Antimicrobial resistance in Campylobacter spp. isolated from Ontario sheep flocks and associations between antimicrobial use and antimicrobial resistance

The objectives of this study were to determine the prevalence of antimicrobial resistance (AMR) in faecal Campylobacter spp. from lambs and adult sheep and associations between antimicrobial use (AMU) and AMR. A total of 275 faecal samples collected during initial and final visits from 51 sheep flocks, including one feedlot, across southern Ontario were tested for the presence of Campylobacter spp. Campylobacter jejuni was detected in 52% (143/275) of the faecal samples, Campylobacter coli in 7% (19/275), Campylobacter lari in 1% (2/275) and 2% (4/275) were non-speciated Campylobacter. Broth microdilution was used to test antimicrobial susceptibility of 162 isolates to nine antimicrobials. Campylobacter jejuni isolates (n = 142) were resistant to tetracycline (39%), ciprofloxacin (4%), nalidixic acid (4%) and telithromycin (1%). C. coli isolates (n = 19) were resistant to tetracycline (74%), and azithromycin, clindamycin, erythromycin, and telithromycin (5%). The C. lari isolate displayed resistance to nalidixic acid. No statistically significant associations were found between AMU and AMR during multivariate modelling in this study.     

Antimicrobial resistance in generic fecal Escherichia coli from 29 beef farms in Ontario

The occurrence of antimicrobial resistance in generic Escherichia coli can serve as an indicator of the pool of resistance genes potentially available for transfer to pathogenic organisms. This study was conducted on 29 volunteer beef farms in Ontario to describe the prevalence and patterns of antimicrobial resistance in E. coli, and to describe changes in the prevalence of resistance during the feedlot stage of production. From the pooled fecal samples on 28 of the 29 farms, 31% of isolates from feedlots (n = 993) and 12% of isolates from cow-calf farms (n = 807) were resistant to one or more of 16 antimicrobials tested. No isolates were resistant to ceftriaxone, ciprofloxacin, gentamicin, or nalidixic acid, and < 1% of the pooled isolates were resistant to ceftiofur. Two percent of both feedlot and cow-calf isolates were resistant to > or = 5 antimicrobials. Cow-calf farms were at significantly lower risk than feedlots for having E. coli isolates that were resistant to streptomycin, sulfamethoxazole, and tetracycline. On average, the prevalence of sulfamethoxazole resistant E. coli isolates was significantly higher in calves than in cows. No resistance was observed to ceftriaxone or ciprofloxacin among isolates (n = 1265) obtained from individually sampled feedlot animals on 2 farms. Less than 1% of these isolates were resistant to gentamicin, nalidixic acid, and ceftiofur. From the individually sampled feedlot animals, resistance to streptomycin (on 1 farm), sulfamethoxazole, and tetracycline increased significantly from arrival to mid-point during the feeding period, and these levels persisted until market-readiness.     

Comparison of antimicrobial resistance in generic Escherichia coli and Salmonella spp. cultured from identical fecal samples in finishing swine

The objectives of this study were to investigate the associations between antimicrobial resistance patterns in generic Escherichia coli and Salmonella spp. isolates recovered from identical pen pooled fecal samples, and to evaluate potential clustering of multiple isolates of these organisms within identical fecal samples. Up to 5 generic E. coli (n = 922 isolates) and Salmonella spp. (n = 922 isolates) isolates were obtained from each of 188 pen pooled fecal samples that had been collected from 45 finishing swine farms in Alberta in 2000, and tested for susceptibility to 15 antimicrobials. No isolates of either organism were resistant to 3rd generation cephalosporins or fluoroquinolones, which in Canada are considered antimicrobials of very high importance to human health. Approximately twice as many generic E. coli isolates as Salmonella spp. isolates were resistant to at least 1 antimicrobial. In addition, E. coli isolates showed more multidrug-resistance patterns. No significant association was observed between the resistance phenotypes of Salmonella spp. and E. coli at the fecal sample level. More clustering at the sample level was observed for proportions of antimicrobial resistance (AMR) in Salmonella spp. isolates than E. coli indicating that in future studies it might be sufficient to test fewer than 5 Salmonella spp. isolates per sample.     

