PALCAM Agar Research Articles

Prevalence, molecular detection and antimicrobial susceptibility of Listeria monocytogenes isolated from milk, poultry meat and meat products

Listeria monocytogenes is a food borne zoonotic pathogen that causes listeriosis in people and animals. It has a low incidence but a high case fatality rate. The goal of this study was to assess the prevalence of L. monocytogenes in raw and frozen milk, raw and frozen poultry meat and meat products as well as their molecular identification and antimicrobial susceptibility. A total of 100 samples were collected from four different locations in Mymensingh town, including raw milk (n = 20), frozen milk (n = 20), raw poultry meat (n = 20), frozen poultry meat (n = 20), frozen chicken meat ball (n = 10), and chicken burger (n = 10). Listeria selective PALCAM agar was used to isolate L. monocytogenes from the samples. Listeria spp. created a black zone around the colonies on this agar. Gram staining, motility testing, Christie, Atkins, Munch-Petersen (CAMP) testing, haemolysis testing, sugar fermentation testing and other biochemical assays were used to confirm the presence of L. monocytogenes. The disc diffusion method was used to test antibiotic sensitivity against ten antibiotics: ampicillin, vancomycin, gentamycin, streptomycin, cefixime, cefalexin, norfloxacin, colistin, erythromycin, and amikacin. The prevalence of L. monocytogenes in various samples was found to be 30% in raw milk, 0% in frozen milk, 40% in raw poultry meat, 10% in frozen poultry meat and not found in meat products. Market 1 had a prevalence of 13.33%, market 2 had a prevalence of 15%, market 3 had a prevalence of 0%, and market 4 had a prevalence of 0%. The isolates of L. monocytogenes were shown to be susceptible to amikacin, gentamycin, vancomycin, streptomycin and norfloxacin but resistant to ampicillin, cefixime, cefalexin, colistin and erythromycin. According to the findings of this study, multidrug-resistant L. monocytogenes can be found in milk, poultry meat, and meat products, posing a public health risk.

Molecular characterization and hematological analysis of Listeria monocytogenes infection in dairy cows in Punjab (Pakistan)

Listeriosis is an emerging bacterial disease of animals and humans worldwide, caused by Listeria monocytogenes. The infected dairy cows continuously shed the microbes in their milk, a human being's concern. This study was designed to molecular characterize the Listeria monocytogenes isolated from symptomatic cow's milk of tehsils Samundri, Gujar khan, and Alipur of Punjab. A total of 175 milk samples were collected, pre-enriched and cultured on PALCAM agar. The affirmation of the hlyA gene of Listeria monocytogenes was performed by polymerase chain reaction (PCR) and 3.43% of isolates were found positive. The phylogenetic analysis showed a resemblance of our isolates of Listeria monocytogenes with India (KP965733), the USA (DQ812484), and 3 of our isolates made a clade. The leucocytes and neutrophils count were found significantly increased in listeriosis affected cows. The Chi-square test showed a significant association between poor quality silage feeding and listeriosis. The presence of L.monocytogenes in cow's milk indicates a potential threat to humans. It is further recommended that it should be consistently monitored to ensure food safety.

Developing an affordable hyperspectral imaging system for rapid identification of Escherichia coli O157:H7 and Listeria monocytogenes in dairy products

