Listeria Seeligeri Research Articles

Crosstalk between three CRISPR-Cas types enables primed type VI-A adaptation in Listeria seeligeri.

CRISPR-Cas systems confer adaptive immunity to their prokaryotic hosts through the process of adaptation, where sequences are captured from foreign nucleic acids and integrated as spacers in the CRISPR array, and thereby enable crRNA-guided interference against new threats. While the Cas1-2 integrase is critical for adaptation, it is absent from many CRISPR-Cas loci, rendering the mechanism of spacer acquisition unclear for these systems. Here we show that the RNA-targeting type VI-A CRISPR system of Listeria seeligeri acquires spacers from DNA substrates through the action of a promiscuous Cas1-2 integrase encoded by a co-occurring type II-C system, in a transcription-independent manner. We further demonstrate that the type II-C integration complex is strongly stimulated by preexisting spacers in a third CRISPR system (type I-B) which imperfectly match phage targets and prime type VI-A adaptation. Altogether, our results reveal an unprecedented degree of communication among CRISPR-Cas loci encoded by a single organism.

Complete genome sequence of Listeria seeligeri strain 43-1 isolated from a Danish forest freshwater swamp.

Here, we report the genome sequence of Listeria seeligeri 43-1 isolated from a Danish freshwater swamp using Oxford Nanopore sequencing. The isolate shared a high genomic similarity to two other L. seeligeri isolates from soil and water.

Aptamer-based magnetic isolation and specific detection system for Listeria monocytogenes from food samples

In this work, an aptamer-based magnetic system was designed for specific and rapid detection of Listeria monocytogenes in food samples. To prepare the selective magnetic system against the target bacterium, firstly, magnetic particles (Fe3O4) were coated with two hydrophilic polymer layers. The specific aptamer immobilized magnetic system efficiently captured L. monocytogenes cells in a competitive response time of approximately 10 min. The magnetic aptamer detection system was very specific to L. monocytogenes and had high selective, up to 97.6 % compared to the Listeria species (Listeria ivanovii, Listeria innocua, and Listeria seeligeri) and other bacteria species Escherichia coli, Staphylococcus aureus, and Basillus subtilus. The isolation and detection of L. monocytogenes from food samples using the presented method are fast and reliable. Moreover, another significant factor to be contemplated is the use of a few chemicals for detection, reducing the cost of analysis, and the results can be obtained within 18 h.

Design of a novel affinity probe using the cell wall-binding domain of a Listeria monocytogenes autolysin for pathogen detection.

Rapid identification of foods and food-processing environments contaminated with Listeria monocytogenes is crucial for controlling human listeriosis, a leading cause of fatality related to foodborne illnesses. The L. monocytogenes autolysin IspC anchors to the bacterial surface non-covalently via its C-terminal cell wall-binding domain (CWBD), which contains conserved Gly-Trp (GW) dipeptides. This study explored the binding property of CWBDIspC to design an affinity probe for detecting L. monocytogenes. Immunogold electron microscopy analysis of a ∆ispC mutant and its wild type (WT) revealed that exogenously added CWBDIspC bound to surface ligands that were evenly distributed and remained mostly unoccupied in the wild type. CWBDIspC detected, via recognizing the cell wall component lipoteichoic acid, L. monocytogenes strains primarily belonging to the serotype 4 group, as well as Listeria innocua, and Listeria welshimeri but did not detect three other Listeria spp. (Listeria seeligeri, Listeria ivanovii, and Listeria grayi) nor any non-Listeria spp. tested. CWBDIspC, when tagged with the enhanced green fluorescent protein, was capable of detecting L. monocytogenes by fluorescence microscopy, a colony lift filter assay, and a microtube binding assay. CWBDIspC, when covalently attached to magnetic beads, showed the ability to separate L. monocytogenes cells with a maximum capture rate of 90 to nearly 100% from 1 × 103 to 1 × 105 target cells. This study demonstrated for the first time that the CWBD derived from a GW surface protein IspC is a novel antibody alternative for the rapid detection and isolation of L. monocytogenes despite binding to two other Listeria species.IMPORTANCEHuman listeriosis is caused by consuming foods contaminated with the bacterial pathogen Listeria monocytogenes, leading to the development of a severe and life-threatening foodborne illness. Detection of L. monocytogenes present in food and food processing environments is crucial for preventing Listeria infection. The L. monocytogenes peptidoglycan hydrolase IspC anchors non-covalently to the bacterial surface through its C-terminal cell wall-binding domain (CWBD), CWBDIspC. This study explored the surface binding property of CWBDIspC to design, construct, characterize, and assess an affinity molecular probe for detecting L. monocytogenes. CWBDIspC recognized a cell wall ligand lipoteichoic acid that remains evenly displayed and mostly unoccupied on the bacterial surface for interaction with the exogenously added CWBDIspC. CWBDIspC, when fused to the enhanced green fluorescent protein reporter or covalently conjugated onto magnetic beads, exhibited the functionality as an antibody alternative for rapid detection and efficient separation of the pathogen.

