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 ID 50 : infectious dose for 50% of population –inhalation anthrax: <10 4 spores –V. cholerae: 10 8 cells LD 50 : lethal dose for 50% –botulinum toxin: 0.03 ng/kg –E. coli shiga toxin: 250 ng/kg

pathogenesis: enzymes coagulase & kinase hyaluronidase & collagenase leukocidins

toxicity: bacterial toxins exotoxinendotoxin sourceGram positive/entericsGram negative expressed geneouter membrane component chemical make-upproteinlipid neutralized by antitoxin? yesno fever?noyes LD 50 (relative)smalllarge allow spread and cause damage to the host toxigenicity: ability to produce a toxin toxemia: toxin in blood toxoid: immunization antitoxin: Ab to toxin

cytotoxins: hemolysins

neurotoxins: Clostridium

enterotoxins: V. cholerae

endotoxins: fever

Salmonella virulence

mechanisms of pathogenicity Inactivating host defenses

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 defensesinactivating/avoiding the host defenses (just for your information) avoiding host defensesavoiding host defenses (just for your information)

chapter 20 antimicrobial compounds

chemotherapeutic agents Paul Ehrlich- 1910’s salvarsan (synthetic arsenic) to treat syphilis Alexander Fleming Penicillium notatum Howard Florey P. notatum effectivity

antimicrobials inhibition of protein synthesis: chloramphenicol, erythryomycin, tetracyclines, streptomycin TranscriptionTranslation Replication Enzyme Protein DNAmRNA inhibition of NA replication & Xscription: quinolones, rifampin inhibition of cell wall synthesis: penicillins, cephalosporins, bacitracin, vancomycin injury to plasma membrane: polymyxin B inhibition of metabolite synthesis: sulfanimide, trimethoprim

protein synthesis inhibition Translation Streptomycin Tetracyclines Chloramphenicol Messenger RNA Direction of ribosome movement 70S prokaryotic ribosome tRNA Protein synthesis site 30S portion 50S portion Changes shape of 30S portion, causing code on mRNA to be read incorrectly Interfere with attachment of tRNA to mRNA–ribosome complex Binds to 50S portion and inhibits formation of peptide bond

GFA: metabolite inhibition & synergism

Phosphate Nucleoside Guanine nucleotide Cellular thymidine kinase DNA polymerase Incorporated into DNA Phosphate DNA polymerase blocked by false nucleotide. Assembly of DNA stops. False nucleotide (acyclovir triphosphate) Acyclovir (resembles nucleoside) Viral Thymidine kinase GFAs: nucleic acid inhibition

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 Resistance mechanisms

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 1 st generation: moderate cephalexin, cephalothin cefazolin 2 nd generation: moderate, anti-Haemophilus cefaclor, cefuroxime, cefamandole 2 nd generation cephamycins: moderate, anti- anaerobe cefotetan, cefoxitin 3 rd generation: broad spectrum ceftriaxone, cefotaxime cefpodoxime, cefixime ceftazidime (anti-Pseudomonas activity) 4 th 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