title: Macrolide-lincosamide-streptogramin resistance phenotypes and genotypes of coagulase-positive Staphylococcus aureus and coagulase-negative staphylococcal isolates from bovine mastitis.
abstract: BACKGROUND
  There are limited data available on macrolide-lincosamide-streptogramin (MLS) resistance of Staphylococcus aureus (S. aureus) and coagulase-negative staphylococci (CoNS) from bovine milk in China. To address this knowledge gap, MLS resistance was determined in 121 S. aureus and 97 CoNS isolates. Minimum inhibitory concentrations (MICs) of MLS antibiotics were determined by an agar dilution method, while differentiation of MLS phenotypes was performed by a double-disc diffusion test. MLS resistance genotypes were determined by PCR for corresponding resistance genes.
  
  
  RESULTS
  Forty (33.1%) S. aureus and 65 (67.0%) CoNS were resistant to erythromycin, whereas all 218 isolates were susceptible to quinupristin/dalfopristin. Among 40 erythromycin-resistant (ER-R) S. aureus and 65 ER-R CoNS isolates, 38 S. aureus and 40 CoNS isolates exhibited the inducible MLS (iMLS) resistance phenotype and 2 S. aureus and 20 CoNS isolates expressed the constitutive MLS resistance (cMLS) phenotype. At the same time, 5 CoNS isolates exhibited resistance to erythromycin but susceptibility to clindamycin (the MS phenotype). An inactivating enzyme gene lnu(A), methylase genes erm(C) and erm(B), efflux genes msr(A)/msr(B), a phosphotransferase gene mph(C), an esterase gene ere(A) and the streptogramin resistance determinant vga(A) were detected individually or in combinations. Among them, genes lnu(A), erm(C) and mph(C) predominated. The ereA gene was detected for the first time in staphylococci of bovine milk origin. Resistance genes also existed in erythromycin-susceptible isolates.
  
  
  CONCLUSIONS
  Our study demonstrated a high level of resistance to MLS antibiotics in staphylococci from bovine mastitic milk, especially with a high rate of the iMLS phenotype in S. aureus isolates. These data suggest that MLS antibiotics should be used judiciously to treat or prevent bovine mastitis caused by staphylococci.
authors.affiliation: College of Animal Science and Technology, Northwest A&F University, Yang Ling, Shaanxi, P. R. China. llp315@nwsuaf.edu.cn.
authors.forename: Longping
authors.initials: L
authors.lastname: Li
authors.affiliation: College of Animal Science and Technology, Northwest A&F University, Yang Ling, Shaanxi, P. R. China. fengweiwei@nwsuaf.edu.cn.
authors.forename: Weiwei
authors.initials: W
authors.lastname: Feng
authors.affiliation: College of Animal Science and Technology, Northwest A&F University, Yang Ling, Shaanxi, P. R. China. zzpd163yx@163.com.
authors.forename: Zhiping
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: College of Animal Science and Technology, Northwest A&F University, Yang Ling, Shaanxi, P. R. China. xuehuping@hotmail.com.
authors.forename: Huping
authors.initials: H
authors.lastname: Xue
authors.affiliation: College of Animal Science and Technology, Northwest A&F University, Yang Ling, Shaanxi, P. R. China. zhaoxin@nwsuaf.edu.cn.|Department of Animal Science, McGill University, 21,111 Lakeshore, Ste. Anne de Bellevue, H9X 3 V9, QC, Canada. zhaoxin@nwsuaf.edu.cn.
authors.forename: Xin
authors.initials: X
authors.lastname: Zhao
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002417:Cattle; D024901:Drug Resistance, Multiple, Bacterial; D005260:Female; D005838:Genotype; D055231:Lincosamides / Q000494:pharmacology; D018942:Macrolides / Q000494:pharmacology; D008414:Mastitis, Bovine / Q000382:microbiology*; D008826:Microbial Sensitivity Tests; D013210:Staphylococcus / Q000145:classification / Q000187:drug effects* / Q000302:isolation & purification; D025381:Streptogramin B / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D055231:Lincosamides; D018942:Macrolides; D025381:Streptogramin B