The Anti-Listeria Activity of Pseudomonas fluorescens Isolated from the Horticultural Environment in New Zealand

Beneficial bacteria with antibacterial properties are attractive alternatives to chemical-based antibacterial or bactericidal agents. Our study sourced such bacteria from horticultural produce and environments to explore the mechanisms of their antimicrobial properties. Five strains of Pseudomonas fluorescens were studied that possessed antibacterial activity against the pathogen Listeria monocytogenes. The vegetative culture of these strains (Pseudomonas fluorescens-PFR46I06, Pseudomonas fluorescens-PFR46H06, Pseudomonas fluorescens-PFR46H07, Pseudomonas fluorescens-PFR46H08 and Pseudomonas fluorescens-PFR46H09) were tested against Listeria monocytogenes (n = 31), Listeria seeligeri (n = 1) and Listeria innocua (n = 1) isolated from seafood and horticultural sources and from clinical cases (n = 2) using solid media coculture and liquid media coculture. All Listeria strains were inhibited by all strains of P. fluorescens; however, P. fluorescens-PFR46H07, P. fluorescens-PFR46H08 and P. fluorescens-PFR46H09 on solid media showed good inhibition, with average zones of inhibition of 14.8 mm, 15.1 mm and 18.2 mm, respectively, and the other two strains and P. fluorescens-PFR46H09 had a significantly greater zone of inhibition than the others (p < 0.05). There was no inhibition observed in liquid media coculture or in P. fluorescens culture supernatants against Listeria spp. by any of the P. fluorescens strains. Therefore, we hypothesized that the structural apparatus that causes cell-to-cell contact may play a role in the ejection of ant-listeria molecules on solid media to inhibit Listeria isolates, and we investigated the structural protein differences using whole-cell lysate proteomics. We paid special attention to the type VI secretion system (TSS-T6SS) for the transfer of effector proteins or bacteriocins. We found significant differences in the peptide profiles and protein summaries between these isolates' lysates, and PFR46H06 and PFR46H07 possessed the fewest secretion system structural proteins (12 and 11, respectively), while PFR46H08 and PFR46H09 had 18 each. P. fluorescens-PFR46H09, which showed the highest antimicrobial effect, had nine tss-T6SS structural proteins compared to only four in the other three strains.

Restriction endonuclease cleavage of phage DNA enables resuscitation from Cas13-induced bacterial dormancy.

Type VI CRISPR systems protect against phage infection using the RNA-guided nuclease Cas13 to recognize viral messenger RNA. Upon target recognition, Cas13 cleaves phage and host transcripts non-specifically, leading to cell dormancy that is incompatible with phage propagation. However, whether and how infected cells recover from dormancy is unclear. Here we show that type VI CRISPR and DNA-cleaving restriction-modification (RM) systems frequently co-occur and synergize to clear phage infections and resuscitate cells. In the natural type VI CRISPR host Listeria seeligeri, we show that RM cleaves the phage genome, thus removing the source of phage transcripts and enabling cells to recover from Cas13-induced cellular dormancy. We find that phage infections are neutralized more effectively when Cas13 and RM systems operate together. Our work reveals that type VI CRISPR immunity is cell-autonomous and non-abortive when paired with RM, and hints at other synergistic roles for the diverse host-directed immune systems in bacteria.

Contrasting Genetic Diversity of Listeria Pathogenicity Islands 3 and 4 Harbored by Nonpathogenic Listeria spp.

