Answers to these questions are available on LF is a zinc-dependent protease EF is a calmodulin-dependent adenylate cyclase

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1 21 Bacillus Two hours after a dinner, a family of four developed acute abdominal cramps with nausea and vomiting. The illness lasted for less than a day. 1. Bacillus cereus is associated with two forms of food poisoning. Discuss the epidemiology and clinical presentation of each. 2. B. cereus is also associated with eye infections. Discuss the epidemiology and clinical presentation. What virulence factor is important in these infections? Answers to these questions are available on The family Bacillaceae consists of a diverse collection of bacteria, including organisms that grow only aerobically or only anaerobically, organisms shaped as cocci or rods, and organisms that stain gram-positive or gramnegative. The one feature this diverse group of bacteria all share is the ability to form endospores (Figure 21-1). Despite the dozens of genera in this family, students need to know only two clinically important genera: Bacillus (the aerobic and facultative anaerobic spore formers; Table 21-1) and Clostridium (the strict, anaerobic spore formers; see Chapter 36). Almost 250 species are in the genus Bacillus. Fortunately, the species that are of medical interest are relatively limited. Bacillus anthracis, the organism responsible for anthrax, is the most important member of this genus. This species is considered one of the most feared agents of biologic warfare, and since the release of B. anthracis spores in the U.S. Postal Service in 2001, the potential danger associated with this organism has been reemphasized. The other clinically important species in this genus is Bacillus cereus, an organism responsible for gastroenteritis, traumatic eye infections, catheter-associated sepsis, and, rarely, severe pneumonia. BACILLUS ANTHRACIS (Box 21-1) Physiology and Structure B. anthracis is a large (1 3 to 8 µm) organism arranged as single or paired rods (Figure 21-2) or as long, serpentine chains. Although spores are readily observed in 2- to 3-day-old cultures, they are not seen in clinical specimens. Because of the unique medical importance of B. anthracis, it is important to understand the functional details of this organism s toxins. Virulent B. anthracis carries genes for three toxin protein components on a large plasmid, pxo1. The individual proteins, protective antigen (PA), edema factor (EF), and lethal factor (LF), are nontoxic individually but form important toxins when combined: PA plus EF forms edema toxin, and PA plus LF forms lethal toxin. PA is an 83-kDa protein that binds to one of two receptors on host cell surfaces that are present on many cells and tissues (e.g., brain, heart, intestine, lung, skeletal muscle, pancreas, macrophages). After PA binds to its receptor, host proteases cleave PA, releasing a small fragment and retaining the 63-kDa fragment (PA 63 ) on the cell surface. The PA 63 fragments self-associate on the cell surface, forming a ring-shaped complex of seven fragments (pore precursor or prepore ). This heptameric complex can then bind up to three molecules of LF and/or EF. Both factors recognize the same binding site of PA 63, so the binding is competitive. Formation of the complex stimulates endocytosis and movement to an acidic compartment. In this environment, the heptameric complex forms a transmembrane pore and releases LF and EF into the cell cytosol. LF is a zinc-dependent protease that is capable of cleaving mitogen-activated protein (MAP) kinase, leading to cell death by incompletely understood mechanisms. EF is a calmodulin-dependent adenylate cyclase that increases the intracellular cyclic adenosine monophosphate (camp) levels, resulting in edema. EF is related to the adenylate cyclases produced by Bordetella pertussis and Pseudomonas aeruginosa. A second, important virulence factor carried by B. anthracis is a prominent polypeptide capsule (consisting of poly-d-glutamic acid). The capsule is observed in clinical specimens but is not produced in vitro unless special growth conditions are used. Three genes (capa, capb, and capc) are responsible for synthesis of this capsule and are carried on a second plasmid (pxo2). Only one serotype of capsule has been identified, presumably because the capsule is composed of only glutamic acid. Pathogenesis and Immunity The major factors responsible for the virulence of B. anthracis are the capsule, edema toxin, and lethal toxin. The capsule inhibits phagocytosis of replicating cells. The adenylate cyclase activity of edema toxin is responsible for the fluid accumulation observed in anthrax. The zinc metalloprotease activity of lethal toxin stimulates macrophages to release tumor necrosis factor-α (TNFα), interleukin-1β (IL-1β), and other proinflammatory 209

2 BACILLUS 209.e1 ANSWERS 1. The emetic form of food poisoning is associated with consumption of rice contaminated with B. cereus. Heatstable enterotoxin is produced when the bacteria are able to grow in the rice. Because it is an intoxication, the incubation period and duration of illness are short. The diarrheal form of disease is associated with contaminated meat and vegetables. This disease form, characterized by diarrhea, nausea, and abdominal cramps, has a longer incubation and duration of illness because the bacteria replicate in the patient. 2. B. cereus eye infections are typically associated with traumatic injury to the eye, where a soil-contaminated foreign body strikes the eye, introducing the bacteria into the eye. Disease progresses rapidly because of the tissue destruction caused by the necrotic toxin, cereolysin, and phospholipase C.

