Objectives
Assessment of the antimicrobial effects of oxacillin and green tea on two S. aureus small colony variant (SCVs) strains and their parents.

Methods
Bacterial lawns of S. aureus NCTC 6571 and Mu50 were prepared on Mueller Hinton agar (MHA) and MHA containing 6 µg/ml oxacillin according to BSAC guidelines. Filter disks were placed on the surface, and were impregnated with varying concentrations of green tea powder (resuspended in sterile water). Inhibition zones were measured after 24 h incubation at 37ºC. This procedure was repeated using triclosan selected SCVs derived from both wild type (WT) strains. Media were supplemented with 3 µg/ml triclosan to maintain SCV phenotypes, and incubation times were varied to obtain WT starting densities.

Results
NCTC 6571 was more susceptible to green tea than Mu50, and did not grow on oxacillin agar. The inhibition zones of Mu50 on oxacillin agar were up to 45% larger than on MHA. Both SCVs were less susceptible to green tea than WTs (MICs: 100 µg SCVs, 25 µg WTs). There was no significant difference between zone sizes with or without oxacillin against SCVs, and NCTC 6571 SCV grew on oxacillin agar.

Conclusions
These results show that green tea can increase oxacillin susceptibility in a strain of MRSA, as previously shown (e.g. Shiota S. et al. Biol. Pharm. Bull. 1999). However, these results also show that SCVs are considerably less susceptible to green tea than WT isolates, and that green tea does not affect the susceptibility of SCVs to oxacillin.