Monitoring of chicken houses and an attached egg-processing facility in a laying farm for Salmonella contamination between 1994 and 1998

Persistence of microbiological hazards in food and feed production and processing environments

Listeria monocytogenes (in the meat, fish and seafood, dairy and fruit and vegetable sectors), Salmonella enterica (in the feed, meat, egg and low moisture food sectors) and Cronobacter sakazakii (in the low moisture food sector) were identified as the bacterial food safety hazards most relevant to public health that are associated with persistence in the food and feed processing environment (FFPE). There is a wide range of subtypes of these hazards involved in persistence in the FFPE. While some specific subtypes are more commonly reported as persistent, it is currently not possible to identify universal markers (i.e. genetic determinants) for this trait. Common risk factors for persistence in the FFPE are inadequate zoning and hygiene barriers; lack of hygienic design of equipment and machines; and inadequate cleaning and disinfection. A well-designed environmental sampling and testing programme is the most effective strategy to identify contamination sources and detect potentially persistent hazards. The establishment of hygienic barriers and measures within the food safety management system, during implementation of hazard analysis and critical control points, is key to prevent and/or control bacterial persistence in the FFPE. Once persistence is suspected in a plant, a 'seek-and-destroy' approach is frequently recommended, including intensified monitoring, the introduction of control measures and the continuation of the intensified monitoring. Successful actions triggered by persistence of L. monocytogenes are described, as well as interventions with direct bactericidal activity. These interventions could be efficient if properly validated, correctly applied and verified under industrial conditions. Perspectives are provided for performing a risk assessment for relevant combinations of hazard and food sector to assess the relative public health risk that can be associated with persistence, based on bottom-up and top-down approaches. Knowledge gaps related to bacterial food safety hazards associated with persistence in the FFPE and priorities for future research are provided.

Research Note: Longitudinal monitoring of chicken houses in a commercial layer farm for antimicrobial resistance in Escherichia coli with special reference to plasmid-mediated quinolone resistance

Plasmid-mediated quinolone resistance (PMQR) genes located on conjugative plasmids can be transferred to other bacteria in the absence of antimicrobial selective pressure. To elucidate the prevalence of resistance, including PMQR in an egg-producing commercial layer farm in western Japan where no antimicrobials were used, minimum inhibitory concentrations (MIC) for a total of 375 Escherichia coli isolates obtained from chicken houses in the farm between 2012 and 2017 were determined using the agar dilution methods. Eighty-seven isolates resistant to oxytetracycline (OTC) accounted for 23.0% of the tested isolates, followed by isolates resistant to dihydrostreptomycin (DSM) (18.4%), sulfisoxazole (18.1%), ampicillin (AMP) (14.4%), trimethoprim (TMP) (14.4%), and nalidixic acid (10.1%). The prevalence rate of multidrug-resistant (MDR) isolates—which are resistant to 3 or more antimicrobial classes, including β-lactams, aminoglycosides, quinolones, folate pathway inhibitors, tetracyclines, and phenicols—was inversely related to the age of chickens at the time of bacterial examination. Probably, the prevalence of MDR isolates in layer chickens may have decreased with age owing to the absence of selective pressure. Furthermore, 45 isolates exhibiting enrofloxacin MICs of more than 0.25 μg/mL were examined for PMQR genes. The transfer of PMQR genes was tested by conjugation analysis. Southern blot analysis of genomic DNA revealed that the qnrS1 (5 isolates), qnrS2 (1 isolate), and qnrS13 genes (1 isolate) were located on plasmids with sizes ranging from approximately 60 to 120 kpb. In 1 of the 5 qnrS1-positive isolates and in an isolate with qnrS13, the qnrS genes were transferred to recipient strains. The plasmid harboring the qnrS1 gene was typed as IncF by PCR-based replicon typing. On this plasmid, the bla_TEM, aadA, tetA, and dfrA1 genes responsible for resistance to AMP, DSM, OTC, and TMP, respectively, were detected. The tetA gene was detected in the plasmid harboring the qnrS13 gene, which was typed as IncI1. These results suggest that despite the low prevalence of quinolone resistance in this farm, various PMQR genes, located on diverse plasmids, exist.

An association of genotypes and antimicrobial resistance patterns among Salmonella isolates from pigs and humans in Taiwan

We collected 110 Salmonella enterica isolates from sick pigs and determined their serotypes, genotypes using pulsed-field gel electrophoresis (PFGE), and antimicrobial susceptibility to 12 antimicrobials and compared the data with a collection of 18,280 isolates obtained from humans. The pig isolates fell into 12 common serovars for human salmonellosis in Taiwan; S. Typhimurium, S. Choleraesuis, S. Derby, S. Livingstone, and S. Schwarzengrund were the 5 most common serovars and accounted for a total of 84% of the collection. Of the 110 isolates, 106 (96%) were multidrug resistant (MDR) and 48 (44%) had PFGE patterns found in human isolates. S. Typhimurium, S. Choleraesuis, and S. Schwarzengrund were among the most highly resistant serovars. The majority of the 3 serovars were resistant to 8–11 of the tested antimicrobials. The isolates from pigs and humans sharing a common PFGE pattern displayed identical or very similar resistance patterns and Salmonella strains that caused severe infection in pigs were also capable of causing infections in humans. The results indicate that pigs are one of the major reservoirs to human salmonellosis in Taiwan. Almost all of the pig isolates were MDR, which highlights the necessity of strictly regulating the use of antimicrobials in the agriculture sector in Taiwan.

