Evidence Suggesting Importance of Role of Interbacterial Inhibition in Maintaining Balance of Normal Flora

SUMMARY

Evidence presented in support of the hypothesis that interrelationships among organisms in the pharynx provide one of the mechanisms that maintain the bacterial status quo. Many organisms in the normal pharynx are capable in vitro of preventing the growth of other bacterial species—species with which they coexist in vivo or test organisms to which they are exposed experimentally. The majority of these "inhibitors" as revealed by the aerobic techniques described are alpha hemolytic streptococci. Detailed study of cultures from the posterior pharynx of patients undergoing massive antibiotic therapy for open heart surgery shows that as virtually all inhibitors (alpha hemolytic streptococci) in the patient's normal flora are suppressed by antibiotic therapy, overgrowth of bacteria not usually found in the pharynx routinely occurs. When therapy is withdrawn inhibitors reappear, and normal flora is reestablished. When inhibitors are resistant to the antibiotics used, no such overgrowth occurs. The data presented indicate that presence of the inhibitors plays a key role in maintaining the balance of normal flora.