Mixed Bacterial Infections in Relation to Antibiotic Activities

Abstract

Summary A high degree of protection was obtained by antibiotic-producing Micrococcus pyogenes var. albus strains of the human ocular microflora in mixed infections of mice with Clostridium septicum. Protection was obtained against at least 1,000 LD50 doses of this latter organism. The protection is most probably associated with in vivo secretion of functioning antibiotics. Strong correlation of in vitro and in vivo results with strains of varying antibiotic properties points to this conclusion. Failure to observe any differences in the abilities of these strains to survive in the tissues tends to rule out the possibility of nonspecific factors being operative. Solid protection was obtained both against the Clostridium septicum spores and vegetative cells. Living micrococci were more protective than heat-killed organisms. The latter apparently owe their small to moderate degree of prophylactic abilities to strongly adsorbed or intracellular antibiotic. This could not be washed off, and attempts to grow these organisms without antibiotic production were failures. Antibiotic-producing micrococci injected at sites removed from the Cl. septicum inoculation site, also seemed to confer a small degree of protection against lethal outcome. Delay in the injection of the antibiotic-producing micrococci until 2 or 5 hours after the Cl. septicum inoculum, greatly reduced the effectiveness of the protection, but did not completely eliminate it. Some of the animals injected after 5 hours had already developed local gas gangrene. The data presented strongly indicate that the human bacterial flora may represent a rich source of potentially valuable antibiotics for certain limited infections.