Epizootiologic role of feeds in the epidemiology of Salmonella Senftenberg contamination in commercial layer farms in eastern Japan

In total, 40 commercial layer farms and 32 replacement pullet farms with a combined population of 7.5 million adult layers and 6.6 million replacement pullets from six prefectures in eastern Japan were investigated for Salmonella Senftenberg contamination. We randomly collected 17,956 environmental samples, 5816 feed samples, and 218,470 egg samples from commercial layer farms; and 427 feed samples and 2896 environmental samples from replacement pullet farms. We monitored all samples for Salmonella. Samples were primarily enriched in Hajna tetrathinoate broth for 24 hr at 37 C followed by incubation in desoxycholate hydrogen sulfide lactose agar for 18 hr at 37 C. Salmonella colonies were confirmed and identified by biochemical tests and serotyped using Salmonella O and H antigens. We recorded 171 environmental samples (0.95%) and 10 feed samples (0.17%) that were positive for Salmonella spp. in which 36 environmental samples (0.20%) and six feed samples (0.10%) were identified as Salmonella Senftenberg. All Salmonella Senftenberg strains were isolated from nine replacement pullet farms. No Salmonella Senftenberg strains were isolated from adult layer farms and from eggs. Pulse field gel electrophoresis of BlnI-digested chromosomal DNA of 19 Salmonella Senftenberg isolates from feeds and environmental samples yielded a single identical DNA pattern. Traceback information showed that all positive feed samples were from a single feed source. Timeline studies showed that Salmonella Senftenberg contamination occurred first mostly in the feeds and then spread to the environment and other farms. This study demonstrated that the prevalence of Salmonella Senftenberg contamination in commercial layer facilities in eastern Japan is very low. Moreover, feed contamination played a major role in the epizootiology and spread of this pathogen in commercial poultry flocks. Given the resilient and persistent nature of this particular Salmonella serotype, routine monitoring and strict quality control measures at the feed level are recommended to prevent the colonization of poultry facilities with Salmonella Senftenberg that may lead to future outbreaks.

Evidence for horizontal and vertical transmission in Campylobacter passage from hen to her progeny

Campylobacter is an important human pathogen, and consumption of undercooked poultry has been linked to significant human illnesses. To reduce human illness, intervention strategies targeting Campylobacter reduction in poultry are in development. For more than a decade, there has been an ongoing national and international controversy about whether Campylobacter can pass from one generation of poultry to the next via the fertile egg. We recognize that there are numerous sources of Campylobacter entry into flocks of commercial poultry (including egg transmission), yet the environment is often cited as the only source. There has been an abundance of published research globally that refutes this contention, and this article lists and discusses many of them, along with other studies that support environment as the sole or primary source. One must remember that egg passage can mean more than vertical, transovarian transmission. Fecal bacteria, including Campylobacter, can contaminate the shell, shell membranes, and albumen of freshly laid fertile eggs. This contamination is drawn through the shell by temperature differential, aided by the presence of moisture (the "sweating" of the egg); then, when the chick emerges from the egg, it can ingest bacteria such as Campylobacter, become colonized, and spread this contamination to flock mates in the grow house. Improvements in cultural laboratory methods continue to advance our knowledge of the ecology of Campylobacter, and in the not-so-distant future, egg passage will not be a subject continuously debated but will be embraced, thus allowing the development and implementation of more effective intervention strategies.

Transmission and shedding patterns of Salmonella in naturally infected captive wild roof rats (Rattus rattus) from a Salmonella-contaminated layer farm