Prevalence and antimicrobial resistance among Escherichia coli and Salmonella in Ontario smallholder chicken flocks

Surveillance is an important component of an overall strategy to address antimicrobial resistant bacteria in food animals and the food chain. The poultry market has many points of entry into the Canadian food chain, and some production practices are underrepresented in terms of surveillance. For example, pathogen carriage and antimicrobial resistance surveillance data are limited in smallholder chicken flocks raised for slaughter at provincially inspected abattoirs. In Canada, antimicrobial resistance in Escherichia coli and Salmonella isolated from commercial broiler chicken flocks, slaughtered at federally inspected abattoirs, is monitored by the Canadian Integrated Program for Antimicrobial Resistance Surveillance (CIPARS ). The objective of this study was to establish baseline information of antimicrobial resistance presence in E. coli and Salmonella isolated from smallholder flocks in Ontario, utilizing CIPARS collection and isolation methodologies, and to compare findings with CIPARS federally inspected abattoir data from Ontario, Canada. Five chickens per flock were sampled from 205 smallholder flocks. Of 1,025 samples, the E. coli prevalence was 99% (1,022/1,025), and 47% (483/1,022) of positive E. coli isolates were resistant to one or more of the 14 antimicrobials. Furthermore, as compared to results reported for the CIPARS commercial flocks, E. coli isolates from smallholder flocks had significantly lower resistance prevalence to six of 14 individual antimicrobials. Recovery of E. coli did not differ between federally inspected and provincially inspected flocks. Salmonella prevalence at the bird level in smallholder flocks was 0.3% (3/1,025), significantly lower (p  ? 0.0001, 95% CI 0.080%–0.86%) than federally inspected commercial flocks. The overall differences found between the commercial and smallholder flocks may be explained by differences in poultry husbandry practices and hatchery sources.     

Antimicrobial resistance in generic Escherichia coli isolated from swine fecal samples in 90 Alberta finishing farms

The objective of this study was to determine the prevalence of antimicrobial resistance in generic Escherichia coli isolates obtained from 90 Alberta finisher swine farms. Up to 5 isolates were obtained from each of 269 pooled fecal samples and were classified as susceptible or resistant according to Clinical and Laboratory Standards Institute guidelines. Of the 1322 isolates, 166 (12.6%) were susceptible to all 15 antimicrobials. No resistance to amikacin, ceftiofur, ceftriaxone, or ciprofloxacin, antimicrobials of importance in human medicine, was observed. Relatively low frequencies of resistance were observed to gentamicin (1.1%), amoxicillin/clavulanic acid (0.7%), and cefoxitin (0.7%). Higher frequencies of resistance were observed for tetracycline (78.9%), sulfisoxazole (49.9%), streptomycin (49.6%), ampicillin (30.6%), chloramphenicol (17.6%), kanamycin (10%), and trimethoprim/ sulfamethoxazole (6.4%). Among the isolates resistant to > or = 2 antimicrobial classes, 20.8%, 20.6%, 18.2%, 7.0%, 1.8%, 0.2%, and 0.2% were resistant to 2, 3, 4, 5, 6, 7, and 8 antimicrobials, respectively. The most common multidrug-resistance patterns (resistance to > or = 2 antimicrobial classes) were streptomycin-tetracycline (9.4%), streptomycin-sulfisoxazole-tetracycline (6.2%), and ampicillin-streptomycin-sulfisoxazole-tetracycline (6.1%). More clustering (higher intra-class correlation coefficients) in antimicrobial resistance was observed for isolates at the same visit than for isolates from different visits in the same farm, indicating that sampling more farms, testing fewer isolates per visits, and taking longer periods between visits may be appropriate and more efficient for a better understanding of potential shifts in resistance over time.     

Drug use and antimicrobial resistance among Escherichia coli and Enterococcus spp. isolates from chicken and turkey flocks slaughtered in Quebec,Canada

An observational study was conducted of chicken and turkey flocks slaughtered at federal processing plants in the province of Quebec, Canada. The objectives were to estimate prevalence of drug use at hatchery and on farm and to identify antimicrobial resistance (AMR) in cecal Escherichia coli and Enterococcus spp. isolates and factors associated with AMR. Eighty-two chicken flocks and 59 turkey flocks were sampled. At the hatchery, the most used antimicrobial was ceftiofur in chickens (76% of flocks) and spectinomycin in turkeys (42% of flocks). Virginiamycin was the antimicrobial most frequently added to the feed in both chicken and turkey flocks. At least 1 E. coli isolate resistant to third-generation cephalosporins was present in all chicken flocks and in a third of turkey flocks. Resistance to tetracycline, streptomycin, and sulfisoxazole was detected in > 90% of flocks for E. coli isolates. Antimicrobial resistance (AMR) was observed to bacitracin, erythromycin, lincomycin, quinupristin-dalfopristin, and tetracycline in both chicken and turkey flocks for Enterococcus spp. isolates. No resistance to vancomycin was observed. The use of ceftiofur at hatchery was significantly associated with the proportion of ceftiofur-resistant E. coli isolates in chicken flocks. In turkey flocks, ceftiofur resistance was more frequent when turkeys were placed on litter previously used by chickens. Associations between drug use and resistance were observed with tetracycline (turkey) in E. coli isolates and with bacitracin (chicken and turkey), gentamicin (turkey), and tylosin (chicken) in Enterococcus spp. isolates. Further studies are needed to provide producers and veterinarians with alternative management practices and tools in order to reduce the use of antimicrobial feed additives in poultry.     