3 210 MEDICAL MICROBIOLOGY BOX 21-1 Summary: Bacillus anthracis Figure 21-1 Bacillus cereus. The clear areas in the gram-positive rods are unstained spores (arrows). cytokines. This toxin also mediates lysis of macrophages in selected cell cultures. Of the major proteins of B. anthracis, PA is the most immunogenic (hence the name). Both LF and EF inhibit the host s innate immune system. Epidemiology Anthrax is primarily a disease of herbivores; humans are infected through exposure to contaminated animals or animal products. The disease is a serious problem in countries where animal vaccination is not practiced or is impractical (e.g., disease established in African wildlife). In contrast, natural infections with B. anthracis are rarely seen in the United States, with only five cases reported between 1981 and This statistic may now be meaningless, with the deliberate contamination of the U.S. Postal Service with B. anthracis spores in The risk of exposing a large population to the dangerous pathogen has increased dramatically in this era of bioterrorism. A number of nations and independent terrorist groups have biologic warfare programs. Iraq, the former Soviet Union, and the Aum Shinrikyo terrorist group in Japan have experimented with using B. anthracis as a weapon. Indeed, much of what we know about anthrax acquired via the inhalation route was learned from the accidental release in 1979 of spores in Sverdlovsk in the former Soviet Union (at least 79 cases of anthrax, with 68 deaths) and the terrorist contamination of employees of the U.S. Postal Service with letters containing B. anthracis (11 patients with inhalation anthrax and 11 patients with cutaneous anthrax). Human B. anthracis disease (Box 21-2) is acquired by one of the following three routes: inoculation, ingestion, Table 21-1 Important Bacillus Species Organism Historical Derivation Bacillus bacillum, a small rod B. anthracis anthrax, charcoal, a carbuncle (refers to the black, necrotic wound associated with cutaneous anthrax) B. cereus cereus, waxen, wax-colored (refers to colonies with a typical dull or frosted-glass surface) Biology, Virulence, and Disease Spore-forming, nonmotile, nonhemolytic gram-positive rods Polypeptide capsule consisting of poly-d-glutamic acid observed in clinical specimens Virulent strains also produce three exotoxins that combine to form edema toxin (combination of protective antigen and edema factor) and lethal toxin (protective antigen with lethal factor) B. anthracis primarily infects herbivores, with humans as accidental hosts Rarely isolated in developed countries but is prevalent in impoverished areas where vaccination of animals is not practiced The greatest danger of anthrax in industrial countries is the use of B. anthracis as an agent of bioterrorism Three forms of anthrax are recognized: cutaneous (most common in humans), gastrointestinal (most common in herbivores), and inhalation (bioterrorism) Diagnosis Organism is present in high concentrations in clinical specimens (microscopy typically positive) and grows readily in culture Preliminary identification is based on microscopic (gram-positive, nonmotile rods) and colonial (nonhemolytic, adherent colonies) morphology; confirmed by demonstrating capsule and either lysis with gamma phage, a positive direct fluorescent antibody test for the specific cell wall polysaccharide, or positive nucleic acid amplification assay Treatment, Prevention, and Control Inhalation or gastrointestinal anthrax or bioterrorismassociated anthrax should be treated with ciprofloxacin or doxycycline, combined with one or two additional antibiotics (e.g., rifampin, vancomycin, penicillin, imipenem, clindamycin, clarithromycin) Naturally acquired cutaneous anthrax can be treated with amoxicillin Vaccination of animal herds and people in endemic areas can control disease, but spores are difficult to eliminate from contaminated soils Animal vaccination is effective, but human vaccines have limited usefulness Alternative treatments interfering with the activity of anthrax toxins are under investigation and inhalation. Approximately 95% of anthrax infections in humans result from the inoculation of Bacillus spores through exposed skin from either contaminated soil or infected animal products, such as hides, goat hair, and wool. Ingestion anthrax is very rare in humans, but ingestion is a common route of infection in herbivores. Because the organism can form resilient spores, contaminated soil or animal products can remain infectious for many years. Inhalation anthrax was historically called wool-sorters disease because most human infections resulted from

