Comparison of antibiotic susceptibility tests, plasmid profiles and restriction enzyme analysis of plasmid DNA of methicillin susceptible and resistant-Staphylococcus aureus strains isolated from intensive care units.

OBJECTIVES: To differentiate methicillin-resistant Staphylococcus aureus (S. aureus) (MRSA) and methicillin-sensitive S. aureus (MSSA) strains and detect the source of epidemic strains and prevent their access to patients.

METHODS: All the procedures were carried out in the Department of Microbiology, Medical Faculty Hospital, Dokuz Eylul University, Izmir, Turkey from 1996-1998, and antibiotic susceptibility tests continued in the laboratory of King Fahad Hospital, Al-Baha, Kingdom of Saudi Arabia (KSA), from 2001-2004. A total of 81 S. aureus strains (71 MRSA, 10 MSSA) from Turkey were isolated from different sites of patients in Intensive Care Unit's (ICU's), evaluated by plasmid profile, Restriction Endonuclease Analysis of Plasmids (REAP), and antibiotic sensitivity tests. A total of 117 S. aureus strains (24 MRSA, 93 MSSA) from KSA were isolated from different sites of patients in ICU's, evaluated by antibiotic sensitivity tests as recommended by National Committee for Clinical Laboratory Standards (NCCLS).

RESULTS: Seventy-one MRSA from Turkey were divided into 13 groups by antibiotic sensitivity tests and into 4 groups by plasmid profiles, in which 3rd and 4th groups subdivided into 2 subgroups, and into 5 groups by REAP. The 1st, 2nd, 3rd and 5th groups were subdivided into 2 subgroups. Ten MSSA were divided into 4 groups by antibiotic sensitivity tests, 3 in plasmid profiles and 2 in REAP tests. Twenty-four MRSA strains from KSA were divided into 9 groups by antibiotic sensitivity tests while 93 MSSA strains were divided into 7 groups.

CONCLUSIONS: In respect to epidemiological survey, plasmids profiles and REAP seems to discriminate more respect to antibiotic sensitivity tests but at the same time neither of them were 100% accurately differential. According to the plasmid profile of the 3rd MSSA (Turkey) group, a multi-drug resistance by antibiotic susceptibility tests were noticed and showed the same plasmid profile in MRSA first subgroup of the 3rd group, but the same groups were different in REAP tests. In order to distinguish the discriminatory power of the strains, where REAP is better than plasmid profile and antibiotic sensitivity tests, we may formulate the statement into the following; REAP > plasmid profile > antibiotic sensitivity tests. For typing and gathering of epidemiological data, it is suggested that all 3 methods should be employed in clinical laboratories as they are cheap, practical and easily interpreted.