Gram-positive spore formersNon spore formers

AEROBIC GRAM POSITIVE BACILLIAerobic Gram (+) spore-forming, non-branching, catalase (+) bacilli

BACILLUS spp.General CharacteristicsFound in natureMost are saprophytic and are isolated as contaminantsBacillus anthracis is a major pathogenOthers are opportunistsCommonly encountered in the microbiology laboratory

BACILLUS spp.A large group of bacteria50 species are found in the environmentNon motileFerments glucose but not mannitol, arabinose or xyloseProduces lecithinase and produces an opaque zone in egg yolk agar colonies Grow in high salt (7% NaCl) and low pH (< 6)

BACILLUS spp.Non hemolytic on BAPFound in the environment and can be isolated from water and soilMajority are not highly pathogenic but are being isolated from clinical infections increasing frequencyOn Gram stain, spores do not stain but just appear as empty spaces

BACILLUS spp.Spore stain is used to demonstrate sporesFound in soils of all climates subarctic, desert regions, thermal springs, fresh and salt water, and plant materials, growing at -5oC or as high as 75oCThey survive because endospores are resistant to conditions to which vegetative cells are intolerant

BACILLUS spp.Most species grow well on BAP and other common enriched mediaFound as contaminants in specimens from a number of sourcesColony characteristics vary considerably among species and are influenced by type of medium used

BACILLUS sppPigment formation from pink to blue black are formed in a number of species depending on the growth conditions and substrate

Significant Bacillus sppBacillus anthracisAgent of anthrax, a disease in livestockHumans acquire infection by contamination of wound or ingestion or inhalation of sporesBacillus cereusCauses food poisoningAn opportunistsBacillus subtilisCommon laboratory contaminant

Bacillus anthracisMorphologyLarge, sporeforming Gram (+) bacilliSpores viable for up to 50 yearsNonhemolytic on sheep blood agar or BAPSpore formation is aerobicNon motile

Bacillus anthracisVirulence factorsPolypeptide capsulePotent exotoxinEdema factor (EF)Protective antigen (PA)Lethal factor (LF)

Bacillus anthracisDepends on a glutamic acid capsule and a complex toxinThe capsule (polypeptide of D-glutamic acid) protects the organism from phagocytosis and is resitant to hydrolysis by host proteolytic enzymes because it is the unnatural formAlthough capsule is necessary for virulence, antibodies against the capsule do not confer immunity

The Anthrax ToxinsThe effect of edema factor and lethal factor is seen when either is combined with protective antigenEdema results from the combination of PA with EF, but death occurs when PA combines with LFIncreases vascular permeability

The Anthrax ToxinsInterferes with phagocytosisGenes are carried by a plasmid but if a virulent strain is repeatedly cultured in vitro, the plasmid is eventually lost and the organism is no longer virulent

AnthraxZoonotic infections transmitted by direct contact or inhalationNot spread from animal to animal but from animals feeding on plants contaminated with sporesDisease is named according to its occupational association: Woolsorters disease, Ragpickers disease

Epidemiology

Primarily a disease of herbivorous animals such as sheep, cattle, goats, and horsesCommon disease in livestock worldwide

Epidemiology

Human acquired the infection accidentally in agricultural or industrial setting Man- infected upon contact with the animal or animal product sIncidence in US is very low at < 5 cases/year, however, worldwide, cases number by several thousandIn other parts of the world including Central and South America, disease is enzoonotic

Epidemiology

During processing of hides or animal hair Gains access through cuts or inhalation

3 Clinical Manifestations

1.Cutaneous anthrax begins 2 to 5 after inoculation of spores (95%)Wounds contaminated with spores acquired to skin cuts, abrasions, insect bites Lesion starts as an erythematous papule that progresses into an ulcerative black eschar or malignant pustule

Cutaneous anthrax or malignant pustule:begins when the organisms gain access through cuts; localized infection

Symptoms:Small pimple or papule appears at site of inoculation 2 to 3 days after exposureA ring of vesicles develops & the vesicles coalesce to form an erythematous ringA small dark area appears in the center of the ring and eventually ulcerates and dries forming a depressed black necrotic central area known as eschar (black eschar or malignant pustule)

Lesion is painless and does not produce pus unless secondary pyogenic infection comes in Eschar is 1 to 3 cm in diameter but may become more extensive. This heals after 1 to 2 weeks. It dries then separates from the underlying base, and falls off, leaving a scarUsually infection remains localized but regional lymphangitis and lymphadenopathy appear

If septicemia occurs, there is fever, malaise and headacheNormally in uncomplicated cases, no systemic symptoms are present

2.Pulmonary anthrax (rare) is acquired by inhalation of spores Pulmonary anthrax or woolsorters disease: acquired through inhalation of spores; may result in respiratory distress and deathMalaise, mild fever, nonproductive cough follows

Symptoms:Acquired when spores are inhaled into pulmonary parenchymaInfection begins as a nonspecific illness consisting of mild fever, fatigue, and malaise 2 to 5 days after exposure to spores Resembles URT like colds and fluThis initial form lasts 2 to 3 days and is followed by sudden severe phase where respiratory distress is common

Severe phase is extremely serious (dypsnea, cyanosis, pleural effusion) then disorientation, coma then deathCourse of the severe phase from respiratory symptoms to death may last only 24 hours

3. Gastrointestinal (very rare)Gastrointestinal: acquired by ingestion of contaminated raw meatOccurs when spores are inoculated into a lesion on the intestinal mucosa following ingestion of sporesAbdominal pain, nausea, anorexia and vomiting; bloody diarrhea may occurRare (