Listeria spp. in broiler flocks: recovery rates and species distribution investigated by conventional culture and the EiaFoss method

Listeria Occurrence in Conventional and Alternative Egg Production Systems

Listeria continues to be a persistent foodborne pathogen that is responsible for human cases of listeriosis when contaminated food products are consumed. Human subjects considered to be most susceptible include the elderly, immunocompromised, and pregnant women. Listeria is characterized as a saprophytic organism with the capability of responding and adapting to constantly changing environments because it possesses multiple stress response mechanisms to overcome varying temperatures, salt concentrations, and pH, among others. Primary foods and food products associated with listeriosis include dairy products and ready-to-eat meats such as turkey products. Historically, chicken eggs have not been identified as a primary source of Listeria, but the potential for contamination during egg production and processing does exist. Listeria species have been isolated from egg-processing plant equipment and are presumed to occur in egg-processing plant environments. Whether Listeria is consistently disseminated onto eggs beyond the egg-processing plant is a risk factor that remains to be determined. However, research has been conducted over the years to develop egg wash solutions that generate combinations of pH and other properties that would be considered inhibitory to Listeria. Even less is known regarding the association of Listeria with alternative egg production systems, but Listeria has been isolated from pasture flock broilers, so it is conceivable, given the nature of the outdoor environments, that layer birds under these conditions would also be exposed to Listeria and their eggs become contaminated. This review focuses on the possibility of Listeria occurring in conventional and alternative egg-laying production and processing systems.

Contamination Pathways can Be Traced along the Poultry Processing Chain by Whole Genome Sequencing of Listeria innocua

Foodborne infection with Listeria causes potentially life-threatening disease listeriosis. Listeria monocytogenes is widely recognized as the only species of public health concern, and the closely related species Listeria innocua is commonly used by the food industry as an indicator to identify environmental conditions that allow for presence, growth, and persistence of Listeria spp. in general. In our study, we analyze the occurrence of Listeria spp. in a farm-to-fork approach in a poultry production chain in Egypt and identify bacterial entry gates and transmission systems. Prevalence of Listeria innocua at the three production stages (farm, slaughterhouse, food products) ranged from 11% to 28%. The pathogenic species Listeria monocytogenes was not detected, and Listeria innocua strains under study did not show genetic virulence determinants. However, the close genetic relatedness of Listeria innocua isolates (maximum 63 SNP differences) indicated cross-contamination between all stages from farm to final food product. Based on these results, chicken can be seen as a natural source of Listeria. Last but not least, sanitary measures during production should be reassessed to prevent bacterial contamination from entering the food chain and to consequently prevent human listeriosis infections. For this purpose, surveillance must not be restricted to pathogenic species.

The Distribution of Listeria in Pasture-Raised Broiler Farm Soils Is Potentially Related to University of Vermont Medium Enrichment Bias toward Listeria innocua over Listeria monocytogenes

The occurrence of Listeria monocytogenes has been widely investigated in the poultry production chain from the processing plant to the final product. However, limited data are available on Listeria species, including Listeria monocytogenes, in the poultry farm environment. Therefore, fecal and soil samples from 37 pastured poultry flocks from 10 all-natural farms over 3 years were assessed to determine the prevalence and diversity of Listeria within these alternative poultry farm environments using standard cultural and molecular methods. Listeria species were isolated in 15% of poultry farm samples and included Listeria innocua (65.7%), L. monocytogenes (17.4%), and Listeria welshimeri (15.1%). Additional multiplex PCR serotyping showed group 1/2a-3a to be the most dominant L. monocytogenes serovar group. Based on these results, monoculture growth experiments were conducted on four Listeria soil isolates (three L. monocytogenes isolates representing the three recovered serovar groups and one L. innocua isolate) to determine if culture medium [tripticase soy broth (TSB) and University of Vermont modified Listeria enrichment broth (UVM)], inoculum concentration (102 or 105 CFU/ml), or incubation temperature (20, 30, and 42°C) differentially affected these Listeria species. Overall, very few significant growth differences were observed between the behavior of the three L. monocytogenes isolates (representing the three recovered serovar groups) under the growth conditions tested. Alternatively, at 30°C in UVM with the lower inoculum concentration, the L. innocua isolate had a significantly shorter lag phase than the L. monocytogenes isolates. In coculture growth studies under these same incubation conditions, the lag phase of L. innocua and L. monocytogenes was similar, but the final concentration of L. innocua was significantly higher than L. monocytogenes. However, cocultures in UVM for high inoculum concentration did not show preferential growth of L. innocua over L. monocytogenes. These results indicate that the use of UVM as an enrichment medium may preferentially allow L. innocua to outcompete L. monocytogenes at low concentrations, biasing the Listeria prevalence from these farm samples toward L. innocua and potentially underreporting the presence of L. monocytogenes in these environments.

