There are four main routes of infection:
1. Oral/fecal - Vibrio Cholera (Cholera)
2. Respiratory - Streptococcus pneumoniae (meningitis, bacteremia/sepsis, pneumonia)
3. Sexual transmission - Chlamydia trachomatis (STD)
4. Blood-borne pathogens are usually acquired by blood transfusions or insect/animal bites.
There is Methicillin resistant Staphylococcus aureus - usually acquired by nosocomial infection. Also, Group B Streptococcus (flesh eating bacteria) can infect an open sore in a hospital.
1. A great oral/fecal example is the bacterium Vibrio cholerae, the causative agent of cholera (a food-borne illness). In Soho, London (1854), John Snow identified Vibrio clones living in a community well and we now know it likes to live in marine/brackish water. There have been at least seven pandemic outbreaks since 1817. So how does this organism cause disease?
First, we need to understand that only two serotypes will cause disease. People drink infected water and within hours, the bacteria will reach the small intestine where cholera toxin (CT) subunits will bind to GM1 receptors present on intestinal cell surfaces. This causes invagination of the CT-GM1 complex into the intestinal cell. CT later inhibits GTP hydrolysis, which causes adenylyl cyclase to become constitutively active causing the cell to pump out Chlorine ions into the lumen. This change in the osmotic gradient causes the cell to release water into the lumen to balance the salt. This is when we recognize the rapid onset of diarrhea and ultimately severe dehydration.
Cholera is treatable with antibiotics and oral rehydration with Na+ coupled to glucose transport. Glucose enables more efficient absorption of fluids and salts.
2. Streptococcus pneumoniae is acquired when the bacteria colonizes the nasopharynx is spread from person to person via infected nasal mucosa. Sometimes, the bacteria can cross into the blood to cause bacteremia and eventually infect the CSF and brain to cause meningitis. Some evidence suggests the bug can cross directly from the nasopharynx into the brain.
Ok, so I just realized my answer may be beyond the scope of your needs, but I am just so fascinated by bacterial pathogenesis. It's amazing how a single-celled organism can quickly replicate and cause disease in humans. Good luck!
I am a Microbiology Graduate Student
· 9 years ago