Characteristics of Staphylococcus aureus strains isolated from clinical and non-clinical human sources in Trinidad: susceptibility to bacteriophages and antimicrobial agents, and toxigenicity.

The susceptibility of Staphylococcus aureus strains isolated from human clinical and non-clinical sources in Trinidad to bacteriophages and antimicrobial agents was determined. The ability of the strains to produce enterotoxins and toxic shock syndrome toxin-1 (TSST-1) was also investigated. Of the 554 strains tested, 454 (81.8%) were susceptible to international phage set (IPS) phages with strains isolated from bacteruria (57.1%) and bacteremia (53.3%) having a low sensitivity compared to isolates from aspirates (87.3%) and anterior nares (97.4%). All sources combined, strains were most susceptible to phages belonging to several groups (mixed). Overall, 419 (75.6%) strains were resistant to one or more of nine antimicrobial agents tested. Resistance to penicillin was most prevalent, with 413 (74.5%) strains found to be resistant. Prevalence of resistance to tetracycline, gentamicin, oxacillin, cefuroxime and ciprofloxacin was 5.1%, 2.0%, 0.7%, 0.4% and 0.4%, respectively. Of the 554 strains tested, 307 (55.4%) produced staphylococcal enterotoxins A (SEA), B (SEB), C (SEC) and D (SED) singly or in combination. Strains recovered from high vaginal swabs were least enterotoxigenic (40.0%) as compared to umbilical infection isolates which were most enterotoxigenic (78.9%). TSST-1 was produced by 95 (19.0%) out of 499 strains tested, with isolates from bacteruria found to be most toxigenic (33.3%). It was concluded that the S. aureus strains tested were highly susceptible to bacteriophages and antimicrobial agents (except penicillin) and that enterotoxigenic and TSST-1 producers were widespread and have an aetiologic potential.