Listeria monocytogenes is common in wild birds in Helsinki region and genotypes are frequently similar with those found along the food chain

Aims: To evaluate the prevalence and genetic diversity of Listeria monocytogenes in wild birds and to compare the genotypes with isolates previously collected from foods and food processing environments. Methods and Results: Samples of wild birds’ faeces (n = 212) were collected from a municipal landfill site and from urban areas in the Helsinki region and analysed by two‐step enrichment and plating onto L. monocytogenes‐selective agar. The overall prevalence of L. monocytogenes in bird faeces was 36% (95% CI 30–43%), and prevalence on the landfill site was significantly higher. All isolates were analysed with pulsed‐field gel electrophoresis and compared with the L. monocytogenes profiles in an existing collection. Similar pulsotypes were found in birds and in isolates collected along the food chain. Conclusions: Birds commonly carry L. monocytogenes, and strains are frequently similar with those detected in foods and food processing environments. Thus, birds may disseminate L. monocytogenes in nature and may also contaminate foods when entering the food processing environments and outdoor market places. Significance and Impact of the Study: Populations of L. monocytogenes in wild birds and along the food processing chain overlap. Our findings add to the epidemiological data on this significant foodborne pathogen.     

Do leafy green vegetables and their ready-to-eat [RTE] salads carry a risk of foodborne pathogens?

Over the past 10 years, there is an increasing demand for leafy green vegetables and their ready-to-eat (RTE) salads since people changed their eating habits because of healthier lifestyle interest. Nevertheless fresh leafy green vegetables and their RTE salads are recognized as a source of food poisoning outbreaks in many parts of the world. However, this increased proportion of outbreaks cannot be completely explained by increased consumption and enhanced surveillance of them. Both in Europe and in the USA, recent foodborne illness outbreaks have revealed links between some pathogens and some leafy green vegetables such as mostly lettuces and spinaches and their RTE salads since fresh leafy green vegetables carry the potential risk of microbiological contamination due to the usage of untreated irrigation water, inappropriate organic fertilizers, wildlife or other sources that can occur anywhere from the farm to the fork such as failure during harvesting, handling, processing and packaging. Among a wide range of pathogens causing foodborne illnesses, Escherichia coli O157:H7, Salmonella spp., and Listeria monocytogenes are the most common pathogens that contaminate leafy green vegetables. Children, the elderly, pregnant women and immunocompromised people are the most at risk for developing complications from foodborne illness as a result of eating contaminated leafy greens or their RTE salads. These outbreaks are mostly restaurant associated or they sometimes spread across several countries by international trade routes. This review summarizes current observations concerning the contaminated leafy green vegetables and their RTE salads as important vehicles for the transmission of some foodborne pathogens to humans.     

Antibody–aptamer functionalized fibre‐optic biosensor for specific detection of Listeria monocytogenes from food

Aim: To develop antibody–aptamer functionalized fibre‐optic biosensor for specific detection of Listeria monocytogenes from food products. Methods and Results: Aptamer, a single‐stranded oligonucleotide ligand that displays affinity for the target molecule, was used in the assay to provide sensor specificity. Aptamer‐A8, specific for internalin A, an invasin protein of L. monocytogenes, was used in the fibre‐optic sensor together with antibody in a sandwich format for detection of L. monocytogenes from food. Biotinylated polyclonal anti‐Listeria antibody, P66, was immobilized on streptavidin‐coated optical waveguide surface for capturing bacteria, and Alexa Fluor 647‐conjugated A8 was used as a reporter. The biosensor was able to selectively detect pathogenic Listeria in pure culture and in mixture with other bacteria at a concentration of approx. 10³ CFU ml^?1. This sensor also successfully detected L. monocytogenes cells from artificially contaminated (initial inoculation of 10² CFU 25 g^?1) ready‐to‐eat meat products such as sliced beef, chicken and turkey after 18 h of enrichment. Conclusion: Based on the data presented in this study, the antibody–aptamer functionalized fibre‐optic biosensor could be used as a detection tool for sensitive and specific detection of L. monocytogenes from foods. Significance and Impact of the Study: The study demonstrates feasibility and novel application of aptamer on fibre‐optic biosensor platform for the sensitive detection of L. monocytogenes from food products.     

