The genera Actinomyces, Bifidobacterium, Eubacterium, Eggerthella, Collinsella, anaerobic Lactobacillus, Mobiluncus, Atopobium, and Propionibacterium are among the anaerobic, gram-positive, non–spore-forming bacilli. These organisms are typically found as normal flora on the mucosal surfaces of the human digestive tract and urogenital tract and on the skin. These organisms rarely cause infections independently. They typically are identified in a polymicrobic infection of a mucosal surface, such as the oral or vaginal cavity or the urogenital tract.

The genera Actinomyces (anaerobic and aerotolerant) and Mobiluncus (strictly anaerobic) include species that show non–acid-fast, gram-positive, pleomorphic branching rods or coccobacilli. Direct examination and the macroscopic presence in purulent exudate of “sulfur granules,” which reveal gram-positive filaments when crushed, is diagnostic for an infection with Actinomyces spp. Mobiluncus spp., a cause of bacterial vaginosis, usually is diagnosed on Gram staining of vaginal secretions by observation of gram-variable, curved rods with tapered ends. It is rarely isolated in the clinical laboratory, because vaginal secretions are not acceptable specimens for anaerobic culture. Propionibacterium spp. are anaerobic and aerotolerant, pleomorphic, gram-positives rods. The bacterium produces propionic acid from glucose. Bifidobacterium spp. are strictly anaerobic or microaerophilic, gram-positive, pleomorphic rods that appear as rods or as branched or club shaped. Lactobacillus spp. contain microaerophilic, catalase-negative, gram-positive rods capable of producing lactic acid from glucose fermentation. The genus Eubacterium remains poorly characterized, although its species are commonly isolated from oral infections.

Laboratory Diagnosis

 Differentiation of the gram-positive, non–spore forming anaerobes is based on colony and Gram stain morphology. Follow-up tests to identify the organism are determined by the interpretation of the initial Gram stain results. Additional tests include an aerotolerance test or growth in 5% CO2, followed by routine screening of special-potency antibiotic susceptibility patterns. The gram-positive organisms typically are resistant to colistin (10 µg), susceptible to vancomycin (5 µg), and have variable sensitivity to kanamycin (1 mg). Additional rapid testing includes a 15% catalase test, production of indole, and nitrate reduction. Although currently no rapid molecular amplification tests are available in the clinical laboratory, iso lates can be submitted to reference laboratories for 16s RNA sequence analysis. Table 1 provides an identification scheme for representative anaerobic organisms.

Table1. Differentiation of Representative Gram-Negative Bacilli and Gram-Positive Cocci

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مواضيع ذات صلة

Gram-Negative Rods

Gram-Positive, Spore Forming Bacilli

Morphology and Identification of Enterobacteriaceae

Clinical Findings of Enterococci

Streptococcus pneumoniae

Anaerobic Media

Specimen Processing of Anaerobic Bacteriology

Specimen Collection and Transport of Anaerobic Bacteriology

Gonococcal Arthritis

Nongonococcal Bacterial Arthritis

Acute Bacterial Arthritis

Streptococcus pyogenes