Rodents play a major role in the transmission and maintenance of Salmonella contamination cycles in poultry facilities. However, very limited field data are available regarding the transmission routes, infection cycle, and shedding patterns of Salmonella by naturally infected wild rodents from commercial layer farms. In this study, a total of 128 resident wild roof rats (Rattus ratus) were captured from a Salmonella-contaminated layer facility. All roof rats were divided into 51 laboratory cages, and weekly monitoring of Salmonella fecal shedding patterns was conducted for 53 wk. Seven roof rats from cages that were observed to frequently shed Salmonella were isolated in individual cages, and daily Salmonella monitoring was performed for 35 days. At the end of monitoring, each roof rat was euthanatized, and isolation of Salmonella from different organs was performed. Results of weekly monitoring of Salmonella showed that 21 of 51 cages (41.2%) were positive for Salmonella Infantis, while two cages (3.92%) were positive for Salmonella Enteritidis. Moreover, 11 cages were positive for Salmonella for at least two sampling weeks. Isolation of Salmonella from fecal droppings was mainly observed during the first 12 wk of captivity. The longest interval between two Salmonella-positive fecal dropping was 24 wk. In the daily Salmonella monitoring, only Salmonella Infantis was isolated from fecal droppings, in which the highest number of Salmonella Infantis organisms per fecal dropping was at 1 x 10(8) colony-forming units (cfu), while the lowest measured quantity was 1 x 10(3) cfu. It was noted that the frequency of Salmonella shedding in fecal droppings appeared to have a linear correlation (r = 0.85) with the number of Salmonella organisms (cfu) per fecal pellet (P < 0.05). Moreover, pulsed-field gel electrophoresis analysis of Salmonella Infantis isolates revealed a single identical pulsed-field pattern. Salmonella Enteritidis isolates from fecal droppings and internal organs also generated a single identical pulsed-field pattern. Interestingly, Salmonella Infantis was not isolated from any of the organs examined, while Salmonella Enteritidis was isolated from the spleen and liver of one roof rat. These results may indicate that wild roof rats could persistently carry Salmonella and contaminate commercial poultry facilities through intermittent fecal shedding. Moreover, Salmonella Enteritidis in wild roof rats appears to be more of a systemic infection, in which isolation is most likely to occur in internal organs, whereas Salmonella Infantis is more likely an enteric type of infection, in which isolation is most likely to occur in the intestinal contents. It is very plausible that layer chickens could become infected with Salmonella through ingestion of Salmonella-positive fecal droppings or feeds contaminated with these fecal droppings from infected resident roof rats. This is likely one of the major reasons why layer houses can be persistently infected by Salmonella even if the facilities are thoroughly cleaned and disinfected and if replacement stocks are obtained from Salmonella-free breeders and rearing units. It is therefore a noteworthy suggestion that rodent control programs inside poultry premises comprise an essential and effective tool in the management and control of Salmonella contamination in layer flocks.

Variation in Salmonella enteritidis RAPD-PCR patterns may not be due to genetic differences

Salmonella Enteritidis is a leading cause of gastroenteritis associated with consumption of contaminated poultry meat and eggs. Because pulsed-field gel electrophoresis (PFGE) has limited utility in distinguishing between clonal Salmonella Enteritidis isolates, random amplified polymorphic DNA (RAPD) PCR has been recommended as an alternative molecular fingerprinting tool. This study's objective was to determine whether increasing PCR stringency would improve the repeatability of RAPD DNA patterns based on assessment of target sites within the genome. An in silico PCR was performed to predict amplification products from an Salmonella Enteritidis genome sequence for three different RAPD primers (1247, 1283, and OPA4) and to determine whether any primer would be more likely to amplify variable regions within the genome. A comparison of within- and between-isolate similarities in RAPD patterns was performed using primer 1247, which was predicted by in silico analysis to yield a variable size range of amplicons. In order to reduce artifactual variability associated with the method, three different methods for template preparation were evaluated. All were found to provide comparable results with respect to the similarities observed with repeated analyses of the same Salmonella Enteritidis isolates (n = 18, P = 0.91). Although the median within-isolate similarity (76.0%) was significantly greater than the median between-isolate similarity (66.7%; P = 0.001), duplicate RAPD-PCR runs of the same Salmonella Enteritidis isolates produced DNA patterns that ranged in similarity between 61.5 and 100%. These results indicate that the repeatability of RAPD-PCR is insufficient to distinguish genetic differences among related and unrelated Salmonella Enteritidis isolates.

Risk factors for Salmonella prevalence in laying-hen farms in Japan

Human salmonellosis cases, particularly those caused by Salmonella Enteritidis, have been closely linked to egg consumption. This epidemiological survey was conducted to determine the baseline Salmonella prevalence and identify the risk factors for Salmonella prevalence in laying-hen farms in Japan. Caecal excrement samples and dust samples were obtained from 400 flocks in 338 laying-hen farms. Salmonella was identified in 20·7% of the farms and 19·5% of the flocks. The prevalence of Salmonella was significantly higher in flocks reared in windowless houses than in those reared in open houses. In addition, the risk of Salmonella presence was significantly higher when the windowless house farms implemented induced moulting or in-line egg processing. Efforts to reduce human salmonellosis in Japan should continue to focus on the establishment of control measures in laying-hen farms, especially those with windowless houses implementing induced moulting and equipped with in-line egg processing.

Analysis of microbiological and chemical quality of poultry meat in the vicinity of the Mbeubeuss landfill in Malika (Senegal)

A total of 100 samples of poultry meat were collected in poultry farms in the vicinity of the Mbeubeuss landfill in the Niayes (Senegal) for microbiological and chemical analysis. Fifty-four (54) samples were collected in farms located less than 1 km from the landfill and 46 samples were collected in farms located a bit further (more than 1 km from the landfill). Microbiological quality was determined using techniques recommended by Association Française de Normalisation (AFNOR). Lead and cadmium concentration in poultry meat was measured by flame spectrometry while total mercury was determined by atomic absorption spectrometry. Three percent (3%) of the samples' quality were unsatisfactory for E. coli, 1% for Staphylococci and 7% for Salmonella spp. Poor meat quality was found either in farms located less than 1 km of the landfill or in farms located at more than 1 km of the landfill. Except for Salmonella, only meat samples from poultry receiving drinking water from well showed unsatisfactory microbiological quality. The samples were free of cadmium and lead but were contaminated by mercury. Sixty-eight percent (68%) of the samples contained mercury with a high contamination level (>0.011 mg/kg) in 20% of the samples. No significant difference was found between the farms that were nearest to and further away from the landfill while the source of drinking water seemed to be the main cause of contamination of poultry meat by mercury.