The role of the Listeria monocytogenes surfactome in biofilm formation

Listeria monocytogenes is a highly pathogenic foodborne bacterium that is ubiquitous in the natural environment and capable of forming persistent biofilms in food processing environments. This species has a rich repertoire of surface structures that enable it to survive, adapt and persist in various environments and promote biofilm formation. We review current understanding and advances on how L. monocytogenes organizes its surface for biofilm formation on surfaces associated with food processing settings, because they may be an important target for development of novel antibiofilm compounds. A synthesis of the current knowledge on the role of Listeria surfactome, comprising peptidoglycan, teichoic acids and cell wall proteins, during biofilm formation on abiotic surfaces is provided. We consider indications gained from genome-wide studies and discuss surfactome structures with established mechanistic aspects in biofilm formation. Additionally, we look at the analogies to the species L. innocua, which is closely related to L. monocytogenes and often used as its model (surrogate) organism.     

Adaptational changes in cellular phospholipids and fatty acid composition of the food pathogen Listeria monocytogenes as a stress response to disinfectant sanitizer benzalkonium chloride

Aims: This study provides a first approach to observing the alterations of the cell membrane lipids in the adaptation response of Listeria monocytogenes to the sanitizer benzalkonium chloride. Methods and Results: A thorough investigation of the composition of polar and neutral lipids from L. monocytogenes grown when exposed to benzalkonium chloride is compared to cells optimally grown. The adaptation mechanism of L. monocytogenes in the presence of benzalkonium chloride caused (i) an increase in saturated‐chain fatty acids (mainly C_16:0 and C_18:0) and unsaturated fatty acids (mainly C_16:1 and C_18:1) at the expense of branched‐chain fatty acids (mainly C_a‐15:0 and C_a‐17:0) mainly because of neutral fatty acids; (ii) no alteration in the percentage of neutral and polar lipid content among total lipids; (iii) a decrease in lipid phosphorus and (iv) an obvious increase in the anionic phospholipids and a decrease in the amphiphilic phosphoaminolipid. Conclusions: These lipid changes could lead to decreased membrane fluidity and also to modifications of physicochemical properties of cell surface and thus changes in bacterial adhesion to abiotic surfaces. Significance and Impact of the Study: The adaptation and resistance of L. monocytogenes to disinfectants is able to change its physiology to allow growth in food‐processing plants. Understanding microbial stress response mechanisms would improve the effective use of disinfectants.     

Colorimetric assay for biofilms in wet processing conditions

Controlling bacterial biofilms is necessary for food safety and industrial processing in clean room environments. Our goal was to develop a method to quantitatively measure biofilm produced by pathogens under wet poultry production and processing conditions. Stainless steel and glass coupons were incubated in aqueous media containing reduced nutrients and exposed to Listeria monocytogenes under static temperature and humidity conditions. Samples were measured separately by biofilm assay and viable cell density, and then confirmed by spectrophotometry and microscopy. The biofilm assay resulted in different t groupings from the cell density. The mean from the biofilm assay was 0.50, and the error% was 0.595. The mean of the log₁₀ density (cfu/cm²) was 5.90, and the standard deviation ranged from 0.127 to 0.438 on 24 coupons. The typical sequence of biofilm development, followed by microscopy of biofilm grown on glass coupons, exhibited a change from dispersed single cells to an all-over pattern of clumps with few dispersed cells. L. monocytogenes formed biofilms on all of the substrata tested. Bacterial counts from planktonic cultures at 24, 48, 72, and 144 h confirmed that L. monocytogenes remained viable throughout the experiment and reached equilibrium between 6 and 24 h. The cell density log₁₀/ml was 8.01, 8.03, 7.69, and 6.66, respectively; and the standard deviation ranged from 0.156 to 0.394. The data will be used to grow stable biofilms of Listeria spp. collected from the food processing environment for further study. This is the first use of the crystal violet assay for measurement of bacterial biofilms on stainless steel under these conditions. The methods tested are applicable to other bacteria and substrata.     

