Studies On Coagulase‐Negative Staphylococci In Patients Undergoing Cardiac Surgery

Abstract

Hypotheses for the origin of multiply‐resistant coagulase‐negative staphylococci from 146 patients undergoing cardiac surgery were tested. All received cephalothin per‐operatively. Antibiotic susceptibility testing, phage‐typing, bio‐typing, and test for Tween‐80‐splitting enzyme were used to characterize 132 isolates from nose swabs. Seventy‐five percent of the pre‐operative susceptible isolates were of biotype 1, while biotypes 3 and 4 made up 59% of the post‐operative, multiply‐resistant isolates. Fifty‐three percent of the isolates were typable by phage‐typing. Typability of isolates of biotype 1 was high (56%) while almost 75% of biotype 4 were untypable. Susceptible isolates were more often typable than multiply‐resistant ones. Of the 146 patients, 105 (72%) carried coagulase‐negative staphylococci pre‐operatively, only two of them carried multiply‐resistant strains. Fifty‐nine patients (41%) were colonized with multiply‐resistant coagulase‐negative staphylococci post‐operatively. By combining the results of bio‐typing, phage‐typing, and test for Tween‐splitting enzyme the study made it probable that a maximum of ten patients (6.8%) already carried multiply‐resistant strains on admission to the hospital or were carriers of initially susceptible strains which developed multiple‐resistance during administration of antibiotics. It therefore seemed likely that most of the patients were deprived of their natural bacterial flora by antibiotic treatment and subsequently colonized post‐operatively with multiply‐resistant coagulase‐negative staphylococci from the environment.