Listeria monocytogenes causes the severe foodborne disease listeriosis. Several clonal groups of L. monocytogenes possess the pathogenicity islands Listeria pathogenicity island 3 (LIPI-3) and LIPI-4. Here, we investigated the prevalence and genetic diversity of LIPI-3 and LIPI-4 among 63 strains of seven nonpathogenic Listeria spp. from the natural environment, i.e., wildlife (black bears [Ursus americanus]) and surface water. Analysis of the whole-genome sequence data suggested that both islands were horizontally acquired but differed considerably in their incidence and genetic diversity. LIPI-3 was identified among half of the L. innocua strains in the same genomic location as in L. monocytogenes (guaA hot spot) in a truncated form, with only three strains harboring full-length LIPI-3, and a highly divergent partial LIPI-3 was observed in three Listeria seeligeri strains, outside the guaA hot spot. Premature stop codons (PMSCs) and frameshifts were frequently noted in the LIPI-3 gene encoding listeriolysin S. On the other hand, full-length LIPI-4 without any PMSCs was found in all Listeria innocua strains, in the same genomic location as L. monocytogenes and with ~85% similarity to the L. monocytogenes counterpart. Our study provides intriguing examples of genetic changes that pathogenicity islands may undergo in nonpathogenic bacterial species, potentially in response to environmental pressures that promote either maintenance or degeneration of the islands. Investigations of the roles that LIPI-3 and LIPI-4 play in nonpathogenic Listeria spp. are warranted to further understand the differential evolution of genetic elements in pathogenic versus nonpathogenic hosts of the same genus. IMPORTANCE Listeria monocytogenes is a serious foodborne pathogen that can harbor the pathogenicity islands Listeria pathogenicity island 3 (LIPI-3) and LIPI-4. Intriguingly, these have also been reported in nonpathogenic L. innocua from food and farm environments, though limited information is available for strains from the natural environment. Here, we analyzed whole-genome sequence data of nonpathogenic Listeria spp. from wildlife and surface water to further elucidate the genetic diversity and evolution of LIPI-3 and LIPI-4 in Listeria. While the full-length islands were found only in L. innocua, LIPI-3 was uncommon and exhibited frequent truncation and genetic diversification, while LIPI-4 was remarkable in being ubiquitous, albeit diversified from L. monocytogenes. These contrasting features demonstrate that pathogenicity islands in nonpathogenic hosts can evolve along different trajectories, leading to either degeneration or maintenance, and highlight the need to examine their physiological roles in nonpathogenic hosts.

Influence of the food matrix on dual-species biofilm of Listeria monocytogenes and Pseudomonas fluorescens

In the food industry, the formation of biofilms results in serious microbial recontamination problem. This work aimed to study Listeria sp. obtained from sliced products and food handling surfaces, for the preparation of food of animal origin to be consumed cold. Listeria monocytogenes, Listeria innocua and Listeria seeligeri were detected. In the evaluation of antibiotic susceptibility, the isolates were sensitive to ampicillin and penicillin, which were the main antibiotics used in treatment. The isolates showed the ability to form biofilm in microplate, in stainless steel and polypropylene surfaces, with a variation of sessile cells between 4.29±0.23 and 7.03±0.01 log10 CFU cm-2 in TSBYE. This ability was also observed in food matrix composed of UHT whole milk in mono-species cultivation and in associated cultivation of L. monocytogenes with Pseudomonas fluorescens. The application of sanitizers peracetic acid and sodium hypochlorite revealed efficiency in the eradication of adhered cells and biofilms formed in stainless steel surfaces. Therefore, Listeria sp. showed to be persistent and able to form biofilm in mono-species cultivation or associated with P. fluorescens, under different conditions. Taking these aspects into account, the need for proper hygiene in the food production process is highlighted in order to avoid risks to the consumers health

Diagnostic challenges with accurate identification of Listeria monocytogenes isolates from food and environmental samples in South Africa

