Antibiotic Resistance inEscherichia coliof the Normal Intestinal Flora of Swine

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.

Resistance to antibiotics in the normal flora of animals

“…The way of selecting normal flora isolates for further study is crucial to the results obtained [41,52].…”

“…Normal fecal flora E. coli (1200 isolates) of healthy fattening pigs in ten different herds with a different history of antibiotic use was studied with respect to antibiotic resistance features and the genetic mechanisms responsible [51,52]. The ten herds had different histories of exposure to antimicrobial agents for therapeutic purposes.…”

Molecular tools for the characterisation of antibiotic-resistant bacteria

“…In this case, hybridisations are generally performed with bacterial colonies transferred onto filters. For instance, hybridisation with probes specific for nine antibiotic resistance genes was successfully used for the analysis of multi-resistant E. coli strains which were selected from 1200 strains isolated from the normal intestinal flora of healthy swine to prove that swine could be a considerable reservoir of antibiotic resistance genes that might be transferable to pathogens [61]. Considering developments in molecular technology, such as the use of miniaturised micro-arrays, hybridisation will probably become more important in future DNA applications as shown by recent reports on Mycobacterium species identification and rifampicin resistance typing obtained with high-density DNA probe arrays [65].…”

Impact of oral and intramuscular administration amoxicillin on the selection of amoxicillin-resistant <i>Enterobacteriaceae</i> in the digestive flora of piglets

“…When antibiotics are administered, digestive bacteria that are resistant to the antibiotic are selected, and these resistant bacteria can then colonize the digestive tract (Sorum and Sunde, 2001). Sunde et al (1998) reported the prevalence of resistance in E. coli isolated from pigs in 10 farms with a history of antibiotic use for different therapeutic purposes. They showed that the highest percentage of resistant bacteria was found in farms where the use of antibiotics was considered high.…”

“…The massive uses of these antimicrobials contribute an important selection of resistant or multi-resistant bacteria in the digestive microbiota of pigs (Sunde et al, 1998). A transfer of resistance genes from commensal or pathogenic bacteria of animal origin to the human digestive flora via the food chain or the environment is now a real public health problem (Phillips and Casewell, 2004;Sanders et al, 2011).…”