4 BACILLUS 211 CLINICAL CASE 21-1 Inhalation Anthrax Figure 21-2 anthrax. Bacillus anthracis in the blood of a patient with inhalation the inhalation of B. anthracis spores during the processing of goat hair. This is currently an uncommon source for human infections; however, inhalation is the most likely route of infection with biologic weapons, and the infectious dose of the organism is believed to be low. Person-to-person transmission does not occur because bacterial replication occurs in the mediastinal lymph nodes rather than the bronchopulmonary tree. Clinical Diseases (Clinical Case 21-1) Typically, cutaneous anthrax starts with the development of a painless papule, at the site of inoculation, that rapidly progresses to an ulcer surrounded by vesicles, BOX 21-2 Bacillus Diseases: Clinical Summaries Bacillus anthracis Cutaneous anthrax: painless papule progresses to ulceration with surrounding vesicles and then to eschar formation; painful lymphadenopathy, edema, and systemic signs may develop Gastrointestinal anthrax: ulcers form at site of invasion (e.g., mouth, esophagus, intestine) leading to regional lymphadenopathy, edema, and sepsis Inhalation anthrax: initial nonspecific signs followed by the rapid onset of sepsis with fever, edema, and lymphadenopathy (mediastinal lymph nodes); meningeal symptoms in half the patients, and most patients with inhalation anthrax will die unless treatment is initiated immediately Bacillus cereus Gastroenteritis: emetic form characterized by a rapid onset of vomiting and abdominal pain and a short duration; diarrheal form characterized by a longer onset and duration of diarrhea and abdominal cramps Ocular infections: rapid, progressive destruction of the eye after traumatic introduction of the bacteria into the eye Severe pulmonary disease: severe anthrax-like pulmonary disease in immunocompetent patients Bush and associates (N Engl J Med 345: , 2001) reported the first case of inhalation anthrax in the 2001 bioterrorism attack in the United States. The patient was a 63-year-old man living in Florida who had a 4-day history of fever, myalgias, and malaise without localizing symptoms. His wife brought him to the regional hospital because he awoke from sleep with fever, emesis, and confusion. On physical examination, he had a temperature of 39 C, blood pressure of 150/80 mm Hg, pulse of 110 beats/min, and respiration of 18 breaths/ min. No respiratory distress was noted. Treatment was initiated for presumed bacterial meningitis. Basilar infiltrates and a widened mediastinum were noted on the initial chest radiograph. Gram stain of cerebrospinal fluid (CSF) revealed many neutrophils and large gram-positive rods. Anthrax was suspected, and penicillin treatment was initiated. Within 24 hours of admission, CSF and blood cultures were positive for Bacillus anthracis. During the first day of hospitalization, the patient had a grand mal seizure and was intubated. On the second hospital day, hypotension and azotemia developed, with subsequent renal failure. On the third hospital day, refractory hypotension developed and the patient had a fatal cardiac arrest. This patient illustrates the rapidity with which patients with inhalation anthrax can deteriorate despite a rapid diagnosis and appropriate antimicrobial therapy. Although the route of exposure is via the respiratory tract, patients do not develop pneumonia; rather, the abnormal chest radiograph is caused by hemorrhagic mediastinitis. then to a necrotic eschar (Figure 21-3). Systemic signs, painful lymphadenopathy, and massive edema may develop. The mortality rate in patients with untreated cutaneous anthrax is 20%. Clinical symptoms of gastrointestinal anthrax are determined by the site of the infection. If organisms invade the upper intestinal tract, ulcers form in the mouth or esophagus, leading to regional lymphadenopathy, edema, and sepsis. If the organism invades the cecum Figure 21-3 Cutaneous anthrax demonstrating marked erythema, edema, and vesicle rupture. (From Cohen J, Powderly WG: Infectious diseases, ed 2, St Louis, 2004, Mosby.)

