Silver-resistant Enterobacteriaceae from hospital patients.

The inclusion of agar medium containing 0.5 mM AgNO3 in the hospital laboratory replicating 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 silver resistance. Since the study began in October, 1975, 11 in-hospital patients receiving silver sulfadiazine for burn wound prophylaxis have yielded silver-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 silver-resistant, and 38 of which were untested for silver resistance. Seven silver-resistant but sulfonamide-sensitive isolates were incidentally recovered from respiratory specimens from four nonburn patients with silver tracheostomy tubes, one silver-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 four patients were serologically untypable. Serotyping of representative isolates of K. pneumoniae showed a diversity of types except from two patients who had been in the same ward at the same time.