The normal human anaerobic microflora.

Anaerobic bacteria are prevalent among the bacterial populations of the human body, particularly on mucous membrane surfaces. The major sites with a rich anaerobic normal microflora are the mouth, the gastrointestinal tract and the female genital tract. The oral cavity harbours more than 300 different bacterial species. The concentrations of bacteria in saliva are 10(8) to 10(9) colony forming units/ml and anaerobic bacteria outnumber aerobic bacteria by 10:1. On the tooth surfaces, the concentrations of bacteria are 10(10) to 10(11) cfu/ml with a predominance of anaerobes. Bacterial concentrations in gingival scrapings are 10(11) to 10(12) cfu/ml with anaerobic bacteria outnumbering aerobic bacteria by 1000:1. In the saliva and on the tongue surface, the predominant anaerobic bacteria are cocci, while in the gingival crevice large concentrations of gram-negative rods are recovered. Microorganisms found in the upper intestinal tract are different from those in the lower intestinal tract. In the stomach and the proximal small bowel, the microorganisms found as normal flora are a reflection of the oral flora. Bacterial concentrations in this region are 10(2)-10(5) cfu/ml intestinal content. In the colon, bacterial concentrations of 10(11)-10(12) cfu/g faeces are found. About 500 different bacterial species are recovered in the lower intestine. The most common anaerobic microorganisms are bifidobacteria, lactobacilli and bacteroides. Recent studies have used quantitative techniques for analyses of the vaginal flora and it has been found that anaerobic bacteria outnumber aerobic bacteria in the vagina by approximately 10:1. The most prevalent bacteria are peptococci, present in counts of 10(7)-10(8) cfu/ml. Lactobacilli, corynebacteria, eubacteria and bacteroides are also isolated.