Nationwide survey of salmonella prevalence in environmental dust from layer farms in Japan

A nationwide survey was conducted to determine Salmonella prevalence in airborne dust from layer farms. Of the 4,090 layer farms in Japan, 203 were surveyed and 48 (23.6%) of these were positive for Salmonella. Salmonella isolation rates were higher in the eastern (24.3%), central (25.6%), western (23.9%), and southern (27.5%) prefectures than they were in the northern (13.3%) prefecture. We recovered 380 Salmonella isolates and identified 34 different Salmonella serovars. Salmonella Infantis was the most prevalent serovar (42 [11.1%] of 380), followed by Salmonella Agona (39 [10.3%] of 380), Salmonella Mbandaka (37 [9.7%] of 380), Salmonella Cerro (32 [8.4%] of 380), Salmonella Thompson (29 [7.6%] of 380), and Salmonella Braenderup (27 [7.1%] of 380). Of the 380 isolates, 273 (71.8%) were resistant to more than one antibiotic. Salmonella Infantis (41 [97.6%] of 42), Salmonella Agona (38 [97.4%] of 39), and Salmonella Mbandaka (34 [91.9%] of 37) showed the highest resistance rates. We found 18 different resistance patterns and the most common (179 [47.1%] of 273) was resistant to dihydrostreptomycin. One of the 13 Salmonella Hadar isolates was resistant to eight antibiotics. To investigate characteristics of Salmonella Agona, Salmonella Infantis, and Salmonella Mbandaka isolates across different prefectures, we performed pulsed-field gel electrophoresis by using XbaI and BlnI. The Salmonella Agona and Salmonella Mbandaka dendrograms were grouped into seven clusters, with 80 and 70% similarity, respectively. Because the Salmonella Infantis dendrogram showed low similarity, there is a possibility of genetic diffusion of this serovar across Japan. This report is the first to describe Salmonella contamination in airborne dust from layer farms in Japan. Our findings should be useful for future Salmonella infection monitoring and control.

Characterization of 13 multi-drug resistant Salmonella serovars from different broiler chickens associated with those of human isolates

Background

Salmonella are frequently isolated from chickens and their products. Prevalent serogroups and serovars of Salmonella as well as their genotypes and antibiograms were determined for cloacal samples from 1595 chickens. To understand the possible serovar and H antigens for transmission between chicken and human, serovars and their H antigens of 164 chicken and 5314 human isolates were compared.

Results

Prevalence of Salmonella differed among chicken lines and ages. Chicken and human isolates belonged mainly to serogroup B, C1, C2-C3, D, and E. 13 serovars and 66 serovars were identified for chicken and human isolates respectively. The common serovars for chicken and human isolates were S. Typhimurium, S. Enteritidis, S. Albany, S. Derby, and S. Anatum and shared common H1 antigens "g complex; i; e,h; and z4,z24" and H2 antigens "1 complex and -". In human isolates, H1 antigen "i" and H2 antigen "-" were common in all serogroups. In chicken, antimicrobial susceptibility differed among serogroups, serovars and three counties. All isolates were susceptible to cefazolin and ceftriaxone, but highly resistant to ampicillin, chloramphenicol, flumequine, streptomycin, sulfamethoxazole-trimethoprim, and tetracycline. Except those isolates of serogroup C1 of Chick group and serogroup G, all isolates were multi-drug resistance. Only S. Kubacha, S. Typhimurium, S. Grampian, and S. Mons were resistant to ciprofloxacin and/or enrofloxacin.

Conclusion

In chicken, prevalent serogroups and serovars were associated with chicken ages, lines and regions; and flouroquinolone-resistant and MDR isolates emerged. H1 antigens "g complex and i" and H2 antigens "1 complex and -" might be important for transmission of Salmonella between chicken and human.

The role of roof rats ( Rattus rattus) in the spread of Salmonella Enteritidis and S. Infantis contamination in layer farms in eastern Japan

The prevalence of Salmonella in four layer farms in eastern Japan was investigated between 2004 and 2006 to determine the role of roof rats (Rattus rattus) in the epizootology of Salmonella enterica subsp. enterica serovar Enteritidis (S. Enteritidis). Persistent S. Enteritidis and S. Infantis contamination of the environment and pooled egg samples were detected in three out of four layer farms. A total of 113 (13.3%) and 158 (18.6%) out of 851 rats examined were positive for S. Enteritidis and S. Infantis, respectively. By pulsed-field gel electrophoresis, only one indistinguishable pulsed-field pattern was yielded by S. Enteritidis strains from rats, eggs and environmental samples from each of the two contaminated layer farms. Although, a variety of pulsed-field patterns were generated by S. Enteritidis isolates from rats, eggs, and the environment of the other contaminated farms, there are, however, some S. Enteritidis strains that are closely related clones. These results suggest that roof rats are carriers of S. Enteritidis and S. Infantis and that persistent S. Enteritidis and S. Infantis infections in a rat population may play an important role in the spread and maintenance of these pathogens inside the layer premises.