BackgroundThe 2017–2018 listeriosis outbreak in South Africa warranted testing for Listeria monocytogenes in food products and processing environments. Diagnostic tests are needed to accurately differentiate L. monocytogenes from other Listeria species.ObjectiveThe study assessed the performance of the commonly used tests in our setting to accurately identify L. monocytogenes.MethodsThe study was conducted in a public health laboratory in South Africa. Cultured isolates from food and environmental samples were tested both prospectively and retrospectively between August 2018 and December 2018. Isolates were phenotypically identified using tests for detecting β-haemolysis, Christie-Atkins-Munch-Peterson, alanine arylamidase (AlaA), mannosidase, and xylose fermentation. Listeria monocytogenes isolates were identified using automated systems, Microscan Walkaway Plus 96, Vitek® MS, Vitek® 2 and Surefast Listeria monocytogenes PLUS PCR. All results were compared to whole-genome sequencing results.Resultsβ-haemolysis and Christie-Atkins-Munch-Peterson tests gave delayed positivity or were negative for L. monocytogenes and falsely positive for one strain of Listeria innocua. The AlaA enzyme and Colorex Listeria agar lacked specificity for L. monocytogenes identification. Based on a few phenotypic test results, an aberrant L. monocytogenes strain and Listeria seeligeri strain were reported. All automated platforms overcalled L. monocytogenes in place of other Listeria species.ConclusionNo test was ideal in differentiating Listeria species. This is an issue in resource-limited settings where these tests are currently used. Newer technologies based on enzyme-linked immunosorbent assay and other molecular techniques specific to L. monocytogenes detection need to be investigated.

Prevalence, quantification and antibiotic resistance of Listeria monocytogenes in poultry preparations

A total of 100 samples of fresh poultry preparations were obtained from 10 retail outlets in North-Western Spain. Listeria spp. were found in 73 samples. Isolates were identified through polymerase chain reaction (PCR) as Listeria monocytogenes (56 samples), Listeria innocua (32), Listeria grayi (3), Listeria seeligeri (1) and Listeria spp. (6). In 24 samples, several different Listeria species were found. The loads of L. monocytogenes detected by quantitative polymerase chain reaction (q-PCR) in the 56 positive samples ranged from <2.15 log units (limit of detection) up to 5.96 log units. Neither the type of sample nor the retail outlet involved had any significant influence ( P > 0.05) on concentrations of L. monocytogenes . A total of 163 L. monocytogenes isolates were tested (disc diffusion) against 15 antimicrobials of clinical significance. The average number of resistances per isolate was 5.83 ± 1.64. All strains showed resistance to multiple antimicrobials (between 4 and 11). In all, 80 isolates (49.1%) showed a multi-drug resistant (MDR) phenotype, and two isolates (1.2%) showed an extensively drugresistant (XDR) phenotype. More than 50.0% of isolates showed resistance or reduced susceptibility to oxacillin, cefoxitin, cefotaxime, cefepime, rifampicin, ciprofloxacin, enrofloxacin or nitrofurantoin. This is a cause for concern because these substances are among the antibiotics used to treat human listeriosis, with rifampicin and fluoroquinolones frequently being used. The results from this research work show that poultry preparations are a potential major source of resistant L. monocytogenes strains, since these are present in some samples at high concentrations. This highlights the pressing need to handle poultry preparations correctly, so as to ensure they are sufficiently cooked and to avoid cross-contamination events. • A hundred poultry preparations from retail outlets in North-West Spain were tested. • Listeria spp. and L. monocytogenes were found in 73 and 56 samples, respectively. • L. monocytogenes loads ranged from <2.15 log units to 5.96 log units. • The 163 L. monocytogenes isolates tested were resistant to five to fifteen antibiotics. • The need to avoid insufficient cooking or cross-contamination was highlighted.

Listeria Species Occurrence and Associated Risk Factors and Antibiogram of Listeria Monocytogenes in Milk and Milk Products in Ambo, Holeta, and Bako Towns, Oromia Regional State, Ethiopia.

