INVITRO BACTERIOCIN-MEDIATED ANTAGONISM BY ORAL STREPTOCOCCI AGAINST HUMAN CARRIER STRAINS OF STAPHYLOCOCCI

All strains of oral streptococci tested and specially those of Streptococcus mutans, Strep. sanguis and Strep. mitior produced more than one distinct bacteriocin-like substance with variable inhibitory activity on 20 indicator staphylococci. Inhibitory activity was comparatively higher on nasal strains of Staph. aureus and Staph. epidermidis than on strains of both species isolated from the mouth. Nineteen of 20 staphylococcal indicators were inhibited by 1-12 of the 12 effector streptococci. Sensitivity of nasal staphylococci to bacteriocins (frequency of positive inhibitor tests and total inhibition zone diameters) was significantly higher (P < 0.001, chi-2 test and P < 0.05, t test respectively) than that of oral ones. The sensitivity of nasal over oral Staph. aureus (P < 0.001 and P < 0.01) and of oral Staph. epidermidis over oral Staph. aureus (P < 0.01 and P < 0.05) was also significantly higher. The evaluation of variability of inhibitory patterns of bacteriocins produced by streptococci (p-typing), of sensitivity patterns of staphylococci to bacteriocins (s-typing) and of the significantly higher sensitivity of nasal over oral staphylococci to bacteriocins from the epidemiological and ecological viewpoints are discussed.