The objective of this foundational study was to develop and evaluate the efficacy of an affordable hyperspectral imaging (HSI) system to identify single and mixed strains of foodborne pathogens in dairy products. This study was designed as a completely randomized design with three replications. Three strains each of Escherichia coli O157:H7 and Listeria monocytogenes were evaluated either as single or mixed strains with the HSI system in growth media and selected dairy products (whole milk, and cottage and cheddar cheeses). Test samples from freshly prepared single or mixed strains of pathogens in growth media or inoculated dairy products were streaked onto selective media (PALCAM and/or Sorbitol MacConkey agar) for isolation. An isolated colony was selected and mixed with 1 ml of HPLC grade water, vortexed for 1 min, and spread over a microscope slide. Images were captured at 2000× magnification on the built HSI system at wavelengths ranging from 400 nm to 1100 nm with 5‐nm band intervals. For each image, three cells were selected as regions of interest (ROIs) to obtain hyperspectral signatures of respective bacteria. Reference pathogen libraries were created using growth media, and then test pathogenic cells were classified by their hyperspectral signatures as either L. monocytogenes or E. coli O157:H7 using k‐nearest neighbor (kNN) and cross‐validation technique in R‐software. With the implementation of kNN (k = 3), overall classification accuracies of 58.97% and 61.53% were obtained for E. coli O157:H7 and L. monocytogenes, respectively.

Growth and No-Growth boundary of Listeria monocytogenes in beef – A logistic modeling

Listeria monocytogenes is a potentially fatal foodborne pathogen. Its growth in ready-to-eat (RTE) foods must be strictly controlled to protect public food safety. This study was conducted to define the growth and no-growth boundary of L. monocytogenes with sodium tripolyphosphate (STPP), sodium lactate (NaL), sodium diacetate (NaDiAc), sodium chloride (NaCl), sodium nitrite (NaNO2), and pH as control factors.The growth of L. monocytogenes was first examined using a solid medium incubated under 37 °C for 48 h in 96-well microtiter plates. NaNO2 (1,800 ppm) and NaDiAc (2,500 ppm) were found not effective in preventing the growth when applied alone. STPP was shown highly effective in preventing the growth of L. monocytogenes. Its growth was unhindered at pH 6–7 but was increasingly inhibited beyond the neutral range. High concentrations of NaL and NaCl were needed to inhibit the growth of L. monocytogenes. A multifactor logistic regression model (LRM) was developed to calculate the growth probability (p) and then define the growth boundary using 2 thresholds.With Threshold 1 (p = 0.0104), the Accuracy of classification for growth events is 0.686, with a True positive rate (TPR) of 0.776 (or False negative rate (FNR) of 0.234), True negative rate (TNR) of 0.455 (or False positive rate (FPR) of 0.545), and Precision of 0.803, in PALCAM agar. However, with Threshold 2 (p = 0.04), the Accuracy becomes 0.826, with a TPR of 0.955 (or FNR of 0.045), a TNR of 0.690 (or FPR of 0.310), and Precision of 0.764. For validation in ground beef, the Accuracy of prediction of growth was 0.85, with a TPR of 0.9, TNR of 0.8, and Precision of 0.818 for Threshold 1. With Threshold 2, the Accuracy, TPR, TNR, and Precision are all 0.8, with both FNR and FPR of 0.2. Both thresholds and LRM may be used to formulate RTE products that may prevent the growth of L. monocytogenes even stored under the optimum temperature.

Immunotherapeutic effect of chitosan and listeriolysin O on Listeria monocytogenes infection in mice

This study aimed to evaluate the effect of dietary chitosan and listeriolysin O (LLO) on the immune response against Listeria monocytogenes infection in mice. L. monocytogenes isolate was obtained from the unit of Zoonotic Disease, College of Veterinary Medicine, University of Baghdad. It was reactivated and cultured on PALCAM agar and exposed to a confirmatory diagnostic test. listeriolysin O (LLO) was extracted and purified. Sixty mice were used and divided into four groups each one involving 15 mice; the first group was fed on diet supplemented with a chitosan for 4 weeks. At the end of the 2nd week, normal saline was injected S/C; the second group was fed on a normal diet without any addition. At the end of 2nd week, 0.3 ml of LLO was injected S/C, then the booster dose of LLO was given after 14 days of 1st injection; the third group was fed on a diet supplemented with chitosan as in G1, and treated as in G2 and the fourth group fed on a normal diet without any addition and treated as in G1. A skin test was performed on 5 mice of each group while a Challenge test by injection of 0.2ml of 1x109 CFU/ml of viable L. monocytogenes intraperitoneally was performed on other mice. The concentration of IgG titer and IL6 were measured. The results revealed that the third group recorded significantly higher values in the skin thickness, IgG, and IL6 concentrations when compared with other groups at different times which indicate that LLO and chitosan may support each other to provide the most beneficial effect by eliciting of good cellular and humeral immunity against listeriosis.

