Methicillin-Resistant Strains of Staphylococcus aureus Phage Type 92

Abstract

Methicillin-resistant (Mec ^r ) strains of Staphylococcus aureus received for phage typing from several hospitals in New York City were resistant to the international set of typing phages but susceptible to experimental phage 92. Subsequently, strains of type 92 were detected in two outbreaks with Mec ^r strains in two other locations in the United States. In all instances, type 92 was predominant among the Mec ^r strains isolated in each hospital. With the exception of one strain, the methicillin resistance of the Mec ^r strains investigated was homogeneous. In most instances, isolates from the same hospital were closely similar in their antibiotic resistance patterns. The strains isolated in New York City could be divided into three groups by the host range of their lysogenic phages and by antigenic structure. Transduction experiments indicated that the transfer of chromosomal tetracycline resistance from Mec ^r strains into a strain susceptible to several international typing phages renders the latter nontypable. However, the acceptor strain remains susceptible to experimental phages 92 and 88. Transduction of methicillin resistance had no effect on the phage susceptibility of the acceptor strain. It is possible that the presence of chromosomal tetracycline resistance is a determining factor in the phage susceptibility of Mec ^r strains isolated in New York City.