Notes by dr Claudio Italiano
Anaerobic bacteria are microorganisms that do not require oxygen for growth and
develop in CO2-rich soils. Microaerophilic bacteria can grow in an atmosphere
containing 10% CO2. Non-spore-forming anaerobes are part of the normal bacterial
flora of the mucous surfaces of humans and animals, being present mainly in the
oral cavity, the gastrointestinal tract, the skin and the female genital tract.
In oral cavity, the gram-negative bacteria species associated with bad breath
In the oral flora the anaerobes are predominant
varying in their concentration between 109 germs / ml in saliva and 1012 in the
gingival plaque. These microorganisms grow better in the presence of only a
small amount of atmospheric oxygen. Optional bacteria can grow in the presence
and absence of air. This chapter describes infections caused by
non-spore-forming anaerobic bacteria. In general, the pathogenic anaerobes for
humans tolerate air relatively. In fact, although they can not multiply, they
can survive for 72 hours in the presence of oxygen. A very small number of
pathogenic anaerobes (which are also part of the normal endogenous flora),
instead, die after brief contact with oxygen, even if in low concentration. In
the oral cavity the ratio between the concentrations of the anaerobic bacteria
and those of the aerobic bacteria ranges from 1: 1 on the surface of the teeth
to 1000: 1 in the gingival pockets. The anaerobic bacteria are not detectable in
appreciable number inside the intestine under normal conditions, if not starting
from the distal ileum; in the colon the share of anaerobes increases
significantly, as is the case with the total amount of bacteria. For example, in
the colon there are 1011 to 1012 microorganisms / g of faeces, with an anaerobic
/ aerobic ratio of about 1000: 1.
At the level of the female genital tract there are about 109 germs / ml of secretions, with the ratio already cited equal to about 10: 1. Hundreds of species of anaerobes have been identified as belonging to the normal bacterial flora of man. In faeces, the identification of at least 500 different species of anaerobes reflects the remarkable polymorphism of normal anaerobic flora and, despite this huge variety, relatively few species isolate themselves during human infections. Anaerobic infections occur when the balance between host and bacteria is altered. Each district of the organism can be the site of infection by these commensal germs, when the mucosal barriers or the skin are damaged by surgery, trauma, neoplasia, ischemia or necrosis, which locally reduce the redox potential. Because the districts colonized by the anaerobes contain numerous other bacterial species, a possible alteration of the anatomical barriers allows the penetration of many microorganisms, often giving rise to mixed infections with numerous species of anaerobes associated with optional or microaerophilic bacteria. Mixed infections of this type occur at the head and neck (chronic sinusitis, chronic average otitis, Ludwig's angina and periodontal abscesses). The cerebral abscess and the subdural empyema represent the most common anaerobic pathologies affecting the central nervous system. Anaerobes are also responsible for pleuropulmonary infections, such as aspiration pneumonia, necrotizing pneumonia, abscesses and empyema. Anaerobes play an important role in the genesis of various abdominal infections, including peritonitis, intra-abdominal abscesses and hepatic abscesses. These bacteria are then frequently isolated in infections of the female genital tract such as salpingitis, pelviperitonitis, tubal abscess, septic abortions and endometritis; finally, they are often found in infections of the skin, soft tissues, bones and in septicemia.
All of these bacteria voraciously consume mouth debris
containing proteins that, once digested, produces volatile sulfur compounds.
These compounds are comprised of: