A novel molecular pattern for methicillin-resistant Staphylococcus aureus in Milwaukee, WI clinical isolates

Methicillin-resistant Staphylococcus aureus is a significant problem in healthcare settings around the world. To effectively track different strains, we used a number of genetic procedures. In this study, 252 clinical isolates from the Milwaukee, WI, area were analyzed by the multiplex polymerase chain reaction (PCR) method to determine which of the described types were present. Most strains were categorized into one of the known groups, although types III and IIIA strains were not found. An unusual variant was found in 17% of the samples. This variant (v1) contains an 800-base pair amplimer that was created from a unique configuration of 2 primers from different sets in the multiplex PCR procedure. Although superficially similar to a type I pattern, sequencing of the amplimer demonstrated that it is identical to a sequence from the USA300 strain, a type IV strain. It is suggested that this variant may have resulted from acquisition of an IS431 element near the dcs region. There is potential for misidentification of strains because of slight genetic alterations such as this one. Statistical analysis using a chi(2) contingency table demonstrated that amoxicillin/clavulanic acid resistance was significantly lower in types I and IA when compared with the other types, whereas erythromycin resistance was significantly lower in type I when compared with other types. However, there was not a significant difference for any of the new variants.