Dynamic model to describe kinetic behavior of Listeria monocytogenes in smoked salmon

AbstractIn this study, the dynamic model was developed to describe cell counts of Listeria monocytogenes in smoked salmon under distribution conditions. A 9‐strain mixture of L. monocytogenes was inoculated in smoked salmon at 3–4 Log CFU/g. The inoculated samples were stored at 4°C, 10°C, and 20°C for up to 16 days, and the bacterial cell counts were enumerated on PALCAM agar. The Baranyi model was fitted to the L. monocytogenes cell counts to calculate the lag phase duration (LPD; hr) and maximum growth rate (μmax; Log CFU/g/hr). LPD was 74.22 hr at 4°C, and the value was rapidly decreased to 4.84 hr at 20°C as temperature increased. μmax ranged from 0.01 to 0.13 Log CFU/g/hr, depending on the storage temperature. The kinetic parameters were fitted with secondary models as a function of temperature. Cell counts predicted by the developed model were compared with the predicted cell counts obtained at 8°C and 15°C, and the differences between predicted and observed cell counts were indicated by root mean square error (RMSE). The dynamic model was then developed with the kinetic parameters derived from the secondary model and simulated the L. monocytogenes growth. RMSE (0.368) indicates that the model performance was appropriate. These results suggest that the developed kinetic models can be useful in predicting the fates of L. monocytogenes in smoked salmon under the dynamic conditions of storage temperature and time.

LISTERIA MONOCYTOGENES IN COW’S MILK PRODUCED BY FAMILY-OWNED DAIRY FARMS

Refrigeration is an important milk preservation method. However, milk quality may deteriorate if the product is refrigerated for long periods, mainly due to the growth of psychrotrophic bacteria. This group of microorganisms includes pathogenic genera, most notably Listeria monocytogenes. The detection of this bacterium in food is important, given its pathogenic effects on human and animal health and also its economic relevance. This study focused on detecting the presence of L. monocytogenes in milk samples collected at small family-owned dairy farms. Samples were cultivated on PALCAM and ALOA agars for microbiological analysis and a molecular analysis by polymerase chain reaction was performed for the detection of L. monocytogenes. Despite the negative results obtained in both these analyses, further studies are recommended to confirm or refute the negligible effect of L. monocytogenes on small dairy farms.

LISTERIA MONOCYTOGENES IN COW’S MILK PRODUCED BY FAMILY-OWNED DAIRY FARMS

Refrigeration is an important milk preservation method. However, milk quality may deteriorate if the product is refrigerated for long periods, mainly due to the growth of psychrotrophic bacteria. This group of microorganisms includes pathogenic genera, most notably Listeria monocytogenes. The detection of this bacterium in food is important, given its pathogenic effects on human and animal health and also its economic relevance. This study focused on detecting the presence of L. monocytogenes in milk samples collected at small family-owned dairy farms. Samples were cultivated on PALCAM and ALOA agars for microbiological analysis and a molecular analysis by polymerase chain reaction was performed for the detection of L. monocytogenes. Despite the negative results obtained in both these analyses, further studies are recommended to confirm or refute the negligible effect of L. monocytogenes on small dairy farms.

Development of Hydrogels to Improve the Safety of Yukhoe (Korean Beef Tartare) by Reducing Psychrotrophic Listeria monocytogenes Cell Counts on Raw Beef Surface.