A cross-sectional study was conducted to estimate the prevalence and associated risk factors of Listeria species and assess the antibiogram of Listeria monocytogenes (L. monocytogenes) isolated from milk and milk products from Holeta, Ambo, and Bako towns, Ethiopia. A total of 482 samples (384 milk, 35 cottage cheeses, 30 bulk tank milk, and 33 curdle milk) were collected using a systematic random sampling method and isolation and identification of Listeria species were done using standard microbiological techniques. An antimicrobial susceptibility test for L. monocytogenes was performed using the Kirby–Bauer disk diffusion technique. Descriptive statistics were used to summarize the prevalence of Listeria, while the Chi-square test and logistic regression were used to determine the association between the prevalence of Listeria and the risk factors and the magnitude of association, respectively. The overall isolation rate of Listeria species from milk and milk products was 7.67% (37/482; 95% confidence interval (CI): 5.46, 10.42). The highest prevalence of Listeria species (15.15%; 95% CI: 5.11–31.90) was detected in bulk tank milk and the lowest prevalence of Listeria species (6.67%; 95% CI: 0.82–22.07) and L. monocytogenes (0.00; 95% CI: 0.00–1.15) was found in curdled milk. The other species isolated were Listeria welshimeri 0.62% (3/482; 95% CI: 0.13–1.81), Listeria seeligeri 1.04% (5/482; 95% CI: 0.33–2.40), Listeria ivanovi 1.24%, (6/482; 95% CI: 0.45–2.68), and Listeria grayi 2.49% (12/482; 95% CI: 5.46–10.42). Univariable logistic regression showed that study town, herd size, farm size, number of lactating cows, and management system were the factors significantly associated with the isolation of Listeria species at farm level, while the intensive management system was the independent predictor at cow level in the multivariable model (adjusted odds ratio = 3.38, P=0.046). L. monocytogenes isolates showed the highest resistance against oxacillin (100%), amoxicillin (90.91%), and vancomycine (81.82%). L. monocytogenes showed a very high multidrug resistance (MDR) [81.82%]. In conclusion, the current study showed the widespread type of Listeria species MDR L. monocytogenes isolates in cow raw milk and milk products from Ambo, Holeta, and Bako towns, Oromia Regional State, Ethiopia.

Assessment of Reference Method Selective Broth and Plating Media with 19 Listeria Species Highlights the Importance of Including Diverse Species in Listeria Method Evaluations

Reference methods developed for detection of Listeria monocytogenes are commonly used for detection of Listeria at the genus level. Improved method performance data are needed because this genus has expanded from 6 to 26 species and now includes several Listeria sensu lato species, which can have phenotypes distinct from those of Listeria sensu stricto. We evaluated growth of 19 Listeria species, including 12 recently described Listeria sensu lato species, using the media specified by (i) the U.S. Food and Drug Administration (FDA) Bacteriological Analytical Manual, (ii) the U.S. Department of Agriculture (USDA) Microbiology Laboratory Guidebook, and (iii) the International Organization for Standardization (ISO). The FDA broth enrichment procedure allowed all species to grow to detectable levels (≥4 log CFU/mL), yielded the highest mean growth (7.58 log CFU/mL), and was the only procedure with which no Listeria sensu lato species yielded significantly higher growth than did a comparison Listeria sensu stricto species. With the USDA and ISO broth enrichment procedures, several Listeria sensu lato species yielded significantly higher growth than did either Listeria seeligeri or Listeria ivanovii, suggesting that these two Listeria sensu stricto species could be outgrown by Listeria sensu lato species. On selective and differential agar media, L. seeligeri, L. ivanovii, and Listeria grayi produced colonies with atypical morphology and/or growth of these species was inhibited (which may lead to incorrect classification of a sample as negative), whereas several newly described Listeria sensu lato species grew to high levels and produced colonies with typical morphology. Overall, our study results indicate that the ability to detect various Listeria species can be impacted by the specific broth and selective and differential agar used. Our data can help guide selection of appropriate media and detection methods for environmental Listeria monitoring programs and methods that are most likely to detect the targeted Listeria groups (e.g., Listeria sensu stricto, which appear to be the most appropriate index organisms for the pathogen L. monocytogenes).

Listeria Species Occurrence and Associated Factors and Antibiogram of Listeria monocytogenes in Beef at Abattoirs, Butchers, and Restaurants in Ambo and Holeta in Ethiopia.

