Comparison of the prevalences and antimicrobial resistances of Escherichia coli isolates from different retail meats in the United States, 2002 to 2008.

Escherichia coli isolates were recovered from the National Antimicrobial Resistance Monitoring System retail meat program and examined for antimicrobial susceptibility. Retail meat samples (n = 11,921) from four U.S. states collected during 2002 to 2008, consisting of 2,988 chicken breast, 2,942 ground turkey, 2,991 ground beef, and 3,000 pork chop samples, were analyzed. A total of 8,286 E. coli isolates were recovered. The greatest numbers of samples contaminated with the organism were chicken (83.5%) and turkey (82.0%), followed by beef (68.9%) and pork (44.0%). Resistance was most common to tetracycline (50.3%), followed by streptomycin (34.6%), sulfamethoxazole-sulfisoxazole (31.6%), ampicillin (22.5%), gentamicin (18.6%), kanamycin (8.4%), amoxicillin-clavulanic acid (6.4%), and cefoxitin (5.2%). Less than 5% of the isolates had resistance to trimethoprim, ceftriaxone, ceftiofur, nalidixic acid, chloramphenicol, and ciprofloxacin. All isolates were susceptible to amikacin. Compared to beef and pork isolates, the poultry meat isolates had a greater percentage of resistance to all tested drugs, with the exception of chloramphenicol, to which pork isolates had the most resistance. More than half of the turkey isolates (56%) were resistant to multidrugs (≥3 classes) compared to 38.9% of chicken, 17.3% of pork, and 9.3% of beef isolates. The bla(CMY) gene was present in all ceftriaxone- and ceftiofur-resistant isolates. The cmlA, flo, and catI genes were present in 45%, 43%, and 40% of chloramphenicol-resistant isolates, respectively. Most nalidixic acid-resistant isolates (98.5%) had a gyrA mutation in S83 or D87 or both, whereas only 6.7% had a parC mutation in either S80 or E84. The results showed that E. coli was commonly present in the retail meats, and antimicrobial resistance profiles differed according to the animal origin of the isolates.

Genotyping of Campylobacter spp. from retail meats by pulsed-field gel electrophoresis and ribotyping.

AIMS: To determine the genetic relatedness of Campylobacter spp. from retail meat products, and compare the discriminatory power of pulsed-field gel electrophoresis (PFGE) and automatic ribotyping. METHODS AND RESULTS: A total of 378 Campylobacter isolates recovered from 159 raw meats (130 chicken, 25 turkey, three pork and one beef) sampled from 50 retail grocery stores of four supermarket chains in the Maryland suburban area from August 1999 to July 2000 were analysed by PFGE with SmaI, 120 isolates of which were also characterized by ribotyping with PstI using RiboPrinter system. A total of 148 unique PFGE patterns were identified, 91 of which were present in multiple Campylobacter isolates and 24 in multiple meat samples. Nineteen Campylobacter clones with identical PFGE patterns recurred frequently (up to nine times) throughout the sampling period. Comparing ribotyping with PFGE, we identified 44 PFGE patterns and 22 RiboGroups among the 120 isolates tested. Multiple PFGE patterns within one RiboGroup were commonly observed, as well as multiple RiboGroups within one PFGE pattern. CONCLUSIONS: Although Campylobacter present in retail meats were genetically diverse, certain clones persisted in poultry meats. PFGE had a greater discriminatory power than ribotyping, and the two methods were complementary in genotyping Campylobacter. SIGNIFICANCE AND IMPACT OF THE STUDY: Genomic DNA fingerprinting of Campylobacter confirmed diverse and recurrent Campylobacter clones in the retail meats, which provides additional data for a better understanding of the epidemiological aspect of Campylobacter infection.

Modeling residue uptake by eggs. 1. Similar drug residue patterns in developing yolks following injection with ampicillin or oxytetracycline.

This study was conducted to model the pattern of antibiotic drug uptake within yolks of developing follicles. In two separate experiments, 16 hens were divided into equal groups (n = 8) and injected only once with either 400 mg/kg ampicillin or 200 mg/kg oxytetracycline (OTC: total hens = 32) approximately 1 h after oviposition. Twenty-four hours following injections, hens were euthanatized and the ovaries were collected. Yolks were dissected free from the individual follicles with a blunt probe. Individual large yellow yolks (> or = 0.2 g) and a pool of 5 small yellow yolks (< 0.2 g) were collected for determination of ampicillin or OTC content. Samples were prepared and assayed using an agar diffusion microbiological method. Selected parameters were not different (P > 0.05) between Experiments 1 and 2 and the data were combined. Results indicate that short-term exposure in hens produced incorporation of drug residues in developing yolks in a specific pattern that does not appear to be drug dependent (P > 0.05). These incurred residues are contained in developing yolks that are days to weeks from being ovulated. Drug residues were greater (total microgram content) in some of the less mature yolks vs the largest preovulatory yolk. This may lead to a sequential release of eggs with increasing residue content, even after drug withdrawal. These data were used to construct a model to predict the pattern of incurred residues in formed eggs following a hen's exposure to drugs or other contaminants.

Characterization of a Pasteurella multocida (serotype B) bovine pneumonic pasteurellosis model and the effect of antimicrobials during peracute infection.

