Anaerobic bacteria produce many different enzymes that are of importance in providing nutrients to the bacterial cell, as virulence factors, and in p… - Sydney M. Finegold

... a recent study of ours employing the powerful pyrosequencing technique on stools of subjects with regressive autism showed that Desulfovibrio was more common in autistic subjects than in controls. We subsequently confirmed this with pilot cultural and real-time PCR studies and found siblings of autistic children had counts of Desulfovibrio that were intermediate, suggesting possible spread of the organism in the family environment. Desulfovibrio is an anaerobic bacillus that does not produce spores but is nevertheless resistant to aerobic and other adverse conditions by other mechanisms and is commonly resistant to certain antimicrobial agents (such as cephalosporins) often used to treat ear and other infections that are relatively common in childhood. This bacterium also produces important virulence factors and its physiology and metabolism position it uniquely to account for much of the pathophysiology seen in autism.

The bacteria typically described from biliary tract infection include Escherichia coli, Klebsiella, Enterobacter, and enterococci. It has also been recognized for some time that Clostridium perfringens may occasionally be involved in serious complications of biliary tract infection such as sepsis and emphysematous cholecystitis. Other anaerobes, including various Bacteroides and Fusobacterium sp, clostridia other than C perfringens, anaerobic cocci and streptococci, and Actinomyces have been reported from a variety of biliary tract infections, usually as single case reports ... More recently, several reports indicate that anaerobes, and especially B fragilis, may be more common in biliary tract infections than had been appreciated ... Anaerobes have been recovered in approximately 40% of such infections; B fragilis is the most common anaerobe encountered. Anaerobes may also be found, as aerobes are, in asymptomatic bactibilia.

Most gastrointestinal infections secondary to the use of antimicrobial agents that have been documented are related to overgrowth of Clostridium difficile which produces a spectrum from severe pseudomembranous colitis to mild diarrhea or asymptomatic carriage. The most common inducers of pseudomembranous colitis or antimicrobial agent-associated diarrhea are ampicillin, clindamycin, and various cephalosporins, but almost all antimicrobials may cause this problem. Symptoms vary from watery to bloody diarrhea; the extent and severity of the diarrhea, fever, and abdominal cramps and the incidence of complications (such as toxic megacolon and perforation of the bowel) and of fatality are variable. Normal carriage of C. difficile in infants and asymptomatic carriage in adults who have received antimicrobial therapy make it impossible to rely on culture for diagnosis. The presence of cytotoxin or enterotoxin produced by C. difficile is much more reliable diagnostically, but there may be false-positives with this as well, particularly in infants.