This study developed an antimicrobial hydrogel to control Listeria monocytogenes in Yukhoe (Korean beef tartare). Four hydrogels (hydrogel 1: 5% alginate+1% chitosan+0.2% CaCl2, hydrogel 2: 1% κ-carrageenan+1% chitosan, hydrogel 3: 2% κ-carrageenan+1% CaCl2, and hydrogel 4: 2% κ-carrageenan+3% CaCl2) were prepared. The hydrogels then absorbed 0.1% grapefruit seed extract (GSE) and 0.1% citrus extract (CE) for 30, 60, 120, and 240 min to be antimicrobial hydrogels. To select the most effective antimicrobial hydrogel, their swelling ratio (SR) and antilisterial activities were determined. The selected hydrogel (2×2 cm) was then placed on surface of beef (round; 3×3 cm), where L. monocytogenes (ca. 106 CFU/g) were inoculated, and the cell counts were enumerated on PALCAM agar. Among the hydrogels, the SR of hydrogel 1 increased with absorbing time, but other hydrogels showed no significant changes. Antimicrobial hydrogel 1 showed higher (p<0.05) antilisterial activity than other antimicrobial hydrogels, especially for the one absorbed the antimicrobial for 120 min. Thus, the antimicrobial hydrogel 1 absorbed antimicrobials for 120 min was applied on raw beef at 4℃, and reduced (p<0.05) more than 90% of L. monocytogenes on raw beef. These results indicate that antimicrobial hydrogel 1 formulated with 0.1% GSE or 0.1% CE is appropriate to improve the safety of Yukhoe by reducing psychrotrophic L. monocytogenes cell counts on raw beef.

Phenotypic and genotypic characterization of listeria species isolated from poultry and milk products

Listeria monocytogenes has become increasingly important as a food-associated pathogen. It cancause a rare but serious disease called listeriosis with high fatality rates (20–30%) compared withother foodborne microbial pathogens. To estimate the incidence and levels of Listeria spp. indifferent food sources, A total of 200 random samples which collected from different sources 65samples isolated from poultry , 45 from poultry byproducts (Frozen chicken meat balls (kofta),Frozen chicken burger and frozen chicken sausages), 20 from pasteurized milk ,30 from milkproducts (Feta cheese ,cream cheese )and 40 from poultry eggs .Only 7 of total 200 samples (14%)that collected from suspected isolates and detected on Oxford agar, PALCAM agar and ALOA agarwere suspected to be Listeria spp. In poultry, poultry byproducts, pasteurized milk, milk byproductsand poultry eggs, listeria percentage were 0/65(0%), 4/45(1.8), 0/20(0%), 0/30(0%), 3/40(1.2%)isolates, respectively. The in-vitro antimicrobial sensitivity test showed that the isolated L.monocytogenes were sensitive to Sulphamethoxazole /trimethoprim, Gentamycin, Ceftazidime andCephazoline followed by Sulphamethoxazole, ceftriaxone , weak sensitivity to Penicillin . Whilethey were resistant to Erythromycin, Clindamycin, Ampicillin. The results of virulence tests forisolated listeria strains appeared that all of L .monocytogenes were virulent strains as all of themwere positive to CAMP test; showed narrow zone of β–hemolysis on sheep blood agar .The PCRresults for Listeria isolates showed that all strains are L. monoctogenes and have Inl A and hly Agenes positive as virulence genes while negative Inl B, iap and prf A genes.

Native bacterial communities and Listeria monocytogenes survival in soils collected from the Lower Mainland of British Columbia, Canada.

Soil is an important reservoir for Listeria monocytogenes, a foodborne pathogen implicated in numerous produce-related outbreaks. Our objectives were to (i) compare the survival of L. monocytogenes among three soils, (ii) compare the native bacterial communities across these soils, and (iii) investigate relationships between L. monocytogenes survival, native bacterial communities, and soil properties. Listeria spp. populations were monitored on PALCAM agar in three soils inoculated with L. monocytogenes (∼5 × 106 CFU/g): conventionally farmed (CS), grassland transitioning to conventionally farmed (TS), and uncultivated grassland (GS). Bacterial diversity of the soils was analyzed using 16S rRNA targeted amplicon sequencing. A 2 log reduction of Listeria spp. was observed in all soils within 10 days, but at a significantly lower rate in GS (Fisher's least significant difference test; p < 0.05). Survival correlated with increased moisture and a neutral pH. GS showed the highest microbial diversity. Acidobacteria was the dominant phylum differentiating CS and TS from GS, and was negatively correlated with pH, carbon, nitrogen, and moisture. High moisture content and neutral pH are likely to increase the ability of L. monocytogenes to persist in soil. This study confirmed that native bacterial communities and short-term survival of L. monocytogenes varies across soils.

