Antimicrobial DrugsAntimicrobial Drugs

I. Terminology of chemotherapyI. Terminology of chemotherapy

II. Where antimicrobial drugs come fromII. Where antimicrobial drugs come from

III. How antimicrobials workIII. How antimicrobials work

IV. Drug resistanceIV. Drug resistance

V. Interactions between drugs and hostsV. Interactions between drugs and hosts

VI. Selecting the right antimicrobial drugVI. Selecting the right antimicrobial drug

I. TermsI. TermsWhen a drug is used to control an infection, the When a drug is used to control an infection, the

practice is termed practice is termed antimicrobial chemotherapyantimicrobial chemotherapy

Antimicrobial drugsAntimicrobial drugs: : a class of compounds which a class of compounds which inhibit or kill microorganisms.inhibit or kill microorganisms.

– AntibioticsAntibiotics -- _____________ antimicrobial drugs -- _____________ antimicrobial drugs..

– SyntheticsSynthetics -- ______________ antimicrobials. -- ______________ antimicrobials.

Antibiotics which have been chemically modified are Antibiotics which have been chemically modified are

called called _________________._________________.

– Broad spectrumBroad spectrum agents --agents --

– Narrow spectrumNarrow spectrum agents --agents --

Where do antimicrobials come from?

Where do antimicrobials come from?

• Fleming’s discovery of _______________Fleming’s discovery of _______________

• Main sources of useful antibiotics: Main sources of useful antibiotics: Streptomyces Streptomyces

andand Bacillus Bacillus (____________), (____________), Penicillium Penicillium and and

Cephalosporium Cephalosporium (_________)(_________)

• Thousands have been discovered; relatively few of Thousands have been discovered; relatively few of

these are ___________.these are ___________.

How do they work?How do they work?

• The main trick if one were to “design” an antibiotic: find The main trick if one were to “design” an antibiotic: find something the target pathogen has or does (e.g. a structure or something the target pathogen has or does (e.g. a structure or pathway) which the host cell doesn’t. For example, most bacteria pathway) which the host cell doesn’t. For example, most bacteria have peptidoglycan while eukaryotes don’t so a compound which have peptidoglycan while eukaryotes don’t so a compound which destroys it or inhibits its production (like penicillin) shouldn’t destroys it or inhibits its production (like penicillin) shouldn’t affect eukaryotes.affect eukaryotes.

• Toxicity to the host is a major concernToxicity to the host is a major concern

Therapeutic IndexTherapeutic Index -- ratio of a drug’s_________ _________ to -- ratio of a drug’s_________ _________ to

its minimum __________________ dose. For example:its minimum __________________ dose. For example:

16 µg/ml effective dose16 µg/ml effective dose= ____= ____

20 µg/ml toxic dose20 µg/ml toxic dose

2 µg/ml2 µg/ml= ___= ___

20 µg/ml20 µg/mlversusversus

How do they work (cont.)?How do they work (cont.)?

Four main approaches:Four main approaches:1) 1) Inhibition of ________ _______ formationInhibition of ________ _______ formation -- --

e.g. penicillin and cephalosporine.g. penicillin and cephalosporin

2) 2) Inhibition of ________ ________ synthesisInhibition of ________ ________ synthesis -- -- e.g. sulfonamidese.g. sulfonamides

3) 3) Inhibition of ___________ synthesisInhibition of ___________ synthesis -- e.g. -- e.g. tetracyclinetetracycline

4) 4) Inhibition of cell ______________ functionInhibition of cell ______________ function (less common) e.g. polymixin (less common) e.g. polymixin

Cellular targets of antimicrobial drugsCellular targets of antimicrobial drugs•PenicillinsPenicillins•CephalosporinsCephalosporins•VancomycinVancomycin•BacitracinBacitracin

•NovobiocinNovobiocin•Nalidixic acidNalidixic acid

•RifampinRifampin

•ErythromycinErythromycin•ChloramphenicolChloramphenicol

•TetracyclinesTetracyclines•Aminoglycosides Aminoglycosides (Streptomycin,(Streptomycin,Kanamycin, Kanamycin, Gentamicin)Gentamicin)

•PolymyxinsPolymyxins

Inhibition of cell wall synthesisInhibition of cell wall synthesis

Penicillin family Penicillin family (“Beta-lactams”)(“Beta-lactams”) PenicillinPenicillin AmoxicillinAmoxicillin AmpicillinAmpicillin CarbenicillinCarbenicillin etc.etc.

