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Gram-Positive Bacilli Part One

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1 Gram-Positive Bacilli Part One
MLAB 2434: Microbiology Keri Brophy-Martinez

2 General Characteristics: Bacillus
Habitat Thermal springs, fresh and salt water, soil, on plants Aerobic Spore-formers Resistant to radiation, heat, disinfections, and desiccation Mostly contaminants in clinical specimens EXCEPTION: Bacillus anthracis

3 More on Spores Produced when the bacteria gets stressed
Drying Temperature extremes Aid in organism’s survival Heat shock induces spores Temperature raised to 56o Gram stain Appear as clear areas within the bacterial cell


5 Significant Bacillus Species
Bacillus anthracis Agent of anthrax, a disease in livestock Humans acquire infection by contamination of wound or ingestion or inhalation of spores Bacillus cereus Causes food poisoning An opportunist Bacillus subtilis Common laboratory contaminant Used in sterility testing

6 Bacillus anthracis Cutaneous anthrax Inhalation anthrax
“Malignant pustule” (also called “black escher”) Woolsorter’s disease/ Rag-pickers disease Organisms gain access through cuts; localized infection Majority of cases in the world are cutaneous Inhalation anthrax Acquired through inhalation of spores May result in respiratory distress and death Gastrointestinal Acquired by ingestion of contaminated raw meat Usually fatal

7 Bacillus anthracis: Clinical Infections in Humans
Cutaneous anthrax

8 Laboratory Diagnosis Media Catalase positive
Most species grow well on SBA Most species beta-hemolytic, except B. anthracis No growth on MacConkey Fast growers Colony characteristics vary Catalase positive

9 Laboratory Diagnosis Goal in identification is to RULE OUT B. anthracis If B. anthracis is suspect, MUST work under safety hood Other Bacillus, identified to genus level ONLY

10 Identification of Bacillus anthracis
Microscopic morphology Large, square-ended gram-positive rods Bamboo appearance Spores may be absent in patient smears

11 Identification of Bacillus anthracis
Colony Morphology Nonhemolytic on blood agar; raised, large, grayish white, irregular, fingerlike edges “Medusa head” or “beaten egg whites”

12 Bacillus cereus Food poisoning Diarrheal syndrome Emetic form
Associated with meat, poultry, and soups Incubation period of 8 to16 hours Fever uncommon Resolves within 24 hours Emetic form Associated with fried rice Abdominal cramps and vomiting Incubation period of 1 to 5 hours Resolves in 9 hours

13 Bacillus cereus Local infections Postsurgical/traumatic wounds Burns
Eye infections Rare conditions Meningitis Bacteremia Endocarditis Osteomyelitis

14 Bacillus subtilis Found in the environment
Common laboratory and hospital contaminant Used as a QC agent for sterilization procedures

15 Key Characteristics of Bacillus Species
B. Anthracis B. Cereus Other Bacillus Beta-hemolysis Negative Positive, Large zones variable Motility Positive Pencillin Sensitive Resistant Variable

16 References thinking-caps.html 38/detail/ e.htm Kiser, K. M., Payne, W. C., & Taff, T. A. (2011). Clinical Laboratory Microbiology: A Practical Approach . Upper Saddle River, NJ: Pearson Education. Mahon, C. R., Lehman, D. C., & Manuselis, G. (2011). Textbook of Diagnostic Microbiology (4th ed.). Maryland Heights, MO: Saunders.

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