Bacillus
The genus bacillus includes large aerobic, gram-positive rods occurring in chains. Most members of this genus are saprophytic organisms prevalent in soil, water, and air and on vegetation, such as Bacillus cereus and Bacillus subtilis. B. anthracis, which causes anthrax, is the principal pathogen of the genus.The typical cells are a large gram positive rods have square ends and are arranged in long chains; spores are located in the center of the non-motile bacilli. Culture Colonies of B anthracis are round and have a "cut glass" appearance in transmitted light. Hemolysis is uncommon with B anthracis but common with the saprophytic bacilli. Gelatin is liquefied .
In humans, the infection is usually acquired by the entry of spores through injured skin (cutaneous anthrax) or rarely the mucous membranes (gastrointestinal anthrax), or by inhalation of spores into the lung (inhalation anthrax). The spores germinate in the tissue at the site of entry, and growth of the vegetative organisms and produce toxin results in formation of a gelatinous edema and congestion. Bacilli spread via lymphatics to the bloodstream, and they multiply freely in the blood and tissues shortly before and after death.
B anthracis that does not produce a capsule is not virulent . The poly-D-glutamic acid capsule is antiphagocytic. Anthrax toxin is made up of three proteins: protective antigen (PA), edema factor (EF), and lethal factor (LF). PA binds to specific cell receptors, and following proteolytic activation it forms a membrane channel that mediates entry of EF and LF into the cell. EF is an adenylate cyclase; with PA it forms a toxin known as edema toxin. LF plus PA form lethal toxin, which is a major virulence factor and cause of death in infected animals.
In humans, approximately 95% of cases are cutaneous anthrax and 5% are inhalation. Gastrointestinal anthrax is very rare .Cutaneous anthrax generally occurs on exposed surfaces of the arms or hands . A pruritic papule develops 1–7 days . The papule rapidly changes into a vesicle that coalesce and a necrotic ulcer develops. Lesions have a characteristic central black eschar. Marked edema occurs. Lymphangitis and lymphadenopathy and systemic signs and symptoms of fever, malaise, and headache may occur. After 7–10 days the eschar is fully developed. it dries, loosens, and separates; healing is by granulation and leaves a scar. In as many as 20% of patients, cutaneous anthrax can lead to sepsis, systemic infections including meningitis then death.
The incubation period in inhalation anthrax may be as long as 6 weeks. hemorrhagic necrosis and edema of the mediastinum , Substernal pain may be prominent, . Hemorrhagic pleural effusions ; cough . Sepsis occurs, and there may be hematogenous spread to the gastrointestinal tract, causing bowel ulceration, or to the meninges, causing hemorrhagic meningitis. The fatality rate in inhalation anthrax is high .
Diagnostic Laboratory Tests Specimens are fluid , pus from lesion, blood and sputum. Stained smears or immunfluorescence staining techniques can be used to detect anthrax bacilli . Culture on blood agar plates , anthrax bacilli produce nonhemolytic gray to white colonies with a rough texture and a ground-glass appearance. Comma-shaped outgrowths (Medusa head) may project from the colony. In semisolid medium, anthrax bacilli are non-motile, whereas related nonpathogenic organisms (eg, B cereus) exhibit motility by "swarming . An enzyme-linked immunoassay (ELISA) used to measure antibodies against edema and lethal toxins .
TreatmentMany antibiotics are effective against anthrax in humans, like: Ciprofloxacin is recommended for treatment of anthrax. penicillin G, in combination with gentamicin or streptomycin.In the setting of potential exposure to B anthracis as an agent of biologic warfare, prophylaxis with ciprofloxacin or doxycycline should be continued to 4 weeks .Some other gram-positive bacilli, such as B cereus, are resistant to penicillin by virtue of β-lactamase production. Doxycycline, erythromycin, or ciprofloxacin may be effective alternatives to penicillin.
Epidemiology, Prevention, & Control Soil is contaminated with anthrax spores from the carcasses of dead animals. These spores remain viable for decades. Control measures include (1) disposal of animal carcasses by burning or deep burial in lime pits, (2) decontamination (usually by autoclaving) of animal products, (3) protective clothing and gloves for handling potentially infected materials, and (4) active immunization of domestic animals with live attenuated vaccines.
Bacillus Cereus
Food poisoning caused by Bacillus cereus has two distinct forms: the emetic type, associated with fried rice, and the diarrheal type, associated with meat dishes and sauces. B cereus produces toxins that cause disease that is more an intoxication than a food-borne infection. The emetic form is manifested by nausea, vomiting, abdominal cramps, and occasionally diarrhea and is self-limiting, with recovery occurring within 24 hours. It begins 1–5 hours after ingestion of rice and occasionally pasta dishes. B cereus is a soil organism that commonly contaminates rice.When large amounts of rice are cooked and allowed to cool slowly, the B cereus spores germinate and the vegetative cells produce the toxin during log-phase growth or during sporulation. The diarrheal form has an incubation period of 1–24 hours and is manifested by profuse diarrhea with abdominal pain and cramps; fever and vomiting are uncommon. The enterotoxin may be produced in the food or in the intestine. The presence of B cereus in a patient's stool is not sufficient to make a diagnosis of B cereus disease .
B cereus is an important cause of eye infections, severe keratitis, endophthalmitis, etc. Typically, the organisms are introduced into the eye by foreign bodies associated with trauma. B cereus has also been associated with localized infections and with systemic infections, including endocarditis, meningitis, osteomyelitis, and pneumonia .