Methicillin-resistant Staphylococcus aureus (MRSA) is a significant
epidemiological problem. Detecting the sources of epidemic strains and
preventing their access to patients, however, depend upon the availability of
techniques to reliably distinguish among MRSA strains. Molecular typing of
MRSA generally demonstrates improved discriminatory power compared with
assays of phenotypic traits, and it is frequently preferred.
Objective :Evaluation of the discriminatory power and stability of restricted
enzyme analysis of plasmid (REAP) DNA among MRSA strains.
Material and Methods: 54 sequential MRSA isolates from 18 patients collected
within 30-36 days ( Three isolate from every patient , in average 15 days
interval between each isolate) .Isolates were subjected to plasmid screening ;
isolates with positive plasmid underwent typing by REAP using Hind III
restriction enzyme . Comparison were done to detect plasmid stability and
discriminatory power among sequential MRSA isolates.
Result :Among 54 sequential MRSA isolates; 45 were plasmid- positive
isolates from 15 patients by plasmid screening gel . Patient’s plasmid digestion
profile remained unchanged over a period up to one month except in two
cases (4.4%) . In one case , two distinctly different digestion profiles were
detected from a patient ( between the initial isolate and the second successive
isolate) .In the other case, two distinctly different digestion profiles were
detected from a patient (between the initial isolate and the third successive
isolate).Nine (16.6%) out of 54 MRSA isolates from 3 patients lacked plasmid.
Conclusion The frequency of genetic alteration in plasmid among MRSA
strains in vivo are infrequent and REAP profile of MRSA isolates is very stable
in vivo. The diversity and stability of MRSA plasmid types make them excellent
epidemiological markers. |