Molecular Studies on the Ecology of Listeria monocytogenes in the Smoked Fish Processing Industry

We have applied molecular approaches, including PCR-based detection strategies and DNA fingerprinting methods, to study the ecology of Listeria monocytogenes in food processing environments. A total of 531 samples, including raw fish, fish during the cold-smoking process, finished product, and environmental samples, were collected from three smoked fish processing facilities during five visits to each facility. A total of 95 (17.9%) of the samples tested positive for L. monocytogenes using a commercial PCR system (BAX for Screening/Listeria monocytogenes), including 57 (27.7%) environmental samples (n = 206), 8 (7.8%) raw material samples (n = 102), 23 (18.1%) samples from fish in various stages of processing(n = 127), and 7 (7.3%) finished product samples (n = 96). L. monocytogenes was isolated from 85 samples (16.0%) using culture methods. Used in conjunction with a 48-h enrichment in Listeria Enrichment Broth, the PCR system had a sensitivity of 91.8% and a specificity of 96.2%. To track the origin and spread of L. monocytogenes, isolates were fingerprinted by automated ribotyping. Fifteen different ribotypes were identified among 85 isolates tested. Ribotyping data established possible contamination patterns, implicating raw materials and the processing environment as potential sources of finished product contamination. Analysis of the distribution of ribotypes revealed that each processing facility had a unique contamination pattern and that specific ribotypes persisted in the environments of two facilities over time (P ≤ 0.0006). We conclude that application of molecular approaches can provide critical information on the ecology of different L. monocytogenes strains in food processing environments. This information can be used to develop practical recommendations for improved control of this important food-borne pathogen in the food industry.     

Estimation of Microbial Contamination of Food from Prevalence and Concentration Data: Application to Listeria monocytogenes in Fresh Vegetables

A normal distribution and a mixture model of two normal distributions in a Bayesian approach using prevalence and concentration data were used to establish the distribution of contamination of the food-borne pathogenic bacteria Listeria monocytogenes in unprocessed and minimally processed fresh vegetables. A total of 165 prevalence studies, including 15 studies with concentration data, were taken from the scientific literature and from technical reports and used for statistical analysis. The predicted mean of the normal distribution of the logarithms of viable L. monocytogenes per gram of fresh vegetables was −2.63 log viable L. monocytogenes organisms/g, and its standard deviation was 1.48 log viable L. monocytogenes organisms/g. These values were determined by considering one contaminated sample in prevalence studies in which samples are in fact negative. This deliberate overestimation is necessary to complete calculations. With the mixture model, the predicted mean of the distribution of the logarithm of viable L. monocytogenes per gram of fresh vegetables was −3.38 log viable L. monocytogenes organisms/g and its standard deviation was 1.46 log viable L. monocytogenes organisms/g. The probabilities of fresh unprocessed and minimally processed vegetables being contaminated with concentrations higher than 1, 2, and 3 log viable L. monocytogenes organisms/g were 1.44, 0.63, and 0.17%, respectively. Introducing a sensitivity rate of 80 or 95% in the mixture model had a small effect on the estimation of the contamination. In contrast, introducing a low sensitivity rate (40%) resulted in marked differences, especially for high percentiles. There was a significantly lower estimation of contamination in the papers and reports of 2000 to 2005 than in those of 1988 to 1999 and a lower estimation of contamination of leafy salads than that of sprouts and other vegetables. The interest of the mixture model for the estimation of microbial contamination is discussed.     

