The document provides an overview of aerobic spore-forming bacilli, specifically focusing on Bacillus anthracis and Bacillus cereus. It details their classifications, morphological characteristics, virulence factors, pathogenesis, clinical diseases, and laboratory diagnosis methods. Additionally, it discusses treatment options and preventive measures against anthrax and food poisoning caused by these bacilli.

1. Aerobic spore forming bacilli
U.Kibwana
Microbiology and Immunology-MUHAS

3. Introduction

4. Aerobic spore forming bacilli
• Genus Bacillus
• Large aerobic, Gram-positive rods occurring in chains
• Most are saprophytic organisms prevalent in soil, water, and air and
on vegetation
•B.anthrancisantharx
• B.cereus food poisoning
• Some are insect pathogens

5. Classification
• Kingdom: Bacteria
• Phylum-Firmicutes
• Class-Bacilli
• Oder-Bacillales
• Family-Bacillaceae
• Genus:Bacillus

7. Bacillus anthracis
Morphology and Identification
Spore forming gram positive rods
1 x 3–4 µm, square ends, in long chains;
spores are located in the center of the non motile bacilli
Spores observed in culture not in clinical specimen
Has polypeptide capsule consisting of poly-D-glutamic acid observed in
clinical specimen

8. Bacillus anthracis
Morphology and Identification
Colonies on sheep BA are large, non pigmented, irregular and have a cut
glass appearance in transmitted light
Non haemolytic on sheep BA
Gelatin is liquefied, growth in gelatin stabs resembles an inverted fir tree

9. Bacillus anthracis

10. Predominant polypeptide capsule

11. Bacillus anthracis
Spores
 Are Resistant to environmental changes
 Withstand dry heat and certain chemical disinfectants for moderate
periods
Persist for years in dry earth
Animal products contaminated with anthrax spores (eg, hides, bristles,
hair, wool, bone) can be sterilized by autoclaving

12. Virulence factors
 Polypeptide capsule in virulent strains
 Potent 3 anthrax toxin on large plasmid PX01
-Protective antigen (PA)
-Edema factor (EF)
-Lethal factor (LF)
 Combine to form edema toxin (PA+EF), Lethal toxin (PA+LF)

13. Pathogenesis
 Anthrax is primarily a disease of herbivores
 Humans infected incidentally by contact with infected animals or
product
 In humans, the infection is usually acquired by the entry of spores
- Injured skin (cutaneous anthrax)
- Rare mucous membranes (gastrointestinal anthrax)
- Inhalation of spores into the lung (inhalation anthrax)

14. Pathogenesis
• The spores germinate at the site of entry, and growth of the
vegetative organisms results in formation of a gelatinous edema and
congestion
• Bacilli spread via lymphatics to the bloodstream
• Capsule antiphagocytic, organism lacking capsule is not virulent

15. Pathogenesis
 Edema toxin has adenylate cyclase responsible for fluid
accumulation
 Lethal toxin major virulent factor stimulate release of TNF-α,
interleukin-1β and other proinflammatory factors
 Leading to cell death

16. Clinical diseases
• In humans, approx 95% are cutaneous anthrax and 5% are inhalation
• Gastrointestinal anthrax is very rare
• The bioterrorism events : 22 cases of anthrax: 11 inhalation and 11
cutaneous, 5 inhalation anthrax died

17. Clinical diseases
Cutaneous anthracis
A painless papule develops 1 – 7 days after entry of spores
Papule progress to vesicles and then ulceration forming necrotic
ulcer
The lesions typically are 1–3 cm in diameter and have a
characteristic central black eschar
Mortality rate in untreated cases is 20%

18. Clinical diseases
Inhalation anthrax (woolsorter's disease)
Incubation period 2 months or more
Has rapid onset of sepsis with fever, edema, and lymphadenopathy
Meningeal symptoms seen in half of cases
The fatality rate is high

19. Clinical diseases
Gastrointestinal anthrax
Uncommon in human
Abdominal pain, vomiting, and bloody diarrhea are clinical signs

20. Epidemiology
• Primarily a disease of herbivores with human accidental hosts
• Prevalent in impoverished areas where animal vaccination is not
practiced
• At risk include people in endemic areas in contact with infected or
contaminated soil
• The greatest danger is use of B.anthracis as a agent of bioterrorism

21. Laboratory diagnosis
 Specimens: fluid or pus from a local lesion, blood, and sputum
Microscopy
 Gram stain: large, square-ended gram-positive rods; may appear
end-to-end giving a "bamboo appearance
 Indian ink or Direct fluorescent antibody (DFA) for capsule
detection.

22. Laboratory diagnosis
Culture
 On BAP , colonies nonhaemolytic gray to white colonies with a
rough texture and a ground-glass appearance
Comma-shaped outgrowths (Medusa head) may project from the
colony
Nuclei acid amplification [Polymerase chain reaction (PCR)] –reference
lab

23. Treatment, prevention and control
• Ciprofloxacin is drug of choice; penicillin, erythromycin may be used if
susceptible
• Bacteria are resistance to sulphonamides and extended spectrum
cepharosporin
• Vaccination of animal herds and people in endemic areas can control
the disease
• Animal vaccination is effective ,but human vaccine have limited
usefulness

24. Bacillus cereus
 Spore forming, motile gram positive rods
 β haemolytic on sheep blood agar
 Virulent factor includes
heat stable and heat-labile enterotoxin
Cytotoxic enzymes including cereolysin and phospholipase c

25. Bacillus cereus
Clinical diseases
•2 form of food poisoning
Emetic form
•Consumption of contaminated rice
•Heat stable enterotoxin
•Incubation period 1 – 6 hrs
•Consist of nausea, vomiting and abdominal cramp

26. Bacillus cereus
Diarrheal form
•Consumption of contaminated meat, sauces
•Incubation period 1 – 24 hrs
•manifested by profuse diarrhea with abdominal pain and cramps;
•Heat labile enterotoxin produced in the intestine

27. Bacillus cereus
• Ocular infections
• Endocarditis, meningitis, osteomyelitis, and pneumonia

29. Distinguishing characteristics between
B.anthracis and B.cereus
characteristics B. anthracis B. cereus
Haemolytic on
sheep blood agar
_ +
Motility _ + (swarming
motility)
Gelatin liquified + -
Susceptibility to
penicillin
+ _

31. The end

32. References
1. https://www.gov.uk/uk-standards-for-microbiology-investigations
-smi-qualityand-consistency-in-clinical-laboratories
2. https:/www.slideshare.net/bkramkadas/medical-bacteriology-
bacillus