Study of the cross-contamination and survival of Salmonella in fresh apples.

The present work aimed at studying the cross contamination of apples by Salmonella during the processing of commercial fresh apples and its survival capacity on apple at room temperature. For the first study, the typical process of fresh apples was simulated at laboratory scale in which an apple that was artificially contaminated by Salmonella at different concentration levels (8, 6 and 5 log cfu/apple) was introduced in one batch and processed including a simulated transport/washing step and drying step using sponges to simulate the porous material used in the industry. Results indicated that at 8 log cfu/apple, 50% fresh apples were contaminated after processing, with all analysed environmental samples being positive for the pathogen, consisting of washing water and sponges. However, at lower inoculum levels (5-6 log cfu/apple) no cross contamination was detected in apples, and only environmental samples showed contamination by Salmonella after processing including both water and sponges. Experiments on the survival of Salmonella on apple showed that the pathogen was capable to survive for 12 days, only showing a significant drop at the end of the experiment. Finally, two-class attribute sampling plans were assessed as tool to detect Salmonella in different contamination scenarios in fresh apple. This analysis indicated that with the highest inoculum level, a total of 16 apples would be needed to reach 95% of detecting Salmonella (i.e. lot rejection). In turn, when low levels were assessed (5-6 log cfu/apple), a large number of apples (n=1021) would have to be sampled to obtain the same confidence level (95%). If the environment is sampled (i.e. water and sponges), a lower number of samples would be needed to detect the pathogen. However, the feasibility of environmental sampling has not been assessed from a practical point of view. Overall, the results in this study evidenced that cross contamination by Salmonella might occur during processing of fresh apples and subsequently, the pathogen might survive for a noticeable period of time.

Prevention of intestinal Campylobacter jejuni colonization in broilers by combinations of in-feed organic acids.

AIM: We have tested the effect of various combinations of formic acid and sorbate on Campylobacter jejuni colonization in broiler chickens to reduce the colonization of this zoonotic pathogen in broiler chicken flocks. METHODS AND RESULTS: Chickens were offered feed supplemented with different concentrations and combinations of formic acid and/or potassium sorbate. We found little or no effect on the Camp. jejuni colonization levels in chickens that were given feed supplemented with formic acid alone. A combination of 1.5% formic acid and 0.1% sorbate reduced the colonization of Camp. jejuni significantly, while a concentration of 2.0% formic acid in combination with 0.1% sorbate prevented Camp. jejuni colonization in chickens. This inhibition was replicated in two independent trials with a combination of three different Camp. jejuni strains. CONCLUSIONS: Our results show a novel and promising intervention strategy to reduce the incidence of Camp. jejuni in poultry products and to obtain safer food. SIGNIFICANCE AND IMPACT OF THE STUDY: To ensure food safety, a reduction of the carcass contamination with Camp. jejuni through reduced colonization of this pathogen in broiler chicken flocks is important. A range of organic acids as additives in feed and drinking water have already been evaluated for this purpose. However, no studies have yet shown a complete inhibition of Camp. jejuni colonization in broiler chickens.

Shigella sonnei infections in Norway associated with sugar peas, May-June 2009.

In May 2009, the Norwegian Institute of Public Health (NIPH) identified a possible outbreak of Shigella sonnei infection involving four cases. Additionally, five suspected cases in two separate households were reported. Inspectors from the Norwegian Food Safety Authority (NFSA) visited the two households and found an unopened package of sugar peas imported from Kenya in one of the households. One sample from the sugar peas was positive for Shigella sonnei by two PCR methods. Based on this result and information from patient interviews, the NFSA prohibited all sales of sugar peas imported from Kenya.

Enumeration of thermotolerant Campylobacter spp. from poultry carcasses at the end of the slaughter-line.

AIM: To enumerate Campylobacter on poultry carcasses at the end of the slaughter-line, and investigate the extent to which Campylobacter from a positive flock were transmitted to other flocks during slaughter. METHODS AND RESULTS: The presence (in caeca) and the level (from carcasses) of Campylobacter were determined. The isolates were fingerprinted by amplified fragment length polymorphism (AFLP). A total of three of 13 broiler flocks and three of four-layer flocks harboured caecal Campylobacter. Carcasses from the caeca-positive broiler flocks were Campylobacter positive with numbers ranging from 2.6 x 10(4) to 2.6 x 10(6) CFU per carcass. Two caeca-negative broiler flocks, slaughtered directly after the positive broiler flocks, had the first carcasses contaminated with Campylobacter, with numbers below 2 x 10(4) CFU per carcass of the same AFLP haplotypes as the preceding flock. Campylobacter was detected on carcasses from only one of the caeca-positive layer flocks in numbers below 2 x 10(4) CFU per carcass. No Campylobacter was detected on carcasses from a flock succeeding the positive-layer flocks. CONCLUSION: Carcasses from Campylobacter-positive broiler flocks were heavily contaminated with Campylobacter, and transmitted low levels of Campylobacter to carcasses from negative flocks, slaughtered directly after. Campylobacter-positive layer flocks had low numbers of Campylobacter on the carcasses. SIGNIFICANCE AND IMPACT OF THE STUDY: The results indicate limited cross-contamination of Campylobacter between flocks at the slaughterhouse, reducing the advantage of logistic slaughter.

Genetic variability of Campylobacter jejuni isolated from fresh and frozen broiler carcasses.

