Chapter 34
Antimicrobial Chemotherapy
1-6-2009
Chemotherapeutic agents
„
Chemical agents used to treat disease
„
„
destroy pathogenic microbes or inhibit their
growth within host
most are antibiotics
„
microbial products or their derivatives that kill
susceptible microbes or inhibit their growth
The Development of Chemotherapy
„
Paul Ehrlich (1904)
„
„
„
Sahachiro Hato (1910)
„
„
selective toxicity
dyes Æ African sleeping sickness
arsenic compounds Æ syphilis
Gerhard Domagk, and Jacques and Therese
Trefouel (1935)
„
sulfonamides and sulfa drugs
Penicillin
„
„
1896, first discovered by
Ernest Duchesne
1928, Alexander Fleming
„
„
„
observed penicillin activity on
contaminated plate
1939, Florey, Chain, and
Heatley Æ effectiveness
1945, Fleming, Florey and
Chain received Nobel Prize
Figure 34.1
Later discoveries
„
„
„
1944, Waksman: StreptomycinÆ tuberculosis
1952, Nobel Prize
1953, chloramphenicol, terramycin,
neomycin, and tetracycline isolated
General Characteristics
„
„
selective toxicity
therapeutic index
„
„
ratio of toxic dose to therapeutic dose
toxic dose
„
„
drug level at which drug becomes too toxic for
patient (i.e., produces side effects)
therapeutic dose
„
drug level required for clinical treatment
Activity
„
„
„
Bacteriacidal: kill
Bacteriastatic: inhibit growth
broad-spectrum drugs:
„
„
attack many different pathogens
narrow-spectrum drugs
„
attack only a few different pathogens
Antibiotic Production
„
„
„
bacteria and fungi are natural producers
synthetic chemotherapeutic agents
Semisynthetic antibiotics
„
chemically modified Æ less susceptible to
pathogen inactivation
ampicillin and amoxycillinÆsemisynthetic
„ penicillin G and penicillin V Æ naturally produced
„
Naturally produced
chemotherapeutic agents
„
microbial products or
their derivatives that kill
susceptible microbes or
inhibit their growth
„
most are antibiotics
Level of antimicrobial activity
„
effectiveness expressed in two ways
„
minimal inhibitory concentration (MIC)
„
„
lowest concentration of drug that inhibits growth of
pathogen
minimal lethal concentration (MLC)
„
lowest concentration of drug that kills pathogen
Antimicrobial tests
„
Dilution Susceptibility Tests
„
„
involves inoculating media containing
different concentrations of drug
Disk Diffusion Tests
„
disks impregnated with specific drugs are
placed on agar plates inoculated with test
microbe
drug diffuses from disk into agar, establishing
concentration gradient
„ observe clear zones (no growth) around disks
„
Kirby-Bauer method
„
„
„
disk diffusion test
sensitivity and resistance
determined using tables that
relate zone diameter to degree
of microbial resistance
table values plotted and used
to determine if concentration of
drug reached in body will be
effective
The Etest- strip test
The MIC concentration is
read from the scale at
the point it intersects the
zone of inhibition
Each strip contains a
gradient of antibiotic
AB Biodisk, Solna, Sweden
Action of Antimicrobial Agents
„
targeting some function necessary for its
reproduction or survival
„
targeted function is very specific to
pathogen → higher therapeutic index
Antimicrobial Drugs
„
inhibitors of cell wall synthesis
„
„
„
„
Penicillins, cephalosporins, vancomycin
protein synthesis inhibitors
metabolic antagonists
nucleic acid synthesis inhibition
Penicillins- PG synthesis inhibitors
inhibit the last step of transpeptidation
„
β-lactam ring
„ resistant organismsÆ β-lactamase (penicillinase)
Fig. 34.5
Semisynthetic penicillins
„
„
„
have a broader spectrum
resistance continues to be a problem
~1-5% of adults in US are allergic to penicillin
„
„
allergy Æa violent allergic response and death
broad-spectrum antibiotics (used to treat penicillinallergic patients)
Cephalosporins
„
