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Biochemical and molecular characterization of erthromycin-resistant avian Staphylococcus spp. isolated from chickens
M S Nawaz1, A A Khan, S A Khan
1Division of Microbiology, National Center for Toxicological Research, Food and Drug Administration, Jefferson, Arkansas 72079, USA. MNAWAZ@NCTR.FDA.GOV
Abstract:
The epidemiology of the two common erythromycin-resistant methylase (erm) genes ermC and ermA was analyzed in 12 coagulase-negative Staphylococcus spp. and 34 coagulase-positive Staphylococcus spp. isolated from chicken. Southern hybridization indicated that only 2 of the 12 coagulase-negative Staphylococcus spp. strains contained the ermC gene on the plasmid; 1 strain of Staphylococcus xylosus harbored the ermC gene on a 2.5-kb plasmid, and 1 strain of Staphylococcus cohnii harbored the gene on a 4.0-kb plasmid. Twelve of the 34 strains of Staphylococcus aureus contained the ermC gene. Eleven of these strains had the ermC gene on a 2.5-kb plasmid, and 1 strain had the gene on a 4.0-kb plasmid. Ten of the 12 coagulase-negative Staphylococcus spp. and 22 of the 34 coagulase-positive Staphylococcus spp. harbored the ermA gene exclusively on the chromosome. Two different ermA EcoRI restriction fragment length polymorphisms (RFLP) were identified. A majority of the isolates was found to have two chromosomal inserts (8.0- and 6.2-kb EcoRI fragments) of ermA. One strain of S. aureus had different chromosomal inserts (6.4- and 5.8-kb EcoRI fragments) of ermA. Our results indicate that either the ermC or ermA gene, homologous to those described in human isolates, was present in all avian Staphylococcus spp. and that ermA was the predominant gene in coagulase-negative and coagulase-positive avian Staphylococcus spp. The size and copy numbers of the ermA gene were different from its human counterpart.
Insights
Erythromycin resistance genes ermC and ermA were found in chicken Staphylococcus isolates. The ermA gene was predominant, often located on the chromosome, differing in size from human strains.
Area of Science:
- Veterinary Microbiology
- Antimicrobial Resistance
- Molecular Epidemiology
Background:
- Staphylococcus species are common in poultry.
- Erythromycin resistance is a growing concern in food-producing animals.
- The ermC and ermA genes are key determinants of erythromycin resistance.
Purpose of the Study:
- To investigate the prevalence and genetic characteristics of ermC and ermA genes in Staphylococcus isolates from chickens.
- To compare these genes with their counterparts found in human isolates.
Main Methods:
- Isolation and identification of Staphylococcus species from chicken samples.
- Detection of ermC and ermA genes using Southern hybridization.
- Analysis of gene location (plasmid or chromosome) and restriction fragment length polymorphisms (RFLP).
Main Results:
- All avian Staphylococcus isolates harbored either ermC or ermA genes.
- The ermA gene was more prevalent than ermC in both coagulase-negative and coagulase-positive Staphylococcus.
- ermC was primarily plasmid-located, while ermA was predominantly chromosomal.
- ermA showed variations in EcoRI restriction patterns and fragment sizes compared to human isolates.
Conclusions:
- Avian Staphylococcus isolates carry erythromycin resistance genes homologous to human strains.
- The ermA gene is the predominant resistance determinant in these avian isolates.
- Differences in ermA gene characteristics suggest potential host-specific adaptations or distinct evolutionary pathways.