title: In vitro activities of spectinomycin and comparator agents against Pasteurella multocida and Mannheimia haemolytica from respiratory tract infections of cattle.
abstract: OBJECTIVE
  Prior to the renewal of spectinomycin licensing for veterinary uses in Germany, 154 Pasteurella multocida and 148 Mannheimia haemolytica strains from respiratory tract infections in cattle were investigated for their MICs of spectinomycin and other antimicrobial agents. The data obtained should serve as a baseline from which to judge the future development of resistance. Moreover, the in vitro activity of spectinomycin in comparison with other antimicrobials should be assessed.
  
  
  METHODS
  MIC determination for all 302 strains was performed by the broth dilution method and evaluated according to NCCLS standards. MIC(50) and MIC(90) values were calculated. Strains resistant to spectinomycin were subjected to PCR assays for genes known to mediate spectinomycin resistance in Gram-negative and Gram-positive bacteria.
  
  
  RESULTS
  With the exception of resistance to sulfamethoxazole in P. multocida and M. haemolytica, and resistance to ampicillin in M. haemolytica, an overall low level of resistance was detected. A total of 93.5% of the P. multocida and 98.6% of the M. haemolytica strains were susceptible to spectinomycin, with MIC(90)s of 32 mg/L. PCR analysis showed that none of the spectinomycin-resistant strains carried any of the aadA gene subtypes, nor the genes spc or aad(9).
  
  
  CONCLUSIONS
  Prior to the renewal of spectinomycin, only a small number of spectinomycin-resistant strains was detected among bovine P. multocida and M. haemolytica. The genes responsible for spectinomycin resistance in these strains seemed to be different from those so far known to occur in other Gram-negative and Gram-positive bacteria.
authors.affiliation: Institut für Tierzucht der Bundesforschungsanstalt für Landwirtschaft (FAL), Höltystrasse 10, 31535 Neustadt-Mariensee, Germany. stefan.schwarz@fal.de
authors.forename: Stefan
authors.initials: S
authors.lastname: Schwarz
authors.forename: Corinna
authors.initials: C
authors.lastname: Kehrenberg
authors.forename: Sarah A
authors.initials: SA
authors.lastname: Salmon
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Watts
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002417:Cattle; D002418:Cattle Diseases / Q000453:epidemiology / Q000382:microbiology*; D004269:DNA, Bacterial / Q000235:genetics; D005858:Germany / Q000453:epidemiology; D016978:Mannheimia haemolytica / Q000187:drug effects* / Q000235:genetics; D008826:Microbial Sensitivity Tests; D016979:Pasteurella multocida / Q000187:drug effects* / Q000235:genetics; D012141:Respiratory Tract Infections / Q000453:epidemiology / Q000382:microbiology* / Q000662:veterinary*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000198:Spectinomycin / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D000198:Spectinomycin