MOLECULAR-DISTRIBUTION OF ROB-1 BETA-LACTAMASE IN ACTINOBACILLUS-PLEUROPNEUMONIAE

The plasmid content and molecular distribution of the ROB-1 beta-lactamase was investigated in 31 swine isolates of Actinobacillus pleuropneumoniae. Three types of plasmid patterns were observed in ampicillin-resistant isolates: a predominant one consisting of 2.6-, 2.9-, and 5.0-kb plasmids and two other patterns consisting of 4.2- and 5.5-kb plasmids and of a 6.8-kb plasmid. Plasmid DNA preparations were hybridized with a bla(ROB-1) intragenic fragment from the Haemophilus influenzae R(rob) plasmid. Positive hybridizations were observed with all ampicillin-resistant isolates. The bla(ROB-1) gene was found on 3 plasmids of 2.6, 5.5, and 6.8 kb. One swine isolate of Pasteurella multocida also had a 2.6-kb plasmid bearing bla(ROB-1). ROB-1 was confirmed in typical isolates by isoelectric focusing and bla(ROB-1) sequences were confirmed by polymerase chain reaction amplification with an intragenic set of primers. Plasmids bearing bla(ROB-1) were successfully electro-transformed in a susceptible A. pleuropneumoniae isolate. These results emphasize the importance of ROB-1 in A. pleuropneumoniae and identify a possible reservoir of beta-lactam resistance.