Medical Bacteriology Lecture 7

Lecture 7: Medical Bacteriology (II)

• This lecture covers bacilli bacteria, spirochetes, mycobacterium, and normal flora.
• The presenter is Dr. Rasha Mokhtar Elnagar, a medical microbiology and immunology specialist.

Gram Positive Bacilli

• Gram-positive bacilli are categorized into spore formers and non-spore formers based on their ability to produce spores.
• Aerobic spore formers include Bacillus anthracis and Bacillus cereus.
• Anaerobic spore formers 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 Caused by Bacillus anthracis

• Cutaneous anthrax: Spore germination in skin leads to malignant pustules.
• Pulmonary anthrax (Wool sorter's disease)
• Intestinal anthrax

2-Genus Clostridium

• Morphology: Gram-positive, spore-forming, obligate anaerobes, bacilli.
• Important species: Clostridium tetani, Clostridium botulinum, Clostridium perfringens, and Clostridium difficile.
• All species produce exotoxins.
• C. tetani has a microscopic drum-stick appearance.
• C. perfringens has sub-terminal spores.

Diseases Caused by Clostridium

• Tetanus (C. tetani): Tetanus neurotoxin causes spastic muscle paralysis.
• Gas gangrene (C. perfringens): Myonecrosis (post-trauma).
• Botulism (C. botulinum, Shellfish, salted fish, canned food): Botulinum neurotoxin causes flaccid muscle paralysis.
• Antibiotic-associated diarrhea (C. difficile): Diarrhea and pseudomembranous colitis due to long-term antibiotic use.

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

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

Gram Negative Bacilli

• Vibrio cholerae (Comma-shaped): Motile, gram-negative, comma-shaped bacilli.
• Culture conditions: Alkaline media, e.g., alkaline peptone water.
• Disease: Cholera (rice water diarrhea).
• Helicobacter pylori: Curved, motile, gram-negative bacilli. Culture conditions: Micophilic and acidophilic
• Disease: Peptic ulcer.
• Brucella: Gram-negative coccobacilli. Capnophilic (5-10% CO2). Zoonotic disease: Malta fever (undulating fever). Important species: Brucella melitensis (goats and sheep) and Brucella abortus (cows and cattle).
• Haemophilus influenzae: Cause meningitis and pneumonia in infants. Grow on chocolate agar, needing X (hemin) and V (NAD) growth factors.

Pseudomonas aeruginosa

• Morphology: Gram-negative rod (pleomorphic), motile, obligate aerobes.
• Diseases: Urinary tract infections, bacteremia, bone and joint infections, severe burns and immunosuppressed patients.

Spirochetes: Treponema pallidum

• Morphology: Spiral-shaped, motile (endoflagella), difficult to see with Gram stain.
• Stained with Giemsa and silver stain.
• Motility viewed under dark-field microscope.
• Not culturable
• Disease: Syphilis (sexually transmitted disease)

Acid-Fast Bacilli: Genus Mycobacterium

• Morphology: 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) and Mycobacterium leprae (leprosy)
• Mycobacterium tuberculosis: Chronic cough, night fever, sweating.

Commensal Bacteria (Normal Flora)

• Primarily bacteria, but fungi like Candida can also be involved.
• Inhabit the human body and typically do not cause disease in immunocompetent individuals.
• Beneficial roles: competing for nutrients, producing antimicrobial substances, aiding immune system development in newborns, providing important nutrients (gut bacteria).
• Lactobacilli in the vagina maintain an acidic pH.
• Harmful effects: infections in immunocompromised individuals, infection when transferred to other sites in the body (e.g., S. epidermidis in bloodstream), or when the number of bacteria changes (e.g., antibiotic overuse causing C. difficile overgrowth).

Distribution of Normal Flora

• Skin: Staphylococcus epidermidis, Staphylococcus aureus, Propionibacterium acnes.
• Nose: Similar to skin flora.
• Eye: Staphylococcus epidermidis, Staphylococcus aureus, Moraxella catarrhalis.
• Mouth: Streptococcus mutans, Lactobacillus, Candida spp.
• Intestinal tract: E. coli, Klebsiella, Enterococcus faecalis, Candida.
• Female vagina: Lactobacillus, Candida albicans, Streptococcus agalactiae.

Pathogenicity of Microorganisms: Sources of Infection

• Environmental (soil, air, water)
• Animals (zoonotic diseases)
• Humans (cases, carriers)

Modes of Transmission

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

Case Study

• A 25-year-old woman presented with dysuria, afebrile, and normal vital signs with mild pubic tenderness.
• Urinalysis showed many pus cells and gram-negative bacilli.
• Likely cause of UTI is Escherichia coli.