Silver-resistant Enterobacteriaceae from hospital patients

Abstract

The inclusion of agar medium containing 0.5 mM AgNO3 in the hospital laboratory replica-plating system for routine antibiotic-susceptibility determinations resulted in identification of species of Enterobacteriaceae (Escherichia coli, Enterobacter cloacae, Klebsiella pneumoniae, Proteus mirabilis and Citrobacter freundii) with Ag resistance. Since Oct. 1975, 11 inpatients receiving silver sulfadiazine for burn wound prophylaxis have yielded Ag-resistant bacteria from their infected burns. During this treatment routine burn-site cultures from these patients yielded 230 isolates of Enterobacteriaceae, including 211 which were sulfonamide-resistant, 97 of which were also Ag-resistant and 38 of which were untested for Ag resistance. Seven Ag-resistant but sulfonamide-sensitive isolates were incidentally recovered from respiratory specimens from 4 nonburn patients with Ag tracheostomy tubes; 1 Ag-resistant sulfonamide-sensitive isolate was recovered from a small infected burn on the foot of an Emergency Room patient. Previous treatment of this burn was unknown. Representative AgNO3-resistant E. coli isolates from 4 patients were serologically untypable. Serotyping of representative isolates of K. pneumoniae showed a diversity of types except from 2 patients who had been in the same ward at the same time.