Associations between antimicrobial use and the prevalence of antimicrobial resistance in fecal Escherichia coli from feedlot cattle in western Canada

A randomized, controlled, blinded clinical trial was performed at a research feedlot in western Canada. Auction-market-derived steers (n = 288) were randomly assigned to 1 of 3 treatments: 1) no antimicrobials on arrival; 2) oxytetracycline in the starter ration for 14 d; and 3) long-acting oxytetracycline subcutaneously on day 0. Minimal inhibitory concentrations of 7 antimicrobials were determined for 3 generic fecal E. coli isolates per animal on arrival and throughout the feeding period. There was a low prevalence of antimicrobial resistance in generic E. coli isolates from calves on arrival. There were increased proportions of cattle with resistant E. coli isolates early in the feeding period among calves in groups 2 and 3. Individual animal treatments were not associated with increased proportions of cattle with resistant E. coli isolates preslaughter. There was no difference in the proportion of animals with E. coli isolates resistant to tetracycline between the treatment groups preslaughter. However, there were significantly more animals with tetracycline resistant isolates of E. coli preslaughter than at arrival.     

Antimicrobial resistance in generic fecal Escherichia coli obtained from beef cattle on arrival at the feedlot and prior to slaughter, and associations with volume of total individual cattle antimicrobial treatments in one western Canadian feedlot

A prospective observational study was carried out to examine antimicrobial resistance patterns of fecal Escherichia coli isolates of calves on arrival at the feedlot, and then evaluate the associations between the total volume of antimicrobial used for disease treatment and changes in antimicrobial resistance, during the feeding period. No macrolides or tetracyclines were administered in the feed during this study. On arrival, at the animal level, all 3 isolates obtained from 36.6% [95% confidence interval (CI): 29.0 to 44.8] of all cattle sampled (n = 153), were susceptible to all antimicrobials, while 5.9% (95% CI: 2.7 to 10.9) of cattle had at least 1 isolate that was resistant to ≥ 3 antimicrobials out of the 7 antimicrobials tested. The most frequent antimicrobials for which resistance was observed were sulphamethoxazole, ampicillin, and tetracycline where, of all cattle, 44.4% (95% CI: 36.4 to 52.7), 20.3% (95% CI: 14.2 to 27.5), and 17.7% (95% CI: 12.0 to 24.6), respectively had at least 1 resistant isolate. All cattle received antimicrobial metaphylaxis on arrival at the feedlot. Antimicrobial use was described for a cohort of 95 cattle. Antimicrobials were given to 42 of the 95 cattle during the feeding period, to treat disease. Amongst the 42 treated cattle, there were a total of 133 animal daily doses (ADD_Feedlot), where 1 ADD_Feedlot represented 1 day of antimicrobial treatment received by a feedlot animal at the approved dose. Only 1 ADD_Feedlot was given in the 100 days immediately prior to slaughter. There were no associations found between antimicrobial use and antimicrobial resistance in this study.     

The prevalence of verocytotoxin-producing Escherichia coli and antimicrobial resistance patterns of nonverocytotoxin-producing Escherichia coli and Salmonella in Ontario broiler chickens.

The prevalence of verocytotoxin-producing Escherichia coli and Salmonella in Ontario broiler chickens was determined by culturing cloacal samples from 500 individual birds selected from 50 poultry farms. Resistance to antimicrobials was determined for each of the isolates. In addition, abattoir and farm-level management data were obtained to evaluate variables that may be considered risk factors for infection. The variables selected included: Percentage of birds condemned at slaughter, percentage of birds dead-on-arrival, bird weight, truck number, farm size, hatchery source, litter source and type, feed source, mortality levels, type of water drinker, water sanitization, down time, barn clean out and history of antibiotic treatment. None of the cloacal samples revealed the presence of verocytotoxin-producing E. coli, though 19/500 (3.8%) contained Salmonella organisms. Nine different Salmonella serotypes were isolated; the most common being S. hadar, S. heidelberg and S. mbandaka. Resistance to tetracycline and streptomycin was common among Salmonella (63%) and E. coli (25.2%) isolates. Resistance to two or more antimicrobials occurred in 420/500 (84%) of the E. coli isolates. No statistically significant associations between abattoir or farm-level management variables and the Salmonella-status of farms were demonstrated.     