AIMS: The aim of this study was to determine the genetic variability of Campylobacter jejuni isolates from poultry before and after freezing treatment in order to identify genotypes that would survive the treatment. METHODS AND RESULTS: C. jejuni was isolated from both fresh and frozen halves of the same carcass after freezing for 2 or more than 20 days at -20 degrees C. From 36 carcasses, representing five unrelated flocks in Norway, a total of 209 isolates were included in the study. Thirty-two of the isolates were recovered with a qualitative method while the remaining 177 were isolated using a quantitative method. Isolates were genotyped with fluorescent amplified fragment length polymorphism using MfeI and BglII restriction enzymes. Nine different genotypes were identified, however, one genotype was shown to be dominant in three different flocks. This genotype and the dominant genotype of another flock were found among isolates from fresh and frozen broiler halves. They were also shown to be identical to genotypes frequently identified among strains isolated from humans, cattle and poultry flocks in previous years. CONCLUSIONS: Freezing treatment or isolation method appeared not to select for a particular genotype. SIGNIFICANCE AND IMPACT OF THE STUDY: The results of the present study indicate that the freezing tolerance of strains is not genotype dependent.

Bacteriological quality of organically grown leaf lettuce in Norway.

AIM: To investigate bacteriological quality in organically grown leaf lettuce, including the presence of selected pathogenic bacteria, and to obtain information about organic lettuce production, including fertilizing regimes. METHODS AND RESULTS: Altogether 179 samples of Norwegian organically grown lettuce were collected from 12 producers. Escherichia coli was isolated from 16 of the lettuce samples, but in 12 of these contamination was sufficiently low (<100 CFU g(-1)) that they would be considered to be of acceptable bacteriological quality. Escherichia coli O157 and Salmonella were not detected in any of the samples. Listeria monocytogenes serogroups 1 and 4 were isolated from two samples. CONCLUSIONS: Organic lettuce produced in Norway was generally of acceptable bacteriological quality, but the results show that contamination of organic lettuce with E. coli and L. monocytogenes do occasionally occur. SIGNIFICANCE AND IMPACT OF THE STUDY: These results suggest that organically grown lettuce may be contaminated with E. coli and L. monocytogenes during cultivation.

Fluctuations in the occurrence of Escherichia coli O157:H7 on a Norwegian farm*.

AIM: To describe the distribution of Escherichia coli O157:H7 on a sporadically positive dairy farm and on possible contact farms over a one-year period. METHODS AND RESULTS: Environmental and faecal samples from all animals at the farm, and faecal samples from animals at contact farms were analysed for E. coli O157:H7 by immunomagnetic separation methods or VIDAS. Confirmed isolates were tested for cytotoxicity in the Vero cell assay and typed by PFGE. Escherichia coli O157:H7 (stx2 and eae) of the same PFGE type were isolated from cattle, sheep, hens and environmental samples at variable levels during summer and fall 2002, but were not detected in 2003. CONCLUSIONS: Escherichia coli O157:H7 had a widespread distribution on the farm investigated, but the original source of contamination could not be identified. The occurrence of this bacterium on the farm did not result in any detectable increase in gastrointestinal disease in the associated population. SIGNIFICANCE AND IMPACT OF THE STUDY: Despite a low endemic level of E. coli O157:H7 in the Norwegian cattle population, the growth and spread of this potentially important bacterium may occur.

Influence of bovine manure as fertilizer on the bacteriological quality of organic Iceberg lettuce.

AIM: To investigate the bacteriological quality, and the occurrence of selected pathogenic bacteria from organically grown Iceberg lettuce fertilized with bovine manure in the form of compost, firm manure and slurry in a 2-year field trial. METHODS AND RESULTS: Samples of soil, fertilizer, fertilized soil, seedlings and lettuce were analysed for aerobic plate counts (APC), thermotolerant coliform bacteria (TCB), Escherichia coli, E. coli O157:H7, Salmonella spp. and Listeria monocytogenes. No difference in bacteriological quality could be shown in lettuce at harvest, however, APC varied significantly from year to year in the study. The various treatments gave significantly different APC and numbers of TCB isolated from fertilized soil. Escherichia coli O157:H7 was isolated from firm manure and slurry, and soils fertilized with the respective fertilizers the second year, but were not recovered from the lettuce. CONCLUSIONS: No difference in bacteriological quality could be detected in lettuce at harvest after application of various types of manure-based fertilizers grown under Norwegian conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: The results may indicate that the use of manure does not have considerable influence on the bacteriological quality of organic lettuce. However, others have suggested that there is a risk by using manure. There is a need for more research in the field.

Occurrence of pathogenic Yersinia enterocolitica in Norwegian pork products determined by a PCR method and a traditional culturing method.

From October 1997 to April 1998, a survey was conducted to assess the occurrence of pathogenic Yersinia enterocolitica in Norwegian pork products, using a traditional culturing method and a PCR assay. A total of 300 pork samples was examined. Five slaughterhouses in the Norwegian Meat Cooperative were represented with 249 samples and another 51 samples were obtained from retail outlets in the city of Oslo. Using the NMKL method, Y. enterocolitica 0:3 was isolated from six (2%) of the samples, while the PCR method indicated presence of pathogenic Y. enterocolitica in 50 (17%) of the samples. The results indicate that a reduction has occurred in the prevalence of pathogenic Y. enterocolitica in Norwegian pork products, as compared to a previous Norwegian study conducted in 1988-1989. The study also highlights the need for further development and improvement of methods applied for the detection of pathogenic Y. enterocolitica in foods.