Transmission of Microbes Flashcards
Routes of Entry of Microbes
Microbes can enter the host through breaches in the skin, by inhalation or ingestion, or by sexual transmission
Skin
Epidermal barrier
Mechanical defects (punctures, burns, ulcers)- Staphylococcus aureus, Candida albicans, Pseudomonas aeruginosa
Needle sticks- HIV, hepatitis viruses
Arthropod and animal bites- Yellow fever, plague, Lyme disease, malaria, rabies, Zika virus
Direct penetration Schistosoma
Gastrointestinal tract Epithelial barrier
Attachment and local proliferation
of microbes- Vibrio chloerae, Giardia
Attachment and local invasion of
microbes- Shigella, Salmonella, Campylobacter
Uptake through M cells- Poliovirus, certain pathogenic bacteria
GIT Acidic
Acid-resistant cysts and eggs Many protozoa and helminths
GIT Bile and pancreatic organism
Resistant microbial external coats Hepatitis A, Rotavirus, Norovirus
GIT Normal protective flora
Broad-spectrum antibiotic use Clostridium difficile
Respiratory tract Mucociliary clearance
attachment and local proliferation
of microbes- Influenza viruses
Ciliary paralysis by toxins- Haemophilus influenzae, M. pneumoniae, Bordetella pertussis
Respiratory tract- Resident alveolar macrophages
Resistance to killing by phagocytes M. tuberculosis
Urogenital tract Urination
obstruction, microbial attachment and local proliferation- E. coli
UGT, normal vaginal flora
Antibiotic use- candida albicans
UGT, Intact epidermal/epithelial barrier
Microbial attachment and local proliferation- Neisseria Gonorrhoeae
Direct infection/Local invasion- Herpes, Zika, T. Pallidum
Local Trauma- HPV
How do pathogens enter GIT?
food, drink, or contaminated water- especially during floods- diarrheal diseases are rampant.
What are some of the most important barriers against GIT infections
Acidic and Gastric secretions
How much dose of V. cholerae is needed for infection to manifest?
10^11
How many times does stomach acid neutralize the pathogen?
10,000 fold for V. cholerae
Shigella and Giardiasis
resistant to gastric acid, fewer than 100 organisms
The other normal defenses in GIT are
Viscous mucus layers; Lytic pancreatic enzymes and bile detergents; Mucosal and anti-microbial peptides called defensis; Normal flora; IgA antibodies made by MALT
Pathogens that use M cells to enter GIT
Polio, E coli, V. Cholerae, Salmonella, Shigella flexneri
how are host defenses weakened in GIT
Low gastric acidity, antibiotics, obstruction, and cessation of peristalsis
TOxins in food
S. aureus, Bacillus Cereus
How is the vagina protected from pathogens from puberty until menopause?
low pH by lactobacilli catabolism, antibiotics kill lactobacillus, causing overgrowth of yeast and result Vaginal candidiasis
Spread and Dissemination of Microbes
Within the Body
Some microorganisms proliferate locally, at the site of
the initial infection, whereas others penetrate the epithelial
barrier and spread to distant sites by way of the lymphatics, the blood, or nerves
Lysis and invasion
Some extracellular bacteria, fungi,
and helminths secrete lytic enzymes that destroy tissue and allow direct invasion.
S. aureus secretes
hyaluronidase, which degrades the extracellular matrix between host cells. Invasive microbes initially follow tissue planes of least resistance and drain
to regional lymphatics. S. aureus may travel from a localized abscess to the draining lymph nodes. This can
sometimes lead to bacteremia and spread to deep organs (heart, bone)