A method to produce bovine pneumonic pasteurellosis for experimental purposes was studied and the clinical response of experimentally infected calves to selected antimicrobials was characterized. Male Holstein calves stressed with multiple hot and cold water applications followed by intratracheal inoculation of broth cultures of Pasteurella multocida serotype B developed acute clinical illness consistent with pneumonia. Infected, untreated calves consistently developed classic pneumonic pasteurellosis, infected calves treated with either oxytetracycline or sulfadimethoxine recovered from acute clinical disease, and the uninfected controls remained healthy. This disease model offers potential for use in pharmacokinetic and target tissue drug concentration studies and for dosage titration of drugs intended for treatment of bacterial pneumonias.

Effect of penicillin and virginiamycin on drug resistance in lactose-fermenting enteric flora.

Three groups of beagle dogs were fed either a control diet, a diet containing virginiamycin (55 microgram/g of diet), or a diet containing penicillin (110 microgram/g of diet). The proportions of lactose-fermenting organisms in their feces that were resistant to ampicillin, dihydrostreptomycin, tetracycline, or chloramphenicol were measured by a comparative plate-counting procedure. Both antibiotic-supplemented diets resulted in an increase (P < 0.001) in the occurrence of ampicillin, dihydrostreptomycin, and tetracycline resistances during the time of their administration. The occurrence of these resistances was greater (P < 0.001) in the group receiving penicillin than in the group receiving virginiamycin. In addition to the above resistances, a greater (P < 0.001) occurrence of resistance to a sulfonamide (sulfamethoxypyridazine) due to treatment was found by susceptibility testing of isolates. Representative isolates were able to transfer their resistance to a strain of Escherichia coli K-12.

Effect of low concentrations of dihydrostreptomycin on drug resistance in enteric bacteria.

Beagle dogs were fed a diet containing 0, 2, or 10 mug of dihydrostreptomycin (DSM) per g of feed. The 2-mug/g level was selected to represent a residue level of the antibiotic. In both treatment groups, medicated feed resulted in a shift from a predominantly streptomycin (SM)-susceptible coliform fecal population to an SM-resistant population. The proportion of resistant organisms was significant (P < 0.01) for both treatment groups. A definitive response did not occur with animals maintained on DSM-free diets. An increase in the prevalence of DSM-resistant organisms was observed after 15 days of DSM-supplemented feeding and persisted during the posttreatment phase of the study. The predominant pattern of resistance was SM-sulfamethoxypyridazine. Fifty-nine percent of SM-resistant strains transferred resistant determinants by conjugation to Escherichia coli K-12 recipients.

Persistence of transferable drug resistance in the lactose-fermenting enteric flora of swine following antimicrobial feeding.

Six groups of swine (85 animals) were fed a combination of antimicrobial drugs (sulfamethazine 100 g/ton, chlortetracycline 100 g/ton and penicillin 50 g/ton). After two weeks the antimicronial drugs were removed from the diet of two groups (28 animals). These swine were compared to four groups fed the medicated diet to determine the effect of duration of treatment and degree of animal isolation on the persistence of resistance in lactose-fermenting enteric organisms. The degree of resistance to penicillin, oxytetracycline, dihydrostreptomycin and neomycin as determined by minimum inhibitory concentrations and the incidence of resistant organisms were examined during and after antibiotic feedings. Ninety-two percent or greater of all isolates tested during and after treatment had minimum inhibitory concentrations for oxytetracycline of greater than 100 mug/ml. Thirty-two weeks after cessation of dietary antibiotic, resistance to oxytetracycline and dihydrostreptomycin remained at 100% and 89% respectively. Variation in degree of contact between swine receiving medicated feed and those receiving nonmedicated feed was not sufficient to reduce the incidence of resistance to oxytetracycline or dihydrostreptomycin in all animals. Factors influencing persistence of resistant enteric organisms are discussed. Addition of the antimicrobials to the ration resulted in significantly greater weight gains for treated animals than for the controls but did not alter feed conversion.

Animal model for determining the no-effect level of an antimicrobial drug on drug resistance in the lactose-fermenting enteric flora.

Mature beagles were fed a ground-meal diet containing 0, 2, or 10 mug of oxytetracycline per g for 44 days. The 10-mug/g diet resulted in a shift from a predominantly drug-susceptible population of enteric lactose-fermenting organisms to a multiply antibiotic-resistant population which peaked at 78% resistant organisms. Since a shift to drug-resistant organisms did not occur in the group fed 2 mug/g, the level of oxytetracycline that results in increased incidence of antibiotic resistance lies between 2 and 10 mug/g in this dog model. Rats and hamsters fed diets containing oxytetracycline (10 mug/g or greater) or dihydrostreptomycin (10 mug/g), and provided suspensions of drug-susceptible Escherichia coli, did not develop a population of antibiotic-resistant organisms.

Survey of infectious multiple drug resistance among salmonella isolated from animals in the United States.

Salmonella cultures were obtained from outbreaks of animal disease from 37 states and 1 territory. They were screened for resistance to 11 antimicrobial drugs. Of the 1,251 strains studied, 935 were resistant to one or more of these agents. The three most common resistance patterns were ampicillin, dihydrostreptomycin, sulfamethoxypyridazine, tetracycline; ampicillin, dihydrostreptomycin, sulfamethoxypyridazine; dihydrostreptomycin, sulfamethoxypyridazine, tetracycline. Resistance transfer was demonstrated on 267 multiply resistant cultures, of which 181 were able to transfer all or part of their resistance pattern to a drug-sensitive recipient.