Anaerobic Bacteria with Clinical Relevance: Morphologic and Taxonomic Classification, Distribution among Human Microbiota and Microbiologic Diagnosis

João Alves, Susana Peres, Elsa Gonçalves, Kamal Mansinho

The wide burden of anaerobic bacteria colonizing human body comprises about 90% of its total biomass. The biotic relationship between humans and its microbiota sets reciprocal benefits, albeit with pathogenic potencial for the human being in particular dysbiosis situations. Infections adjacent to or originating from the skin or mucous membranes of the intestinal, genitourinary and upper respiratory tracts are often polymicrobial in nature, whereby should anaerobes be invariably included in the etiological differential diagnosis of these conditions. Gram negative bacilli such as Bacteroides fragilis group, Fusobacterium spp., Porphyromonas spp., Prevotella spp. and Gram positive cocci such as Peptostreptococcus spp. stand out for their high virulence and frequence of isolation in suppurative infections and abcesses with metastatic or contiguous relation to human microbiota. The fastidious nature of anaerobic bacteria, especially of less aerotolerant species, compels to particular techniques of sample collection, transport and cultural isolation that challenge clinicians and microbiologists for a full efficient practice. Such requirements bring on a poor identification of anaerobic bacteria in the clinical practice and undervaluation of its aetiopathogenic potential amongst common polymicrobial infections. An approach over microbial flora's composition in the different human anatomical sites is a primary goal of the present article. Clinicians are intended to recognize the variability and proportion of likely involved anaerobic microorganisms in certain infectious processes related to human microbiota, in order to optimize samples processing and the establishment of an appropriate empirical antibiotic therapy, mindful of anaerobic coverage and according to known susceptibility profiles.