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Avoparcin was used as a feed additive in Norwegian broiler and turkey production from 1986 until 1995. It was banned due to the selection of VanA‐type vancomycin‐resistant enterococci (VRE) in animal husbandry and to reduce the potential for human exposure to VRE. The aim of the present study was to investigate the prevalence of VRE carriage in Norwegian poultry farmers and their poultry three years after avoparcin was banned. Corresponding faecal samples from poultry and humans on farms where avoparcin had previously been used (exposed farms, n = 73) and farms where avoparcin had never been used (unexposed farms, n = 74) were analysed for the presence of VRE. For each farm, one sample from the poultry house and one sample from the farmer were obtained. VRE were isolated from 72 of 73 (99%) and eight of 74 (11%) poultry samples from exposed and unexposed farms, respectively. VRE were isolated from 13 of 73 (18%) and one of 74 (1%) farmer samples from exposed and unexposed farms, respectively. All VRE isolates were highly resistant to vancomycin and possessed the vanA gene, as shown by PCR. The high prevalence of VRE is in accordance with previous Norwegian studies, and shows a remarkable stability of the VanA resistance determinant in an apparently non‐selective environment.

Shiga-toxin-2 (stx 2 )-encoding bacteriophages were isolated from Norwegian Escherichia coli O157 :H7 isolates of cattle and human origin. The phages were characterized by restriction enzyme analysis, hybridization with probes for toxin genes and selected phage DNA such as the P gene, integrase gene and IS1203, and by PCR studies and partial sequencing of selected DNA regions in the integrase to stx 2 region of the phages. The stx 2 -phage-containing bacteria from which inducible phages were detected produced similar amounts of toxin, as shown by a Vero cell assay. The results indicate that the population of stx 2 -carrying phages is heterogeneous, although the phages from epidemiologically linked E. coli O157 :H7 isolates were similar. There appears to have been frequent recombination of stx 2 phages with other lambdoid phages.

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Aims: To investigate if cattle on the same farm as sheep are a possible risk factor for stx in sheep and to determine whether or not sheep and cattle on the same farm share the same stx pool. Methods and Results: Faecal samples from sheep and cattle were screened for stx by polymerase chain reaction (PCR). Of these samples, 87AE6 and 64AE6% were stx positive in sheep and cattle, respectively. There was no difference in stx occurrence in sheep from farms with or without cattle. From stx positive samples, 118 Shiga toxin-producing Escherichia coli (STEC) isolates were recovered by a filter-hybridization method. Serotyping, PCR and pulsed-field gel electrophoresis (PFGE) showed that there was a distinct association between serotypes, stx profiles and animal species. Conclusions: Keeping animals together in pens, which enhances faecal-oral contact, is suggested as a possible explanation for the differences seen in stx occurrence. Sheep and cattle isolates are distinctly different in serotype and stx profile although isolated from the same farm, and are more related to isolates within the same serotype with the same stx profile than to isolates with different serotype from the same farm. Significance and Impact of Study: The study supports the animal-host relationship hypothesis suggested in other studies and indicates that the STEC sheep reservoir in Norway may not pose a serious public health risk.

Multi-drug-resistant coliform bacteria were isolated from feces of cattle exposed to antimicrobial agents and humans associated with the animals. Isolates from both cattle and humans harbored an R plasmid of 65 kb (pTMS1) that may have been transferred between them due to selective antibiotic pressure in the farm environment.The amount of antimicrobial agents used for therapeutic and nontherapeutic purposes in agriculture far exceeds what is used for humans in many parts of the world (11). Since exposure to antimicrobial agents is the most important factor with regard to development of antimicrobial resistance, animals and animal products could thus be significant sources of resistant bacteria for the human population (1,5,12,17,18). Nonpathogenic, multiple-drug-resistant Escherichia coli in the intestine is probably an important reservoir of resistance genes (3,10,13,15,21), and drug-resistant, intestinal E. coli of animal origin may colonize the human intestine, at least temporarily (14,15,20). However, the ease with which bacteria acquire new resistance genes by self-transmissible and mobilizable plasmids and conjugative transposons may represent a more significant contribution to the increasing incidence of resistant strains (19,23,24).In this study, farm inhabitants were investigated for the occurrence of multi-drug-resistant intestinal E. coli. On the farm studied here, various antimicrobials had been used extensively, primarily to treat recurrent Staphylococcus aureus mastitis in dairy cattle (L. Sølverød, personal communication). One family lived on the farm, and one veterinarian had served the animals. During the spring of 1996, fecal swabs (Culturette; Becton Dickinson Europe, Meyland, France) were collected from 13 cattle, three family members, and the local veterinarian. One year later, sampling of the family members and the veterinarian was repeated, and fecal swabs from four other veterinarians operating sporadically in the area were also included. For a primary screening of the total aerobic fecal flora, each swab was plated onto blood agar (blood agar base [Difco Laboratories, Detroit, Mich.] containing 5% citrated bovine blood) and Mueller-Hinton agar (Difco) with Neo-Sensitabs (Rosco Diagnostica, Taastrup, Denmark) containing 33 g of ampicillin (AMP), 80 g of tetracycline (TET), 100 g of streptomycin (STR), 5.2 g of trimethoprim (TMP), 240 g of sulfonamides (SUL), 60 g of chloramphenicol, and 10 g of enrofloxacin. Agar plates were incubated at 37°C for 24 h. A total of six cattle and five human samples exhibited multipledrug-resistant patterns (Amp r Tet r Str r Tmp r Sul r ). From these plates, three colonies were picked from the zones close to the Neo-Sensitabs containing AMP, TET, and SUL, respectively. Colonies were subcultivated on blood agar and BTB-lactose agar plates to assure pure cultures and retested for susceptibility to the above-mentioned antimicrobials. MICs of AMP, TET, STR, TMP, and SUL were determined (16). A total of 39 of 90 lactose-fermenting (coliform) bovine and human iso...

To investigate the potential transfer of Escherichia coli O157:H7 from contaminated manure to fresh produce, lettuce seedlings were transplanted into soil fertilized with bovine manure which had been inoculated with approximately 10 4 CFU g ؊1 E. coli O157:H7. The lettuce was grown for approximately 50 days in beds in climate-controlled rooms in a greenhouse. As the bacterium was not detected in the edible parts of the lettuce, the outer leaves of the lettuce, or the lettuce roots at harvest it was concluded that transmission of E. coli O157:H7 from contaminated soil to lettuce did not occur. The pathogen persisted in the soil for at least 8 weeks after fertilizing but was not detected after 12 weeks. Indigenous E. coli was detected only sporadically on the lettuce at harvest, and enterococci were not detected at all. The numbers of enterococci declined more rapidly than those of E. coli in the soil. Pseudomonas fluorescens, which inhibited growth of E. coli O157:H7 in vitro, was isolated from the rhizosphere.

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.