Characterization of erythromycin-resistant methylase genes from multiple antibiotic resistant Staphylococcus spp isolated from milk samples of lactating cows

Saeed A. Khan Division of Microbiology, The National Center for Toxicological Research, United States Food and Drug Administration, Jefferson, AR 72079.

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Mohamed S. Nawaz Division of Microbiology, The National Center for Toxicological Research, United States Food and Drug Administration, Jefferson, AR 72079.

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Ashraf A. Khan Division of Microbiology, The National Center for Toxicological Research, United States Food and Drug Administration, Jefferson, AR 72079.

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Roger S. Steele Division of Microbiology, The National Center for Toxicological Research, United States Food and Drug Administration, Jefferson, AR 72079.

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Carl E. Cerniglia Division of Microbiology, The National Center for Toxicological Research, United States Food and Drug Administration, Jefferson, AR 72079.

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Abstract

Objective—To isolate and characterize erythromycinresistant methylase genes in multiple-antibiotic resistant staphylococci isolated from milk samples.

Animals—300 lactating cows.

Procedure—23 erythromycin-resistant staphylococci were isolated from milk samples of 300 lactating cows. The prevalence of erythromycin-resistant methylase (erm) genes, ermC and ermA genes, and the multicomponent macrolide efflux pump in staphylococci msrA genes were identified and characterized by use of multiplex polymerase chain reaction (PCR), Southern hybridization, restricted fragment length polymorphism (RFLP) analysis, and dot-blot hybridization.

Results—Biochemical characterization indicated that 3 of 23 (13%) isolates were coagulase-positive Staphylococcus aureus, and the rest were coagulasenegative. Multiplex PCR resulted in amplification of a 520-base pair (bp) region of the ermC gene from the cell lysates of a strain of S simulans M-21 and S sciuri M-28. The ermC gene in both isolates was found on a 3-kilobase plasmid. The ermA gene was found on the chromosome of 21 isolates, and 6 RFLP patterns were observed. None of the isolates harbored the msrA gene.

Conclusions—Erythromycin-resistantStaphylococcus spp isolated from milk samples of lactating cows may serve as reservoirs of erm genes homologous to those described in human isolates. However, the chromosomal insert patterns and prevalence of these genes, the sizes of plasmids harboring the genes, and the number of inserts of the genes (copy number) may differ from that of human isolates. (Am J Vet Res 2000;61:1128–1132)

Abstract

Objective—To isolate and characterize erythromycinresistant methylase genes in multiple-antibiotic resistant staphylococci isolated from milk samples.

Animals—300 lactating cows.

Procedure—23 erythromycin-resistant staphylococci were isolated from milk samples of 300 lactating cows. The prevalence of erythromycin-resistant methylase (erm) genes, ermC and ermA genes, and the multicomponent macrolide efflux pump in staphylococci msrA genes were identified and characterized by use of multiplex polymerase chain reaction (PCR), Southern hybridization, restricted fragment length polymorphism (RFLP) analysis, and dot-blot hybridization.

Results—Biochemical characterization indicated that 3 of 23 (13%) isolates were coagulase-positive Staphylococcus aureus, and the rest were coagulasenegative. Multiplex PCR resulted in amplification of a 520-base pair (bp) region of the ermC gene from the cell lysates of a strain of S simulans M-21 and S sciuri M-28. The ermC gene in both isolates was found on a 3-kilobase plasmid. The ermA gene was found on the chromosome of 21 isolates, and 6 RFLP patterns were observed. None of the isolates harbored the msrA gene.

Conclusions—Erythromycin-resistantStaphylococcus spp isolated from milk samples of lactating cows may serve as reservoirs of erm genes homologous to those described in human isolates. However, the chromosomal insert patterns and prevalence of these genes, the sizes of plasmids harboring the genes, and the number of inserts of the genes (copy number) may differ from that of human isolates. (Am J Vet Res 2000;61:1128–1132)

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