Mono sulfamethoxazole/trimethoprim and Vancomycin combination antimicrobial zctivity against methicillin-resistant Staphylococcus aureus

Abstract

Activity of trimethoprim/sulfamethoxazole (SXT) alone or in combination with vancomycin (VAN) was evaluated against methicillin-resistant Staphylococcus aureus (MRSA) from 26 clinical isolates from patients admitted to Hua Hin Hospital, Prachuap Khiri Khan Province, Thailand between January 2015 and December 2016. Antimicrobial susceptibility of SXT and VAN was determined using an E-test and of SXT-VAN combination by E-test and an checkerboard (isobologram) method. Clonal relationship among MRSA strains (n = 16) based on spa typing showed the existence of three types: spat045 (75%), spat439 (19%) and spat13880 (6%). All MRSA isolates were susceptible to VAN; STX MIC50 (minimum inhibitory concentration required to inhibit the growth of 50% of organisms), MIC90 and MIC range was 0.047, 0.064 and 0.032-?32 µg/ml, respectively with one strain being resistant. STX-VAN combination demonstrated additive or indifferent effect against the majority of the isolates, except synergism (by checkerboard method) in two isolates. Pharmacodynamics of STX bactericidal activity against six representative strains exhibited concentration (up to 8-16X MIC) and time (over 24 hours) dependency. Thus, SXT-VAN combination provided a possible regimen against MRSA but its efficacy in clinical use has to be evaluated.