Detection and characterization of erythromycin-resistant methylase genes in Gram-positive bacteria isolated from
A A Khan1, M S Nawaz, S A Khan
1Division of Microbiology, National Center for Toxicological Research, Food and Drug Administration, Jefferson, AR 72079, USA.
Abstract:
The epidemiology of four erythromycin-resistant methylase ( erm) genes, ermA, ermB, ermC and msrA, was determined in erythromycin-resistant staphylococci, enterococci and streptococci isolated from poultry litter. All isolates were resistant to multiple antibiotics. Southern hybridization indicated that 4 of the 20 staphylococci contained the ermC gene on plasmids: on a 2.2 kb plasmid in Staphylococcus hominis and S. sciuri, on a 6.0 kb plasmid in S. xylosus, and on a 7.0 kb plasmid in S. lentus. In 16 of the 20 staphylococci, the ermA gene was harbored exclusively on the chromosome, as a double chromosomal insert on 8.0 and 6.2 kb EcoRI fragments. None of the staphylococci harbored the msrA gene. Dot-blot analysis indicated that all enterococci and streptococci hybridized with a biotinylated ermB gene probe. Southern hybridization indicated that only 2 of the 19 erythromycin-resistant enterococci contained the ermB gene on plasmids. The gene was localized on 4.0 kb and 5.9 kb plasmids, respectively, in two Enterococcus faecium isolates. Results from our studies indicate that the patterns of occurrence of erm genes, the sizes of the plasmids and the copy numbers of the inserts were different from the existing information on the presence of erm genes in clinical strains of Staphylococcus spp.
Insights
This study investigated erythromycin resistance genes (ermA, ermB, ermC, msrA) in poultry-associated bacteria. Findings reveal distinct erm gene distribution and plasmid profiles compared to clinical strains, highlighting potential One Health implications.
Area of Science:
- Microbiology
- Molecular Biology
- Veterinary Science
Background:
- Erythromycin resistance is a growing concern in both clinical and veterinary settings.
- Understanding the prevalence and genetic basis of antibiotic resistance in bacteria from animal sources is crucial for public health.
Purpose of the Study:
- To determine the epidemiology of four erythromycin resistance genes (ermA, ermB, ermC, and msrA) in erythromycin-resistant staphylococci, enterococci, and streptococci isolated from poultry litter.
- To compare the genetic characteristics of these resistance genes in poultry-associated bacteria with those found in clinical strains.
Main Methods:
- Isolation and identification of antibiotic-resistant bacteria from poultry litter.
- Detection of ermA, ermB, ermC, and msrA genes using Southern and dot-blot hybridization.
- Plasmid analysis and characterization of gene location (plasmid vs. chromosome).
Main Results:
- Multiple antibiotic resistance was common in all isolates.
- The ermC gene was found on plasmids in 4/20 staphylococci, while ermA was primarily chromosomal.
- The ermB gene was detected in all enterococci and streptococci, with plasmid localization in 2/19 enterococci.
Conclusions:
- The distribution patterns of erm genes, plasmid sizes, and insert copy numbers in poultry-associated staphylococci differ from those reported in clinical strains.
- These findings suggest distinct evolutionary pathways or transmission dynamics of antibiotic resistance in animal-associated bacteria.
- Further research is needed to understand the One Health implications of antibiotic resistance in poultry production systems.
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