Chapter 4.12 : Anaerobic Gram-Positive Bacilli

Abstract:

Anaerobic Gram-positive bacilli of clinical relevance in human infections are divided into two distinct groups: members of the genus Clostridium, which are spore-forming Gram-positive anaerobic bacilli, and a group composed of more than 42 genera of non-spore-forming anaerobic Gram-positive bacilli. Of the non-sporeformers, 10 genera are most commonly associated with clinical infections: Actinomyces, Actinobaculum, Varibaculum, Propionibacterium, Bifidobacterium (and the related genera, Alloscardovia, Parascardovia, and Scardovia), Eubacterium, Eggerthella, and Lactobacillus ( 1 , 2 , 3 ). Two additional genera, Mobiluncus and Atopobium, have more recently been found in association with bacterial vaginosis and other infections; however, they are not easily recovered, and their pathogenicity is not as well understood ( 1 , 2 , 4 , 5 ). There have been many taxonomic changes among the anaerobic Gram-positive non-spore-forming bacilli and more will follow as methods such as matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) and 16S rRNA sequencing are employed for identification in clinical laboratories ( 2 , 6 ). Many of the species that have been found in clinical samples are listed in Table 4.12–1 . Many of these anaerobic Gram-positive bacilli are part of the normal microbiota of the oral cavity, gastrointestinal tract, genitourinary tract, and skin. They can, however, be associated with skin and soft tissue infections, periodontitis and other oral infections, pulmonary infections (usually in combination with other aerobes and anaerobes), genitourinary tract infections, and, in the case of Propionibacterium acnes, infected CSF shunts, prosthetic joint infections, and endophthalmitis ( 7 , 8 ). Many of the non-sporeformers (like P. acnes and Actinomyces spp.) are aerotolerant and can be resistant to metronidazole, an antimicrobial agent that is usually effective against most other anaerobes.