Listeria Occurrence in Poultry Flocks: Detection and Potential Implications

Foodborne pathogens such as Salmonella, Campylobacter, Escherichia coli, and Listeria are a major concern within the food industry due to their pathogenic potential to cause infection. Of these, Listeria monocytogenes, possesses a high mortality rate (approximately 20%) and is considered one of the most dangerous foodborne pathogens. Although the usual reservoirs for Listeria transmission have been extensively studied, little is known about the relationship between Listeria and live poultry production. Sporadic and isolated cases of listeriosis have been attributed to poultry production and Listeria spp. have been isolated from all stages of poultry production and processing. Farm studies suggest that live birds may be an important vector and contributor to contamination of the processing environment and transmission of Listeria to consumers. Therefore, the purpose of this review is to highlight the occurrence, incidence, and potential systemic interactions of Listeria spp. with poultry.

Prevalence and risk factors for Listeria monocytogenes in broiler flocks in Shiraz, southern Iran

Listeria monocytogenes has been identified as an important foodborne pathogen in recent years. In humans, it most commonly affects pregnant women, neonates, children, elderly people, and persons with a suppressed immune system. It could contaminate both raw and cooked meat and poultry products. Studies regarding prevalence and risk factors of L. monocytogenes in broilers flocks are limited. Therefore, the present study was conducted to determine the prevalence and risk factors for L. monocytogenes in poultry flocks in Shiraz, southern Iran. During August to September 2009, in total, 100 broiler flocks were selected at slaughter, and 21 specimens were collected from cloacal samples from each flock. Polymerase chain reaction (PCR) was performed on the samples enriched in buffered Listeria enrichment broth (BLEB), using specific primers. Furthermore, enriched samples in BLEB and/or BLEB treated with 5% KOH were subcultured on Palcam medium. Data about farm and flocks were collected using a structured questionnaire. The prevalence of L. monocytogenes was 7% (95% CI, 2-12%) and 1% using PCR and culture, respectively. Results showed that using antibiotics during rearing period was dramatically reduced the rate of isolation (odds ratio [OR]=0.07, p=0.03), whereas house capacity of more than 10,000 birds (OR=24.03, p=0.04) and number of houses (OR=2, p=0.02) significantly increased the prevalence. The correlation between poor management of large poultry flocks and increasing the risk of contamination was more likely due to the recontamination of cooked poultry/undercooking or cross-contamination of other ready-to-eat foods.

Prevalence of Listeria monocytogenes in poultry production in France

This study aimed to update and create a data set from laying hens and broilers regarding contamination by Listeria monocytogenes. Two hundred laying-hen flocks were sampled, with 88 flocks reared in cages and 112 reared on the floor. One hundred forty-five broiler flocks were sampled, with 85 conventional and 60 free-range flocks. A total of 774 and 725 samples were analyzed from laying hens and broilers, respectively. L. monocytogenes was detected in 31 of 200 flocks, yielding an estimated prevalence of 15.5% in laying-hen flocks. Among positive flocks, there appeared a significant (P = 0.004) difference between caged and floor-reared hens, with a higher detection in dust samples from floor-reared hens. In positive caged hen flocks, significant (P = 0.028) differences between dust and fecal samples appeared, with a higher detection in feces than in dust samples. In broiler flocks, L. monocytogenes was isolated in 46 of 145 flocks, yielding an estimated prevalence of 32% (28% in conventional flocks versus 37% in the free-range flocks). L. monocytogenes was isolated in samples taken from conventional flocks with a lower frequency than in free-range flocks (13 versus 18%, respectively). The serotyping of L. monocytogenes strains showed that the majority belonged to type 1/2a in laying-hen flocks (74.3%) and in broiler flocks (40.5%). A significant difference (P = 0.007) between laying hens and broilers was shown for serogroup 4 and for serovar 1/2b (P = 0.007); these serogroups were more prevalent in broilers (40%) than in laying hens (5.7%).

