An overview is presented of the kinds of anaerobic bacteria that inhibit the surfaces of the human body. The anaerobic floras of the skin, oral cavity, alimentary tract, and genitourinary tract are described. The activities of these organisms that impact on the human host and their interactions are discussed. Emphasis is placed on the protective roles of the floras of the various bodily surfaces in preventing infections. Identified mechanisms of protection on the skin and in the colon and the vagina are explained.

The effect of atmospheric oxygen on the viability of 13 strains of anaerobic bacteria, two strains of facultative bacteria, and one aerobic organism was examined. There were great variations in oxygen tolerance among the bacteria. All facultative bacteria survived more than 72 h of exposure to atmospheric oxygen. The survival time for anaerobes ranged from less than 45 min for Peptostreptococcus anaerobius to more than 72 h for two Clostridium perfringens strains. An effort was made to relate the degree of oxygen tolerance to the activities of superoxide dismutase, catalase, and peroxidases in cell-free extracts of the bacteria. All facultative bacteria and a number of anaerobic bacteria possessed superoxide dismutase. There was a correlation between superoxide dismutase activity and oxygen tolerance, but there were notable exceptions. Polyacrylamide gel electropherograms stained for superoxide dismutase indicated that many of the anaerobic bacteria contained at least two electrophoretically distinct enzymes with superoxide dismutase activity. All facultative bacteria contained peroxidase, whereas none of the anaerobic bacteria possessed measurable amounts of this enzyme. Catalase activity was variable among the bacteria and showed no relationship to oxygen tolerance. The ability of the bacteria to reduce oxygen was also examined and related to enzyme content and oxygen tolerance. In general, organisms that survived for relatively long periods of time in the presence of oxygen but demonstrated little superoxide dismutase activity reduced little oxygen. The effects of medium composition and conditions of growth were examined for their influence on the level of the three enzymes. Bacteria grown on the surface of an enriched blood agar medium generally had more enzyme activity than bacteria grown in a liquid medium. The data indicate that superoxide dismutase activity and oxygen reduction rates are important determinants related to the tolerance of anaerobic bacteria to oxygen.

Swiss white mice were given ampicillin, clindamycin, kanamycin, metronidazole, or streptomycin in drinking water for a period of 3 weeks. One week after the initiation of antibiotic administration, the treated mice and untreated control mice were challenged orally with approximately 108 viable, streptomycin-resistant (SR) Pseudomonas aeruginosa isolates. All five of the antibiotics decreased the resistance of the mice to intestinal colonization with SR P. aeruginosa, as reflected by an increased fecal carriage of the organism and an increase in population levels of SR P. aeruginosa in feces as compared with untreated controls. Metronidazole was least effective in this regard. The antibiotics lowered the dose of SR P. aeruginosa that resulted in implantation in 50% of the mice ID50 to various degrees. Administration of streptomycin, the most effective antibiotic, caused a 10,000-fold decrease in ID50 as compared with untreated controls. Oral inoculation of approximately 108 organisms of SR P. aeruginosa resulted in translocation of the organism to the * Corresponding author.

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The addition of 5 mg of streptomycin sulfate per ml to the drinking water of Swiss white mice resulted in a 100,000-fold reduction in the 50% implantation dose of streptomycin-resistant Salmonella typhimurium for the animals. When streptomycin-treated and untreated mice were challenged orogastrically with 103 viable S. typhimurium organisms, 100% of the treated and none of the untreated mice excreted the pathogen in their feces. Similarly, translocation of S. typhimurium from the intestinal tract to the liver, spleen, and mesentery occurred in 10 of 10 treated mice but in none of the untreated mice 7 days after challenge with 103 CFU. Studies of colonization dynamics showed that S. typhimurium was present at high population levels in the intestines of streptomycin-treated mice and in detectable levels in the liver, spleen, and mesentery within 72 h after challenge with 103, 105, or 108 organisms. In untreated mice challenged with either 103 or 105 S. typhimurium organisms, the organisms were isolated from ileal and cecal tissues but not from ileal or cecal contents or from extraintestinal tissue 72 h after challenge. When untreated mice were challenged with 108 organisms, however, S. typhimurium was present in all organs and in intestinal contents. Streptomycin treatment, therefore, facilitated colonization and development of streptomycin-resistant S. typhimurium populations in intestines of mice and the subsequent translocation of the organisms from the intestinal tract to other tissues.

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Thirty-three strains of anaerobic bacteria isolated from human clinical specimens were examined for the presence of heparinase, hyaluronidase, chondroitin sulfatase, gelatinase, collagenase, fibrinolysin, lecithinase, and lipase activities. Pronounced heparinase activity was limited to species of the genus Bacteroides. A number of species of the genera Bacteroides and Clostridium produced hyaluronidase and chondroitin sulfatase. Gelatinase, collagenase, and fibrinolysin activities were encountered in isolates of the genera Bacteroides, Clostridium, and Peptostreptococcus. All strains capable of degrading collagen also hydrolyzed other protein substrates. Lipolytic activity was minimal among these anaerobic bacteria. No specific hydrolytic activity was consistently associated with the isolates.