Possible misinterpretation of penicillin susceptibility in Staphylococcus aureus blood isolate due to in vitro loss of the blaZ gene

We describe a case of recurrent catheter-related blood stream infections (BSI) withStaphylococcusaureus, in which the first isolate tested susceptible to penicillin, while subsequent isolates were resistant. Phenotypic susceptibility correlated with the absence/presence of theblaZ gene. The in vitro stability of penicillin resistance was investigated by subculturing single colonies. In two out of five colonies, phenotypical resistance was lost after a single subculture, which correlated with loss of theblaZ gene. This in vitro phenomenon probably resulted in a very major error in the microbiology report of the first BSI, where penicillin had been recommended as treatment.
Source: European Journal of Clinical Microbiology and Infectious Diseases - Category: Microbiology Source Type: research