Drug resistance and phage typing of clinical isolates of Staphylococcus aureus

Activities of antimicrobial agents were examined against Staphylococcus aureus strains isolated in 1990. Strains resistant to benzylpenicillin were isolated at the highest frequency (93.6%), and followed by those resistant to kanamycin (51.5%), erythromycin (49.0%), gentamicin (45.1%), fluoroquinolone (33.4%) and minocycline (12.3%). Most of these drug resistant strains of S. aureus were also resistant to methicillin. It should be noted that the MRSA strains were also resistant to other multiple drugs. Annual changes of MRSA in clinical isolates have been increasing since 1981. The isolation frequencies of MRSA strains were 18.9%, 44.8% in 1981 and 1990, respectively. Among methicillin susceptible S. aureus (MSSA), however, drug resistance to other antibiotics have been decreasing year by year. Many strains among both MRSA (73%) and MSSA (86%) were sensitive to typing phages of 100 x RTD. 76% of the MRSA strains were phage typed into groups III or mixed, and 60% of the MSSA strains were typed into these two groups, also.