title: Minimum inhibitory concentrations of cephalosporin compounds and their active metabolites for selected mastitis pathogens.
abstract: OBJECTIVE
  To compare the minimum inhibitory concentration (MIC) of cephapirin and ceftiofur with MICs of their active metabolites (desacetylcephapirin and desfuroylceftiofur) for selected mastitis pathogens.
  
  
  METHODS
  488 mastitis pathogen isolates from clinically and subclinically affected cows in commercial dairy herds in Wisconsin.
  
  
  METHODS
  Agar dilution was used to determine MICs for Staphylococcus aureus (n = 98), coagulase-negative staphylococci (99), Streptococcus dysgalactiae (97), Streptococcus uberis (96), and Escherichia coli (98).
  
  
  RESULTS
  All S aureus isolates were susceptible to cephapirin and ceftiofur. Most coagulase-negative staphylococci were susceptible to cephapirin and ceftiofur. For E coli, 50 (51.0%; cephapirin) and 93 (94.95%; ceftiofur) isolates were susceptible to the parent compounds, but 88 (89.8%) were not inhibited at the maximum concentration of desacetylcephapirin. All S dysgalactiae isolates were susceptible to ceftiofur and cephapirin, and consistent MICs were obtained for all compounds. Most S uberis isolates were susceptible to cephapirin and ceftiofur. Of 98 S aureus isolates classified as susceptible to ceftiofur, 42 (42.9%) and 51 (52%) were categorized as intermediate or resistant to desfuroylceftiofur, respectively. For 99 coagulase-negative staphylococci classified as susceptible to ceftiofur, 45 (45.5%) and 17 (17.2%) isolates were categorized as intermediate or resistant to desfuroylceftiofur, respectively. For all staphylococci and streptococci, 100% agreement in cross-classified susceptibility outcomes was detected between cephapirin and desacetylcephapirin. No E coli isolates were classified as susceptible to desacetylcephapirin.
  
  
  CONCLUSIONS
  Differences in inhibition between parent compounds and their active metabolites may be responsible for some of the variation between clinical outcomes and results of in vitro susceptibility tests.
authors.affiliation: Department of Animal Nutrition and Production, School of Veterinary Medicine, University of São Paulo, Pirassununga, SP-17 13635-900, Brazil.
authors.forename: Cristina S
authors.initials: CS
authors.lastname: Cortinhas
authors.forename: Leane
authors.initials: L
authors.lastname: Oliveira
authors.forename: Carol A
authors.initials: CA
authors.lastname: Hulland
authors.forename: Marcos V
authors.initials: MV
authors.lastname: Santos
authors.forename: Pamela L
authors.initials: PL
authors.lastname: Ruegg
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D001419:Bacteria / Q000145:classification / Q000187:drug effects*; D002417:Cattle; D002511:Cephalosporins / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D024901:Drug Resistance, Multiple, Bacterial; D005260:Female; D008414:Mastitis, Bovine / Q000382:microbiology*; D008826:Microbial Sensitivity Tests; D013045:Species Specificity
chemical_list: D000900:Anti-Bacterial Agents; D002511:Cephalosporins