The laboratory must be informed when specimens are sent for culture of L. monocytogenes because the organism is easily confused with diphtheroids. In all listerial infections, IgG agglutinin titers peak 2 to 4 wk after onset. Cephalosporins are not effective. The causative organism, Bacillus anthracis, is a large, gram-positive, facultatively anaerobic, encapsulated rod. The spores resist destruction and remain viable in soil and animal products for decades.
Human infection is usually through the skin but has occurred after ingestion of contaminated meat.
Pulmonary anthrax follows rapid multiplication of spores in the mediastinal lymph nodes. Rarely, GI anthrax may follow ingestion of contaminated meat when a break is present in the pharyngeal or intestinal mucosa, which facilitates invasion of the intestinal wall. Although anthrax is an important animal disease, it is rare in humans and mainly occurs in countries that do not prevent industrial or agricultural exposure to infected goats, cattle, sheep, and horses or their products. Anthrax also occurs in exotic wildlife such as hippos, elephants, and cape buffalo. Considerable peripheral erythema, vesiculation, and induration are present.