Salmonella enterica subsp. enterica serovar Agona infections in commercial pheasant flocks

Infections in pheasant flocks due to Salmonella enterica subsp. enterica serovar Agona occurred in a commercial pheasant farm in 1995 and 2000. S. enterica serovar Agona isolates obtained from the affected birds in both years and an environmental sample from 1998 showed an identical pulsed-field gel electrophoresis pattern, indicating that the farm was continually contaminated with the strain during this period. Nine hundred and seventy-three of 1850 birds (56.2%) died at 4 to 5 days of age in 1995, whereas 80 of 2004 birds (4%) died at 15 to 25 days of age in 2000. Pericarditis were found in the birds in both years although infiltration of heterophils in the lesion was more remarkable in the birds in 2000 than those in 1995, indicating that the S. enterica serovar Agona infection in pheasants in 1995 may have led to the rapid death. These observations suggest that susceptibility of pheasants to S. enterica serovar Agona is age dependent.

An epidemiological analysis of Salmonella enteritidis contamination in a rat-infested chicken layer farm, an egg processing facility, and liquid egg samples by pulsed-field gel electrophoresis

In order to determine the epidemiological link between the Salmonella Enteritidis contamination in a rat-infested chicken layer farm, an attached egg processing facility and liquid egg samples, several S. Enteritidis isolates were analyzed by pulsed-field gel electrophoresis (PFGE) and bacteriophage typing. A total of 33 S. Enteritidis strains were isolated from a total of 4,081 samples. Similar pulsed-field patterns were generated by S. Enteritidis isolates from liquid eggs, rats and effluent water. Additionally, only two phage types were detected among the S. Enteritidis isolates, PT 1b and PT 6. These results suggest that S. Enteritidis isolates from rats, egg processing facility, and liquid eggs are genetically related. Furthermore, S. Enteritidis infection in rats in layer farms poses a serious public health concern and should be included in future epidemiological studies.

Effects of different molting procedures on incidence of Salmonella infection in flocks of naturally contaminated laying hens in a commercial egg-producing farm by detection of yolk antibodies to Salmonella in eggs

Indirect enzyme-linked immunosorbent assays (ELISAs) have been applied to detect immunoglobulin Y antibodies to different serotypes of Salmonella in the yolks of chicken eggs with heat-extracted antigens of Salmonella enterica serotypes Agona (SA), Cerro (SC), Enteritidis (SE), Montevideo (SM), and Putten (SP). The egg yolk samples examined were classified as positive if their ELISA absorbance values exceeded the value for eggs from specific-pathogen-free flocks by more than two standard deviations. Of 30 egg yolk samples from three flocks vaccinated with a killed SE vaccine, 29 were antibody positive by the ELISA assay for the SE antigen. Four to 29 of the 29 yolk samples showed positive results for the other serovars, although the absorbance values for SE were higher than those obtained for the other serotypes in each of the yolk samples. All 30 yolks from three flocks that were not administered any SE vaccines were found to be antibody negative for SE, and two samples were determined to be positive for SC. Thirty-nine or 40 eggs were obtained from each of four layer flocks in a commercial egg production farm where the laying houses were naturally contaminated with SA, SC, SM, SP, Salmonella serovar Infantis (SI), and untypeable strains. The ELISA absorbance values for SM in the egg yolks obtained from the two flocks molted through feed withdrawal when the birds restarted laying were significantly (P < 0.05) higher than those observed in the yolks obtained before the molt. In egg yolks from the two other flocks that were molted through a wheat bran diet, there was no significant difference between the absorbance values before and after the molt. The observations in the present study provide further evidence to suggest that a molt initiated through the administration of a wheat bran diet can reduce the risk for Salmonella problems in a commercial egg-producing setting.

Molecular characterization and occurrence of extended-spectrum beta-lactamase resistance genes among Salmonella enterica serovar Corvallis from Thailand, Bulgaria, and Denmark

Fifty nine Salmonella Corvallis isolates from humans and food products in Bulgaria, Denmark, and Thailand were examined for antimicrobial susceptibility and characterized by pulsed-field gel electrophoresis (PFGE). Cephalosporin-resistant isolates were examined for the presence of genes encoding beta-lactamases by PCR and sequencing. Ten different PFGE types were observed. One type (30 isolates) was recovered in all three countries; three types were found only in Bulgaria, two only in Denmark, two only in Thailand, and two both in Denmark and Thailand. Ten isolates were susceptible to all antimicrobial agents tested, whereas 41 were resistant to three or more antimicrobials. Most resistance was observed among the isolates from Bulgaria. Of the 25 isolates from Bulgaria, 20 displayed resistance to ampicillin and the cephalosporins ceftiofur and cephalothin. All 20 isolates tested negative for bla (CMY-1), bla (CMY-2), and bla (ACC), but positive for bla (SHV), of which five were sequenced to bla (SHV-2). Plasmid profiling and hybridization revealed that the bla (SHV) gene was located on plasmids of approximately 70 kb. Five plasmid profiles were found among these 20 isolates. The plasmid profiling confirmed the PFGE-type and was able to further subdivide the strains. Seventeen of these 20 isolates contained also bla (TEM), of which nine representatives were sequenced to bla (TEM-1B), or bla (TEM-1H). One isolate contained bla (CTX-M-15), bla (SHV-2), and bla (TEM-1H), with the bla (CTX-M-15), and bla (TEM-1H) genes located on a 63-kb transferable plasmid. This study showed a high frequency of resistance among S. Corvallis isolated from humans and food products in Bulgaria, with a lower frequency in Thailand and Denmark. The clonal relatedness among the isolates from three countries could indicate a recent spread of this serovar.

