G(+) Baccili

• Gram-positive bacilli


  When stained with routine gram staining, their reaction is gram-positive, or purple in color
• Spores


  • Responsible for resistance to extreme conditions
  • If the environment for the bacteria is not suitable for their growth, they will form spores so that they will resist the extreme conditions
• Spore formers

  • Bacillus
  • Clostridium

  
• Bacillus


  Aerobic, positive for the aerobic catalase test (3% H2O2)
• Clostridium


  Anaerobic, negative for anaerobic catalase (15% H2O2), aerogenic
• Bacillus


  • There are more than 100 species within the genus
  • Only a small percentage of the species are medically important
  • Metabolically diverse, some are thermophiles that grow best at 55*C or higher
  • The survival of Bacillus spp. in nature is aided by the formation of spores
• Bacillus anthracis


  Also known as "Anthrax Bacillus", the largest pathogenic bacteria
• Bacillus anthracis identification

  • India ink stain
  • Fluorescent-labeled antibody test

  
• Bacillus anthracis virulence factors

  • D-glutamic acid capsule is the major virulence factor, resistant to hydrolysis by host proteolytic enzymes
  • Anthrax toxin consists of three proteins: Protective antigen (PA), Edema factor (EF), and Lethal Factor (LF)
• Treatment for Bacillus anthracis

  • Most isolates are susceptible to penicillin, but resistance can occur
  • CDC recommends ciprofloxacin or doxycycline for initial intravenous therapy until antimicrobial susceptibility results are known
• Caution should always be used in working with an isolate suspected of being B. anthracis, work should be performed in a biological safety cabinet, and the area should be disinfected when the work is completed
• Bacillus anthracis microscopy

  • Large, square-ended, gram-positive rod found singly or in chains, gives the appearance of bamboo pole arrangement, spores are generally NOT present in clinical samples
• Bacillus anthracis colony morphology

  • Medusa head/ beaten egg whites on blood agar plate, string of pearls on Mueller-Hinton Agar with penicillin
• Bacillus cereus


  Relatively common cause of fried rice poisoning and opportunistic infections in susceptible hosts
• Bacillus cereus food poisoning

  • Diarrheal type: acquired by eating meat and poultry, long incubation period, heat labile enterotoxin
  • Emetic type: most common, acquired by eating fried rice, short incubation period, heat stable enterotoxin
• To confirm Bacillus cereus as the cause of food poisoning, viable counts from the food and stool should be at least 10^5 cells per gram

  
• Treatment for Bacillus cereus

  Most food poisoning cases do not require antimicrobial treatment, B. cereus is resistant to penicillin and other β-lactams except carbapenems, severe cases may be treated with vancomycin or clindamycin with or without an aminoglycoside
• Bacillus cereus microscopy

  • Gram-positive, spore-forming bacilli

  
• To confirm the organism as the cause of the disease, viable counts from the stool should also be at least 10^5 cells per gram
• We need to count how many bacteria is present in one gram of food that caused the incident. There is approximately 100,000 of B. cereus per gram of food poisoning; in other words, at least 100,000 B. cereus cells must be counted in order to confirm a case of food poisoning. The same goes for stool specimens suspected for B. cereus food poisoning, at least 100,000 cells of B. cereus must be detected to confirm diagnosis.
• Most food poisoning cases caused by B. cereus

  Do not require antimicrobial treatment – in cases that are not severe, it is considered as self-limiting
• B. cereus


  Is resistant to penicillin and all of the other b-lactam antibiotics EXCEPT for the carbapenems
• In severe cases, treatment with

  Vancomycin or clindamycin with or without an aminoglycoside has been successful
• B. cereus bacteria

  • Stained with Leifson dye to display their peritrichous flagella (flagella all around the body)

  
• Gram-positive bacilli are purple in color when stained with routine gram staining
• Spores


  Responsible for resistance to extreme conditions
• Spore former


  • Bacillus
  • Clostridium
• Bacillus


  Aerobic, Catalase +, No gas production
• Clostridium


  Anaerobic, Catalase -, Gas production +
• Anaerobes are susceptible to toxic derivatives of oxygen because they lack protective enzymes like superoxide dismutase and/or catalase
• Clostridium tetani


  • Causes tetanus (spasmic paralysis), Racquet Bacillus (round terminal spores), Motile by peritrichous flagella, Spores highly resistant to adverse conditions, Iodine (1%) in water can kill spores within hours
• Tetanospasmin


  Neurotoxin and an essential pathogenic product of C. tetani, Toxic when injected parenterally but not orally, Causes increasing excitability of spinal cord neurons and muscle spasms
• Laboratory diagnosis of C. tetani

  Gram stain shows Gram-positive rod with round terminal spore (drumstick appearance), Culture on blood agar anaerobically shows fine spreading film
• Clostridium perfringens


  • Causative agent of gas gangrene, Non-motile, capsulated, with sub-terminal spores
• Alpha toxin of C. perfringens


  Phospholipase C, lecithinase, lyses RBCs, platelets, leukocytes, and endothelial cells, Increases vascular permeability with massive hemolysis and bleeding tissue destruction
• Beta toxin of C. perfringens


  Responsible for necrotic lesions in necrotizing enterocolitis
• Enterotoxin of C. perfringens


  Heat-labile toxin produced in colon, Causes food poisoning
• Laboratory diagnosis of C. perfringens

  Specimen from deeper areas of wound, Culture anaerobically at 37*C on Robertson's cooked meat medium, Exhibits double zone of beta hemolysis, Nagler reaction positive (lecithinase activity), Acidifies litmus milk with stormy clot formation
• Reverse CAMP test for C. perfringens


  Streaked perpendicular to CAMP positive S. agalactiae, Shows enhanced hemolysis in between
• Clostridium botulinum


  • Causes botulism (flaccid paralysis), 7 neurotoxic subtypes A-G, Toxin irreversibly binds to acetylcholine receptors at neuromuscular junction, Alters acetylcholine release mechanism