Bacterial Infections

Francisella tularensis is the causative agent of tularemia (also called rabbit fever or deerfly fever), an infectious disease that occurs primarily in animals. It may occasionally cause human disease, which most often manifests itself by one or more skin lesions, regional lymphadenopathy, fever, and constitutional symptoms.

Anaerobic bacteria are the predominant component of the normal microbial flora of the human body. The following sites harbor the vast majority of them:

Tetanus is a disease of global incidence produced by the toxin of Clostridium tetani. The risk of acquiring it increases in people > 60 years of age and in neonates, especially in Third World countries where poor sanitary conditions predispose to umbilical stump contamination. Immunization campaigns have played a crucial role in bringing about the observed decreasing incidence in the United States. The pathogenesis of tetanus involves the absorption of preformed toxin, or, less commonly, invasion of toxin-producing organisms from contaminated wounds; it may complicate surgical wounds colonized with C tetani.

Box 1 summarizes different clinical syndromes associated with anaerobic bacteria. The sections that follow describe the various syndromes, including clinical findings. For some syndromes, specific diagnosis and treatment information is included as well.

More than 25 species and 48 serogroups of Legionella have been identified. Legionella pneumophila (especially serogroup 1) causes ~ 70-80% of cases of legionellosis, but L micdadei, L bozemanii, L dumoffi, L feelei, L longbeacheii, and other species are also pathogenic. The true incidence of legionellosis, which includes Legionnaires’ disease and Pontiac fever, is difficult to establish.

Legionella species are associated with outbreaks of either Pontiac fever, a self-limited influenzalike condition in otherwise healthy people, or Legionnaires’ disease, a severe pneumonic disease more common among elderly and immunocompromised individuals.

Cholera is a disease of antiquity and probably represents some of the diarrheal illnesses described by Hippocrates and other early physicians. Robert Koch discovered V cholerae in 1884. Since the 17th century, at least eight epidemics of cholera have swept the globe. At least seven of the eight pandemics originated from the Ganges River delta, where cholera is endemic.

C fetus infection may manifest as fever, chills, and myalgias, without definitive localization; additionally, this organism displays a propensity to infect vascular structures. Endocarditis, intravascular infection of abdominal aortic aneurysms, and septic thrombophlebitis with vessel necrosis have been reported. Fetal death, even with appropriate antibiotic therapy, may occur. Fetal complications most commonly occur during the second trimester of pregnancy.

Campylobacter species are intestinal commensals in many animals, including cattle, pigs, sheep, chickens, and turkeys. Contamination of foodstuffs during meat and dairy processing is thought to significantly contribute to the spread of disease. Unpasteurized dairy products, undercooked meats, and contaminated water serve as the vehicles for Campylobacter and other bacterial pathogens.

Patients with septicemia, wound infections, or ear infections caused by a Vibrio species frequently have a history of shellfish ingestion or saltwater exposure. Clinical manifestations vary depending on the site of infection.