Multiplication and motility of Salmonella enterica serovars enteritidis, infantis, and montevideo in in vitro contamination models of eggs

The invasive ability of Salmonella enterica serovars Enteritidis, Infantis, and Montevideo in eggs was examined. Strains of these serovars originating from egg contents, laying chicken houses, and human patients were experimentally inoculated (0.1-ml dose containing 78 to 178 cells) onto the vitelline membrane of eggs collected from specific-pathogen-free chickens and incubated at 25 degrees C. The test strains were detected in 25 of 138 yolk contents by day 6, indicating the penetration of Salmonella organisms through the vitelline membrane. There were no significant differences in overall rates of penetration between serovars. The organisms were also detected in the albumen from 125 of 138 eggs tested by day 6. Growth to more than 10(6) CFU/ml was observed in 48 of the 125 albumen samples. An inoculum of 1000 Salmonella cells was added to 15 ml of albumen at the edge of a petri plate. A 10-mm-diameter cylindrical well, the bottom of which was sealed with a polycarbonate membrane with 3.0-microm pores, was filled with egg yolk and placed into the albumen at the center of the dish, which was maintained at 25 degrees C. Experiments were performed in triplicate with each strain. Salmonella organisms in all the albumen samples were detected by day 11. However, motility of the organisms toward the yolk was observed in only two dishes inoculated with the Salmonella Enteritidis strain from a human patient and in one dish inoculated with the Salmonella Infantis strain from liquid egg. The albumen samples obtained from the dishes inoculated with the Salmonella Enteritidis strain had high numbers of bacteria (>10(8) CFU/ml). The present study suggests that Salmonella organisms in egg albumen are unlikely to actively move toward the yolk, although depositionon or near the vitelline membrane can be advantageous for proliferation.

Detection of Salmonella enterica in naturally contaminated liquid eggs by loop-mediated isothermal amplification, and characterization of Salmonella isolates

Loop-mediated isothermal amplification (LAMP) assay was effective in detecting Salmonella enterica in naturally contaminated liquid egg samples. Salmonella was detected in 110 samples taken from four egg-breaking plants. The egg samples were pre-enriched in buffered peptone water (BPW) at 37 degrees C for 20 h. The selective enrichment was done in Rappaport-Vassiliadis or tetrathionate broth and plated onto xylose lysine deoxycholate agar and brilliant green agar, modified. In addition, the PCR assay was used to detect Salmonella after pre-enrichment in BPW at 37 degrees C for 20 h. The culture method and PCR assay were compared to the LAMP assay, which was also performed after pre-enrichment in BPW. PCR failed to detect Salmonella in 10% of 110 samples, whereas the culture method and LAMP assay successfully identified Salmonella in all samples. However, the LAMP assay was found to be much more rapid than the culture method and as sensitive in detecting Salmonella from liquid eggs. In all of the egg-breaking plants studied, Salmonella was isolated on most tested days. The positive samples showed that more than 75% of the Salmonella strains had identical genetic patterns when analyzed by pulsed-field gel electrophoresis. This suggests that the same Salmonella strains having survived long periods of time in the plants were contaminating the production line. The LAMP assay is rapid, specific, and sensitive for Salmonella detection in liquid eggs and is able to monitor Salmonella contamination in egg-handling plants more reliably.

Impact of commercial processing on the microbiology of shell eggs

Shell egg microbiology has been studied extensively, but little information is available on how modern U.S. processing conditions impact microbial populations. As regulations are being drafted for the industry, such information can be important for determining processing steps critical to product safety. Five different shell egg surface microbial populations (aerobic bacteria, yeasts and molds, Enterobacteriaceae, Escherichia coli, and Salmonella) were monitored at 12 points along the processing line (accumulator, prewash rinse, washer 1, washer 2, sanitizer, dryer, oiler, scales, two packer head lanes, rewash entrance, and rewash exit). Three commercial facilities were each visited three times, a total of 990 eggs were sampled, and 5,220 microbiological samples were subsequently analyzed. Although variations existed in concentrations of microorganisms recovered from each plant, the patterns of fluctuation for each population were similar at each plant. On average, aerobes, yeasts and molds, Enterobacteriaceae, and E. coli prevalence were reduced by 30, 20, 50, and 30%, respectively, by the end of processing. The microbial concentrations (log CFU per milliliter) in the egg rinse collected from packer head lanes were decreased by 3.3, 1.3, 1.3, and 0.5, respectively, when compared with those of rinses collected from eggs at the accumulator. Salmonella was recovered from 0 to 48% of pooled samples in the three repetitions. Higher concentrations of Salmonella were recovered from preprocessed than from in-process or ready-to-pack eggs. These data indicate that current commercial practices decrease microbial contamination of egg shell surfaces.

