Simultaneous persistence of methicillin-resistant and methicillin-susceptible clones of Staphylococcus aureus in a neonatal ward of a Warsaw Hospital

Fifty-seven methicillin-resistant Staphylococcus aureus (MRSA) isolates from babies (N = 31), carriers amongst health care workers (N = 16; 10% of all staff members) and the environment (N = 10); 39 MSSA isolates, from babies (N = 18), health care workers (N = 5) and environment (N = 16) were analysed. The strains were from the neonatal ward of a teaching hospital in Warsaw and were collected over a period of 16 months (1993/1994). The isolates were characterized by phage-typing, arbitrary-primed polymerase chain reaction (AP PCR), DNA repeat polymorphism within the protein A gene and the resistance pattern to antimicrobial agents. The presence of the mecA gene was determined by PCR. MRSA were classified as heterogeneously resistant to methicillin, susceptible to other antimicrobial agents and, except for three isolates, appeared to be genotypically almost identical. The first example of mupirocin resistant MRSA in Poland was documented. Amongst MSSA isolates, increased variability was seen, however, the persistence of one predominate clone of MSSA was shown. In this particular hospital environment, several different strains of both MRSA and MSSA were capable of maintaining persistent colonization.