Behaviour of Listeria monocytogenes in packaged water buffalo mozzarella cheese

Aims: The aim of the study was to evaluate the behaviour of Listeria monocytogenes in the conditioning liquid of packaged water buffalo mozzarella cheese (WBMC). Methods and Results: The conditioning liquid was contaminated with L. monocytogenes, and the contaminated samples were stored at four different storage temperatures: 5 and 10°C for 22 days; 20°C for 9 days; 20°C for 3 days and then at 5°C for 6 days. The results showed that L. monocytogenes concentration decreased when contaminated samples were stored at 5°C. When WBMC was stored at 20°C and at 10°C, L. monocytogenes started to grow after a lag phase of 3 and 10 days, respectively. When samples were stored at variable temperature conditions, L. monocytogenes numbers showed a lag phase of 5 days. Conclusions: Use of a conditioning liquid characterized by acidity and a correct storage temperature is able to counteract pathogen replication during shelf life. A high concentration of lactic acid bacteria was associated with effective control of L. monocytogenes but the role of lactic acid bacteria in WBMC conditioning liquid requires further investigation. Significance and Impact of the Study: According to European regulations, food producers should be able to justify decision‐making on the shelf life assigned to their products, taking into account reasonable storage conditions and use by consumers. The results of the trial yielded information for producers of WBMC and similar cheeses for decision‐making on product shelf life.     

The impact of nisin on sensitive and resistant mutants of Listeria monocytogenes in cottage cheese

Aims: Listeria monocytogenesΔgadD1 and ΔlisK mutants display enhanced and reduced sensitivity, respectively, to the food preservative nisin in laboratory media. However, the behaviour of these strains in a nisin‐containing food has not been assessed. Here we use cottage cheese as a model food to address this issue. Materials and Results: Antibiotic‐resistant forms of the wild‐type and mutant strains were employed to investigate the behaviour of multiple strains in a single food sample, thereby eliminating the problem of intersample variation. Using this approach, it was established that percentage survival of the ΔlisK mutant was greater than the parent strain in the absence of nisin and that this relative difference became even more dramatic in cottage cheese supplemented with nisin. The numbers of the ΔgadD1 mutant decreased more rapidly than the parent in cottage cheese without nisin, but surprisingly this trend was reversed in nisin‐supplemented cheese. Upon the addition of 10 mmol l^?1 monosodium glutamate, a substrate for the glutamate decarboxylase (GAD) system, the wild‐type LO28 strain regained its relative advantage over ΔgadD1. Conclusions: Care needs to be taken when predicting the behaviour of mutants of L. monocytogenes with altered resistance to nisin in food as experiments in laboratory media are not always a good indicator of how the strains will behave in such food environments. Significance and impact of the Study: This study further emphasizes the importance of utilizing food matrices to confirm observations made using laboratory media.     

Effect of Octenidine Hydrochloride on Planktonic Cells and Biofilms of Listeria monocytogenes

