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

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Presentation on theme: "Gram-Positive Bacilli Part One MLAB 2434: Microbiology Keri Brophy-Martinez."— Presentation transcript:

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 56 o 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 ◦ “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 ◦ 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 Bacillus cereus Food poisoning ◦ Diarrheal syndrome  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 CharacteristicB. AnthracisB. CereusOther Bacillus Beta-hemolysisNegativePositive, Large zones variable MotilityNegativePositive PencillinSensitiveResistantVariable

16 References thinking-caps.html thinking-caps.html 38/detail/ e.htm 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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