Varies (and can Varies (and can be modified)be modified)

ß-_______ ß-_______ ringring

Inhibition of cell wall synthesis (cont.)Inhibition of cell wall synthesis (cont.)

CephalosporinsCephalosporins First isolated from First isolated from Cephalosporium acremoniumCephalosporium acremonium

Similar to ___________ because also has ß-lactam ring:Similar to ___________ because also has ß-lactam ring:

NHNHRR

OO

COOHCOOH

RRNN

SS(Also can be O)(Also can be O)

Most have Most have root “cef” in root “cef” in

namename

Nucleic acid synthesis inhibitorsNucleic acid synthesis inhibitors

ChloroquineChloroquine

TrimethoprimTrimethoprim

Sulfanilamides (sulfa drugs)Sulfanilamides (sulfa drugs)

Are Are metabolic ______________metabolic ______________ of PABA (para- of PABA (para-

aminobenzoic acid), necessary for the synthesis of aminobenzoic acid), necessary for the synthesis of

folic acid. Folic acid is then folic acid. Folic acid is then required for the required for the

synthesis of ___________ and ______________synthesis of ___________ and ______________..

SulfanilamideSulfanilamide

SulfanilamideSulfanilamide PABAPABA

Folic acidFolic acid

Sulfa competes with PABA for the active site Sulfa competes with PABA for the active site on the enzyme which converts PABA to on the enzyme which converts PABA to

dihydrofolic acid, a precursor of folic aciddihydrofolic acid, a precursor of folic acid

Protein synthesis inhibitorsProtein synthesis inhibitors

TetracyclinesTetracyclines -- Semisynthetic drug derived from a natural -- Semisynthetic drug derived from a natural antibiotic made by antibiotic made by StreptomycesStreptomyces. _______________-. _______________-binding, bacteriobinding, bacteriostaticstatic, broad spectrum., broad spectrum.

ErythromycinErythromycin -- Ribosome-binding antibiotic derived from -- Ribosome-binding antibiotic derived from Streptomyces erythraeus. Streptomyces erythraeus. Also bacterio_________ . In Also bacterio_________ . In antibiotic class known as “_________________”antibiotic class known as “_________________”

AminoglycosidesAminoglycosides (e.g. streptomycin, kanamycin, (e.g. streptomycin, kanamycin, gentimycin, neomycin). Also derived from gentimycin, neomycin). Also derived from StreptomycesStreptomyces, also ribosome-binding but , also ribosome-binding but bacteri_________.bacteri_________.

Structure and derivatives of tetracyclineStructure and derivatives of tetracycline

Two New Classes of AntibioticsTwo New Classes of Antibiotics

1) 1) FosfomycinFosfomycin -- phosphoric acid used -- phosphoric acid used primarily against _____________________ primarily against _____________________ due to enteric bacteria (due to enteric bacteria (E. coliE. coli, etc.), etc.)

2) 2) SynercidSynercid (dalfopristin/quinupristin) and (dalfopristin/quinupristin) and ZyvoxZyvox (linezolid)-- narrow spectrum drugs (linezolid)-- narrow spectrum drugs used primarily against _________________ used primarily against _________________ pathogens such as pathogens such as Staphylococcus, Staphylococcus, Enterococcus, Enterococcus, and and Streptococcus.Streptococcus.

Antimicrobial DrugsAntimicrobial Drugs

I. Terminology of chemotherapyI. Terminology of chemotherapy

II. Where antimicrobial drugs come fromII. Where antimicrobial drugs come from

III. How antimicrobials workIII. How antimicrobials work

IV. Drug resistanceIV. Drug resistance

V. Interactions between drugs and hostsV. Interactions between drugs and hosts

VI. Selecting the right antimicrobial drugVI. Selecting the right antimicrobial drug

Drug resistance mechanismsDrug resistance mechanisms

1) 1) Enzyme Enzyme __________________________ -- e.g. ß-lactamases -- e.g. ß-lactamases

Enzyme inactivation (cont.)Enzyme inactivation (cont.)

