Evolution of AntibioticResistanceOctober 14th, 2005BrookeWillJocelynJoAnnwww.giantmicrobes.comwww.thesahara.net/mrsa_lung.JPGBacteria can do this to your mouth.But bacteria can also do thesethings…But bacteria can also do thesethings…• Make yummy yogurtBut bacteria can also do thesethings…• Make yummy yogurt• Clean up polluted environments created byhumans– Precipitation of heavy metals from soil orground water using a combination of sulfate-reducing bacteria (SRB), fermentative bacteria,and iron-reducing bacteria that form metalsulfides and are easily filtered out.But bacteria can also do thesethings…• Make yummy yogurt• Clean up polluted environments created byhumans• Help us digest our food and store energy inadipocytes– Backhed F, Ding H, Wang T, Hooper LV, Koh GY, NagyA, Semenkovich CF, Gordon JI. The gut microbiota asan environmental factor that regulates fat storage.Proc Natl Acad Sci USA. 2004 Nov 2;101(44):15718-23.Ley RE, Backhed F, Turnbaugh P, Lozupone CA, KnightRD, Gordon JI. Obesity alters gut microbialecology.Proc Natl Acad Sci U S A. 2005 Aug2;102(31):11070-5.Staphylococcus aureus infections• Very superficial- boils, styes,• Pneumonia, mastitis, meningitis, UTI• Deep infections- osteomyelitis andendocarditis• Food poisoning• TSSStaphylococcus aureus• Gram-positive– Ribitol-teichoic acid (antigenic and specific)• Capsule (antiphagocytic polysaccharides)• Surface proteins– Protein A binds Fc portion of IgGProtein A says no to opsonization• http://www.cat.cc.md.us/courses/bio141/lecguide/unit2/innate/antibody/phagsum.htmlStaphylococcus aureusStaphylococcus aureus• Virulence Factors:– Capsule– Protein AStaphylococcus aureus• Virulence Factors:– Capsule– Protein A– Coagulase**– Invasins (ex-leukocidin,hylaronidase)– Hemolysins (α-toxin)– Exotoxins (TSST-1)Staphylococcus aureus surfaceproteins• Promote attachment to host proteins such aslaminin and fibronectin that form theextracellular matrix of epithelial andendothelial surfaces.• Most S. aureus express a “clumping factor”that promotes attachment to blood clots andtraumatized tissue.S. Aureus adhesion• Mutants lacking these surface adhesionproteins have decreased virulence in rat andmouse models– Defect in binding fibronectin/fibrinogen showsattenuation for endocarditis– Defect in collagen binding shows attentuationfor septic arthritis.Treatment for S. aureus• Used to be penicillin (now 90% resistant)• Now, penicillinase-resistant penicillins– Methicillin– OxacillinTreatment for S. aureus• Used to be penicillin (now 90% resistant)• Now, penicillinase-resistant penicillins– Methicillin– Oxacillin– Cephalosporins*Mechanisms of Resistance• Mutant proteins thatdegrade or inactivatethe antibiotic• Efflux pumps• Horizontal genetransfer• Biofilm formationBacterial BiofilmsBiofilm on catheterBacterial Biofilms• Increase resistance to antibiotics up to 1000-fold– Many cells are slow growing and not affected byantibiotics– Many antibiotics cannot reach past the surface of thebiofilm• Promote horizontal gene transferMechanisms of Horizontal GeneTransfer• Conjugation• Uptake of naked DNA• Phage delivery**Can occur betweendifferent classes ofbacteria.What makes Staphylococcusaureus methicillin-resistant?What makes Staphylococcusaureus methicillin-resistant?• Acquisition and expression of the mecAgene:– 30-50 Kb of additional chromosomal DNA– mecA, =PBP 2a• Very low affinity for ß-lactam antibiotics• Promoter region and repressor genes are oftendeleted or mutated, producing constitutiveexpression of PBP 2a• Able to substitute for the other PBPs in presence ofß-lactam antibioticsWhat makes Staphylococcusaureus methicillin-resistant?• femA-F (factor essential for methicillinresistance)– fem mutants have altered peptidoglycancomposition and increased suceptibility tomethicillin.Who makes Staphylococcusaureus methicillin-resistant?• Physicians who prescribe antibioticsunnecessarilyWho makes Staphylococcusaureus methicillin-resistant?• Physicians who prescribe antibioticsunnecessarily• Patients who discontinue use of antibioticsafter symptoms go awayWho makes Staphylococcusaureus methicillin-resistant?• Physicians who prescribe antibioticsunnecessarily• Patients who discontinue use of antibioticsafter symptoms go away• Those who treat livestock with antibioticsWho makes Staphylococcusaureus methicillin-resistant?• Physicians who prescribe antibioticsunnecessarily• Patients who discontinue use of antibioticsafter symptoms go away• Those who treat livestock with antibiotics• Agricultural treatment with antibioticaerosolsCommon Theme:• People weigh the individual, short-termbenefit of using antibiotics more heavilyover the long-term effects on societyCommon Theme:• People weigh the individual, short-termbenefit of using antibiotics more heavilyover the long-term effects on society• Bacteria are improving general fitness ofpopulations by sacrificing individuals.Major Problems• Lack of new antibiotic productionMajor Problems• Lack of new antibiotic production• Production of multi-drug-resistantreservoirs in developing countries– Intermittent availability of antibiotics– Questionable potency and quality– Tendency to self-medicate• Currently, pre-op nasal swab screening is[often] done to check for presence ofcommensal SA, MRSA etc. in the patient,– But more often the source of infectiousmicrobes are from healthcare workers (Asmany as 50-90% of healthcare workers areMRSA carriers)One last thought…www.thesahara.net/mrsa_lung.JPG• “At any one time over 30% ofhealthy individuals carryStaphylococcus aureus, includingMRSA on their bodies…www.thesahara.net/mrsa_lung.JPG• “At any one time over 30% ofhealthy individuals carryStaphylococcus aureus, includingMRSA on their bodies…So when younext pick your nose, and thenscrape off a scab, consider that youmight be involuntarily introducing alife threatening disease into yourblood system.”WILLBenedicte, 2005DNA damage: A. RecA is loaded to ssDNA B. RecA filament induces 1) strand exchange for HR 2) LexA autocleavage C. Derepression of ~30 genes at different times and levels: 1. Early repair genes (NER – uvrABD) T=0 min 2. Later repair genes (HR – RecA) T=~10 3. Error-prone polymerases (Pol II, IV, V) T=~40…. genes involved in halting cell cycle are also