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

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 source chemical make-up neutralized by antitoxin?

fever?

LD 50 (relative) exotoxin endotoxin Gram positive/enterics Gram negative expressed gene outer membrane component protein lipid yes no small no yes large

cytotoxins: hemolysins

neurotoxins: Clostridium

enterotoxins: V. cholerae

endotoxins: fever

Salmonella virulence

mechanisms of pathogenicity

chapter 15 learning objectives

1.

2.

3.

4.

Describe pathogenesis from exposure to disease. What factors contribute to disease?

Relate preferred portal of entry and ID50 to the likelihood of infection.

Know how to interpret ID50 and LD50 results.

Describe what is meant by invasiveness and the mechanisms and factors that affect invasiveness (adherence, penetration, avoidance of phagocytosis, ability to cause damage).

5.

6.

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).

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 cell wall synthesis: penicillins, cephalosporins, bacitracin, vancomycin inhibition of protein synthesis: chloramphenicol, erythryomycin, tetracyclines, streptomycin

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 30S portion Streptomycin Changes shape of 30S portion, causing code on mRNA to be read incorrectly 70S prokaryotic ribosome Translation Direction of ribosome movement Tetracyclines 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 Acyclovir (resembles nucleoside) False nucleotide (acyclovir triphosphate) 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.

2.

3.

4.

5.

outdated, weakened, inappropriate Abx use use of Abx in animal feed long-term, low-dose Abx use aerosolized Abx in hospitals 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

Narrow-spectrum

• • • β-lactamase sensitive benzathine penicillin benzylpenicillin (penicillin G) procaine penicillin Penicillinase-resistant penicillins methicillin, oxacillin nafcillin, cloxacillin dicloxacillin, flucloxacillin β-lactamase-resistant penicillins temocillin

Moderate-spectrum

amoxicillin, ampicillin

Broad-spectrum Extended-spectrum

azlocillin, carbenicillin ticarcillin, mezlocillin, piperacillin 

-lactams

Cephalosporins

•

1 st generation: moderate

phenoxymethylpenicillin (penicillin V) co-amoxiclav (amoxicillin+clavulanic acid) • • • • • • 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.

2.

3.

4.

What is the major difference between an antibiotic and a drug? What were the first drug and antibiotic?

Antimicrobial agents target which areas of the bacterial cell? How specifically do antibiotics inhibit protein synthesis?

Describe the mechanism of action of penicillin on the bacterial cell. List and explain the effects of antibiotic/drug action on the bacterial cell and the action of penicillin specifically.

5.

6.

7.

Discuss the mode of action of growth factor analogs in general and sulfa drugs and acyclovir specifically.

How are antibiotic use and antibiotic resistance related? How are antibiotics abused?

Define bacteriolytic, bacteriostatic, bactericidal, MIC, MBC. Describe how MIC is calculated and what it will tell you about a given bacterium.

Understand the four major ways that antibiotic resistance is achieved. Include  -lactamases and clavulanate/clavulinic acid 8.

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