Within-sample and between-sample variation of antimicrobial resistance in fecal Escherichia coli isolates from pigs.
ABSTRACT The present study was initiated to evaluate the effect of sampling time and within-sample variability on the diversity in antimicrobial resistance patterns in fecal Escherichia coli from healthy pigs. Isolates were tested against 11 antimicrobials. A total of 25 different profiles were observed, involving resistance to ampicillin, streptomycin, tetracycline, sulfonamides, trimethoprim, and/or a trimethoprim/sulfonamide combination. No isolates were resistant to enrofloxacin, gentamicin, or chloramfenicol, whereas resistance against neomycin and nalidixic acid was sporadically detected in isolates from grower pigs. A model that clusters pigs within-sampling time as a repeated factor and clusters isolates within individual pigs as a random factor was used. For sows, the variance component ratio of sampling time to residuals was 0.28-0.56 for the different antimicrobials (except ampicillin) and 0.85-1.79 for grower pigs. The variance components for within-sample variation were zero or close to zero, except in isolates from sows where resistance to ampicillin explained 14.8 times more of the variation compared to residuals. Thus, the effect of an animal's status at a given sampling time was more influential on the variability in antimicrobial resistance than within-animal diversity. We conclude that repeated sampling and analysis of one isolate per animal each time may be preferable for screening general tendencies, whereas several isolates have to be tested when individual animals are focused.
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ABSTRACT: Twelve hundred enterobacterial Escherichia coli isolates of porcine origin were screened phenotypically for antibiotic resistance. The bacteria were isolated from 10 herds of swine with different histories of exposure to antimicrobial agents for therapeutic purposes. The bacterial isolates were part of the normal bacterial flora of the intestines of the animals because they were isolated from healthy individuals. The strains were tested for phenotypic antibiotic resistance against sulfonamides, trimethoprim, streptomycin, ampicillin, neomycin, chloramphenicol, and tetracycline. Resistance against streptomycin was found to be most common, followed by resistance against sulfonamides and tetracycline. The highest number of resistant bacteria was found in herds where the use of antimicrobial agents was considered to be high. A selection of multiresistant bacterial isolates were further genetically characterized by hybridization with probes specific for the antibiotic resistance genes; sulI, sulII, dfrI, dfrIIb, dfrIX, and the class A, B, C, and D tetracycline resistance determinants. A PCR was developed and used for detection of the strA-strB gene pair encoding streptomycin resistance in gram-negative bacteria. The strA-strB gene pair was the most frequent resistance determinant in the isolates examined. This study indicates that nonpathogenic E. coli from swine may represent a considerable reservoir of antibiotic resistance genes that might be transferable to pathogens.Microbial Drug Resistance 02/1998; 4(4):289-99. · 2.36 Impact Factor
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ABSTRACT: A highly discriminatory and standardized biochemical fingerprinting method was used to monitor the persistence and colonization of intestinal Escherichia coli isolated from the feces of four sows and their litters (four piglets from each) during the suckling, postweaning, and fattening periods. Altogether, 195 fecal samples were collected and 1,827 E. coli strains were tested (mean number of isolates tested per fecal sample per pig, 9.5). Strains were divided into similarity groups on the basis of their biochemical phenotypes (BPTs). The diversity of E. coli strains in each sample was measured with Simpson's index of diversity, and similarity between E. coli floras of piglets was calculated with a population similarity index. Each fecal sample contained several BPTs of E. coli, some of which dominated that population. The intestinal colonization of piglets consisted of successive waves of different E. coli BPTs, the tenure of which varied from a few days to 2 weeks. Most of these BPTs disappeared in the succeeding samples and were not recovered again from the same piglets. On the other hand, some E. coli strains which colonized piglets early during the suckling period persisted for a long period and were referred to as resident BPTs. Each piglet carried more than one resident BPT (mean of 2.4 BPTs per pig), some of which were also found in other piglets.(ABSTRACT TRUNCATED AT 250 WORDS)Applied and Environmental Microbiology 03/1995; 61(2):778-83. · 3.68 Impact Factor
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ABSTRACT: The effects of heat stress on the antimicrobial drug resistance of Escherichia coli of the intestinal tract of swine were studied in animals from a farm that had not been supplementing antimicrobials in feed for the past 10 years. In one study, 10 finisher hogs were heat stressed (34 degrees C) for 24 h. Antimicrobial resistance levels after stress were significantly higher (P < 0.05) when compared with pre-stress levels for amikacin, ampicillin, cephalothin, neomycin and tetracycline from faecal samples. This high level of resistance persisted to slaughter that occurred at 10 days post-stress for most of the antimicrobials mentioned. In a second study, samples of different sections of the gastrointestinal tract were collected after heat stress and compared with control, non-stressed animals. Results indicated that E. coli which colonized the ileum and caecum had a higher level of resistance to ampicillin and tetracycline than the E. coli which colonized the colon and rectum. When animals were exposed to heat stress, resistance to ampicillin and tetracycline of E. coli in the lower digestive tract increased (P < 0.05) to a level similar to that observed in the ileum and caecum. Based on these findings, an investigation was made to test the hypothesis that (a) an increase in intestinal motility increases shedding of resistant E. coli and (b) heat stress induces a reduction in intestinal transit time in swine. For each study, two groups of three, randomly selected finisher hogs each were formed (treated and control groups). In study (a), induction of increased motility and peristalsis was obtained using an intramuscular injection of the cholinergic drug neostigmine methylsulphate. Escherichia coli isolates were obtained from the ileum, caecum, colon and rectum after animals were slaughtered. A higher level of ampicillin-resistant E. coli was found in the caecum (40%) than in other segments of the intestinal tract. In treated animals, level of resistance increased for organisms from the colon and rectum. Similar results were obtained for tetracycline resistance. In study (b), intestinal transit time was measured using chromium-EDTA as a marker. Swine were euthanized and samples were collected throughout the intestinal tract (duodenum to rectum) 8 h after administration of the marker to control and heat-stressed animals. Results indicated a reduced transit time for the stressed group. These findings corroborate the initial hypothesis that an outflow of resistant organisms moves from the upper tract (ileum and caecum) to the lower tract (colon and rectum).Journal of Applied Microbiology 05/2000; 88(5):836-44. · 2.20 Impact Factor