PurposeListeriosis is one of the globally distributed foodborne diseases with the highest fatality rate. The objectives of this study were to isolate and identify Listeria species, assess factors for contamination of beef, and antibiogram of Listeria monocytogenes in Ambo and Holeta towns, Central Ethiopia.Materials and MethodsA total of 450 meat samples were collected from abattoirs (n=150), butchers (n=150), and restaurants (n=150) for isolation and identification of Listeria species. Logistic regression analysis was used to assess the association between the occurrence of Listeria species in meat and potential risk factors. The antimicrobial susceptibility test was done using the Kirby Bauer test.ResultsThe overall occurrence of Listeria species in Ambo and Holeta towns was 28.4% (128/450; 95% confidence interval [CI]: 24.3–32.9%). The isolation rate of Listeria monocytogenes was 4.4%, Listeria ivanovii 2.2%, Listeria seeligeri 1.8%, Listeria welshimeri 3.8%, Listeria innocua 6.2%, and Listeria grayi 10.2%. The probability of contamination of meat in butchers and restaurants was higher in Holeta than Ambo [OR=3.4; 95%; p=0.001], in dry than wet season [OR=5.2; p=0.009], and where the hygiene of cutting boards was poor (OR=7.7; p=0.008). Of the 20 Listeria monocytogenes isolates, 80%, 70%, 60%, and 55% were resistant to oxacillin, amikacin, and nalidixic acid, chloramphenicol, and tetracycline, respectively. The Listeria monocytogenes isolates were 95%, 90%, and 85% susceptible to amoxicillin, vancomycin, and clindamycin, respectively. About 95% of Listeria monocytogenes isolates were multidrug-resistant. One isolate (5%) had developed resistance to 10 classes of antimicrobial drugs.ConclusionListeria species are widespread and study towns, season, and hygiene of cutting boards are independent predictors of isolation of Listeria species. Multidrug resistance among Listeria monocytogenes was very high. Therefore, adequate cooking of meat, regular training of beef handlers, prudent use of drugs, and further molecular studies on Listeria species are important.

Specific detection of the most prevalent five Listeria strains and unspecific detection of 15 Listeria using multiplex real-time PCR

Listeria in food, are a serious risk to consumer’s health that may even have a fatal outcome. To analyze Listeria in food, the methods used must provide reliable results and detect all strains of Listeria. Several qPCR systems have been published for the identification of Listeria monocytogenes, innocua, ivanovii, welshimeri and seeligeri. PCR systems for Listeria spp. have also been published. However, they do not detect all known Listeria. To achieve this, we have developed a novel multiplex real-time PCR method. This multiplex qPCR system was able to determine DNA specifically from the five most common Listeria as well as 15 other known Listeria strains simultaneously after cultivation on selective plates.

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.

Bacteriocin-like inhibitory substance of Pediococcus pentosaceus as a biopreservative for Listeria sp. control in ready-to-eat pork ham.

The growing demand of consumers for synthetic chemical-free foods has increased the search for natural preservatives such as bacteriocins and bacteriocin-like inhibitory substances (BLIS) to give them adequate microbiological safety, sensory characteristics, and shelf life. In this study, the antimicrobial activity of BLIS produced by Pediococcus pentosaceus ATCC 43200 was compared with that of nisin. Lactobacillus sakei ATCC 15521, Listeria seeligeri NCTC 11289, Enterococcus En2052 and En2865, and Listeria monocytogenes CECT 934 and NADC 2045 exhibited larger inhibition halos in BLIS-treated than in Nisaplin-treated samples, unlike Listeria innocua NCTC 11288. In artificially contaminated ready-to-eat pork ham, BLIS was effective in inhibiting the growth of L. seeligeri NCTC 11289 for 6days (counts from 1.74 to 0.00 log CFU/g) and ensured lower weight loss (2.7%) and lipid peroxidation (0.63mg MDA/kg) of samples compared with the control (3.0%; 1.25mg MDA/kg). At the same time, coloration of ham samples in terms of luminosity, redness, and yellowness as well as discoloration throughout cold storage was not influenced by BLIS or Nisaplin taken as a control. These results suggest the potential use of P. pentosaceus BLIS as a biopreservative in meat and other food processing industries.

