Characterization of borderline oxacillin-resistant Staphylococcus aureus isolated from food of animal origin

J Food Prot. 2010 Jul;73(7):1325-7. doi: 10.4315/0362-028x-73.7.1325.

Abstract

In this study, the molecular characteristics of food-derived oxacillin-resistant Staphylococcus aureus were determined. Eight borderline oxacillin-resistant strains with MICs of 2 to 4 microg/ml were identified from 132 S. aureus isolates of food origin. One of the two isolates with a MIC of 4 microg/ml was methicillin-resistant determinant (mecA) gene positive, and the other six with MICs of 2 microg/ml were mecA negative. The mecA-positive isolate was classified as sequence type (ST)228, staphylococcal protein A (spa) type t041, and carried the staphylococcal cassette chromosome mec type I element. Two borderline oxacillin-resistant strains were classified as spa t008 and ST8, and the remaining five as spa t164 and ST20. The mecA-positive strain and four borderline oxacillin-resistant strains were found enterotoxigenic. The enterotoxin genes detected in these strains included selp, egc1, and sed-sej-selr. The borderline-resistant S. aureus isolates from a manually handled product, i.e., minced pork, were shown genetically related to strains associated with human infections. This suggests that humans can be considered as a source of contamination of this food with oxacillin-resistant S. aureus strains. The genotypes of the investigated milk borderline-resistant isolates were shown to occur not only in cows, but also in humans. Since manual handling is reduced in raw milk production, a human origin of S. aureus seems unlikely. Because knowledge of the genotypes of animal staphylococci is limited, more research is needed to address the question of the origin of antibiotic-resistant S. aureus strains in food.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Anti-Bacterial Agents / pharmacology*
  • Cattle
  • Colony Count, Microbial
  • Consumer Product Safety
  • Dose-Response Relationship, Drug
  • Drug Resistance, Bacterial*
  • Food Contamination / analysis*
  • Genotype
  • Humans
  • Meat Products / microbiology
  • Microbial Sensitivity Tests
  • Milk / microbiology
  • Oxacillin / pharmacology*
  • Staphylococcus aureus / drug effects*
  • Staphylococcus aureus / isolation & purification

Substances

  • Anti-Bacterial Agents
  • Oxacillin