Effect of High Pressure Processing and Water Activity on the Survival of Listeria Monocytogenes on Ready-to-Eat Shelf-Stable Turkey-Based Meat Bars

ObjectivesA study was conducted to evaluate the effects of product water activity (aw) and a post-processing HPP (high pressure processing) treatment on the survival of inoculated Listeria monocytogenes populations on shelf-stable vacuum-packaged meat bars stored at 25°C.Materials and MethodsThe study was repeated on separate start days and cooked batches (2 aw levels: ≤ 0.91, ≤ 0.85) of turkey-based bars for each trial. Ingredients included turkey, fruit, vegetables, seeds, nuts, rice and spices. Following processing, bars of both aw were surface-inoculated with a mixture of L. monocytogenes (LM101, LM108, LM310, V7, Scott A) to a target level of approximately 3 or 6 log CFU/g. Inoculated bars were individually vacuum packaged. Approximately 18 to 20 h post-inoculation, half the bars from each aw and inoculation level received HPP treatment (586 MPa, 180 s, 5°C) while the remaining half were not HPP treated (control). HPP-treated and control vacuum-packaged bars were stored at 25°C for up to 50 d and analyzed for pathogen counts (PALCAM agar). The study was designed as a 2 × 2 factorial, with factors of aw (≤ 0.91, ≤ 0.85) and post-processing treatment (control, HPP) for 2 pathogen inoculation levels (3 and 6 log CFU/g). The Mixed Procedures of SAS version 9.4 was used to assess differences between treatments (a = 0.05). Surviving pathogen counts were fitted with the Baranyi and Roberts mathematical model (DMFit version 3.5, ComBase) to assess shoulder periods (the time in days where the levels of the pathogen remain at the level of inoculation) and inactivation rates (log CFU/g/d).ResultsStorage day affected (P < 0.05) the L. monocytogenes populations recovered from bars inoculated at both levels; populations tended to decrease over time. Additionally, irrespective of inoculation level, aw (≤ 0.91, ≤ 0.85) and post-processing treatment (control, HPP) significantly affected L. monocytogenes populations during storage. For the 6 log CFU/g inoculation level, aw was a significant effect for shoulder period and inactivation rate of the pathogen in each of the treatment combinations during storage; there were no significant effects observed for bars inoculated at 3 log CFU/g. The HPP treatment didn’t affect the survival of L. monocytogenes; it only reduced (P < 0.05) the initial and/or end of storage counts. Initial pathogen reductions obtained with HPP ranged from 0.2–0.6 log CFU/g (6 log CFU/g inoculation) and 0.5–1.0 log CFU/g (3 log CFU/g inoculation). When inoculated to 6 log CFU/g, bars with aw ≤ 0.91 had longer (P < 0.05) shoulder periods (6.5 and 8.8 d) compared to bars dried to aw ≤ 0.85 (1.9, 1.8 d). Likewise, bars dried to aw ≤ 0.91 had slower (P < 0.05) pathogen inactivation rates (–0.06, –0.08 log CFU/g/d) compared to bars dried to aw ≤ 0.85 (–0.12, –0.10 log CFU/g/d). Regardless of treatment, L. monocytogenes populations were still recovered from all bars following 40 or 50 d of storage at 25°C.ConclusionHigh pressure processing of bars with aw ≤ 0.85 showed the greatest potential for increased control of L. monocytogenes presence starting with 3 log CFU/g of post-processing contamination. The aw impacted pathogen inactivation and surviving counts on shelf-stable meat bars. Parameters of HPP should be further investigated to better understand the most effective time and temperature to increase inactivation of L. monocytogenes on meat bars.

