Resistance to antibioticsResistance to antibiotics

Intrinsic resistance (examples)Intrinsic resistance (examples)• penG does not enter gram negative bacteria wellpenG does not enter gram negative bacteria well

why? doesn’t penetrate--ampicillin doeswhy? doesn’t penetrate--ampicillin does

• rifampin doesn’t kill fungirifampin doesn’t kill fungi why? doesn’t get in---weaken barrier with amphotericin and then it doeswhy? doesn’t get in---weaken barrier with amphotericin and then it does

• isoniazid does not kill bugs that don’t require synthesis of mycolic isoniazid does not kill bugs that don’t require synthesis of mycolic acidsacids

Environmental resistanceEnvironmental resistance• e.g. sulfonamide resistance if high purines, methionine, thymidine e.g. sulfonamide resistance if high purines, methionine, thymidine

available (such as in an abscess)available (such as in an abscess)• e.g. aminoglycosides not effective in anaerobic environmente.g. aminoglycosides not effective in anaerobic environment

Acquired ResistanceAcquired Resistance• genetic changes, plasmids with new genesgenetic changes, plasmids with new genes

2006 Antibiogram Harborview/UW2006 Antibiogram Harborview/UW

Acquired Drug ResistanceAcquired Drug Resistance

1. enzymatic inactivation 1. enzymatic inactivation ((-lactams, aminoglyc. chloramph)-lactams, aminoglyc. chloramph)

Bacteria keep up with big pharma in the Bacteria keep up with big pharma in the -lactam antibiotic-lactam antibioticarms racearms race

bacteria can often express more than one bacteria can often express more than one -lactamase-lactamase

Inactivation ofInactivation ofaminoglycosides byaminoglycosides byacetylation, acetylation, phosphorylation, phosphorylation, and adenylation in and adenylation in drug-resistant drug-resistant organismsorganisms

Acquired Drug ResistanceAcquired Drug Resistance

1. enzymatic inactivation 1. enzymatic inactivation ((-lactams, aminoglyc. chloramph)-lactams, aminoglyc. chloramph)

2. rapid efflux of drug out of cell 2. rapid efflux of drug out of cell (tetracyclines,(tetracyclines, ciprofloxacin)ciprofloxacin)

Drug export systems in Gram +Drug export systems in Gram +

Acquired Drug ResistanceAcquired Drug Resistance

1. enzymatic inactivation 1. enzymatic inactivation ((-lactams, aminoglyc. chloramph)-lactams, aminoglyc. chloramph)

2. rapid efflux of drug out of cell 2. rapid efflux of drug out of cell (tetracyclines,(tetracyclines, ciprofloxacin)ciprofloxacin)

3. decreased conversion to active form 3. decreased conversion to active form (isoniazid)(isoniazid)

4. increased concentration of antagonist/competitor 4. increased concentration of antagonist/competitor (sulfonamide(sulfonamideresistance with increased PABA synthesis).resistance with increased PABA synthesis).

5. altered amount of receptor 5. altered amount of receptor (trimethoprim-DHFR amplification)(trimethoprim-DHFR amplification)

6. altered structure of target to reduce binding 6. altered structure of target to reduce binding (methicillin (methicillin resistance, vancomycin resistance, ciprofloxacin res.)resistance, vancomycin resistance, ciprofloxacin res.)

Vancomycin resistance: mechanismVancomycin resistance: mechanism

Vancomycin resistance: mechanismVancomycin resistance: mechanism

Resistance can be transferred between Resistance can be transferred between bacteriabacteria

phage transductionphage transduction transposable elementstransposable elements plasmid transfer during conjugationplasmid transfer during conjugation

• plasmids can contain multiple resistance genesplasmids can contain multiple resistance genes• transfer can occur between non-pathogen and pathogenstransfer can occur between non-pathogen and pathogens

Plasmid-mediated drug resistance

chloramphenicol

aminoglycosidesulfonamide

tetracycline

Problems with Antibiotic resistanceProblems with Antibiotic resistance more than 50% of antibiotics used in domestic animals for sub-more than 50% of antibiotics used in domestic animals for sub-

therapeutic effect: breeding ground for resistancetherapeutic effect: breeding ground for resistance

There are 7.5 billion chickens, 292 million turkeys, 109 million cattle and 92 million pigs in the United States.