Listeria monocytogenes is a food-borne pathogen capable of forming biofilms and persisting in food processing environments for extended periods of time, thereby potentially contaminating foods. The efficacy of octenidine hydrochloride (OH) for inactivating planktonic cells and preformed biofilms of L. monocytogenes was investigated at 37, 21, 8, and 4°C in the presence and absence of organic matter (rehydrated nonfat dry milk). OH rapidly killed planktonic cells and biofilms of L. monocytogenes at all four temperatures. Moreover, OH was equally effective in killing L. monocytogenes biofilms on polystyrene and stainless steel matrices in the presence and absence of organic matter. The results underscore OH''s ability to prevent establishment of L. monocytogenes biofilms by rapidly killing planktonic cells and to eliminate preformed biofilms, thus suggesting that it could be used as a disinfectant to prevent L. monocytogenes from persisting in food processing environments.Listeria monocytogenes is a major bacterial pathogen (2), accounting for approximately 28% of the deaths resulting from food-borne illnesses in the United States (22). It is widespread in nature and occurs in soil, vegetation, fecal matter, sewage, water, and animal feed (14). Because it is ubiquitous, L. monocytogenes is frequently isolated from foods and food processing environments (13, 23), thereby presenting a significant challenge to the food industry. Several studies have shown that L. monocytogenes is capable of adhering to food contact surfaces, such as glass, stainless steel, rubber, and polystyrene (6, 11, 28). Upon attachment to such surfaces, L. monocytogenes establishes biofilms and persists for long periods of time in the food processing environment (18, 30). This potentially poses a food safety hazard since biofilms are an important source of contamination of food products that come into contact with them. In addition, biofilms also protect the underlying bacteria from desiccation, antimicrobials, and sanitizing agents (7, 16). Thus, eradication of L. monocytogenes biofilms in processing plants is critical for improving food safety.When problems with persistent L. monocytogenes are encountered in food processing facilities, plant hygiene and sanitation are emphasized (31). This involves preventing the establishment of L. monocytogenes biofilms in the food processing environment and reducing contamination of product contact surfaces. A variety of cleaners and disinfectants, including quaternary ammonium compounds and hypochlorite, have been evaluated for this purpose (20). Although these compounds are approved by the Food and Drug Administration for use as disinfectants in processing plants, they are not effective in killing L. monocytogenes (24, 25), especially in the presence of soil or organic matter and at low temperatures. Therefore, there is a need for an effective disinfectant that can eliminate listerial biofilms in the presence of organic matter at a wide range of temperatures. Octenidine hydrochloride (OH) is a positively charged bispyridinamine that exhibits antimicrobial activity against plaque-producing organisms, such as Streptococcus mutans and Streptococcus sanguis (5). Toxicity studies with a variety of species have shown that OH is not absorbed through mucous membranes and the gastrointestinal tract, and there have been no reports of carcinogenicity, genotoxicity, or mutagenicity of this compound (17, 19, 29).The objective of this study was to investigate the efficacy of OH for inactivating planktonic cells and preformed biofilms of L. monocytogenes at 37, 21, 8, and 4°C in the presence and absence of organic matter on two matrices, polystyrene and stainless steel.     

Interference of sanitizers,NaCl and curing salts on Listeria monocytogenes adhesion and subsequent biofilm formation

Listeria monocytogenes, a well-known foodborne pathogen and the causative agent of listeriosis, has the ability to persist in food processing environments due to its high adhesion ability in different surfaces, playing an important role in the food industry. The aim of this study was to assess how the main stressing conditions, usually observed in meat processing facilities (sanitizers, NaCl, curing salts), interfere in L. monocytogenes adhesion and biofilm formation. The isolates, representatives of different L. monocytogenes lineages (n = 6) were subjected to four different sanitizers (S1: quaternary ammonium; S2: peracetic acid, hydrogen peroxide and glacial acetic acid, S3: biguanide polyhexamethylene hydrochloride, S4: hydrogen peroxide) to verify adhesion ability and susceptibility based on minimum inhibitory concentration (MIC). In addition, the isolates adhesion and biofilm were assessed up to 72 h under different conditions: sanitizers (MIC values), curing salts and NaCl (both at 5, 7·5, 10%), at different temperatures (4, 12 and 37°C). Despite the effectiveness of sanitizers, isolates presented higher biofilm development when compared to controls in the presence of quaternary ammonium (S1, 1: 1,024) at 4°C, over the tested time (P < 0·05). Furthermore, different responses were observed for the different L. monocytogenes strains tested, providing a better understanding of the persistence of this pathogen in the food processing facilities.     

