Abstract
BackgroundThe aim of this study was to determine the susceptibility of 88 Lactobacillus isolates derived from chickens to antibiotic substances and to detect drug-resistance genes.ResultsThe minimal inhibitory concentration of 13 antimicrobial substances was determined by the broth microdilution method, and resistance genes were detected by PCR. We recorded a high prevalence of resistance to tiamulin (90% resistant isolates), tetracyclines (74%) and lincomycin (70%), and a moderately high frequency of resistance to enrofloxacin (48%), macrolides (42%), aminoglycosides (12.5–31%), ampicillin (26%) and chloramphenicol (23%). Multi-drug resistance was observed in 79.5% of isolates. The presence of resistance genes was generally correlated with phenotypic resistance, but some molecular determinants were also recorded in susceptible isolates. Among tetracycline resistance genes, the most frequently identified was tetW (45% isolates), followed by tetM (26%) and tetL (24%). The ermB, ermC and lnuA genes, associated with resistance to macrolides and lincosamides, were observed in 39, 12 and 39% of isolates, respectively. Among genes determining resistance to aminoglycoside antibiotics, we identified ant(6)-Ia (10% of isolates), aac(6′)-Ie-aph(2′)-Ia (8%), aph(2″)-Ic (6%) and aadE (4.5%). The cat gene was present in 32 isolates, including 8 of 20 found to be resistant to chloramphenicol. Two genes encoding efflux pumps were identified—the acrA gene was present in all isolates tested, and 10 of 79 lactobacilli determined to be phenotypically resistant to tiamulin contained the lsaE gene. We were unable to explain the resistance mechanism of Lactobacillus isolates to ampicillin, but showed that it did not involve the production of β-lactamases.ConclusionsOur findings indicate that intestinal lactobacilli should be considered a reservoir of resistance genes and that antibiotics must be used prudently in poultry production. The data derived from this study can be used as a basis for reviewing current microbiological breakpoints for categorization of susceptible and resistant strains within the genus Lactobacillus.
Highlights
The aim of this study was to determine the susceptibility of 88 Lactobacillus isolates derived from chickens to antibiotic substances and to detect drug-resistance genes
Our work presents a comprehensive study on the antimicrobial nature of chicken lactobacilli, and includes the first report of the susceptibility of bacteria of the genus Lactobacillus to tiamulin
This is the first record demonstrating the presence of the lsaE gene in lactobacilli, as well as some other resistance genes that have not previously been detected in the Lactobacillus species tested in this work
Summary
The aim of this study was to determine the susceptibility of 88 Lactobacillus isolates derived from chickens to antibiotic substances and to detect drug-resistance genes. Lactobacilli are Gram-positive rod-shaped non-pathogenic bacteria considered to be beneficial components of the gastrointestinal microbiota of humans and animals, including birds. They play an important role in the physiology of their host, as they maintain the microbial balance around mucous membranes via ecological interactions with the resident flora and beneficially influence the immune system via the GALT. As modern intensive poultry farming and the associated high density of birds are conducive to the rapid spread of germs, the demand for veterinary drugs, including antibiotics, is high. Antibiotic-resistant strains pose a danger to animals, but as they spread via the food chain, contribute to problems in humans
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