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.&#x0D; 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&#x0D; 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.&#x0D; 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).&#x0D; 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.&#x0D;

Antimicrobial activity of bacteriocin-like inhibitory substance produced by Pediococcus pentosaceus: from shake flasks to bioreactor

Bacteriocins are peptides produced by various species of bacteria, especially lactic acid bacteria (LAB), which have a large spectrum of action against spoilage bacteria and foodborne pathogens. However, when not entirely characterized, they are alternatively called bacteriocin-like inhibitory substances (BLIS). Pediococcus pentosaceus ATCC 43200 grew and produced BLIS optimally when cultivated anaerobically in bioreactor for 24h at 30°C and 200rpm in De Man, Rogosa and Sharp (MRS) medium supplemented with 1.5% peptone. Under such optimal conditions, the cell mass concentration (3.41g/L) was 66% higher, the generation time (1.28h) 38% shorter and the BLIS activity against different indicator strains significantly higher than in MRS medium without any supplement taken as a control, and the exponential phase started 4h before. The agar diffusion method showed BLIS inhibition halos against LAB strains with diameter in the range 11.0-19.5mm and specific areas between 377.1 and 2654.6mm2/mL, while BLIS activity against Listeria strains was better quantified by the liquid medium assay that showed, for the fermented broth without any dilution, 100 and 50% inhibition of Listeria innocua and Listeria seeligeri growth, respectively. These results highlight the potential of P. pentosaceus BLIS as a natural antimicrobial for application in the food industry.

RNA Guide Complementarity Prevents Self-Targeting in Type VI CRISPR Systems

All immune systems use precise target recognition to interrogate foreign invaders. During CRISPR-Cas immunity, prokaryotes capture short spacer sequences from infecting viruses and insert them into the CRISPR array. Transcription and processing ofthe CRISPR locus generate small RNAs containing the spacer and repeat sequences that guide Cas nucleases to cleave a complementary protospacer in the invading nucleic acids. In most CRISPR systems, sequences flanking the protospacer drastically affect cleavage. Here, we investigated the target requirements of the recently discovered RNA-targeting type VI-A CRISPR-Cas system in its natural host, Listeria seeligeri. We discovered that target RNAs with extended complementarity between the protospacer flanking sequence and the repeat sequence of the guide RNA are not cleaved by the type VI-A nuclease Cas13, neither invivo nor invitro. These findings establish fundamental rules for the design of Cas13-based technologies and provide a mechanism for preventing self-targeting in type VI-A systems.

Determinación del perfil de susceptibilidad a antibióticos de Listeria sp. aisladas de leche cruda de vaca en Tunja

Introducción: La presencia de especies de Listeria sp en alimentos, se ha convertido en un problema de salud pública, considerando su patogenicidad, especialmente por L. monocytogenes. &#x0D; Objetivo: Determinar el perfil de susceptibilidad de cepas de Listeria sp. aisladas a partir de muestras de leche cruda de vaca en fincas del municipio de Tunja-Boyacá-Colombia. &#x0D; Metodología: Se analizaron 293 muestras de leche cruda de vaca obtenidas de las cantinas de almacenamiento; para el aislamiento e identificación bioquímica de Listeria sp, se realizó un pre-enriquecimiento en caldo Fraser (Oxoid), incubación a 4°C, aislamiento en medio Palcam (Oxoid) e identificación utilizando Microbact Listeria L-12 (Oxoid). El perfil de susceptibilidad a antibióticos fue determinado por el método de difusión de disco. &#x0D; Resultados: la prevalencia total de Listeria sp. fue de 9.89 % (n= 29). La especie más prevalente fue L. seeligeri (7.17%) y la menos L. grayi (0.34%). L. monocytogenes presentó una prevalencia de 2.7%. Se determinó que todos los aislamientos de Listeria sp fueron susceptibles a la penicilina y la ampicilina. Un aislamiento de L. monocytogenes fue resistente a ciprofloxacina, gentamicina, trimetoprim-sulfametoxazol y tetraciclina, mientras que las demás fueron sensibles a los antibióticos evaluados. &#x0D; Conclusiones: Se determinó la presencia de varias especies de Listeria sp, incluyendo L. monocytogenes la cual es considerada de importancia en salud pública. Se presentó susceptibilidad a la mayoría de los antibióticos analizados excepto a clindamicina, además se reporta un caso aislado de resistencia a tetraciclina en una cepa de L. monocytogenes y se determinó la resistencia a trimetoprim-sulfametoxazole. &#x0D; PALABRAS CLAVE: &#x0D; Inocuidad de los Alimentos, Productos Lácteos, Inspección de Alimentos, Bacterias Grampositivas. &#x0D; SUMMARY