first two vancomycin resistant staphylococcus aureus isolates in mansoura university hospital; epidemiology and antimicrobial study

ABSTRACT

Staphylococcus aureus, a major cause of potentially life threatening infections acquired in health care and community settings, has developed resistance to most classes of antimicrobial agents with dramatic increase in the number of health care associated infections due to methicillin resistant S. aureus [MRSA]. During the period of our study 974 S. aureus strains were isolated from different types of infections in different wards of Mansoura University Hospitals [MUH], 530 [54.4%] isolates were methicillin sensitive S. aureus [MSSA] and 444 [45.6%] isolates were MRSA. Simplified population analysis of MRSA strains revealed, 27 [6.08%] heterogeneous vancomycin intermediate sensitive S. aureus [hVISA], 12 [2.70%] vancomycin intermediate sensitive S. aureus [VISA], while 2 [0.45%] isolates were vancomycin resistant S. aureus [VRSA]. hVISA strains were isolated from different infections, mainly from blood stream infections [29.63%] and infected skin ulcers and bedsores [29.63%], where the 12 VISA strains were isolated from infected skin ulcers and bedsores [41.66%], infected surgical wounds [41.66%] and lower respiratory tract infections [16.67]. The 2 VRSA isolates were isolated from blood stream infection [one case] and an infected bedsore [the other case]. One of the 2 VRSA cases was isolated from children hospital and the other one was isolated from medical wards. Minimal inhibitory concentration [MIC] of different antimicrobial agents for S. aureus with diminished sensitivity to vancomycin was done by microdilution method revealing a significant difference in resistance among VISA, hVISA and VRSA with vancomycin, linzolide, meropenem. Time kill study of different antibiotics for VRSA isolates showed that, vancomycin exhibited no kill activity at 1X MIC, but killing activity was achieved only at 2X and 4X. Other tested antibiotics were significantly had killing activity more than vancomycin at concentration of 1X MIC. Daptomycin, quinipristin/dalfopristin, tigecyclin, meropenem, ciprofloxacin, and erythromycin were significantly had killing activity more than linezolide at concentration of 1X MIC. In conclusion, the first two identified VRSA isolates from children hospital and medical wards still susceptible to some antibiotics which are not used widely such as, daptomycin, quinipristin/dalfopristin and tigecyclin, also hVISA and VISA had antimicrobial susceptibility pattern similar to VRSA isolates