Antibiotics given to pigs as of 2000Antibiotics given to pigs as of 2000

““KFC does not purchase poultry treated KFC does not purchase poultry treated nontherapeutically with medically important antibiotics.” – nontherapeutically with medically important antibiotics.” – Letter to “Keep Antibiotics Working,” August 28, 2002Letter to “Keep Antibiotics Working,” August 28, 2002

McDonald’sMcDonald’s ‘ ‘We’ve listened to the concerns, studied the issue, and We’ve listened to the concerns, studied the issue, and

the bottom line was we thought it was the right thing to do the bottom line was we thought it was the right thing to do to discontinue the use of [fluoroquinolone antibiotics] in to discontinue the use of [fluoroquinolone antibiotics] in poultry,’ said Walt Riker, spokesman for Oak Brook-based poultry,’ said Walt Riker, spokesman for Oak Brook-based McDonald’s. – Walt Riker, McDonald’s, “Chickens Fed McDonald’s. – Walt Riker, McDonald’s, “Chickens Fed With Antibiotics McGone,” Chicago Sun-Times, February With Antibiotics McGone,” Chicago Sun-Times, February 12, 200212, 2002

Prospects for new antibiotics?Prospects for new antibiotics?

new antibiotic development slowed in 80’s/90’snew antibiotic development slowed in 80’s/90’s selective drugs have lower market valueselective drugs have lower market value 5-15 yr time frame to get new drugs to 5-15 yr time frame to get new drugs to

physiciansphysicians recent increase in new antibiotic development recent increase in new antibiotic development

is encouragingis encouraging

active against Strep pneumoniaeactive against Strep pneumoniae

First reported in a strain of First reported in a strain of K. pneumoniaeK. pneumoniae

QnrA protein – 218 aa proteinQnrA protein – 218 aa protein

Protects DNA gyrase and topoisomerase IV from the inhibitory Protects DNA gyrase and topoisomerase IV from the inhibitory

activity of quinolonesactivity of quinolones--exact mechanism is not known yet--exact mechanism is not known yet

Qnr proteinsQnr proteins QnrA2 – QnrA2 – K. oxytoca K. oxytoca (China)(China)

QnrB - QnrB - E. coli, K. pneumoniae, E. cloacae, C. koseri E. coli, K. pneumoniae, E. cloacae, C. koseri (USA and India) - 40% aa (USA and India) - 40% aa

identity with QnrA identity with QnrA

QnrS – QnrS – S. flexneri S. flexneri (Japan) - 59% aa identity with QnrA(Japan) - 59% aa identity with QnrA

The presence of other mechanisms of resistance may increase The presence of other mechanisms of resistance may increase

plasmid-mediated quinolone resistanceplasmid-mediated quinolone resistance

Plasmid Mediated Quinolone Plasmid Mediated Quinolone Resistance (PMQR)Resistance (PMQR)

PREVALENCE OF PLASMID-MEDIATED RESISTANCE TO PREVALENCE OF PLASMID-MEDIATED RESISTANCE TO QUINOLONES IN QUINOLONES IN Escherichia coliEscherichia coli

1% QnrA+ isolates among ciprofloxacin-resistant E.coli 1% QnrA+ isolates among ciprofloxacin-resistant E.coli from different countries [AAC (2003) 47:559]from different countries [AAC (2003) 47:559]

11% QnrA+ isolates among ciprofloxacin-resistant K. 11% QnrA+ isolates among ciprofloxacin-resistant K. pneumoniae and 0% in E.coli from USA [AAC (2004) pneumoniae and 0% in E.coli from USA [AAC (2004) 48: 1295]48: 1295]

7.7% QnrA+ isolates among ciprofloxacin-resistant E. 7.7% QnrA+ isolates among ciprofloxacin-resistant E. coli in Shanghai (China) [AAC (2003) 47: 2242]coli in Shanghai (China) [AAC (2003) 47: 2242]