5 212 MEDICAL MICROBIOLOGY Figure 21-4 Inhalation anthrax demonstrating enlarged mediastinal lymph nodes (arrowheads). or terminal ileum, the patient presents with nausea, vomiting, and malaise, which rapidly progress to systemic disease. The mortality associated with gastrointestinal anthrax is believed to approach 100%. Unlike the other two forms of anthrax, inhalation anthrax can be associated with a prolonged latent period (2 months or more), during which the infected patient remains asymptomatic. Spores can remain latent in the nasal passages or reach the lower airways, where alveolar macrophages ingest the inhaled spores and transport them to the mediastinal lymph nodes. The initial clinical symptoms of disease are nonspecific fever, myalgias, nonproductive cough, and malaise. The second stage of disease is more dramatic, with a rapidly worsening course of fever, edema, massive enlargement of the mediastinal lymph nodes (this is responsible for the widened mediastinum observed on chest radiography [Figure 21-4]), respiratory failure, and sepsis. Although the route of infection is by inhalation, pneumonia rarely develops. Meningeal symptoms are seen in half of patients with inhalation anthrax. Almost all cases progress to shock and death within 3 days of initial symptoms, unless anthrax is suspected and treatment is initiated immediately. Serologic evidence indicates that a subclinical or asymptomatic form of inhalation anthrax does not exist. Virtually all patients who develop disease progress to a fatal outcome, unless there is immediate medical intervention. Laboratory Diagnosis Infections with B. anthracis are characterized by overwhelming numbers of organisms present in wounds, involved lymph nodes, and blood. Anthrax is one of the few bacterial diseases were organisms can be seen when peripheral blood is Gram stained (see Figure 21-2). Therefore the detection of organisms by microscopy and culture is not a problem. The diagnostic difficulty is distinguishing B. anthracis from other members of the taxonomically related B. cereus group. A preliminary identification of B. anthracis is based on microscopic and Figure 21-5 Bacillus cereus. Spores retain the malachite green dye in this special spore stain, and the vegetative cells are gray or colorless. colonial morphology. The organisms appear as long, thin, gram-positive rods arranged singly or in long chains. Spores are not observed in clinical specimens but only in cultures incubated in a low carbon dioxide (CO 2) atmosphere and can be best seen with the use of a special spore stain (e.g., malachite green stain; Figure 21-5). The capsule of B. anthracis is produced in vivo but is not typically observed in culture. The capsule can be observed with a contrasting stain, such as India ink (the ink particles are excluded by the capsule so that the background, but not the area around bacteria, appears black), M Fadyean methylene blue stain, or a direct fluorescent antibody (DFA) test developed against the capsular polypeptide. Colonies cultured on sheep blood agar are large, nonpigmented, and have a dry ground-glass surface and irregular edges with projections along the lines, where the specimen was inoculated onto the agar plate (referred to as Medusa head morphology). The colonies are quite sticky and adherent to the agar, and, if the edge is lifted with a bacteriologic loop, it will remain standing like beaten egg whites. Colonies are not hemolytic, in contrast with B. cereus. B. anthracis will appear nonmotile in motility tests, such as the microscopic observation of individual rods in a suspended drop of culture medium. The definitive identification of nonmotile, nonhemolytic organisms resembling B. anthracis is made in a public health reference laboratory. This is accomplished by demonstrating capsule production (by microscopy or DFA) and either lysis of the bacteria with gamma phage or a positive DFA test for a specific B. anthracis cell wall polysaccharide. In addition, nucleic acid amplification tests (e.g., polymerase chain reaction [PCR]) have been developed and are performed in reference laboratories. The PCR tests are also commercially available.

