health conditions with contamination with these bacteria Methods: The study included 152 samples of salads taken from 39 restaurants chosen randomly and of different levels and places in Baghdad from the period between 1/9/2014 to 20/1/2015. The laboratory tests were carried out on samples based on internationally approved methods in addition to methods of the International Standards Organization. Results: The study revealed that 23 samples (15.13%) from the 152 samples taken from the restaurants were contaminated with Listeria species. of these, 3 (2%) were contaminated with Listeria monocytogenes and 20 (13.2%) were contaminated with other types of different and non-pathogenic Listeria as follows; (Listeria welshimeri, Listeria seeligeri, Listeria ivanovii, Listeria grayi, Listeria innocua) with the following prevalence (7(4.6%), 6(3.9%), 3(2%), 3(2%), 1 (0.7%) respectively). Conclusions: Contamination of salads taken from restaurants with Listeria bacteria is not uncommon. This indicates that routine examination is necessary and should be added to the Iraqi standard for salads.

INFLUENCE OF PEPTIDE P34 ON GENE EXPRESSION OF LISTERIA MONOCYTOGENES AND LISTERIA SEELEGERI

<p><strong>Objective: </strong>Investigate the influence of the antimicrobial peptides P34 and nisin on the expression of genes associated with components of the cell surface of <em>Listeria monocytogenes</em> and <em>Listeria seeligeri</em>.</p><p><strong>Methods: </strong>Antimicrobial activity was determined by addition of peptide P34 and nisin (12.5 µg/ml) onto Brain Heart Infusion agar (BHI) plates previously inoculated with indicator strains (<em>L. monocytogenes</em> ATCC 7644 or <em>L. seeligeri </em>AC 82/4) after incubation for 24 h at 37 °C or 240 h at 4 °C. Ribonucleic acid (RNA) was directly extracted from bacterial colonies at the border of the inhibition zones, and the expression levels of genes D-alanine-D-alanyl carrier protein ligase<em> (dltA), </em>putative phospholipid lysinylation<em> </em>(<em>Imo 1695</em>)<em> </em>and EIIAB^Man of mannose-specific PTS<em> </em>(<em>mptA</em>) were determined using real-time PCR.</p><p><strong>Results</strong><strong>: </strong>A non-significant increase in the levels of transcription of genes <em>dltA, Imo1695 </em>and<em> mptA</em> was observed for <em>L. monocytogenes </em>treated with peptide P34 or nisin. Both peptides caused a similar decrease in <em>dltA</em> gene expression in <em>L. seeligeri</em>. The expression of gene <em>Imo1695</em> significantly decreased (about 2000-fold) after treatment with the peptide P34 at 37 °C, while at 4 °C a reduction of 12-fold and 5-fold was detected for P34 and nisin, respectively. A significant decrease in <em>mptA</em> gene expression was observed by exposition to peptide P34 (31.872-fold) and nisin (16.047-fold) for 24 h at 37 °C.</p><p><strong>Conclusion: </strong>The results suggest that both peptide P34 and nisin influence the expression of genes related with the cell-surface/cell-membrane structure of <em>L. seeligeri</em> and in lesser extent <em>L. monocytogenes</em>.</p>

Listeria monocytogenes and Listeria spp. Contamination Patterns in Retail Delicatessen Establishments in Three U.S. States

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 (&lt;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.

Reservoirs of Listeria Species in Three Environmental Ecosystems

ABSTRACTSoil and water are suggested to represent pivotal niches for the transmission ofListeria monocytogenesto plant material, animals, and the food chain. In the present study, 467 soil and 68 water samples were collected in 12 distinct geological and ecological sites in Austria from 2007 to 2009.Listeriawas present in 30% and 26% of the investigated soil and water samples, respectively. Generally, the most dominant species in soil and water samples wereListeria seeligeri,L. innocua, andL. ivanovii. The human- and animal-pathogenicL. monocytogeneswas isolated exclusively from 6% soil samples in regions A (mountainous region) and B (meadow). Distinct ecological preferences were observed forL. seeligeriandL. ivanovii, which were more often isolated from wildlife reserve region C (Lake Neusiedl) and from sites in proximity to wild and domestic ruminants (region A). The higherL. monocytogenesdetection and antibiotic resistance rates in regions A and B could be explained by the proximity to agricultural land and urban environment.L. monocytogenesmultilocus sequence typing corroborated this evidence since sequence type 37 (ST37), ST91, ST101, and ST517 were repeatedly isolated from regions A and B over several months. A higherL. monocytogenesdetection and strain variability was observed during flooding of the river Schwarza (region A) and Danube (region B) in September 2007, indicating dispersion via watercourses.

Prevalence and Antimicrobial Resistance of Listeria Species Isolated from Different Types of Raw Meat in Iran

Listeria and particularly Listeria monocytogenes are important foodborne pathogens that can cause listeriosis and severe complications in immunocompromised individuals, children, pregnant women, and the elderly. The objective of this study was to determine the prevalence of Listeria spp. in raw meat in Iran. From July 2010 to November 2011, a total of 1,107 samples of various raw meats were obtained from randomly selected retail butcher shops. The results of conventional bacteriologic and PCR methods revealed that 141 samples (12.7%) were positive for Listeria spp. The highest prevalence of Listeria was found in raw buffalo meat samples (7 of 24 samples; 29.2%) followed by quail meat (26 of 116 samples; 22.4%), partridge meat (13 of 74 samples; 17.6%), and chicken meat (27 of 160 samples; 16.9%). The most common species recovered was Listeria innocua (98 of 141 strains; 75.9%); the remaining isolates were L. monocytogenes (19.1% of strains), Listeria welshimeri (6.4% of strains), Listeria seeligeri (3.5% of strains), and Listeria grayi (1.4% of strains). Susceptibilities of the 141 strains to 11 antimicrobial drugs were determined using the disk diffusion assay. Overall, 104 (73.8%) of the Listeria isolates were resistant to one or more antimicrobials, and 17.0% of the isolates were resistant to three or more antimicrobials. The present study provides the first baseline data on the prevalence of Listeria in raw meat derived from sheep, goat, buffalo, quail, partridge, chicken, and ostrich in Iran and the susceptibility of these isolates to antimicrobials.