Microbiology - Anaerobic Bacterial Infections

Anaerobic bacteria are the dominant normal flora of the mucous membranes. The oral cavity, GIT, female genitourinary tract are the sites on the human body with the greatest numbers. Anaerobic infections are usually the result of anaerobic normal flora of the mucosa entering the body through surgery or traumatic wound site. Some serious infections result from exogenous anaerobic flora. Most infections are polymicrobial, with the anaerobes growth being assisted by use of oxygen by aerobes. The signs of an infection by a pathogenic anaerobe are abscess formation, foul smell , gas production, and black, brown or red discolouration. Mucosa trauma, decrease of oxygen in tissues, and dirty wounds predispose individuals to infection by anaerobes. Isolation, identification and antibiotic susceptibility of anaerobes is difficult and problematic, and as a result is often not conducted. As the significant anaerobic bacterial pathogens are often in the soil and/or are asymptomatic colonisers of humans and animals eradication or prevention of exposure is extremely difficult. The most significant anaerobic bacterial pathogens are Clostridium difficile, C. perfringens , C. tetani, C. botulinum, and Bacteroides fragilis. C. difficile colonizes and over-grows the colon of patients undergoing antibiotic therapy, damaging the intestine and creating a pseudomembrane. C. perfringens is an important cause of lethal soft tissue infections. C. tetani causes tetanus, the spastic paralysis symptoms being the result of the neurotoxin tetanospasmin. Immunisation with tetanus toxoid has resulted in tetanus becoming very rare in developed countries. C. botulinum is the bacterium causative of foodborne and neonatal botulism. The flaccid paralysis symptoms being the result of the botulinum neurotoxin. Bacteroides fragilis is the most pathogenic Gram-negative anaerobic rod. Although a normal inhibitant of the GIT it can cause severe infections in sterile sites.