6 BACILLUS 213 Treatment, Prevention, and Control Although penicillin was the drug of choice for B. anthracis, resistance in naturally occurring strains has been observed, as well as resistance to sulfonamides and extended-spectrum cephalosporins. In addition, resistance to other antibiotics can be selected in laboratoryderived strains, so this must be considered for treatment of bioterrorism-associated anthrax. The current empiric treatment recommendation is use of ciprofloxacin or doxycycline combined with one or two additional antibiotics (e.g., rifampin, vancomycin, penicillin, imipenem, clindamycin, clarithromycin). Although penicillin resistance is observe for naturally acquired anthrax, oral penicillin (amoxicillin) is still recommended for naturally acquired cutaneous anthrax. The control of naturally acquired human disease requires the control of animal disease, which involves the vaccination of animal herds in endemic regions and the burning or burial of animals that die of anthrax. Complete eradication of anthrax is unlikely because the spores of the organism can exist for many years in soil. Furthermore, complete eradication of anthrax infections is unlikely with the threat of bioterrorist-related infections a current reality. Vaccination has also been used to protect (1) people who live in areas where the disease is endemic, (2) people who work with animal products imported from countries with endemic anthrax, and (3) military personnel. Although the current vaccine appears to be effective, research to develop a less toxic vaccine is underway. Alternative approaches to inactivating anthrax toxins have focused on PA and its receptor target. Passive infusion of human monoclonal antibodies against B. anthracis PA prevented death in an animal model of inhalation anthrax and was well tolerated in human volunteers. Synthetic peptide complexes that target the cell surface receptors for PA have also been used to neutralize anthrax toxin in animal models. How these alternative approaches can be used to treat human disease remains to be demonstrated. BACILLUS CEREUS Bacillus species other than B. anthracis are primarily opportunistic pathogens that have relatively low capacities for virulence. Although most of these species have been found to cause disease, B. cereus is clearly the most important pathogen, with gastroenteritis, ocular infections, and intravenous catheter-related sepsis being the diseases most commonly observed, as well as rare cases of severe pneumonia (Box 21-3). Pathogenesis Gastroenteritis caused by B. cereus is mediated by one of two enterotoxins (Table 21-2). The heat-stable, proteolysis-resistant enterotoxin causes the emetic form of the disease, and the heat-labile enterotoxin causes the diarrheal form of the disease. The heat-labile enterotoxin is similar to the enterotoxins produced by Escherichia coli and Vibrio cholerae; each stimulates the adenylate cyclase cyclic adenosine monophosphate BOX 21-3 Summary: Bacillus cereus Biology, Virulence, and Disease Spore-forming, motile gram-positive rods Heat-stable and heat-labile enterotoxin Tissue destruction is mediated by cytotoxic enzymes, including cereolysin and phospholipase C Ubiquitous in soils throughout the world People at risk include those who consume food contaminated with the bacterium (e.g., rice, meat, vegetables, sauces), those with penetrating injuries (e.g., to eye), those who receive intravenous injections, and immunocompromised patients exposed to B. cereus Capable of causing an anthrax-like disease in immunocompetent patients Diagnosis Isolation of the organism in implicated food product or nonfecal specimens (e.g., eye, wound) Treatment, Prevention, and Control Gastrointestinal infections are treated symptomatically Ocular infectious or other invasive diseases require removal of foreign bodies and treatment with vancomycin, clindamycin, ciprofloxacin, or gentamicin Gastrointestinal disease is prevented by proper preparation of food (e.g., foods should be consumed immediately after preparation or refrigerated) system in intestinal epithelial cells, leading to profuse watery diarrhea. The mechanism of action of the heatstable enterotoxin is unknown. The pathogenesis of B. cereus ocular infections is also incompletely defined. At least three toxins have been implicated; they are necrotic toxin (a heat-labile enterotoxin), cereolysin (a potent hemolysin named after the species), and phospholipase C (a potent lecithinase). It is likely that the rapid destruction of the eye that is characteristic of B. cereus infections results from the interaction of these toxins and other unidentified factors. Bacillus species can colonize skin transiently and can be recovered as insignificant contaminants in blood cultures. In the presence of an intravascular foreign body, however, these organisms can be responsible for persistent bacteremia and signs of sepsis (i.e., fever, chills, hypotension, shock). Epidemiology B. cereus and other Bacillus species are ubiquitous organisms, present in virtually all environments. Virtually all Table 21-2 Bacillus cereus Food Poisoning Emetic Form Diarrheal Form Implicated food Rice Meat, vegetables Incubation period (hours) <6 (mean, 2) >6 (mean, 9) Symptoms Vomiting, nausea, abdominal cramps Diarrhea, nausea, abdominal cramps Duration (hours) 8-10 (mean, 9) (mean, 24) Enterotoxin Heat stable Heat labile

