Transcript E. coli
chapter 15 microbial mechanisms of pathogenicity pathogenesis portals of entry & exit inoculation vs. disease: preferred portal of entry entry DOES NOT EQUAL disease entry into preferred portal of entry DOES NOT EQUAL disease ID50: infectious dose for 50% of population – inhalation anthrax: <104 spores – V. cholerae: 108 cells LD50 : lethal dose for 50% – botulinum toxin: 0.03 ng/kg – E. coli shiga toxin: 250 ng/kg pathogenesis: enzymes hyaluronidase & collagenase coagulase & kinase leukocidins pathogenesis: enzymes hyaluronidase & collagenase coagulase & kinase toxicity: bacterial toxins allow spread and cause damage to the host • toxigenicity: ability to produce a toxin • toxemia: toxin in blood • toxoid: immunization • antitoxin: Ab to toxin exotoxin source endotoxin Gram positive/enterics Gram negative expressed gene outer membrane component chemical make-up protein lipid neutralized by antitoxin? yes no fever? no yes LD50 (relative) small large cytotoxins: hemolysins neurotoxins: Clostridium enterotoxins: V. cholerae endotoxins: fever Salmonella virulence mechanisms of pathogenicity chapter 15 learning objectives 1. Describe pathogenesis from exposure to disease. What factors contribute to disease? 2. Relate preferred portal of entry and ID50 to the likelihood of infection. 3. Know how to interpret ID50 and LD50 results. 4. Describe what is meant by invasiveness and the mechanisms and factors that affect invasiveness (adherence, penetration, avoidance of phagocytosis, ability to cause damage). 5. Be able to list enzymes produced by microbes than enhance pathogenicity and virulence as well as describe the effects of these enzymes on the host (i.e., hyaluronidase, collangenase, coagulase, kinase). 6. Differentiate between an endotoxin and an exotoxin as far as source, chemistry and type of molecule (protein, or polysaccharide/lipid). List and understand how examples from class work (e.g., cytotoxin, hemolysin, neurotoxin, enterotoxin, endotoxin). It is not necessary to know the particular details of how each of the three types of exotoxins work. STUDY ANIMATION URLs endotoxin production virulence factors animation exotoxin production penetrating host tissues inactivating/avoiding the host defenses (just for your information) avoiding host defenses (just for your information) chapter 20 antimicrobial compounds chemotherapeutic agents Paul Ehrlich- 1910’s • salvarsan (synthetic arsenic) to treat syphilis Alexander Fleming- 1928 • Penicillium notatum Howard Florey- 1940 • P. notatum effectivity antimicrobials inhibition of protein synthesis: inhibition of cell wall synthesis: chloramphenicol, erythryomycin, tetracyclines, streptomycin penicillins, cephalosporins, bacitracin, vancomycin DNA mRNA Transcription Protein Translation Replication Enzyme inhibition of metabolite synthesis: sulfanimide, trimethoprim inhibition of NA replication & Xscription: quinolones, rifampin injury to plasma membrane: polymyxin B protein synthesis inhibition Chloramphenicol Binds to 50S portion and inhibits formation of peptide bond 50S portion Protein synthesis site tRNA Messenger RNA Streptomycin Changes shape of 30S portion, causing code on mRNA to be read incorrectly 30S portion Direction of ribosome movement Tetracyclines 70S prokaryotic ribosome Translation Interfere with attachment of tRNA to mRNA–ribosome complex GFA: metabolite inhibition & synergism GFAs: nucleic acid inhibition Phosphate Cellular thymidine kinase Guanine nucleotide DNA polymerase Nucleoside Phosphate Viral Thymidine kinase False nucleotide (acyclovir triphosphate) Acyclovir (resembles nucleoside) DNA polymerase blocked by false nucleotide. Assembly of DNA stops. Incorporated into DNA penicillin & cell wall