Incidence of class 1 and 2 integrases in clinical and commensal bacteria from livestock, companion animals, and exotics

Many pathogenic and commensal organisms are multidrug resistant due to expo sure to various antibiotics. Often, this antimicrobial resistance is encode d by integrons that occur on plasmids or that are integrated into the bacte rial chromosome. Integrons are commonly associated with bacterial genera in the family Enterobacteriaceae, We determined that class 1 integrases were present in approximately 46% of the isolates from the family Enterobacteria ceae; class 2 integrases were present only among Escherichia coli and Salmo nella isolates. Seven percent of veterinary isolates were positive for clas s 3 integrase by DNA-DNA hybridization but could not be confirmed to be pos itive by PCR. None of the veterinary isolates possessed the class 4 integra se gene. The distribution of these integrase genes was variable within the members of the family Enterobacteriaceae when some or all integrase classes were absent from a particular genus. There was also considerable variabili ty in the distribution of these integrases within a species, depending on t he animal host. Unlike the class 1 integrases, the other integrase class, i ntI2, appears to be more restricted in its distribution among the members o f the family Enterobacteriaceae. There is also considerable variability in the distribution of the class 1 integrases within E. coli strains isolated from different food animals. The class 1 integrases are the most widely dis seminated of the four classes among the members of the family Enterobacteri aceae from both the clinical and normal flora of animals. This is the first report to closely examine the distribution of class 2 integrases in member s of the family Enterobacteriaceae isolated in the United States.