The RAB5‐GEF Function of RIN1 Regulates Multiple Steps During Listeria monocytogenes Infection

Listeria monocytogenes is a food‐borne pathogenic bacterium that invades intestinal epithelial cells through a phagocytic pathway that relies on the activation of host cell RAB5 GTPases. Listeria monocytogenes must subsequently inhibit RAB5, however, in order to escape lysosome‐mediated destruction. Relatively little is known about upstream RAB5 regulators during L. monocytogenes entry and phagosome escape processes in epithelial cells. Here we identify RIN1, a RAS effector and RAB5‐directed guanine nucleotide exchange factor (GEF), as a host cell factor in L. monocytogenes infection. RIN1 is rapidly engaged following L. monocytogenes infection and is required for efficient invasion of intestinal epithelial cells. RIN1‐mediated RAB5 activation later facilitates the fusion of phagosomes with lysosomes, promoting clearance of bacteria from the host cell. These results suggest that RIN1 is a host cell regulator that performs counterbalancing functions during early and late stages of L. monocytogenes infection, ultimately favoring pathogen clearance.      

Acanthamoeba release compounds which promote growth of Listeria monocytogenes and other bacteria

Listeria monocytogenes can grow as a saphrophyte in diverse habitats, e.g., soil, rivers, lakes, and on decaying plant material. In these environments, the bacteria are frequently exposed to predatory protozoa such as Acanthamoeba. Although L. monocytogenes is a facultative intracellular pathogen it does not infect or survive intracellular in Acanthamoeba castellanii, unlike several other facultative intracellular bacteria. Instead, motile L. monocytogenes can form large aggregates on amoebal cells and are effectively phagocytosed and eventually digested by Acanthamoeba. Here, we demonstrate that non-motile L. monocytogenes represent a less preferred prey in co-cultures with A. castellanii. Moreover, we found that the presence of Acanthamoeba strongly promotes growth of the bacteria in non-nutrient saline, by releasing nutrients or other growth promoters. Thus, the lack of motility and ability to utilize amoebal metabolites may aid to avoid eradication by amoebal predation in low-nutrient environments.     

Why is Listeria monocytogenes such a potent inducer of CD8+ T‐cells?

Listeria monocytogenes is a rapidly growing, Gram‐positive, facultative intracellular pathogen that has been used for over 5 decades as a model to study basic aspects of infection and immunity. In a murine intravenous infection model, immunisation with a sublethal infection of L. monocytogenes initially leads to rapid intracellular multiplication followed by clearance of the bacteria and ultimately culminates in the development of long‐lived cell‐mediated immunity (CMI) mediated by antigen‐specific CD8+ cytotoxic T‐cells. Importantly, effective immunisation requires live, replicating bacteria. In this review, we summarise the cell and immunobiology of L. monocytogenes infection and discuss aspects of its pathogenesis that we suspect lead to robust CMI. We suggest five specific features of L. monocytogenes infection that positively impact the development of CMI: (a) the bacteria have a predilection for professional antigen‐presenting cells; (b) the bacteria escape from phagosomes, grow, and secrete antigens into the host cell cytosol; (c) bacterial‐secreted proteins enter the major histocompatibility complex (MHC) class I pathway of antigen processing and presentation; (d) the bacteria do not induce rapid host cell death; and (e) cytosolic bacteria induce a cytokine response that favours CMI. Collectively, these features make L. monocytogenes an attractive vaccine vector for both infectious disease applications and cancer immunotherapy.     