0.4% QnrA+ isolates among nalidixic acid- resistant 0.4% QnrA+ isolates among nalidixic acid- resistant Escherichia coli (France) [AAC (2005) 49: 3091]Escherichia coli (France) [AAC (2005) 49: 3091]

TB drug developmentTB drug development

no new TB drugs in no new TB drugs in past 40 yearspast 40 years

multi-drug resistant multi-drug resistant TB prevalentTB prevalent

Johnson & JohnsonJohnson & Johnson R207910R207910 targets targets

mycobacterium ATP mycobacterium ATP synthetasesynthetase

-Lactam Antibiotic development-Lactam Antibiotic development

spectrum of actionspectrum of action resistance to resistance to -lactamase-lactamase specificspecific -lactamase -lactamase

inhibitorsinhibitors

AmpicillinAmpicillin

Penicillin GPenicillin G

AmoxicillinAmoxicillin

MethicillinMethicillin

DicloxacillinDicloxacillin

RR

Group Spectrum -lactamasesensitivity

Natural penicillinsPe n G/Pen V

narrow spectrumgra m positive

sensitive

-lactam antibiotics-1-lactam antibiotics-1

resistantnarrow spectrumPenicillinase resistant

-methicillin

-dicloxacillin

Methicillin resistanceMethicillin resistance

caused by unique peptidyl caused by unique peptidyl transferase that does not transferase that does not bind bind -lactams-lactams

had been largely confined to had been largely confined to hospital acquired infectionshospital acquired infections

more recently--outbreaks in more recently--outbreaks in athletic teams, iv drug users, athletic teams, iv drug users, school children, gay school children, gay community, general community, general populationpopulation

900 cases in LA county jails 900 cases in LA county jails (2002)(2002)

Structure of PBP2aStructure of PBP2a

Group Spectrum -lactamasesensitivity

Natural penicillinsPen G/Pen V

narrow spectrumgram positive

sensitive

Penicillinase resistantmethicillin

dicloxacillin

narrow spectrum resistant

-lactam antibiotics-1-lactam antibiotics-1

Aminopenicillinsampicillinamoxicillin

gram negative sensitive

Antipseudomonalticarcillin

piperacillin

gram negative includingpseudomonas

sensitive

CephalosporinsCephalosporins

Brody’s Human PharmacologyBrody’s Human Pharmacology

Group Spectrum -lactamasesensitivity

Cephalosporinscefaclor

ceftriaxone

broad spectrum variable

-lactam antibiotics-2-lactam antibiotics-2

Newer Newer -lactams-lactams

aztreonam (monobactam) aztreonam (monobactam) gramgram- - specificspecific resistant to resistant to -lactamase-lactamase

Carbapenems: imipenem, Carbapenems: imipenem, meropenemmeropenem broad spectrum (grambroad spectrum (gram++,gram,gram--)) resistant to resistant to -lactamase-lactamase penetrates CSFpenetrates CSF imipenem a substrate for imipenem a substrate for

dehydropeptidase I in kidney, dehydropeptidase I in kidney, meropenem is notmeropenem is not BrennerBrenner

-lactamase -lactamase inhibitorsinhibitors

-lactamase inhibitors-lactamase inhibitors

Clavulanic acid (suicide inhibitor for most Clavulanic acid (suicide inhibitor for most lactamases)lactamases)

• little antibiotic action on its ownlittle antibiotic action on its own• combine with amoxicillin to get combine with amoxicillin to get AugmentinAugmentin (oral activity) (oral activity)• combine with ticarcillin to get combine with ticarcillin to get TimentinTimentin

Sulbactam (similar inhibitor)Sulbactam (similar inhibitor)• combine with ampicillin to get combine with ampicillin to get Unasyn Unasyn (given iv or im)(given iv or im)

Activity of available Activity of available -lactamase inhibitors against clinically-lactamase inhibitors against clinicallyimportant important -lactamases-lactamases