Associations of antimicrobial uses with antimicrobial resistance of fecal Escherichia coli from pigs on 47 farrow-to-finish farms in Ontario and British Columbia

This study assessed the associations between antimicrobial use and other management practices in pigs and antimicrobial resistance in generic Escherichia coli recovered from feces of weaner and finisher pigs on 39 purposefully selected farrow-to-finish farms in Ontario and 8 in British Columbia. Antimicrobials (n = 13), most frequently penicillins and tetracycline, wer dministered to different age groups of pigs on study farms through various routes of administration. Logistic regression was used to model risk factors to antimicrobial resistance in fecal E. coli of pigs for the following antimicrobials: ampicillin, apramycin, carbadox, cephalothin, chloramphenicol, kanamycin, neomycin, nitrofurantoin, spectinomycin, streptomycin, sulfamethoxazole tetracycline, and cotrimoxazole (trimethoprim and sulfamethoxazole). Use of antimicrobials in weaner pigs compared with use in finisher pigs was associated with resistance in most models. There was phenotypic evidence of different mechanisms of resistance selection, including direct selection [use of carbadox was associated with carbadox resistance (OR = 6.48)]; cross-resistance [use of spectinomycin was associated with streptomycin resistance (OR = 2.29)]; and possible co-selection [ceftiofu use was associated with tetracycline resistance (OR = 6.12)]. These results provide further evidence that use of antimicrobials in pigs selects for resistance among fecal E. coli within and between classes of antimicrobials.     

Antimicrobial resistance of Salmonella and generic Escherichia coli isolated from surface water samples used for recreation and a source of drinking water in southwestern Ontario,Canada

Antimicrobial resistance (AMR) in the aquatic environment represents an important means of introduction and dissemination of resistance genes, and presence of resistant pathogens in surface waters may pose a public health concern to recreational and drinking water users. The purpose of this study was to explore antimicrobial resistance patterns in water samples collected from the Grand River watershed (southwestern Ontario, Canada) to describe the composition, trends and potential risks of AMR in the aquatic environment. As part of FoodNet Canada and the Canadian Integrated Program for Antimicrobial Resistance Surveillance (CIPARS), stream water samples were collected bi‐weekly from sampling sites within the Grand River watershed in the Waterloo, Ontario sentinel site and tested for the presence and antimicrobial susceptibility of Salmonella spp. (2005–2013) and generic Escherichia coli (2012–2013). Of all samples tested, 16% of Salmonella and 22% of E. coli isolates were resistant to at least one antimicrobial, including three Salmonella isolates and two E. coli isolates that were resistant to Category I antimicrobials, which are classified as very high importance for the treatment of serious bacterial infections in humans. The greatest proportion of resistant E. coli isolates were observed from the river site upstream of the drinking water intake, while the greatest proportion of resistant Salmonella isolates were from sites upstream in the watershed, and at one recreational water site. Salmonella resistance trends remained fairly stable between 2007 and 2013, with the exception of streptomycin and tetracycline which increased in 2010 and 2013. Continued surveillance of antimicrobial resistance patterns and exploration of risk factor data will allow for a better understanding of resistance transmission in the aquatic environment.     

Antimicrobial resistance in Enterococcus spp. and Escherichia coli isolated from poultry feed and feed ingredients