The arms race: ß-lactamase inhibitorsThe arms race: ß-lactamase inhibitors

These are not antimicrobial themselves but are prescribed in These are not antimicrobial themselves but are prescribed in conjunction with ß-lactam antibiotics to increase their conjunction with ß-lactam antibiotics to increase their effectiveness. They tend to be expensive.effectiveness. They tend to be expensive.

Other drug resistance mechanismsOther drug resistance mechanisms

2) 2) Decreased permeabilityDecreased permeability to the drug to the drug Early penicillins could not pass the __________ _____________ Early penicillins could not pass the __________ _____________

of Gram-negativesof Gram-negatives

3) 3) Altered Altered ______________ for the drug______________ for the drug -- altered cell wall -- altered cell wall

receptors, altered target proteins (e.g. altering 50S ribosomal binding receptors, altered target proteins (e.g. altering 50S ribosomal binding

site for erythromycin)site for erythromycin)

4) 4) Changes in metabolic pathways or enzymesChanges in metabolic pathways or enzymes -- e.g. alteration -- e.g. alteration

in ________ _________ synthesisin ________ _________ synthesis

5) 5) Efflux Efflux ____________________ -- antibiotics can be pumped out as fast as they -- antibiotics can be pumped out as fast as they

come in. come in. PseudomonasPseudomonas are particularly famous for this. are particularly famous for this.

_____________________ is pumped out of cells by plasmid-_____________________ is pumped out of cells by plasmid-

encoded cytoplasmic membrane proteinsencoded cytoplasmic membrane proteins

The emergence of antibiotic resistanceThe emergence of antibiotic resistanceRelationship between antibiotic use and the percentage of bacteria isolated from diarrheal patients Relationship between antibiotic use and the percentage of bacteria isolated from diarrheal patients

resistant to the antibioticresistant to the antibiotic

Percentage of reported cases of gonorrhea caused by Percentage of reported cases of gonorrhea caused by antibiotic-resistant strainsantibiotic-resistant strains

9000 cases9000 cases

59000 cases59000 cases

Appearance of antibiotic resistance in several human Appearance of antibiotic resistance in several human pathogens since the beginning of antibiotic therapypathogens since the beginning of antibiotic therapy

At Rockingham Memorial Hospital, for example, 88% of At Rockingham Memorial Hospital, for example, 88% of Staphylococcus aureusStaphylococcus aureus strains isolated in 1999 were resistant to penicillin, ampicillin, and amoxicillin.strains isolated in 1999 were resistant to penicillin, ampicillin, and amoxicillin.

The Arms Race Continues: S. aureus resistance to a brand-new antibiotic

The Arms Race Continues: S. aureus resistance to a brand-new antibiotic

07/20/2001Associated Press

LONDON – In a frustrating development in the battle against drug-resistant bacteria, scientists report that the first entirely new type of antibiotic in 35 years has been beaten by the staph supergerm little more than a year after being introduced.

Researchers at Harvard Medical School describe in the Lancet medical journal this week how an 85-year-old man on dialysis came down with a staph infection in the lining of his intestines that was not vulnerable to the new drug, Zyvox [Linezolid]. It is the first report of staph resistance to the medicine.

Antimicrobial Susceptibility Profiles of Selected Aerobes,

Rockingham Memorial Hospital, 1999

Antimicrobial Susceptibility Profiles of Selected Aerobes,

Rockingham Memorial Hospital, 1999

Organism

Number of isolates tested

Ampi-cillin/ Amoxi-cillin

Augmen-tin

Cefoxitin

Ceftazi-dime

Erythro-mycin

Genta-micin

Peni-cillin

Vanco-mycin

Staphylococcus aureus 715 12 55 90 12 100Staphylococcus epidermidis 81 11 38 65 11 100Streptococcus pneumoniae 42 76 52 100Pseudomonas aeruginosa 115 0 3 0 92 82Escherichia coli 118 57 78 99 100 95Klebsiella pneumoniae 62 0 91 95 97 97

Percent Susceptible

EXPOSURE TO DISINFECTANTS SUCH AS PINE-BASED CLEANERS MAY EXPOSURE TO DISINFECTANTS SUCH AS PINE-BASED CLEANERS MAY CONTRIBUTE TO ANTIBIOTIC RESISTANCECONTRIBUTE TO ANTIBIOTIC RESISTANCE

Repeated exposure to household cleaners containing pine oil may cause bacteria to develop Repeated exposure to household cleaners containing pine oil may cause bacteria to develop resistance to some common antibiotics, say researchers from Tufts University School of resistance to some common antibiotics, say researchers from Tufts University School of Medicine in the December 1997 issue of the journal Antimicrobial Agents and Chemotherapy. Medicine in the December 1997 issue of the journal Antimicrobial Agents and Chemotherapy.

