infection and immunity
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what are the advantages of normal flora?
protect by preventing colonisation from other (potentially) pathogenic bacteria
how does our normal flora (commensals) protect against other organisms?
- - compete for colonisation sites
- - produces bacteriocins
- - (anaerobic) - produce toxic metabolites
- - (in female genital tract) - lactobacilli produce lactic acid lowering the pH
what is the innate immune system?
- bodies defense against infection
- consists of physical and chemical barriers, normal flora, antibacterial proteins, phagocytic cells
list some of trhe physical and chemical barriers of the innate immune system
- - skin + sebum + secreted FAs
- - gastric acid
- - mucus containing similar polysaccharides to underlying epithelium
- - mucociliary clearance
- - urinary flushing
- - lysozyme in tears
- - lactoferin in breast milk
organism capable of causing infection
capacity to cause disease
capacity to cause serious disease
what is a parasite?
often used to describe protozoan and metazoan can be either pathogen or commensals
HIV and treponema pallidium are ...
what are conditional pathogens
give an example
- these are commensal organisms that can lead to disease if conditions are met
- eg. stap aureus is a commensla in the anterior nares but can cause an abscess in a wound
who do opertunistic pathogens effect?
give an example
- the immunocompromised
- eg. pneumocystis jiroveci in patients with HIV/AIDS
how do organisms cause disease?
- 1. access vunerable host - transmission
- 2. attach to host
- 3. invasion
- 4. motility
- 5. immune evasion
- 6. damage the host - endo/exotoxins
what is resistance?
when a previously suseptible organism is no longer inhited by an antibiotic that is given at a safe clinical level
how does resistance occur?
- bacteria gene pool changes rapidly - facillitated by rapid division and haploid genome
- organisms can also tranfer genetic material within and between species
- antiobiotic use allows the survival and replication of resistant organisms
how do bacteria transfer resistance between themselves?
- transformation - bacteria pick up naked DNA and incorparate it into their own genome
- conjugation - moving plasmids between bacteria
- transposons - jumping genes
list 6 mechanisms of resitance and give an example of each
- 1. enzyme inactivation - staph aureus produces a betalactamase that breaks down the penicillin ring
- 2. enzyme addition - bacteria adda chemical group to the antibiotic this is how staph aureus and pseudomonas became aminoglycoside resistant
- 3. impermeability - some bacterial are naturally resistant to some antibiotics eg. aminoglycosides taken up by an O2 dependant pathway and are therefore ineffective against anaerobes
- 4. efflux mechanism - acquasition of membrane protein that pumps antibiotic back out of the call eg. E. coli and tetracyclines
- 5. alternative pathway - avoid metabolic block cause by antibiotic eg. staph aureus and mecA gene = MRSA
- 6. alteration of target site- eg. change in RNA polymerase gene = rifampicin resitant
what are the two catergeries of sources of infection
- endogenous - organisms of normal flora invade
- endogenous - animal/environmental pathogens
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