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Pathogenicity and virulence
Virulence factors of bacteria
• Microorganisms cause resulting in human
• Disease causing microorganisms possess
virulence factors.
• Virulence factors are properties of pathogens
to overcome the host defenses and to
establish an infection and cause disease.
Virulence factors
• 1. Adhesion factors
– Capsules, slime layers, surface carbohydrates, proteins, flagella
and pili aid in attachment.
• 2. Invasiveness
• enzymes that enhance invasiveness by enabling the
microorganisms to destroy body tissue and cells. Eg.
Hyluronidase, collagenase etc.
• 3. Toxicity
– Pathogens produce toxins, that disrupt the normal functioning
of the body. Classified into Endotoxins and exotoxins.
– Intoxications are diseases that result from the entrance of a
specific toxin into the host body.
• Exotoxins : Exotoxins are soluble heat-labile proteins
that are released as the bacteria grow
– Examples: i. Neurotoxin – Botulinum toxin
– ii. Cytotoxin – Haemolysin
– iii. Enterotoxin – Cholera toxin
• Endotoxins:
– Most Gram negative bacteria
have lipopolysaccharides (LPS) in
their outer membrane of their cell
LPS is toxic to specific hosts.
Diseases Classification and Glossary
Endemic disease
Nosocomial infections
Types of Disease
– Acute disease
– Chronic
Disease Process
• Patterns of disease
– Signs and symptoms
• Stages of a disease
– Incubation
– Prodromal stage
– Period of illness
– Period of decline
– Full recovery
Transmission of infectious agents
• Portals of Entry
Respiratory tract
Gastro intestinal tract
Genitourinary tract
Skin and wounds and paraenterel routes
• Transmission is effected by
– Direct contact transmission
– Direct faecal – oral route
– Indirect contact transmission
• Portals of exit
– Pathogens of gastrointestinal and genitourinary systems exit through body
fluids or faeces
– Pathogens of respiratory systems exit through nose, mouth fluids – during
coughing, sneezing and speaking
Diseases of the respiratory systems
Pharyngitis or sore throat
Diphtheria – Corynebacterium diphtheria
Tuberculosis – Mycobacterium tuberculosis
Diseases of the gastrointestinal tract
Staphylococcal food poisoning -Staph aureus
Travelers' diarrhea
Other gastroenteritis
Diseases of Central Nervous System
• A. Meningitis - Neisseria meningitis,
Haemosphilus influenza
• B. Tetanus - Clostridium tetani
• C. Botulism - Clostridium botulinum
Diseases of the cardiovascular and lymphatic
• Septicemia or blood poisoning E.coli,
Pseudomonas qeruginosa, Proteus sp etc.,
• Typhoid fever – Salmonella typhi
• Plague – Yersinia pestis
Diseases of the Urino-genital tract
• Urethritis and cystitis – E.coli, Klebsiella
Enterobacter, Proteus, Pseudomonas etc.,
• Leptospirosis – Leptospira interrogans
• Gonorrhea – Neisseria gonorrhoeae
• Syphillis – Treponema palladium
Fungal human Diseases
• Diseases of the respiratory tract
– Histoplarma Capsulatum, Coccidioides immitis Aspergillus
• Diseases of the gastrointestinal tract
– Aspergillus sp.
• Diseases of Vaginal tract – by Candida
• Diseases of central nervous system
– Ergotism - by Claviceps purpurea
– Meningitis - Cryptococcus neoformans
• Diseases of the skin
Dermatomycosis - Trichophyton
• Asporotrichosis - Sporothrix
Diseases caused by Protozoa and Parasites
Amoebiosis - Entamoeba histolytica
Vulvovaginitis - Trichomonas vaginalis
Trypanosomiaris - Trypanosoma gambiense
Malaria - Plasmodium (transmitted by mosquitoes)
• Parasitic Diseases
– Tapeworms, Elephantiasis, Schistosomiasis