7 214 MEDICAL MICROBIOLOGY infections originate from an environmental source (e.g., contaminated soil). Isolation of bacteria from clinical specimens in the absence of characteristic disease usually represents insignificant contamination. Clinical Diseases As mentioned previously, B. cereus is responsible for two forms of food poisoning: vomiting disease (emetic form) and diarrheal disease (diarrheal form). In most patients, the emetic form of disease results from the consumption of contaminated rice. Most bacteria are killed during the initial cooking of the rice, but the heat-resistant spores survive. If the cooked rice is not refrigerated, the spores germinate, and the bacteria can multiply rapidly. The heat-stable enterotoxin that is released is not destroyed when the rice is reheated. The emetic form of disease is an intoxication, caused by ingestion of the enterotoxin and not the bacteria. Thus the incubation period after eating the contaminated rice is short (1 to 6 hours), and the duration of illness is also short (less than 24 hours). Symptoms consist of vomiting, nausea, and abdominal cramps. Fever and diarrhea are generally absent. Fulminant liver failure has also been associated with consumption of food contaminated with large amounts of emetic toxin, which impairs mitochondrial fatty acid metabolism. Fortunately, this is a rare complication. The diarrheal form of B. cereus food poisoning is a true infection, resulting from ingestion of the bacteria in contaminated meat, vegetables, or sauces. There is a longer incubation period, during which the organism multiplies in the patient s intestinal tract, and the release of the heat-labile enterotoxin follows. This enterotoxin is responsible for the diarrhea, nausea, and abdominal cramps that develop. This form of disease generally lasts 1 day or longer. B. cereus ocular infections usually occur after traumatic, penetrating injuries of the eye with a soilcontaminated object (Clinical Case 21-2). Bacillus CLINICAL CASE 21-2 Bacillus cereus Traumatic Endophthalmitis Endophthalmitis caused by the traumatic introduction of Bacillus cereus into the eye is unfortunately not uncommon. This is a typical presentation. A 44-year-old man suffered a traumatic eye injury while working in a vegetable garden, when a piece of metal was deflected into his left eye, damaging the cornea and anterior and posterior lens capsule. Over the next 12 hours, he developed increasing pain and purulence in his eye. He underwent surgery to relieve the ocular pressure, drain the purulence, and introduce intravitreal antibiotics (vancomycin, ceftazidime) and dexamethasone. Culture of the aspirated fluid was positive for B. cereus. Ciprofloxacin was added to his therapeutic regimen postoperatively. Despite the prompt surgical and medical intervention, and subsequent intravitreal antibiotic injections, the intraocular inflammation persisted and evisceration was required. This patient illustrates the risks involved with penetrating eye injuries and the need to intervene aggressively if the eye is to be saved. panophthalmitis is a rapidly progressive disease that almost universally results in the complete loss of light perception within 48 hours of the injury. Disseminated infections with ocular manifestations can also develop in intravenous drug abusers. Other common infections with B. cereus and other Bacillus species are intravenous catheter and central nervous system shunt infections and endocarditis (most common in drug abusers), as well as pneumonitis, bacteremia, and meningitis in severely immunosuppressed patients. It has also been reported that ingestion of tea by immunocompromised patients is associated with an increased risk for invasive B. cereus disease. One rare disease of B. cereus deserves special attention severe pneumonia mimicking anthrax in immunocompetent patients. Four patients with this disease, all metal workers residing in Texas or Louisiana, have been described in the literature. Most interesting is that the strains contained the B. anthracis pxo1 toxin genes and all were encapsulated, although this was not the B. anthracis poly-γ-d-glutamic acid capsule. These strains demonstrate the potential danger and presumed ease of transferring B. anthracis virulence genes into the ubiquitous B. cereus. Laboratory Diagnosis