infection and immunity

protect by preventing colonisation from other (potentially) pathogenic bacteria

• - compete for colonisation sites
• - produces bacteriocins
• - (anaerobic) - produce toxic metabolites
• - (in female genital tract) - lactobacilli produce lactic acid lowering the pH

• bodies defense against infection
• consists of physical and chemical barriers, normal flora, antibacterial proteins, phagocytic cells

• - 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

often used to describe protozoan and metazoan can be either pathogen or commensals

obligate pathogens

• 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

• the immunocompromised
• eg. pneumocystis jiroveci in patients with HIV/AIDS

• 1. access vunerable host - transmission
• 2. attach to host
• 3. invasion
• 4. motility
• 5. immune evasion
• 6. damage the host - endo/exotoxins

when a previously suseptible organism is no longer inhited by an antibiotic that is given at a safe clinical level

• 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

• transformation - bacteria pick up naked DNA and incorparate it into their own genome
• conjugation - moving plasmids between bacteria
• transposons - jumping genes

• 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

• endogenous - organisms of normal flora invade
• endogenous - animal/environmental pathogens