Molecular Characterization of Listeria monocytogenes in white meat samples from Punjab, India

A study was undertaken to assess the prevalence of Listeria monocytogenes in white meats in the Punjab, India. A total of 335 samples including 115 samples of chicken, 75 samples of pork and 145 samples of fish were collected from retail outlets. Isolation of the pathogen was done by selective enrichment in University of Vermont Medium I and II and plating onto PALCAM agar. The recovered Listeria isolates were subjected to in-vitro pathogenicity assays and multiplex PCR targeting virulence-associated genes (prfA, plcA, actA, hlyA and iap) of L. monocytogenes. A total of thirty one (31) L. monocytogenes strains were isolated from meat samples with the prevalence of L. monocytogenes as 9.2%. Maximum prevalence was seen in fish (19.3%) followed by chicken (1.7%) and pork (1.3%). All isolates recovered from the study exhibited pathogenicity in in-vitro pathogenicity assays as well as possessed all the virulence related genes. Thus, the presence of pathogenic strains of L. monocytogenes in white meats with a prevalence of 9.2% appeared to be a cause for concern with profound public health implications.

Thermal inactivation of Listeria monocytogenes and Salmonella spp. in sous-vide processed marinated chicken breast

The heat resistance of a cocktail of five Salmonella strains and five L. monocytogenes strains was determined in teriyaki-marinated chicken breasts. Inoculated meat, packaged in bags, were completely immersed in a circulating water bath and cooked to a final temperature of 55, 57.5 or 60°C in 1h, and then held for predetermined times. The surviving Salmonella and L. monocytogenes cells were enumerated by surface plating on XLD agar and Palcam agar, respectively. D-values, determined by linear regression, of Salmonella in chicken breast ranged from 47.65min at 55°C to 7.48min at 60°C; the values for L. monocytogenes ranged from 54.81min at 55°C to 10.39min at 60°C. Marination rendered the pathogen more sensitive to the lethal effect of heat. The results of this study will assist the food industry in ensuring microbiological safety of sous-vide processed marinated chicken breasts.

Detection of Listeria monocytogenes in Fried Fish, Processing Slab and Tools

This study investigated the prevalence of Listeria monocytogenes in fried fish, processing slab and tool in Kwara state, Nigeria. A total of 2400 fish samples, 800 slabs and 800 tool samples were collected aseptically using stratified sampling methods for L. monocytogenes analysis. The samples were cultured for L. monocytogenes using PALCAM and fraser selective agar and supplements. The isolates were characterized using both biochemical and molecular methods. The data obtained were subjected to descriptive statistics and chi-square test, P=0.05. The results have showed that 528 (22%), 313 (39.13%) and 195 (24.38%) of the fried fish, slab and tool samples are positive for L. monocytogenes respectively. Molecular characterization using PCR has shown that 25.87% of biochemically characterized isolates are identified as L. monocytogenes. Listeria monocyogenes was identified in fried fish (12.88%), slab (36.41%) and tool (26.41%) samples. There was a significant difference between the occurrence of L. monocytogenes in fish, slab and tools. Fried fish, processing slab and tools were heavily contaminated with L. monocytogenes. Processing slab and tools were identified to be predisposing factors, and therefore calls for attentions.

