Phenotyping methods in epidemiological analysis of epidemic Staphylococcus aureus strains

One hundred and fifty hospital Staphylococcus aureus strains isolated on Polish hospitals during an outbreaks were used to evaluate usefulness of S. aureus phenotyping methods. According to the expression of resistance to methicillin (a marker of resistance to all beta-lactam antibiotics) all strains were classified as homogeneously of heterogeneously resistant to methicillin (methicillin resistant S. aureus--MRSA) and as susceptible to this antibiotic (methicillin-susceptible S. aureus--MSSA). All strains were analysed according to the resistance patterns to fifteen antistaphylococcal drugs, results of crystal violet test, phage patterns and results of biochemical fingerprinting by PhenePlate (PhP) System (BioSys inova). All MSSA analysed were resistant to penicillin and 22% to tetracycline, and only occasionally resistant to other antimicrobials. They showed sensitive to phages of all international and additional lytic groups. Heterogeneous MRSA were widely susceptible to almost all antimicrobials except tetracycline and were lysed by phages of Ist, IIIrd international groups and additional phages. All these strains produced penicillinases. Homogeneous MRSA were multi-drug resistant and were not typable by phages of Ist and IInd lytic groups and weakly typable by phages of IIIrd and additional groups. PhP Systems divided all used strains into 13 common (with two dominating) and 50 single strain PhP-types. The combination of various phenotyping methods may be useful in epidemiological investigation of hospitals.