synthesis inhibition CELL WALL FORMATION autolysins cut wall new “bricks” inserted transpeptidase bonds bricks PENICILLIN ACTION transpeptidase binds pen. forms PBP-antibiotic structure no new bond formation cell ruptures Abx resistance 1. outdated, weakened, inappropriate Abx use 2. use of Abx in animal feed 3. long-term, low-dose Abx use 4. aerosolized Abx in hospitals 5. failure to follow prescribed treatment the episilometer (E) test- the MIC Abx resistance 1. loss of porins - Abx/drug movement into cell 2. Abx modifying enzymes -cleave β-lactam ring -Anx non-functional 3. efflux pumps - movement out of cell 4. target site mutations -enzymes -polymerases -ribosomes -LPS layer the effect of -lactamase on -lactam Abx VERY STABLE RESISTANCE • NDM-1 (metallo- -lactamase) • K. pneumoniae & E. coli, plasmids & chromosomal • KPC (K. pneumoniae carbapenemase, class of -lactamase) RESISTANCE RESISTED • clavulinic acid/sulbactam bind lactamase • can be hydrolyzed by high copy # plasmid -lactamase -lactams Narrow-spectrum • β-lactamase sensitive benzathine penicillin benzylpenicillin (penicillin G) phenoxymethylpenicillin (penicillin V) procaine penicillin • Penicillinase-resistant penicillins methicillin, oxacillin nafcillin, cloxacillin dicloxacillin, flucloxacillin • β-lactamase-resistant penicillins temocillin Moderate-spectrum amoxicillin, ampicillin Broad-spectrum co-amoxiclav (amoxicillin+clavulanic acid) Extended-spectrum azlocillin, carbenicillin ticarcillin, mezlocillin, piperacillin Cephalosporins • 1st generation: moderate cephalexin, cephalothin cefazolin • 2nd generation: moderate, anti-Haemophilus cefaclor, cefuroxime, cefamandole • 2nd generation cephamycins: moderate, antianaerobe cefotetan, cefoxitin • 3rd generation: broad spectrum ceftriaxone, cefotaxime cefpodoxime, cefixime ceftazidime (anti-Pseudomonas activity) • 4th generation: broad, anti-G+ & β-lactamase stability cefepime, cefpirome • Carbapenems and Penems: broadest spectrum imipenem (with cilastatin), meropenem ertapenem, faropenem, doripenem • Monobactams aztreonam (Azactam), tigemonam nocardicin A, tabtoxinine-β-lactam bacterial resistance 2009 CASE STUDY, U. of Pittsburgh Medical Center • 6/2008- post-surgical hospitalization, septicemia (E. coli & E. cloacae) • 7/2008- UTI, E. coli & P. mirabilis • 8/2008- UTI, E. coli (imipenem S) & K. pneumoniae (imipenem R & ertapenem R) • 9/2008- abdominal tissue infection, E. coli & K. pneumoniae (both R to Abx) • 11/2008- sputum P. aeruginosa & S. marcescens, K. pneumoniae • 12/2008- MDR-pneumonia, A. baumanii & M. morganii • 1/2009- sputum, S. marcescens (ertapenem & imipenem R) chapter 20learning objectives 1. What is the major difference between an antibiotic and a drug? What were the first drug and antibiotic? 2. Antimicrobial agents target which areas of the bacterial cell? How specifically do antibiotics inhibit protein synthesis? 3. Describe the mechanism of action of penicillin on the bacterial cell. 4. List and explain the effects of antibiotic/drug action on the bacterial cell and the action of penicillin specifically. 5. Discuss the mode of action of growth factor analogs in general and sulfa drugs and acyclovir specifically. 6. How are antibiotic use and antibiotic resistance related? How are antibiotics abused? 7. Define bacteriolytic, bacteriostatic, bactericidal, MIC, MBC. Describe how MIC is calculated and what it will tell you about a given bacterium. 8. Understand the four major ways that antibiotic resistance is achieved. Include -lactamases and clavulanate/clavulinic acid specifically. STUDY ANIMATION URLs mechanisms of Abx resistance the origins of Abx resistance the emergence of Abx resistance cell wall formation, ß-lactam ABx and resistance