Dietary effects on the microbiological safety of food.

The high mortality rate associated with human infections caused by Escherichia coli strains of the serotype O157:H7 has brought to public attention the importance of ruminants as reservoirs of food-borne pathogens. In addition to established examples such as salmonella, campylobacter and listeria, recent evidence is emerging of the role of food in the transmission of Helicobacter pylori and Mycobacterium paratuberculosis. Food-borne pathogens harboured by ruminants are spread through shedding in the faeces and subsequent faecal contamination of raw food. Ruminant shedding appears to be affected by diet and, of particular concern, may be increased during fasting regimens imposed during transport to the slaughterhouse. The survival of food-borne pathogens in the ruminant gut is affected by many factors including microbe-microbe interactions, interactions involving plant metabolites and the presence of inhibitory end-product metabolites such as short-chain fatty acids. The potential importance of digesta flow and bacterial detachment in shedding of food-borne pathogens is discussed. Experimental procedures with dangerous pathogens have constraints, particularly in animal experimentation. This situation may be overcome by the use of rumen-simulating fermentors. One such system which, like the natural rumen, has a different turnover rate for solid and liquid digesta, was found to maintain rumen-like variables over an 11 d period. This system may prove useful for the study of dietary effects on food-borne pathogens.

Lytic and lysogenic infection of diverse Escherichia coli and Shigella strains with a verocytotoxigenic bacteriophage.

A verocytotoxigenic bacteriophage isolated from a strain of enterohemorrhagic Escherichia coli O157, into which a kanamycin resistance gene (aph3) had been inserted to inactivate the verocytotoxin gene (vt2), was used to infect Enterobacteriaceae strains. A number of Shigella and E. coli strains were susceptible to lysogenic infection, and a smooth E. coli isolate (O107) was also susceptible to lytic infection. The lysogenized strains included different smooth E. coli serotypes of both human and animal origin, indicating that this bacteriophage has a substantial capacity to disseminate verocytotoxin genes. A novel indirect plaque assay utilizing an E. coli recA441 mutant in which phage-infected cells can enter only the lytic cycle, enabling detection of all infective phage, was developed.

High frequency of metronidazole resistance among strains of Campylobacter jejuni isolated from birds.

A total of 2157 strains of the enteropathogen Campylobacter jejuni were examined for resistance to metronidazole (5 mg l-1). High rates of metronidazole resistance, between 82 and 100%, were observed amongst strains of avian origin, including commercially reared broiler chickens (90.1%, n = 314) and turkeys (92%, n = 100), as well as wild birds sampled from farms and coastal environments, such as starlings (82%, n = 50), and gulls (100%, n = 20). In comparison, isolates from bovine and ovine ruminants were mostly susceptible to metronidazole, including beef cattle (17.3%, n = 653), dairy cows (19.5%, n = 251), grazing sheep (9.0%, n = 55) and lambs at slaughter (5.5%, n = 615). A moderate number of clinical isolates were resistant (62.8%, n = 99). Avian isolates had a higher average minimum inhibitory concentration (MIC) value (15 mg l-1) than cattle, lambs and clinical isolates (3 mg l-1). A June peak was observed in the percentage of metronidazole resistant strains isolated from beef cattle at slaughter. The induction of growth under aerobic and anaerobic conditions did not affect ability to grow in the presence of metronidazole among four test strains. The observations noted in this study indicate a host-phenotype relationship for which resistance to metronidazole may be a useful epidemiological marker.

The seasonal variation of thermophilic campylobacters in beef cattle, dairy cattle and calves.

The epidemiology of clinical cases of campylobacter in temperate climates shows a striking seasonality. In the search for a seasonal environmental reservoir changes in the carriage rate and population size of campylobacters in bovine hosts with time have been measured. Most probable number (MPN) methodology was used to enumerate thermophilic campylobacters in samples taken from the small intestines of beef cattle at slaughter and the fresh faeces of four dairy herds and new-born calves. Statistical analyses revealed significant evidence for seasonal periodicity in the data from dairy herds (P = 0.044). Not only was there a departure from constancy within a 12-month interval but these data revealed a true seasonality, that is, the same periodicity in numbers from one year to the next. Each herd had two peaks per year, in approximately spring and autumn. Peaks coincided in herds on neighbouring farms but those on farms in the north preceded those on farms in the south by 2 and 1 months, respectively (P = 0.0057). Intestinal carriage by beef cattle at slaughter was 89.4% (n = 360) with an average MPN campylobacters per gram fresh weight (MPN gfw-1) of 6.1 x 10(2). Average MPN gfw-1 in faeces from the dairy herds and calves were 69.9 (S.D. 3) and 3.3 x 10(4) (S.D. 1.7 x 10(2)). There was no evidence of seasonal periodicity in the size of the campylobacter population in beef cattle at slaughter. Calves were campylobacter free at birth but became colonized with a few days.

