ABSTRACT

Anaerobic bacteria differ in their pathogenicity. Not all of them are believed to be clinically significant, while others are known to be highly pathogenic. Table 1.1 lists the major anaerobes that are most frequently encountered clinically. The species of anaerobes most often isolated from clinical infections are, in decreasing frequency, gramnegative rods (Bacteroides, Prevotella, Porphyromonas, Fusobacterium, Bilophila, and Sutterella), gram-positive cocci (primarily Peptostreptococcus), gram-positive spore-forming (Clostridium) and non-spore-forming bacilli (Actinomyces, Propionibacterium, Eubacterium, Lactobacillus, and Bifidobacterium), and gram-negative cocci (mainly Veillonella).1 About 95% of the anaerobes isolated from clinical infections are members of these genera (Table 1.2). The remaining isolates belong to species not yet described, but these can usually be assigned to the appropriate genus on the basis of morphologic characteristics and fermentation products. The frequency of recovery of the different anaerobic strains differs in various infectious sites. We have summarized our experience in recovering anaerobic bacteria over a period of 12 years from both adults and children.2 Anaerobic gram-negative bacilli (Bacteroides, Prevotella, and Porphyromonas) accounted for 43% of anaerobic isolates (Table 1.2). They were predominant in genitourinary infections (56% of all anaerobic isolates), abdominal infections (55%), abscesses (51%), obstetric and gynecologic infections (49%), infected cysts (44%), wounds (43%), and tumors (42%). They were less often recovered in infections of the central nervous system (7%), eye (12%), joint (13%), and lymph glands (15%).