Fifty-nine isolates of Staphylococcus aureus and a single strain of Staphylococcus intermedius were typed by arbitrarily primed PCR (AP-PCR). To study reproducibility and discriminatory abilities, AP-PCR was carried out in seven laboratories with a standardized amplification protocol, template DNA isolated in a single institution, and a common set of three primers with different resolving powers. The 60 strains could be divided into 16 to 30 different genetic types, depending on the laboratory. This difference in resolution was due to differences in technical procedures (as shown by the deliberate introduction of experimental variables) and/or the interpretation of the DNA fingerprints. However, this did not hamper the epidemiologically correct clustering of related strains. The average number of different genotypes identified exceeded those of the more traditional typing strategies (F. C.

A typing procedure for methicillin-resistant Staphylococcus aureus (MRSA) based on the polymerase chain reaction (PCR) amplification of both mecA sequences and variable DNA sequences as present in the prokaryotic genome has been developed. Two primers based on the sequences of DNA repeats as discovered in gram-negative members of the family Enterobacteriaceae allow detection of variable regions in the genome of a gram-positive bacterium such as S. aureus, as does a newly described arbitrary primer. This procedure, enabling the detection of 23 different genotypes in a collection of 48 MRSA isolates, was validated by comparisons with phage typing studies. It appeared that within the same group of isolates only 13 different phagovars could be identified. Combination of the results from both phage typing and genotyping allowed the discrimination of 34 of 48 isolates. However, depending on the primer-variable complexity of the PCR fingerprints, which could also be modulated by combination of PCR primers, clear homologies between the groups defined by either phage typing or fingerprinting were observed. An analysis of an MRSA outbreak in a geriatric institution showed a collection of genetically homogeneous isolates. In agreement with phage typing, PCR fingerprinting revealed the identical natures of the MRSA strains isolated from all patients.

No abstract

Twenty-six methicillin-resistant Staphylococcus aureus strains were genetically differentiated by interrepeat PCR and the results compared with those of ribotyping, pulsed-field gel electrophoresis (PFGE) and random amplified polymorphic DNA analysis obtained in a previous study for the same strains. The comparison showed that the PCR-mediated assays were as discriminatory as PFGE, whereas ribotyping was the least powerful genotyping method. Due to the ease of performance, PCR fingerprinting may become the method of choice for establishing clonal relationship among Staphylococcus aureus isolates.

No abstract