Biocontrol of Listeria monocytogenes on Fresh-Cut Produce by Treatment with Lytic Bacteriophages and a Bacteriocin

The fresh-cut produce industry has been the fastest-growing portion of the food retail market during the past 10 years, providing consumers with convenient and nutritious food. However, fresh-cut fruits and vegetables raise food safety concerns, because exposed tissue may be colonized more easily by pathogenic bacteria than intact produce. This is due to the higher availability of nutrients on cut surfaces and the greater potential for contamination because of the increased amount of handling. We found that applied Listeria monocytogenes populations survived and increased only slightly on fresh-cut Red Delicious apples stored at 10°C but increased significantly on fresh-cut honeydew melons stored at 10°C over 7 days. In addition, we examined the effect of lytic, L. monocytogenes-specific phages via two phage application methods, spraying and pipetting, on L. monocytogenes populations in artificially contaminated fresh-cut melons and apples. The phage mixture reduced L. monocytogenes populations by 2.0 to 4.6 log units over the control on honeydew melons. On apples, the reduction was below 0.4 log units. In combination with nisin (a bacteriocin), the phage mixture reduced L. monocytogenes populations by up to 5.7 log units on honeydew melon slices and by up to 2.3 log units on apple slices compared to the control. Nisin alone reduced L. monocytogenes populations by up to 3.2 log units on honeydew melon slices and by up to 2.0 log units on apple slices compared to the control. The phage titer was stable on melon slices, but declined rapidly on apple slices. The spray application of the phage and phage plus nisin reduced the bacterial numbers at least as much as the pipette application. The effectiveness of the phage treatment also depended on the initial concentration of L. monocytogenes.     

Molecular Epidemiological Survey of Listeria monocytogenes in Seafoods and Seafood-Processing Plants

To evaluate the role of seafoods in the epidemiology of human listeriosis and the role of the processing environment as a source of Listeria monocytogenes in seafood products, 305 L. monocytogenes isolates were characterized by multilocus enzyme electrophoresis using 21 genetic loci and restriction enzyme analysis of total DNA. Forty-four isolates were recovered from patients in Norway; 93 were isolated from seafoods, seafood-processing environments, and seawater from 55 different producers; and the remaining 168 isolates originated from six seafood-processing plants and one transport terminal examined in detail for L. monocytogenes. The patient isolates fell into 11 electrophoretic types, with four of them being responsible for 77% of the listeriosis cases in 1992 to 1996. Isolates from Norwegian seafoods and processing environments showed great genetic diversity, indicating that seafoods and seafood-processing environments do not offer a niche for specific L. monocytogenes strains. On the other hand, isolates from individual processing plants were genetically more homogenous, showing that plants are likely to be colonized with specific subclones of L. monocytogenes. The isolation of identical subclones of L. monocytogenes from both human patients and seafoods, including ready-to-eat products, suggests that such products may have been possible sources for listeriosis cases in Norway.     

Microbial challenges of poultry meat production

Food safety and shelf-life are both important microbial concerns in relation to broiler meat production. Focus is mainly placed on the absence or control of potentially pathogenic microbes such as Salmonella spp. and Campylobacter spp. but, from the commercial point of view, other spoilage bacteria also play a role as potential threats. Regarding food safety, the primary target should be the production of pathogen-free live animals, thus allowing slaughter plants to keep the processing line free of those microorganisms.Consumers believe that quality of foods from organic production is superior to foods from conventional production. The aim of the present study was to evaluate and compare the bacterial quality of chicken meat from organic and conventional production on the basis of traditional meat quality criteria. Fresh free grazing broiler carcasses were purchased directly from rural households (n = 80) and fresh retail chicken parts from conventional broiler carcasses from the local supermarkets in the region of Epirus (Poultry Producers Association. Arta) (n = 200).The samples were microbiologically tested for the presence of bacteria such as: Salmonella spp., Listeria monocytogenes, Staphylococcus aureus, Enterobacteriaceae, Escherichia coli, Campylobacter spp., and C. perfringens. Total count of aerobic mesophilic bacteria was also determined. Bacteriological tests were performed by means of standard methods of isolation and identification of individual species of bacteria according to ISO requirements. API-tests (bioMerieux) and Vitek 2 Identification System (bioMerieux) were used for biochemical determination. High levels of microbial contamination and occurrence of pathogenic bacteria at then fresh free grazing broiler carcasses reflect the poor hygienic quality of the slaughter conditions in the rural households.