Isolation and Molecular Detection of Listeria monocytogenes in Minced Meat, Frozen Chicken and Cheese in Duhok Province, Kurdistan Region of Iraq

Aims: Listeria monocytogenes (L. monocytogenes) is the food-borne pathogen responsible for listeriosis. It is considered a serious public health risk, and is spread through the consumption of food products. The disease can be fatal to humans and animals. The objective of the present study was to isolate and identify L. monocytogenes from frozen chicken, minced meat, and cheese in Duhok province, Iraq. Methodology and Results: Between March and October 2015, equal numbers (n=50) of samples of minced meat, frozen chicken, and cheese were collected (total n=150). Biochemical and microbiological tests, including real-time PCR, were performed to determine the prevalence of L. monocytogenes in the samples. Out of 150 samples, 20 displayed greyish/black colonies with black halos on Oxford and Palcam agar. of these putative Listeria, 12 were subsequently identified as L. monocytogenes by PCR. L. monocytogenes was detected in 1 (2%), 7 (14%), and 4 (8%) of isolates from cheese, minced meat, and frozen chicken, respectively. Conclusion: Significance and Impact of study: Detection of pathogenic bacteria in foods, such as those analysed in this study, is crucial for safeguarding public health. The qPCR technique offers a rapid and reliable method for isolation of many foodborne pathogens in different kinds of foods.

Prevalence and Genetic Characteristics of Meatborne Listeria monocytogenes Isolates from Livestock Farms in Korea

This study aimed to evaluate the prevalence of Listeria monocytogenes on livestock farms in Korea and determine their serotypes and genetic correlations. Twenty-five livestock farms in Korea (central: 15, south west: 7, south east: 3) were visited 2-3 times, and 2,018 samples (feces: 677, soil: 680, silage: 647, sludge: 14) were collected. Samples were enriched in LEB (Listeria enrichment broth) and Fraser broth media, and then plated on Palcam agar. The isolates were identified by PCR and 16S rRNA gene sequencing. Then, the serotypes, presence of virulence genes (actA, inlA, inlB, plcB, and hlyA), and antibiotic resistance were determined. Genetic correlations among the isolates were evaluated by analyzing the restriction digest pattern with AscI. Of the 2,018 samples, only 3 (0.15%) soil samples (FI-1-FI-3) from 1 farm in the south east region were positive for L. monocytogenes. Based on biochemical tests and multiplex PCR, the serotype of the isolates were 4ab (FI-1 and FI-3) and 3a (FI-2), which are not common in foodborne L. monocytogenes. The 3a serotype isolate was positive for all tested virulence genes, whereas the 4ab serotype isolates were only positive for hlyA, actA, and inlA. The isolates were resistant to all 12 tested antibiotics, especially FI-3. The genetic correlations among the isolates were 100% for those of the same serotype and 26.3% for those of different serotypes. These results indicate that the prevalence of L. monocytogenes on livestock farms in Korea is low; however, the isolates are pathogenic and antibiotic resistant.

Determination of virulence and antibiotic resistance pattern of biofilm producing Listeria species isolated from retail raw milk.

BackgroundOne of the foodborne pathogens is Listeria monocytogenes, which causes serious invasive illness in elderly and immunocompromised patients, pregnant women, newborns and infants ranking second after salmonellosis because of its high case fatality rate. Listerial cow mastitis marked by abnormal milk, increased cell counts and reduced production has not been reported. Therefore, apparently healthy cows can be reservoirs of L. monocytogenes. A number of 203 udder milk samples from apparently healthy animals (buffalo, n = 100; cow, n = 103) were collected and tested for Listeria. Isolated colonies on the PALCAM agar were Listeria species confirmed according to their biochemical and the Christie–Atkins–Munch-Petersen (CAMP) reactions. The Listeria species pathogenicity of was tested by phosphatidylinositol-specific phospholipase C, DL-alanine-β-naphthylamide HCl, Dalanine-p-nitroanilide tests, chick embryo, mice inoculation tests, Vero cell cytotoxicity and biofilm formation. The virulence-associated genes, hlyA, plcB, actA and iap associated with Listeria were molecularly assayed.ResultsThe 17 isolated Listeria spp. represented a prevalence rate of 8.4 %. Of these 3 (1.4 %), 2 (1 %), 5 (2.5 %), 4 (2 %) and 3 (1.5 %) were confirmed as L. monocytogenes, L. innocua, L. welshimeri, L. seelegeri, respectively. While the L. monocytogenes isolate displayed all the four virulence-associated genes, L. seelegeri carried the hlyA gene only. The L. monocytogenes had a strong in vitro affinity to form a biofilm, in particular serotype 4 which is associated with human infections. L. monocytogenes showed resistance for 9/27 antibiotics.ConclusionsThe biofilm forming capability of the Listeria spps. makes them particularly successful in colonizing surfaces within the host thus being responsible for persistence infections and due to their antimicrobial resistant phenotype that this structure confers. In addition, strains belonging to serotypes associated with human infections and characterized by pathogenic potential (serotype 4) are capable to persist within the processing plants forming biofilm and thus being a medical hazard.

