Entry, Exit and Transmission Flashcards
What controls entry into the host?
- External host surface - skin (low temperatures do not allow for the multiplication of bacteria, as well as sweat on the skin), mucosal lining and cleansing mechanisms (do not allow for adherence of bacteria on the host)
- need for attachment: receptor molecule (CD4 and CCR5 -HIV, and C3d - EBV)
What is the purpose of exiting the host to the bacteria, and how do they do so?
- to transmit to another new host
- leave via body fluids and vectors
How does skin block entry into a host?
- dead skin cells are part of the innate IS - attachment site for bacteria that is not permanently attached to the body (with viruses, dead skin cells still have a receptor for the virus but will not allow for replication- need to be alive inorder to replicate)
- pH 5.5
- fatty acids
- sebaceous gland secretions
- compounds secreted by the natural flora
How does the conjunctiva block entry of pathogens?
- eyelashes
- tears (creates a flushing action, has lysozyme that cleaves NAM-NAG linkages in peptidoglycan, IgA and lactoferrin)
- damaged defences - conjunctiva or eye lid damage
- contaminated fingers or towels are often the source of infection
What are some common eye infections?
- Pseudomonas origimosa: gram negative and will produce an infection in someone with a weaker immune system (melts the cornea)
- gonnorhea: from touching the finger that is infected by genitalia to the eye
- fly(vector) can bypass defence mechanism in the eye by landing on the eye and planting an egg (egg hatches and a worm goes into the eye)
What are the two ways that organisms can cause an infection of the respiratory tract?
- they can AVOID CLEANSING
- – can attach via adhesins to specific cell-surface receptors on epithelial cells
- – can inhibit ciliary action (Bordetella pertussis- whooping cough)
- they can also AVOID DESTRUCTION BY ALVEOLAR MACROPHAGES
- –if a microbe reaches the alveoli, they typically remove these cells
- – mycobacterium tuberculosis can survive in macrophages
What are the defences of the oropharynx?
- flushing action of saliva (1L/ day)
- chewing and other activities of the tongue, lips and cheeks
- secretory IgA
- lysozyme
- antimicrobial activities of leukocytes in saliva and at mucosal surfaces
How is the oropharynx invaded by pathogens?
- both invading and resident microbes need to attach to the mucosa or the tooth surfaces
- decreased resistance to infection
- when oral microflora is gone, yeast can gain access to the mouth and colonize it ( see this after a course of antibiotics)
- gum infections can be caused by vitamin C deficiencies
How have pathogens evolved to survive in the GI tract?
- survive peristalsis by attaching to receptors (vibrio cholera, rotavirus)
- motile bacteria (E.coli and V. cholera) propel through mucous
- E.coli has efflux pumps that pump out bile salts that allow them to survive in our GI tract- has evolved this mechanism to survive
V. cholera has mucinase
What are the host defences in the GI tract?
- mucosal barrier than blocks microbial adhesion (microbe specific IgA)
- bile has an extremely high microbial activity
- – bile salts have detergent activity and act on the membrane of the bacteria
How does H. pylori survive in the stomach?
H. pylori breaks down urea into ammonia and CO2 using urease
- ammonia will create a bubble around the H. pylori to survive the acid environment of the stomach (increases the pH)
How do infections occur in the vagina?
- vagina has no cleansing mechanism and foreign objects are introduced into it
- lactobacilli colonization can occur in the reproductive years (takes glycogen and produces lactic acid, lowering the pH of the vagina and allowing for the growth of yeast)
- vagina usually at a more alkaline pH - gets lowered to a pH of 5
What is one way to test whether or not someone has a yeast infection?
- put a drop of vaginal secretions on a pH paper and test it - yeast infection will have a decreased pH
What are the defences that the bladder and urethra have against bacteria?
- flushing action of urine
- IgA in the mucosal layer of the bladder
What are the mechanisms of urinary tract invasion?
- by the urethra - avoiding flushing of the urine
- attachment of gonococci, pili - allows the bacteria to be adhered to the wall of the urogenital tract
- bacteria that cause UTI’s also typically produce a lot of proteases - degrade IgA antibodies
- women also more susceptible to infections then men, because there is less distance from the anus to the urethra