Similar to B. anthracis, B. cereus and other species can be readily cultured from clinical specimens collected from patients with the emetic form of food poisoning. Because individuals can be transiently colonized with B. cereus, the implicated food (e.g., rice, meat, vegetables) must be cultured for confirmation of the existence of foodborne disease. In practice, neither cultures nor tests to detect the heat-stable or heat-labile enterotoxins are commonly performed, so most cases of B. cereus gastroenteritis are diagnosed by epidemiologic criteria. Bacillus organisms grow rapidly and are readily detected with the Gram stain and culture of specimens collected from infected eyes, intravenous culture sites, and other locations. Treatment, Prevention, and Control Because the course of B. cereus gastroenteritis is short and uncomplicated, symptomatic treatment is adequate. The treatment of other Bacillus infections is complicated because they have a rapid and progressive course and a high incidence of multiple-drug resistance (e.g., B. cereus carries genes for resistance to penicillins and cephalosporins). Vancomycin, clindamycin, ciprofloxacin, and gentamicin can be used to treat infections. Penicillins and cephalosporins are ineffective. Eye infections must be treated rapidly. Rapid consumption of foods after cooking and proper refrigeration of uneaten foods can prevent food poisoning. CASE STUDY AND QUESTIONS A 56-year-old female postal worker sought medical care for fever, diarrhea, and vomiting. She was offered symptomatic treatment and discharged from the community hospital emergency department. Five days later, she returned to the

8 BACILLUS 215 hospital with complaints of chills, dry cough, and pleuritic chest pain. A chest radiograph showed a small right infiltrate and bilateral effusions but no evidence of a widened mediastinum. She was admitted to the hospital, and the next day her respiratory status and pleural effusions worsened. A computed tomography scan of her chest revealed enlarged mediastinal and cervical lymph nodes. Pleural fluid and blood were collected for culture, and these cultures were positive within 10 hours for gram-positive rods in long chains. 1. The clinical impression is that this woman has inhalation anthrax. What tests should be performed to confirm the identification of the isolate? 2. What are the three primary virulence factors found in B. anthracis? 3. Describe the mechanisms of action of the toxins produced by B. anthracis. 4. Describe the two forms of B. cereus food poisoning. What toxin is responsible for each form? Why is the clinical presentation of these two diseases different? 5. B. cereus can cause eye infections. What are two risk factors for this disease? Answers to these questions are available on Please visit to view an animation demonstrating the functions of anthrax toxins. BIBLIOGRAPHY Avashia S, et al: Fatal pneumonia among metal workers due to inhalation exposure to Bacillus cereus containing Bacillus anthracis toxin genes, Clin Infect Dis 44: , Baggett HC, et al: No evidence of a mild form of inhalational Bacillus anthracis infection during a bioterrorism-related inhalational anthrax outbreak in Washington, D.C., in 2001, Clin Infect Dis 41: , Basha S, et al: Polyvalent inhibitors of anthrax toxin that target host receptors, Proc Natl Acad Sci U S A 103: , Bell CA, et al: Detection of Bacillus anthracis DNA by LightCycler PCR, J Clin Microbiol 40: , Bottone E: Bacillus cereus, a volatile human pathogen, Clin Microbiol Rev 23: , Collier RJ, Young JAT: Anthrax toxin, Annu Rev Cell Dev Biol 19:45 70, Doganay M, Metan G, Alp E: A review of cutaneous anthrax and its outcome, J Infect Public Health 3:98 105, Hoffmaster A, et al: Characterization of Bacillus cereus isolates associated with fatal pneumonias: strains are closely related to Bacillus anthracis and harbor B. anthracis virulence genes, J Clin Microbiol 44: , Krantz BA, et al: A phenylalanine clamp catalyzes protein translocation through the anthrax toxin pore, Science 309: , Mahtab M, Leppla SH: The roles of anthrax toxin in pathogenesis, Curr Opin Microbiol 7:19 24, Melnyk RA, et al: Structural determinants for the binding of anthrax lethal factor to oligomeric protective antigen, J Biol Chem 281: , Pickering AK, Merkel TJ: Macrophages release tumor necrosis factor alpha and interleukin-12 in response to intracellular Bacillus anthracis spores, Infect Immun 72: , Saleeby CM, et al: Association between tea ingestion and invasive Bacillus cereus infection among children with cancer, Clin Infect Dis 39: , Subramanian GM, et al: A Phase 1 study of PAmAb, a fully human monoclonal antibody against Bacillus anthracis protective antigen, in healthy volunteers, Clin Infect Dis 41:12 20, Turnbull, PC: Introduction: anthrax history, disease and ecology, Curr Top Microbiol Immunol 271:1 19, 2002.