The colonization of turkeys by thermophilic campylobacters.

The rate at which five broods of turkey chicks became colonized by thermophilic campylobacters was investigated. Day-old chicks were normally free of campylobacters on arrival on the farm with colonization beginning within 7 d. The carriage rate was 100% by day 14 in three of the broods and by day 21 in the other two. Higher carriage rates were obtained with enrichment procedures than with direct plating. Two broods were investigated over an extended interval for the number of campylobacters shed in their faeces. In brood A, Campylobacters increased from day l to day 14 concomitant with increase in the carriage rate and in the number of chicks with diarrhoea. By day 39, when the birds were sold to other farms, the excretion rate had reached 6 x 10(7) campylobacters g-1 fresh faeces. Brood B. was monitored over 91 d and showed peaks in Campylobacter numbers on days 19 and 75, corresponding to peaks in the number of diarrhoeic samples. The introduction of new birds into the brood resulted in an increase in the Campylobacter population and in the number of birds with diarrhoea. Campylobacter jejuni was the only species isolated but comprised several different biotypes. Analysis of the number of campylobacters at different sites along the gastrointestinal tract of mature turkeys at slaughter showed that numbers increased with distance from the beak and were highest in the caeca.

Seasonal variation of thermophilic campylobacters in lambs at slaughter.

A survey of the isolation rate and population size of thermophilic campylobacters in lambs at slaughter was carried out to determine the seasonal variation of thermophilic campylobacters in ovine hosts. Isolation rates determined by enrichment methods were always higher than those using direct plating onto selective agar and showed that Campylobacter could be isolated from 91.7% (n = 360) of samples from the small intestine of the lambs. Enumerations (MPN), done monthly over a 2-year period, averaged 4.00 log 10 (n = 1080, S.D. 0.16) campylobacters g-1 fresh weight (fw) intestinal contents with some samples giving values higher than 7 log MPN gfw-1. These results show that the prevalence of thermophilic campylobacters in sheep intended for slaughter is much higher than previously reported. Statistical analyses showed that there was a significant seasonal periodicity in the Campylobacter populations in the small intestines of lambs at slaughter (P = 0.004) but that there was no statistical relationship with environmental parameters such as minimum and maximum temperature, rainfall or hours of sunshine. In an analysis along the length of the intestinal tract of lambs, campylobacters were isolated from 80% of small intestine and 30% of rumen samples, but not from the true stomach, large intestine or caecal samples. A survey of sheep grazing on salt marsh, fell (upland) and farm pasture showed that the isolation rate of thermophilic campylobacters in fresh faeces was substantially lower (29.3% (n = 420)) than that from the small intestine of lambs at slaughter. No significant difference (> 0.05) was found between the isolation rate of campylobacters from faeces sampled in late spring/early summer and autumn, nor between the different types of grazing.

The Orct gene of Drosophila melanogaster codes for a putative organic cation transporter with six or 12 transmembrane domains.

Mutations at the lemming (lmg) locus of Drosophila melanogaster cause apoptotic cell death in dividing imaginal cells. Genomic DNA flanking the P element insertion corresponding to the lmg allele lmg03424 has been cloned and found to give rise to multiple transcripts. Several cDNA clones corresponding to this genomic region were isolated and shown to differ due to alternative splicing. The complete nucleotide sequences of two of the longest cDNAs were determined and found to encode proteins with similarity to mammalian organic cation transporter (OCT) proteins. One cDNA potentially encodes a protein with six transmembrane (TM) domains, corresponding to the N-terminal half of a mammalian OCT protein, whereas the other cDNA potentially encodes a protein with 12 TM domains, corresponding to the complete mammalian OCT protein. The gene giving rise to these alternative transcripts has been named Organic cation transporter-like (Orct). The previously identified Acer gene (Taylor, C.A.M., Coates, D., Shirras, A.D., 1996. The Acer gene of Drosophila codes for an angiotensin-converting enzyme homologue. Gene 181, 191 197) appears to lie within an intron of the Orct gene.

Seasonality of thermophilic Campylobacter populations in chickens.

The small intestines and caeca of chickens were monitored for seasonal variation of thermophilic campylobacters over a 12-month period. There was a significant seasonal fluctuation in the carriage rate which correlated with the following environmental parameters: sunshine hours (P = 0.0003) and minimum (P = 0.007) and maximum temperatures (P = 0.003). The number of campylobacters in the small intestine and caeca also showed significant seasonal variation (P = 0.0008); however, the periodicity in the caeca was significantly different from that in the small intestine (P = 0.007). The numbers of Campylobacter in the caeca were significantly higher than those in the small intestine (P = 0.001). No significant correlation was found between the numbers of campylobacters in the caeca and small intestines and the environmental parameters monitored.