Antimicrobial susceptibilities of Salmonella isolates obtained from layer chicken houses on a commercial egg-producing farm in Japan, 1997 to 2002

Susceptibility to antimicrobial agents was examined for 325 isolates of Salmonella enterica serotypes Cerro, Infantis, Livingstone, and Montevideo isolated from layer houses on a commercial egg-production farm in the western region of Japan between 1997 and 2002. No antimicrobials were used for therapeutic purposes on the farm during this period. From 1.8 to 3.1% of the isolates were resistant to ampicillin, chloramphenicol, and tetracycline. Resistance to streptomycin and sulfisoxazole was found in 52.9 and 65.5%, respectively, of Salmonella Montevideo isolates and in 0 to 13.2% of the isolates of the other serotypes. All the streptomycin-resistant isolates of Salmonella Montevideo also exhibited resistance to sulfisoxazole. Salmonella Montevideo isolates were first isolated in 1998, and 80.0% of the isolates obtained in this year were resistant to streptomycin and sulfisoxazole. The results suggest that Salmonella Montevideo isolates that had already acquired resistance may have been introduced into the layer houses, although the route and vehicle of transmission were uncertain. The proportion of Salmonella Montevideo isolates resistant to streptomycin and sulfisoxazole significantly decreased (P < 0.01) from 79.5% for 1998 through 1999 to 37.3% for 2000 through 2002. This decrease probably was due to the fact that no antimicrobials were used on the farm. Among 10 isolates from different serotypes obtained from 1997 to 2002 that were resistant to ampicillin, two and five isolates harbored 42- and 63-kb R plasmids and identical DraI restriction enzyme digest patterns, respectively, and carried the blaTEM gene. The results suggest that the ampicillin resistance determinants were transferred among different serotypes of Salmonella in the layer houses.

Impact of science and management on the welfare of egg laying strains of hens

Discoveries in behavior and welfare science have improved the health and well-being of egg laying flocks of chickens. The objectives of this review are to highlight research findings in genetics, health, environment, molting, morphological alterations, euthanasia, handling during depopulation, transportation, and harvesting to improve poultry welfare and to provide examples of additional opportunities to continue this progress. Although selection for disease resistance has improved the welfare of birds, use of genetic marker technologies may eventually advance the selection of healthier birds with fewer metabolic disease and cannibalistic tendencies. Animal health and welfare have been improved through development of vaccines, establishment of stringent biosecurity measures, and training of animal caretakers. Industry is currently making adjustments in bird space allocations to allow for less crowded conditions. Continued research in molting shows promise to avoid feed withdrawal regimens for laying hens. Beak trimming by trained personnel improves livability, reduces cannibalism, and should be used when nonaggressive strains are unavailable and when light intensity cannot be controlled. Extension specialists and veterinarians provide information on proper procedures for euthanasia. New systems for euthanasia of spent hens are being implemented by egg producers. New opportunities exist for use of enrichments in production facilities to offer environmental complexity. Further research on how sound and odors affect birds could provide new avenues for improving production systems.

Vertical and Horizontal Transmission ofSalmonellaWithin Integrated Broiler Production System

Salmonella remains one of the leading causes of food-borne illness in the United States, and many key questions regarding the introduction and persistence in animal production systems still remain. In order to understand the ecology of Salmonella within an integrated commercial broiler production system, 289 Salmonella enterica were recovered from two integrated poultry farms during the production and processing of seven consecutive flocks. The variety and prevalence of Salmonella serotypes differed between farms. Overall, 15 serotypes were identified, with the most common being Typhimurium (55%), Montevideo (7.9%), Kentucky (9%), and Enteritidis (9.7%). Salmonella Typhimurium and Enteritidis isolates recovered from processed carcasses from Farm One were further characterized using pulsed-field gel electrophoresis (PFGE), and were shown to be indistinguishable from isolates recovered from the poultry house environment and mice trapped on this farm. Additionally, the same broiler S. Typhimurium and S. Enteritidis strains, identified by PFGE, were also isolated from samples taken at a company breeder farm, suggesting vertical transmission of these Salmonella serotypes in this poultry production system. Results indicate that management practices at the breeder level may have a profound effect on the transmission and persistence of salmonellae within an integrated production system, as well as on the potential contamination of poultry-derived products.

The effect of killed Salmonella enteritidis vaccine prior to induced molting on the shedding of s. enteritidis in laying hens

Effects of administering killed Salmonella enterica serovar enteritidis (SE) vaccines to laying hens prior to induced molting on egg production and on shedding of SE were investigated. Forty hens were vaccinated with one of two SE vaccines available commercially in the United States and Japan. Twenty-five days after vaccination, feed was withdrawn for 2 wk from 20 vaccinated plus 10 unvaccinated hens to induce molt. Four days after molt induction, all hens were challenged with a dose of 2.4 X 10(9) of SE. For the 25 days following administration of the SE bacterins, egg production in vaccinated hens showed approximately a 15% decrease. After molt induction, egg production in molted hens ceased and then returned to normal levels 8 or 9 wk postvaccination. Through the 3-mo experimental period, the decreases in numbers of eggs laid in the unvaccinated/molted group and two vaccinated/molted groups were 225 (26.2%), 245 (28.4%), and 274 (31.9%), respectively, compared with 860 in the unvaccinated/unmolted group. There was no significant difference in egg lay at the P < 0.05 level among the former three groups. Hens in the vaccinated/molted groups shed about two logs less SE than hens in the unvaccinated/molted group 3 14 days postchallenge (P < 0.05 or 0.01). These results indicate that vaccination prior to induced molting might be effective in preventing the exacerbation of SE problems within flocks in which the potential for SE contamination may exist.

