DEMONSTRATION OF AN R-PLASMID IN A STRAIN OF PASTEURELLA-HAEMOLYTICA ISOLATED FROM FEEDLOT CATTLE

Abstract

A strain of P. haemolytica isolated from the lungs of feedlot cattle with pneumonia was resistant to ampicillin, tetracycline and streptomycin. Two small, nontransmissible plasmids were responsible: for tetracycline resistance, a 5.7 .times. 106 dalton plasmid, and for streptomycin resistance, a 5.5 .times. 106 dalton plasmid. Ampicillin resistance passed by transformation to Escherichia coli was not shown conclusively to be on a plasmid. Ampicillin resistance was mediated by a .beta.-lactamase with high activity against cephaloridine.