Poultry feed is at the start of the food safety chain in the "farm-to-fork" model, and might serve as a source of antimicrobial resistant bacteria present in poultry meat. Antimicrobial resistance was investigated in 1137 enterococci and 163 Escherichia coli strains recovered from 23 samples of commercial broiler feed and 66 samples of raw feeding materials taken over half a year timespan. Enumeration of enterococci and E. coli were also performed using traditional plating and fluorescent in situ hybridisation methods. Viable enterococci were detected in all feed samples and in 66% of samples of separate feed ingredients, while E. coli was present in 50% and 32% of feed and raw feeding materials, respectively. The median values (50th percentile) for plate and FISH counts for feeds were, respectively, 2.70 log CFU/g and 5.52 log cells/g for enterococci, and 0.15 log CFU/g and 6.00 log cells/g for E. coli. Among enterococci recovered from feed ingredients, resistance to rifampicin, erythromycin, nitrofurantoin, tetracycline, and ciprofloxacin was found in 59.8%, 21.6%, 21.2%, 18.0% and 6.9% of the isolates, respectively. A considerable proportion of the enterococci isolates obtained from broiler feed displayed resistance to tetracycline (69.1%), rifampicin (58.5%), erythromycin (52.9%) and nitrofurantoin (36.2%). Lower percentage of resistance was observed to chloramphenicol (4.6%), ciprofloxacin (3.9%), vancomycin (1.9%) and ampicillin (1.2%). Among E. coli recovered from feed ingredients and poultry feeds, resistance to ampicillin, tetracycline and streptomycin was found in 22.9%, 27.6% and 19.0% and in 22.4%, 41.4% and 17.0% of the isolates, respectively. These data show that feedstuffs and poultry feeds are extensively contaminated by resistant enterococci and, in a lesser extent, by E. coli, thus leading to their introduction in the farm environment.     

Antimicrobial resistance in fecal Escherichia coli isolated from growing chickens on commercial broiler farms

To investigate the effects of rearing practices of commercial broiler chickens on the incidence of antimicrobial resistance in commensal Escherichia coli isolates, fecal E. coli isolates obtained in 4 farms were screened for anitimicrobial resistance. Ten E. coli isolates were recovered from each of the fecal samples collected from 10 birds in the farms at the ages of 2 days, 14-17 days, and 47-50 days. In 2 out of the 4 farms, no antimicrobials were used during the rearing period. In the other two farms, following collection of the fecal samples at 14 and 15 days of age, oxytetracycline (OTC), sulfadimethoxine (SDMX), and tylosin were given to birds on one farm and SDMX was used in the other. Isolates resistant to ampicillin and OTC that were obtained from an untreated flock at different sampling times were closely related to each other by pulsed-field gel electrophoresis patterns (PFGE) of XbaI-digested chromosomal DNA. PFGE analysis together with in vitro conjugation experiments suggested that diversity of resistance phenotypes within a clone may be resulted from the acquisition and loss of R-plasmids in an untreated and a treated flock. The numbers of resistance phenotypes observed among fecal isolates increased during the growth of the chickens in all the farms. The results in the present study suggest that persistence of commensal E. coli strains resistant to antimicrobials even in the absence of antimicrobial administration. It is also hypothesized that horizontal transmission of resistance determinants resulted in the emergence of different resistance phenotypes in those farms.     

Antimicrobial resistance of fecal Escherichia coli isolated from grow-finish pigs in 20 herds in Alberta and Saskatchewan.

Escherichia coli (n = 1439), isolated from the feces of apparently healthy grow-finish pigs in 20 herds in Alberta and Saskatchewan, were tested for susceptibility to 16 antimicrobials. All isolates were susceptible to amikacin, ceftriaxone, and ciprofloxacin and less than 1% was resistant to amoxicillin-clavulanic acid, cefoxitin, ceftiofur, gentamicin, and nalidixic acid. Resistance was most common to tetracycline (66.8%), sulfamethoxazole (46.0%) and streptomycin (33.4%). Twenty-one percent of the isolates were susceptible to all drugs, while 57% were resistant to 2 or more antimicrobials. Unconditional associations between resistances provided insight into the potential for co-selection. Every resistance-outcome was associated with at least 2 other drug-resistances. These associations illustrate the propensity for resistance phenotypes to occur together and the importance of considering co-selection in antimicrobial use decisions. A 2nd analysis explored the associations between resistance phenotypes in E. coli and Salmonella spp. from the same herd. Only 2 resistances in Salmonella were associated with herd-level E. coli resistance, indicating that E. coli is a poor sentinel for Salmonella AMR within herds. Herd-level management, including antimicrobial use, could affect antimicrobial resistance. The intra-class correlation between isolates within herds ranged from 0.1 to 0.46, which confirmed resistance clustered within herds. This suggests herd-level interventions might mitigate antimicrobial resistance. Overall, these results reflect the on-farm selection pressure for resistance and the potential food-safety risk from near-market animals. These data provide a baseline for comparisons with future on-farm monitoring of antimicrobial resistance in E. coli.     