Effects of prior coinfection with different Salmonella serovars on the progression of a Salmonella enterica serovar enteritidis infection in hens undergoing induced molt

Four trials were conducted to evaluate whether prior infection with Salmonella enterica serovar typhimurium (S. typhimurium) or Salmonella enterica serovar muenchen (S. muenchen) would modify the severity or the transmission of Salmonella enterica serovar enteritidis (S. enteritidis) challenge in hens undergoing molt via feed withdrawal. Hens were separated into two groups where one group received a prior S. typhimurium or S. muenchen infection, whereas the other group remained untreated until S. enteritidis challenge. In trials 1 and 2, one group of hens was infected with S. typhimurium 5 days prior to feed withdrawal. Both groups of hens were then challenged with S. enteritidis on day 4 post feed withdrawal. In trials 3 and 4, one group of hens received S. typhimurium or S. muenchen, respectively, 1 day after feed was withdrawn. Transmission of S. enteritidis was evaluated by challenging the center hen in rows of 11 hens per row with S. enteritidis at 4 days post feed withdrawal and following the progression of the S. enteritidis down the row of hens over time. In trials 1 and 2, where hens received S. typhimurium 5 days prior to feed withdrawal, shedding of the S. enteritidis challenge was significantly reduced in hens on day 10 postchallenge in trial 1 and on days 3 and 10 postchallenge in trial 2 compared with the hens subjected only to the molt procedure. Significantly fewer S. enteritidis were recovered in livers and spleens at day 9 postchallenge in trial 2 from hens receiving the prior S. typhimurium infection. In trial 3, where hens received S. typhimurium 1 day after feed withdrawal, S. enteritidis transmission was significantly reduced in these hens on days 3, 10, and 24 postchallenge. In trial 4, similar in methodology to trial 3 except that, rather than S. typhimurium, hens received S. muenchen, a Salmonella organism totally lacking any antigen cross-reactive with S. enteritidis, S. enteritidis transmission was significantly reduced on days 3, 10, 17, and 24 postchallenge, suggesting that factors other than specific immunity were involved in the observed resistance to S. enteritidis infection. These results indicate that prior infection of a flock with a non-S. enteritidis paratyphoid Salmonella can reduce S. enteritidis problems that may occur during a molt.

Pulsed-field gel electrophoresis-based subtyping of DNA degradation-sensitive Salmonella enterica subsp. enterica serovar Livingstone and serovar Cerro isolates obtained from a chicken layer farm

Salmonella enterica serovar subsp. enterica Livingstone and serovar Cerro isolates from a commercial egg-producing farm, which had previously been untypeable by pulsed-field gel electrophoresis (PFGE) because of DNA degradation during the PFGE process, successfully gave banding patterns using electrophoresis buffer supplemented with 50 microM thiourea. By PFGE in the presence of thiourea, DNA degradation-sensitive S. enterica serovar Cerro isolates from the commercial egg-producing farm were found to be genetically unrelated to S. enterica serovar Cerro isolates that gave the patterns in the absence of thiourea. Forty-five of 50 (90%) S. enterica serovar Livingstone isolates from the farm showed arbitrarily designated XbaI-digested patterns X1 and X2 that were distinguished by one-band difference and had an identical BlnI-digested pattern. In one of the two layer houses in the farm, the numbers of isolates having the pattern X2 increased from 57% in 1997 to 89% in 1998, whereas virtually all the isolates obtained from the other house in the same period showed the profile X1. This suggests that strains having the pattern X2 might have an advantage to preferentially colonize in the former house.

Molting and Salmonella enterica serovar enteritidis infection: the problem and some solutions

Induced molting is an important economic tool used by the egg industry to recycle an aging layer flock. It is estimated that approximately 70% of the flocks nationwide and almost 100% in California are molted annually. Considering that there are approximately 240 million hens in production in the U.S., a rough estimate of the numbers of hens molted every year would be between 144 and 168 million birds, a substantial number. There are many methods to induce molt, but feed removal until hens lose a specific weight is the most prevalent molt strategy in the U.S. However, experimental studies in our laboratory have shown that induced molting via feed removal depresses the immune system of hens and exacerbates a Salmonella enteritidis (SE) problem in a simulated flock situation. Molted hens excreted significantly higher SE numbers in the feces, had higher numbers of SE in internal organs, and exhibited more intestinal inflammation. Molted hens were 100- to 1,000-fold more susceptible to infection by SE and therefore more readily transmitted the organism to uninfected hens in neighboring cages. With the problems identified, solutions were sought, and several were successful in ameliorating the SE issue. Antibiotic therapy, vaccination, and use of low-energy, low-calcium diets to molt hens all dramatically decreased SE shedding during molt. All of the solutions provide the producer with many potential solutions to the SE food safety issue and still allow them to recycle their hens.