Antimicrobial Activity of Chitosan Films With Essential Oils Against Listeria monocytogenes on Cabbage.

BackgroundThe highest incidence of listeriosis, due to consumption of ready-to-eat foods and fresh, shredded, minimally processed vegetables, occurs among pregnant women and the elderly. In order to reduce the prevalence of listeriosis among consumers, better protective measures are recommended. Chitosan films, with or without added essential oils, represent a modern, safe method of preserving the quality of such vegetables and significantly reducing the incidence of Listeria monocytogenes in these foods.ObjectivesThe present study was conducted to evaluate the antimicrobial properties of composite chitosan-gelatin films with and without essential oils against two strains of L. monocytogenes, ATCC 19115 and ATCC 19112, in fresh shredded cabbage.MethodsShredded cabbage was inoculated with L. monocytogenes and packed between two layers of the chitosan composite film, then placed in Petri dishes. The prepared samples were stored at 4°C then analyzed for total viable count on PALCAM agar while incubated at 37°C, every 24 hours for 7 days.ResultsAverage L. monocytogenes content ranged from 4.2 - 5.4 log CFU/g, reaching values of 7.2 - 8.6 log CFU/g in samples of untreated cabbage. A complete reduction of L. monocytogenes ATCC 19115 on cabbage was achieved after 120 hours in the presence of 0.5% chitosan film, whereas reduction of L. monocytogenes ATCC 19112 was achieved after 144 hours. In the presence of 1% chitosan film, the bacteria withered more quickly and complete reduction of both species of L. monocytogenes was achieved after 96 hours.ConclusionsAll tested formulations of chitosan films exhibited strong antimicrobial activity on the growth of both strains of L. monocytogenes on cabbage. The best effect was achieved with a 1% chitosan concentration. The addition of essential oils increased the antimicrobial activity of all tested films.

Isolation and Detection of Listeria monocytogenes in Minced Meat, Frozen Chicken and Cheese in Duhok Province, Kurdistan Region by using RT-PCR

Listeria monocytogenes (L. monocytogenes) is the food borne pathogen responsible for listeriosis, which is considered a serious public health risk and are the most important pathogens which can be spread through food products consumption. The disease that can be serious and fatal to human and animals. The objective of present study was carried out to detect, isolate and identify L-monocytogenes from frozen chicken, minced meat and cheese in duhok province. Within a period of six months from march to October 2015, a total of 150 samples were collected including 50 samples of minced meet, 50 samples of frozen chickens and 50 samples of cheese. Biochemical and microbiological test with Real time PCR technique by using specific primer was performed to determine the prevalence of the L-monocytogenes in the samples. Detection of such bacteria in different kinds of food product is crucial to safeguard public health due to it is potential hazard in human and animals. Out of 150 samples 20 samples displayed garish and black colonies with black halos on Oxford and Palcam agar. From the total of 20 suspected Listeria 12 isolate of L. monocytogenes identified by PCR. L. Monocytogenes were detected in 1(2%), 7(14%), and 4(8%) isolates from cheese, minced meat and frozen chicken respectively. The PCR technique has demonstrated to be a rapid and reliable method appropriate for the routine analysis of different types of food.