Medical Bacteriology Lecture 7

Lecture 7: Medical Bacteriology (II)

• Lecture covered bacilli bacteria, spirochetes, mycobacterium, and normal flora
• Presented by Dr. Rasha Mokhtar Elnagar
• Included Gram-positive and Gram-negative bacilli
• Also included normal flora and pathogenic organisms

Gram-Positive Bacilli

• Divided into spore-forming and non-spore-forming types
• Spore-forming aerobes: Bacillus anthracis, Bacillus cereus
• Spore-forming anaerobes: C. perfringens, C. Tetani, C. botulinum, C. difficile
• Non-spore-forming types: Corynebacterium, Lactobacillus

Bacillus

• Morphology: Gram-positive, spore-forming, aerobic or facultative anaerobic bacilli.
• Important Species: Bacillus anthracis (has a polypeptide capsule) and Bacillus cereus
  • Both are exotoxin producers
• Diseases:
  • Bacillus anthracis: Zoonotic disease
    • Cutaneous anthrax: Spore germination in skin forms malignant pustule.
    • Pulmonary anthrax: "Wool sorter disease"
    • Intestinal anthrax
  • Bacillus cereus: Food poisoning caused by enterotoxins

Clostridium

• Morphology: Gram-positive, spore-forming, obligate anaerobes
• Important Species: Clostridium tetani, Clostridium botulinum, Clostridium perfringens, Clostridium difficile
• Note: All species are exotoxin producers
  • Clostridium tetani = Motile.
  • Clostridium botulinum = Motile.
  • Clostridium perfringens = Non-motile
• Diseases:
  • Clostridium tetani: Tetanus (Spastic muscle paralysis)
  • Clostridium perfringens: Gas gangrene (myonecrosis), often post-trauma.
  • Clostridium botulinum: Botulism (Shellfish, Salted fish, Canned food) (flaccid muscle paralysis)
  • Clostridium difficile: Antibiotic-associated diarrhea & pseudomembranous colitis

Corynebacterium

• Morphology: Gram-positive bacilli with club-shaped ends, arranged in Chinese-letter arrangement.

• Important Species: Corynebacterium diphtheria

• Important Points: Produces exotoxin

• Culture conditions: Grows on Löffler's medium, aerobically, at 37°C

• Disease: Diphtheria (upper respiratory tract infection)

Gram-Negative Bacilli

• Divided based on shape and lactose fermentation

  • Rod-shaped: Enterobacteriaceae (lactose fermenters and non-lactose fermenters)
    • E. coli, Klebsiella
    • Salmonella, Shigella, Proteus
  • Curved shape: Vibrio cholera, Campylobacter, Helicobacter pylori
  • Coccobacilli: Brucella, Haemophilus influenzae

• diseases of Enterobacteriaceae: urinary tract infection, neonatal meningitis, pneumonia, urinary tract infection, bacteremia.

• Salmonella: enteric fever, food poisoning, septicemia

• Shigella: bacillary dysentery (bloody diarrhea).

• Vibrio cholera: Cholera (Rice water diarrhea)

• Helicobacter pylori: Peptic ulcer

• Brucella: Malta fever, zoonotic, Brucella melitensis (goats & sheep), Brucella abortus (cows & cattle)

• Haemophilus influenzae: meningitis, pneumonia in infants

Pseudomonas aeruginosa:

• Morphology: Gram-negative rod (pleomorphic), motile, obligate aerobes
• Symptoms: urinary tract infections, bacteremia, bone and joint infections, particularly in patients with severe burns and immunosuppressed patients

Spirochetes: Treponema pallidum

• Morphology: Spiral shape, motile (endoflagella)
• Staining: Difficult to see by Gram stain, stained by Giemsa and Silver stain
• Observation: Dark Field microscopy for motility
• Culture: Cannot be cultured
• Disease: Syphilis (sexually transmitted disease)

Mycobacterium

• Morphology: Acid-fast, non-motile, non-spore-forming bacilli
• Staining: Cannot be stained by Gram stain due to presence of waxy lipid (mycolic acid) in cell wall
• Important Species: Mycobacterium tuberculosis (pulmonary tuberculosis), Mycobacterium leprae (Leprosy)
• Diseases:
  • Mycobacterium tuberculosis: Chronic cough, night fever, and sweating
  • Mycobacterium leprae: Leprosy

Normal Flora (Commensal Bacteria)

• Normally inhabit the human body
• Mostly bacteria, but may include fungi like Candida
• Do not cause disease in immunocompetent individuals
• Beneficial roles: compete for nutrients, produce antimicrobial substances, important in newborn development
• harmful effects: infections in immunocompromised individuals, change of site in body, changes in normal flora (due to antibiotics)
  • Colon: Clostridium difficile and pseudomembranous colitis
  • Vagina: Lactobacilli depletion and Candidiasis.
• Distribution: Skin, Nose, Eyes, Mouth, Intestinal Tract, Female Vagina

Pathogenicity

• Source of Infection

  • The environment (soil, air, water)
  • Animals (zoonotic diseases)
  • Humans (patients, carriers)

• Case patients: Patients carrying the pathogen

• Carrier: Persons without the disease that carry the pathogen, can spread infection without exhibiting signs of illness.

Mode of Transmission

• Contact (direct, indirect)
• Airborne
• Droplet
• Ingestion (fecal-oral)
• Bloodborne
• Arthropod-borne (insect-borne)
• Vertical (mother to fetus)
• Tran-placental transmission

Case Study

• 25-year-old woman with dysuria, afebrile, mild tenderness.
• Urine analysis: Many pus cells, Gram-negative bacilli present.
• Diagnosis: Urinary tract infection
• Most likely cause: Escherichia coli