GRAM POSITIVE BACILLI

Clinically important Gram positive bacilli

Spore forming

1. Bacillus

2. Clostridium

Non spore forming

1.Corynebacterium

2.Listeria

3.Lactobacillus

Bacilli w/ branching filaments

1.Actinomyces

2.Nocardia

1- Spore-Forming Gram-Positive Bacilli: A- Strict aerobic – Genus Bacillus.B- Strict anaerobic – Genus Clostridium.

Spore- forming gram positive strict aerobic capsulated bacilli, 1x3-4 u size, arranged in long chains;

• Highly resistant spores

spores may central, subterminal or terminal, depending on the species,seen as unstained, usually oval spaces, one in each stained mother cell

(sporangium) ,

• In vitro – prominent capsule(A unique anti-phagocytic capsule is composed of D-glutamate.

.

Most members are saprophytic prevalent in soil, water, air and vegetation such B. cereus ,

and B. subtilius. Bacillus anthracis non motile while Bacillus cereus motile. Most strain • Catalase positive• indole negative, • simmon citrate variable.

• Bacillus anthracis– Human pathogen– Isolation also considered to be clinically significant– Zoonosis

• Bacillus cereus– Environmental organism– Contaminates food– Common cause of food poisoning

• Bacillus stearothermophilus– Tolerates very high temperatures– Used for quality control of autoclaves Bacillus subtilis common lab contaminant

Cause the disease Anthrax in animals in which the organism is transmitted through eating vegetations containing the spores. Human is infected through contact with animals or their products.

B. anthracis

Disease in HumanA- Cutaneous Anthrax(malignant pustule): Generally occurs on exposed surfaces of the arms, face and neck through wound contamination by the spores of the

organism. About 95% of the cases with a mortality rate 20% .

B- Inhalation Anthrax(wool A sorter disease): About 5% of the cases with 85-90% mortality.

C- Gastrointestinal Anthrax: Is very rare.

Anthrax Pathogenesis and clinical presentations

Virulence factorsCapsule

(antiphagocytic)Toxin

(oedema & death)

Cutaneous anthraxAbout 20% mortality

Cutaneous anthraxAbout 20% mortality

Gastrointestinal anthraxHigh mortality

Gastrointestinal anthraxHigh mortality

Inhalation anthraxHigh mortality

Inhalation anthraxHigh mortality

Anthrax Has Been Used As a Bioweapon

Because it is deadly, noncontagious, and dispersed by spores, anthrax has always been considered a good candidate for a bioweapon. Late in 2001, this possibility became a reality. Letters containing anthrax spores were sent to several news reporters and two United States Senators. Five people died of inhalational anthrax as a result of exposure to these spores.

Anthrax - Diagnosis

• Specimen– Aspirate or swab from cutaneous lesion– Blood culture– Sputum , Fluid , pus,

• Laboratory investigation– Gram stain– Culture– Identification of isolate

Diagnostic Laboratory TestsCulture on blood agar.

• Gram Stained smears from the local lesion or of blood from dead animals often show chains of large gram-positive rods.

• Anthrax can be identified in dried smears by immunofluorescence staining techniques.( Spores not seen in smears of exudate).

• When grown on blood agar plates, the organisms 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 always nonmotile, whereas related

nonpathogenic organisms (eg, B cereus) exhibit motility by "swarming.“• Carbohydrate fermentation is not useful• Virulent anthrax cultures kill mice or guinea pigs upon intraperitoneal injection. • Demonstration of capsule requires growth on bicarbonate-containing medium in 5–

7% carbon dioxide. • An enzyme-linked immunoassay (ELISA) has been developed to measure

antibodies against edema and lethal toxins, but the test has not been extensively studied.

The cells have characteristic squared ends. The endospores are ellipsoidal shaped and located centrally in the sporangium. The spores are highly refractile to light and resistant to staining.

Bacillus anthracis. Gram stain. a "bamboo appearance”

Laboratory Diagnoses

Characteristic Bacillus anthracis Other Bacillus spp.Hemolysis Neg PosMotility Neg Pos (usually)Gelatin hydrolysis Neg Pos

Key Characteristics to Distinguish between B. anthracis & Other Species of Bacillus

Gram-Variable Stain of B. cereus with Endospores

Cause food poisoning: Two types

1 -Emitic type associated with fried rice.

2 -Diarrheal type associated with meat dishes and

sauces

Infections in the immunosuppressed hosts

Opportunistic infections of the eye

Meningitis, septicemia, and osteomyelitis

Found as contaminants in drug paraphernalia

Bacillus cereus

Gastroenteritis

Gastroenteritis

Bacillus cereus clinical presentation

Incubation period < 6 hoursSevere vomitingLasts 8-10 hours

Incubation period > 6 hoursDiarrhoea

Lasts 20-36 hours

EMETIC FORM DIARRHOEAL FORM

Foodborne Diseases of B. cereus (Intoxication) (Foodborne Infection)

b.Bacillus cereus

• Large, motile, saprophytic bacillus• Heat resistant spores• No capsule• Pre formed heat and acid stable toxin

(Emetic syndrome)• Heat labile enterotoxin (Diarrhoeal disease)• Lab diagnosis – Demonstation of large

number of bacilli in food

Laboratory Identification: Bacillus anthracis

Characteristics B. anthracis B.cereus

Hemolysis onBAP

= +

Motility = +

String of pearls + =

Growth on PEA = +

Gelatin hydrolysis = +

Susceptibility toPenicillin (10U/ml)

Susceptible Resistant

Bacillus stearothermophilus• Spores used to test efficiency of killing in autoclaves

Other Bacillus spp.

Other Bacillus species

• Bacillus subtilis– Common laboratory contaminant

Points to Remember

• Differentiating characteristics between B. anthracis and saprophytic species

• Characteristic, microscopic appearance of Bacillus species• Clinical forms of infection attributed to B. anthracis• Clinical significance of Bacillus cereus in healthy as well as

in at-risk populations