Medical Bacteriology Lecture 7

Lecture 7: Medical Bacteriology (II)

• Lecture covers bacilli bacteria, spirochetes, mycobacterium, and normal flora.
• Dr. Rasha Mokhtar Elnagar is the lecturer.
• Her credentials include M.B.B.C, MSc, PhD, MD, Associate Professor of Medical Microbiology & Immunology and Consultant Microbiology & Immunology.

Gram Positive Bacilli

• Divided into spore formers and non-spore formers.
• Spore forming are further divided into Aerobes and Anaerobes.
  • Aerobes include Bacillus anthracis and Bacillus cereus.
  • Anaerobes include C. perfringens, C. Tetani, C. botulinum, and C. difficile.
• Non-spore formers include Corynebacterium and Lactobacillus.

1-Genus Bacillus

• Morphology: Gram-positive, spore-forming, aerobic or facultative anaerobic bacilli.
• Important species: Bacillus anthracis (polypeptide capsule) and Bacillus cereus.
• Both species produce exotoxins.

Diseases of Bacillus Anthracis

• Zoonotic disease.
• Cutaneous anthrax: spore germination in skin forms malignant pustule.
• Pulmonary anthrax (Wool sorter disease).
• Intestinal anthrax.

2-Genus Clostridium

• Morphology: Gram-positive, spore-forming, obligate anaerobic bacilli.
• Important species: Clostridium tetani (motile), Clostridium botulinum (motile), Clostridium perfringens (non-motile), and Clostridium difficile.
• All species produce exotoxins.

Culture Conditions for Obligate Anaerobes

• Require anaerobic jars or incubators and blood agar.
• Cooked meat media is also used in anaerobic condition.

Diseases of Clostridium

• Clostridium tetani: Tetanus, spastic muscle paralysis.
• Clostridium perfringens: Gas gangrene (myonecrosis), post-trauma.
• Clostridium botulinum: Botulism (shellfish, salted fish, canned food), flaccid muscle paralysis.
• Clostridium difficile: Antibiotic-associated diarrhea, pseudomembranous colitis (due to long-term antibiotic therapy).

2-Non-Spore Formers Gram Positive Bacilli: Genus Corynebacterium

• Morphology: Gram-positive bacilli with club-shaped ends arranged in a Chinese-letter arrangement.
• Important Species: Corynebacterium diphtheria.
• Produces exotoxin.
• Culture Conditions: Grow on Löffler's medium, aerobic, at 37°C..
• Disease: Diphtheria (upper respiratory tract infection).

2. Gram Negative Bacilli

• Divided into Rod-shaped (Enterobacteriaceae), Curved, and Coccobacilli.
  • Rod-shaped (Enterobacteriaceae) are further divided by lactose fermentation (positive or negative) and motility (motile or non-motile). Key genera include E. coli, Klebsiella, Salmonella, Shigella, and Proteus
  • Curved: Vibrio cholera (comma-shaped), H. pylori, Campylobacter.
  • Coccobacilli: Brucella, Haemophilus influenzae

Enterobacteriaceae

• Gram-negative bacilli.
• Facultative anaerobes.
• Important genera include E. coli, Klebsiella, Salmonella, Shigella, Proteus.

Diseases caused by Enterobacteriaceae

• E. coli: Urinary tract infection, Neonatal meningitis.
• Klebsiella: Urinary tract infection, Pneumonia.
• Proteus: Urinary tract infection, Bacteremia.
• Salmonella: Enteric fever (Typhoid and paratyphoid), Food poisoning, Septicemia.
• Shigella: Bacillary dysentery (bloody diarrhea).

1. Vibrio cholerae

• Gram-negative, comma-shaped, motile bacilli.
• Alkaliphilic: grows on alkaline media like alkaline peptone water.
• Disease: Cholera (rice water diarrhea).

2. Helicobacter pylori

• Gram-negative, curved, motile bacilli.
• Microphilic, Acidophilic.
• Disease: Peptic ulcer.

3-Coccobacilli

• Brucella: Gram-negative coccobacilli, Capnophilic (5-10% CO2), Zoonotic disease (Malta fever).
• Important species: Brucella melitensis (in goats and sheep), Brucella abortus (in cows and cattle).
• Haemophilus influenzae: causes meningitis, pneumonia in infants. Requires X (hemin) and V (NAD) growth factors on Chocolate agar.

Pseudomonas aeruginosa

• Gram-negative rod (pleomorphic), motile, obligate aerobes.
• Diseases: Urinary tract infections, Bacteremia, Bone and joint infections, particularly in patients with severe burns and immunocompromised patients.

Spirochetes: Treponema pallidum

• Spiral shape, motile (endoflagella).
• Difficult to see by Gram stain, can be stained by Giemsa and Silver stain.
• Motility observed using dark field microscopy.
• Cannot be cultured.
• Disease: Syphilis (sexually transmitted disease).

Genus Mycobacterium

• Acid-fast, non-motile, non-spore-forming bacilli.
• Cannot be stained by Gram stain due to waxy lipid (mycolic acid) in cell wall.
• Important species:
• Mycobacterium tuberculosis: Pulmonary tuberculosis (chronic cough, night fever, sweating).
• Mycobacterium leprae: Leprosy.

Commensal Bacteria (Normal Flora)

• Normally inhabit the human body.
• Mostly bacteria but may also include fungi (e.g., Candida).
• Do not cause disease in immunocompetent individuals.
• Beneficial role: compete for nutrients, produce antimicrobial substances, stimulate immune system development in newborns, provide nutrients to the body, maintain vaginal pH (lactobacilli).

Harmful Effects of Normal Flora

• Cause infections in immunocompromised individuals (opportunistic infections).
• Change of site in the body: (e.g., S. epidermidis into the bloodstream).
• Change in normal flora (e.g., overuse of antibiotics).
  • Colon: Clostridium difficile overgrowth causing pseudomembranous colitis.
  • Vagina: Lactobacilli depletion leads to overgrowth of other pathogens (e.g., Candida).

Distribution of Normal Flora in the Body

• Skin: Staphylococcus epidermidis (90%) and Staphylococcus aureus, Propionibacterium acnes.
• Nose: Same as skin flora.
• Eye: Staphylococcus epidermidis, Staphylococcus aureus and Moraxella catarrhalis.
• Mouth: Streptococcus mutans, Lactobacillus, and Candida species.
• Intestinal tract: E. coli, Klebsiella, Enterococcus faecalis, and Candida.
• Female Vagina: Lactobacillus, Candida albicans, and Streptococcus agalactiae.

Pathogenicity of Microorganisms: Source of Infection

• Environment (soil, air, water).
• Animals (zoonotic diseases).
• Humans (patient or carrier).

Mode of Transmission

• Direct contact (hand-to-hand, body secretions, sexual)
• Indirect contact (contaminated surfaces/objects)
• Airborne, droplet, ingestion (fecal-oral), bloodborne, arthropod-borne, vertical (mother to fetus), tranplacental,

Case Study

• 25-year-old woman with dysuria, afebrile, mild pubic tenderness.
• Urine analysis shows many pus cells and Gram-negative bacilli.
• Likely cause: Escherichia coli urinary tract infection.