Anaerobic Non-Spore Forming Opportunistic Bacteria

• Anaerobic: Grow in atmospheres of 20% or less oxygen. Some strains are facultative anaerobes, whereas others die upon exposure to higher oxygen levels; this is important during transfer of specimens.
• Opportunistic pathogens: The bacteria we'll learn about in this tutorial are common colonizers of the skin and mucosal surfaces in healthy individuals; however, these opportunistic pathogens cause infection after spreading to sterile sites and/or in immunocompromised patients.

– Samples from infected sites often yield a mixture of anaerobic and aerobic bacterial types, which is an important consideration for treatment.

• Actinomyces commonly colonize the oral cavity; as we learn in more detail, elsewhere, these bacteria were originally thought to be a type of fungi.

– When trauma or other events facilitate bacterial spread, localized infections, called actinomycosis, can occur. Indicate that infections are most common in the cervicofacial area, where lesions produce a "lumpy jaw" appearance. – Actinomyces is generally susceptible to penicillin.

• Mobiluncus bacteria are small, slightly curved rods with variable staining patterns.

– Mobiluncus curtisii is associated with bacterial vaginosis, although its role in pathogenesis is uncertain. – Mobiluncus is susceptible to **vancomycin and other antibiotics; it is resistant to colistin.

• Lactobacillus is found throughout the body, particularly in the gastrointestinal and urogenital tracts.

– The bacteria can spread from these sites to cause bacteremia, and, in some cases, endocarditis. – Treatment includes penicillin and aminoglycosides.

• Propionibacterium is found on the skin, conjunctiva, and ears.

– It is responsible for acne vulgaris due to inflammation of the sebaceous follicles. – Treatment with erythromycin or clindamycin is generally effective. – Propionibacterium has also been associated with opportunistic infections in patients with medical devices and shunts. Inhabit the oral cavity, digestive tract, urinary tract, and skin* Anaerococcus, Atopobium, Finegoldia, Micromonas, Peptoniphilus, Schleiferella* – These species were formerly classified as Peptostreptococcus – Treatment typically includes penicillin or carbapenems; however, when present in mixed infections, broad-spectrum antibiotics are more effective.

• Gram-negative rods are the predominant bacteria on mucosal surfaces.

– Many pathogenic strains produce catalase and superoxide dismustase, which detoxify molecules of the host's innate immune response. Bacteriodes, especially Bacteriodes fragilis,* is a key member of this group. – It causes abscess formation and bacteremia; an antiphagocytic capsule is its key virulence factor.

• Other important Gram-negative anaerobic rods are: Fusobacterium, Porphyromonas, and Prevotella

Central nervous infections are associated with Prevotella, Porphyromonas, and Fusobacterium* Upper respiratory tract infections are associated with Prevotella, Porphyromonas, Fusobacteriam, and Bacteriodes* Intra-abdominal infections & gastroenteritis are caused by Bacteriodes fragilis* – Some strains of Bacteriodes fragilis produce an enterotoxin that triggers fluid loss, which leads to diarrhea, and inflammation, which damages the lining of the intestines. Gynecological infections are caused by Bacteriodes fragillis,* which produces abscesses, and Prevotella. Skin and soft tissue infections (necrotizing fasciitis) and Bacteremia are caused by Bacteria fragilis*

• Treatment for these infections includes metronidazole, carbapenems, and beta-lactam-beta-lactamase inhibitors. – Removal of necrotic tissue, abscess drainage, or other surgical interventions may be necessary.

• Anaerobic strains are rarely isolated from infection sites.
• Veillonella is an opportunistic pathogen which tends to colonize the oral cavity, respiratory and digestive tracts.