In the study the researchers repeatedly exposed the bacteria Escherichia coli to a household cleaner In the study the researchers repeatedly exposed the bacteria Escherichia coli to a household cleaner containing the disinfectant pine oil or pure pine oil itself in order to isolate pine-oil resistant containing the disinfectant pine oil or pure pine oil itself in order to isolate pine-oil resistant strains. The resistant strains were then tested against a variety of antibiotics. All pine oil-strains. The resistant strains were then tested against a variety of antibiotics. All pine oil-resistant strains were also multidrug resistant. resistant strains were also multidrug resistant.

““To our knowledge, the selection of chromosomal antibiotic resistance, albeit low level, by a To our knowledge, the selection of chromosomal antibiotic resistance, albeit low level, by a disinfectant has not previously been reported for gram-negative bacteria,” say the researchers. disinfectant has not previously been reported for gram-negative bacteria,” say the researchers. “Whether pine oil in products meant for household use could lead to a significant problem of “Whether pine oil in products meant for household use could lead to a significant problem of antibiotic resistance is not know. However, it seems possible that additional disinfectants might antibiotic resistance is not know. However, it seems possible that additional disinfectants might be capable of selecting for resistance to antibiotics and vice versa.” be capable of selecting for resistance to antibiotics and vice versa.”

(M.Moken, L.M. McMurry and S. Levy. 1997. Selection of multiple-antibiotic-resistant mutants of (M.Moken, L.M. McMurry and S. Levy. 1997. Selection of multiple-antibiotic-resistant mutants of Escherichia coli by using the disinfectant pine oil: roles of the mar and acrAB loci. Escherichia coli by using the disinfectant pine oil: roles of the mar and acrAB loci. Antimicrobial Agents and Chemotherapy. 41:2770-2772.) Antimicrobial Agents and Chemotherapy. 41:2770-2772.)

Host/drug reactions (adverse or “side” effects)Host/drug reactions (adverse or “side” effects)

Tissue toxicityTissue toxicity -- kidneys, liver, heart, skin, nerves, teeth -- kidneys, liver, heart, skin, nerves, teeth and bonesand bones

_____________ reactions_____________ reactions • sensitized on first contact.sensitized on first contact.• often due to reaction to a often due to reaction to a metabolic byproductmetabolic byproduct

Disruption of normal flora Disruption of normal flora (‘mucking with the microbial (‘mucking with the microbial ecology of our bodies’)ecology of our bodies’) • frequent cause of diarrheafrequent cause of diarrhea

• ________________________________________ -- secondary infection caused by -- secondary infection caused by

destruction of normal microflora. destruction of normal microflora. Example: yeast (Example: yeast (Candida albicansCandida albicans) infections caused by ) infections caused by

destruction of vaginal lactobacilli with broad-spectrum destruction of vaginal lactobacilli with broad-spectrum antibioticsantibiotics

Picking the right antimicrobial drugPicking the right antimicrobial drug

1) Identify (if possible) the agent1) Identify (if possible) the agent

2) Determine (if possible) the _______________ of 2) Determine (if possible) the _______________ of the agent -- e.g. the agent -- e.g. Kirby-Bauer susceptibility test (will do in lab)Kirby-Bauer susceptibility test (will do in lab)

tube dilution testtube dilution test

Minimum Inhibitory ConcentrationMinimum Inhibitory Concentration = minimum concentration of = minimum concentration of

a drug that visibly __________ ________.a drug that visibly __________ ________.

Tube dilution testTube dilution test

Minimum Inhibitory Concentration (MIC)Minimum Inhibitory Concentration (MIC)