Antimicrobial resistance of fecal Salmonella spp. isolated from all phases of pig production in 20 herds in Alberta and Saskatchewan

Salmonella spp. (n = 468), isolated from the feces of sows, nursery, and grow-finish pigs in 20 farrow-to-finish herds in Alberta and Saskatchewan, were tested for susceptibility to 16 antimicrobials. No resistance was identified to amikacin, amoxicillin-clavulanic acid, ceftiofur, ceftriaxone, ciprofloxacin or nalidixic acid, and less than 1% of the isolates were resistant to cefoxitin and gentamicin. Isolates were most commonly resistant to tetracycline (35%) and sulfamethoxazole (27%). Overall, 59% of the Salmonella were susceptible to all 16 drugs (pansusceptible). Isolates from sows were more likely to be pansusceptible than isolates from nursery or grow-finish pigs. Resistance to 2 or more drugs occurred in 29% of the isolates and was significantly more likely to occur in Salmonella from nursery pigs than from sows. The odds of resistance to 4 of the drugs, streptomycin, ampicillin, kanamycin and cephalothin, were significantly higher in isolates from nursery pigs than grow-finish pigs, while the odds of resistance to 2 drugs, tetracycline and streptomycin, were higher in Salmonella from nursery pigs than from sows. More age-specific risk factor studies are needed to investigate these differences between production phases.     

Observational study on antimicrobial resistance in Escherichia coli and Salmonella isolates from Ontario calf samples submitted to a diagnostic laboratory from 2007 to 2020

The objectives of this study were to i) describe Escherichia coli and Salmonella isolates; ii) investigate the temporal trends in antimicrobial resistance (AMR) profiles; and iii) evaluate the impact of season and age on these AMR profiles from diagnostic and post-mortem samples in Ontario calves ≤ 2-months-old submitted from 2007 to 2020 to the Animal Health Laboratory in Guelph, Ontario, Canada. Antimicrobial susceptibility testing results were measured by the Kirby-Bauer disk diffusion method. A total of 1291 isolates with AMR profiles were obtained from calves, with E. coli (n = 434) and Salmonella (n = 378) being the most common bacteria characterized for AMR. For E. coli, 79% of isolates tested showed a positive result in F5/K99, whereas for Salmonella isolates, S. Typhimurium (33%) and S. Dublin (22%) were the 2 most common serotypes identified. Multivariable logistic regression models were built to evaluate AMR profiles for E. coli (n = 414) and Salmonella (n = 357) to each antimicrobial tested. Most E. coli isolates (91%) and Salmonella isolates (97%) were resistant to at least one of the antimicrobials tested. In general, E. coli and Salmonella had higher odds of resistance in calves aged ≥ 2 wk compared to 1-week-old calves, and little difference was seen in the level of resistance over the years observed or between seasons in most of the antimicrobials tested. Prospective research should investigate potential risk factors for the development of AMR in calves examples being antimicrobial use and farm management practices.     

Characteristics of Salmonella spp. and Escherichia coli isolated from broiler flocks classified as "good" or "poor" producers

Cecal samples from 100 broiler flocks were cultured for Escherichia coli and Salmonella. Samples were selected from flocks classified as either "good" or "poor" producers by a production formula. In an attempt to identify predictors of flock productivity, isolates were studied for differences in antibiotic resistances, hemagglutination of erythrocytes, production of colicins, production of siderophores, type of hemolysis, resistance to host complement, and presence of plasmids. S. typhimurium (copenhagen) was isolated from one poor producing flock and three good producers. Salmonella isolates showed no significant differences in the parameters studied. The E. coli isolates showed significant differences only for the presence of plasmids. These data indicate that differences in host intestinal E. coli from good and poor producing flocks do not predict flock productivity.     

Prevalence of antimicrobial resistance in fecal generic Escherichia coil isolated in western Canadian cow-calf herds. Part I--beef calves.

The objective of this study was to describe antimicrobial resistance patterns in fecal generic Escherichia coli obtained from calves in western Canadian cow-calf herds. Susceptibility testing was completed on 1677 isolates obtained from 480 beef calves in 91 herds in the spring, and from 1187 isolates obtained from 394 calves in 45 herds in the fall of 2002. Resistance was rare to antimicrobials classified as being of very high importance to human health. Isolates were most commonly resistant to tetracycline, sulphamethoxazole, and streptomycin. Resistance to at least one antimicrobial was identified in 48.8% of the isolates collected in the spring, and 7.0% of those collected in the fall. Spring or fall calf resistance status was not associated with calf gender, breed, age of the dam, or if the calf was treated before sample collection. Calves < or = 3 days of age were less likely to be resistance positive than calves > 10 days of age.