Antibiotic resistance in Providencia stuartii isolated in hospitals

A total of 238 isolates of Providencia stuatii obtained from infected patients in six Dublin hospitals were grouped by using serological and bacteriocin typing methods and tested for sensitivity to a number of antimicrobial agents. Most isolates were resistant to several of these agents. Resistance to tetracycline, resistance to pencillin, resistance to polymyxin, and probably resistance to nitrofurantoin were intrinsic. Plasmid screening coupled with resistance transfer studies showed that both chromosome-encoded and plasmid-encoded resistance mechanisms were clinically important. Ampicillin resistance was both chromosomally and plasmid encoded, whereas resistance to kanamycin and resistance to carbenicillin were exclusively plasmid encoded. Gentamicin resistance was more common than kanamycin resistance, and although gentamicin-resistant strains contained aminoglycoside acetyltransferase activity, no association could be demonstrated with plasmid deoxyribonucleic acid in the strains tested. Unlike minimal inhibitory concentrations for kanamycin, minimal inhibitory concentrations for gentamicin varied over wide range. P. stuartii isolates obtained from several different countries were tested for comparison. As a group, these strains were less resistant, but they did exhibit similar resistance properties.