Methods for the isolation and identification of Listeria spp. and Listeria monocytogenes: a review

Listeria monocytogenes is an important food-borne pathogen and is widely tested for in food, environmental and clinical samples. Identification traditionally involved culture methods based on selective enrichment and plating followed by the characterization of Listeria spp. based on colony morphology, sugar fermentation and haemolytic properties. These methods are the gold standard; but they are lengthy and may not be suitable for testing of foods with short shelf lives. As a result more rapid tests were developed based on antibodies (ELISA) or molecular techniques (PCR or DNA hybridization). While these tests possess equal sensitivity, they are rapid and allow testing to be completed within 48 h. More recently, molecular methods were developed that target RNA rather than DNA, such as RT-PCR, real time PCR or nucleic acid based sequence amplification (NASBA). These tests not only provide a measure of cell viability but they can also be used for quantitative analysis. In addition, a variety of tests are available for sub-species characterization, which are particularly useful in epidemiological investigations. Early typing methods differentiated isolates based on phenotypic markers, such as multilocus enzyme electrophoresis, phage typing and serotyping. These phenotypic typing methods are being replaced by molecular tests, which reflect genetic relationships between isolates and are more accurate. These new methods are currently mainly used in research but their considerable potential for routine testing in the future cannot be overlooked.

Development of a protocol for the isolation of Listeria monocytogenes from sludge

Given the high level of background flora in sludge, methods for detecting Listeria monocytogenes are not well established. In this study, two critical parameters for the detection of L. monocytogenes were evaluated: the concentration of Listeria sp. in a modified Fraser broth (first stage of the method) and the proportion of L. monocytogenes on Palcam agar (second stage of the method). Concentrations of Listeria sp. estimated in 118 modified Fraser enrichment broths inoculated with four types of sludge, reached 10(4) bacteria per mL for 83% of the positive enrichment broths. Proportion of L. monocytogenes on Palcam agar, which was estimated by transferring all characteristic colonies of Listeria sp. onto Rapid'L Mono agar, was highly variable regardless of the type of sludge. According to these results, we proposed a protocol that consisted of an enrichment in modified Fraser broth for 48 h at 37 degrees C, followed by plating 0.1 mL of appropriate dilutions of broth onto Palcam agar. After an incubation of 48 h at 37 degrees C, a systematic identification of characteristic colonies of Listeria sp. on Rapid'L Mono agar allowed to enhance the detection of Listeria monocytogenes.

Application of a multiplex polymerase chain reaction assay for the simultaneous confirmation of Listeria monocytogenes and other Listeria species in turkey sample surveillance

A multiplex polymerase chain reaction was developed to simultaneously identify Listeria monocytogenes and species of the genus Listeria. Two sets of primers were used, with the first amplifying a 938-bp region of the 16S rRNA gene that is highly conserved in all Listeria species and the second amplifying a 174-bp region of the listeriolysin (hlyA) gene of L. monocytogenes. Thus, isolates of Listeria spp. yield a single 938-bp product, whereas L. monocytogenes isolates yield both the 938-bp product and a 174-bp product. The specificity of the assay was verified with all six Listeria species and 11 serotypes of L. monocytogenes, as well as nonrelated bacteria. The multiplex PCR assay was used to determine the incidence of Listeria spp., especially L. monocytogenes, in mechanically separated turkey samples (n = 150 samples). L. monocytogenes strains were selected by using the University of Vermont two-step enrichment protocol and plating to selective Palcam agar. The multiplex PCR assay was used for verification of presumptive Listeria colonies. Approximately 38% of mechanically separated turkey samples (57 of 150) yielded L. monocytogenes; an additional 18% of these samples (27 of 150) harbored other Listeria spp. Fifty-one percent (29 of 57) of the L. monocytogenes isolates were of serogroup 1, 44% (25 of 57) were of serogroup 4, and 2% (1 of 57) were assigned to serogroups other than 1 and 4.