structurally and functionally similar to penicillins
Figure 34.6
Vancomycin and Teicoplanin
„
„
glycopeptide antibiotics
vancomycin Æ treatment of antibiotic
resistant staphylococcal and enterococcal
infections
„
previously considered “drug of last resort”
Protein Synthesis Inhibitors
„
many specifically to the procaryotic
ribosome
„
„
30S (small) or 50S (large) ribosomal subunit
others inhibit a step in protein synthesis
„
„
„
„
aminoacyl-tRNA binding
peptide bond formation
mRNA reading
translocation
Aminoglycoside antibiotics
„
„
contain a cyclohexane ring and amino sugars
bind to 30S ribosomal subunit
Figure 34.7
Tetracyclines
„
„
„
broad spectrum and bacteriostatic
inhibits bind of aminoacyl-tRNA molecules to the
A site of the ribosome
sometimes used to treat acne
Macrolide antibiotics
Figure 34.9
„
12 ~22-C lactone rings
linked to sugar(s)
„ erythromycin
broad spectrum and
usually bacteriostatic
„ binds to 23S rRNA
„
(inhibits peptide chain
elongation)
„
used for patients allergic to
penicillin
Chloramphenicol
„
chemically synthesized
binds to 23s rRNA to inhibit peptidyl transferase
„
toxic with numerous side effects
„
„
only used in life-threatening situations
Figure 34.10
Metabolic Antagonists
„
Antimetabolites
„
„
antagonize or block functioning of metabolic
pathways by competitively inhibiting the use of
metabolites by key enzymes
are structural analogs
„
molecules that are structurally similar to, and
compete with, naturally occurring metabolic
intermediates
„ block normal cellular metabolism
Sulfonamides or Sulfa Drugs
„
Structurally related to sulfanilamide, a paminobenzoic acid (PABA) analog used for the
synthesis of folic acid (precursor for synthesis of purines
and pyrimidines) which is made by many pathogens
Fig.34.11.12
Synergistic Interaction
Trimethoprim
- synthetic antibiotic
that also interferes
with folic acid
production
Figure 34.14
Nucleic Acid Synthesis Inhibition
„
block DNA replication
„
„
„
block transcription
„
„
inhibition of DNA polymerase
inhibition of DNA helicase
inhibition of RNA polymerase
Not as selectively toxic as other antibiotics
Quinolones
„
„
broad-spectrum
synthetic drugs containing
the 4-quinolone ring
„
„
„
1962, nalidixic acid was first
synthesized quinolone
Ciprofloxacin (Cipro) used to
treat anthrax in 911 (2001)
U.S. bioterrorist attacks
act by inhibiting bacterial
DNA-gyrase complex
„
disrupts many cell
processes involving DNA
Quinolone Inhibition of DNA gyrase action
Figure 34.16
Factors influencing antimicrobial drugs
„
„
„
„
ability of drug to reach site of infection
susceptibility of pathogen to drug
ability of drug to reach concentrations in body
that exceed MIC of pathogen
Modes of administration
„
„
„
Oral- some drugs destroyed by stomach acid
topical
parenteral routes
„
„
Non-oral routes of administration
drug can be excluded by blood clots or necrotic tissue
Drug Concentrations in the Blood
„
„
must be > MIC at infection site to be effective
Factors influencing the concentrations
„
„
„
„
amount administered
route of administration
speed of uptake
rate of clearance (elimination) from body
Drug Resistance
„
„
„
resistance can be transmitted to other bacteria
resistance mutants arise spontaneously and are
then selected
Drug Resistant “Superbug”
„
a methicillin-resistant S. aureus (MSRA) that
developed resistance to vancomycin
„
„
this VRSA was also resistant to most other antibiotics
isolated from foot ulcers on a diabetic patient
Figure 34.17
Mechanisms of drug resistance
„
(1) Alteration of target
enzyme or organelle
„
„
(2), (3) inactivation of drug
„
„
chemical modification of drug
by pathogen
(4) prevent entrance of drug
„
„
„
use of alternative pathways or
increased production of target
metabolite
drug can’t bind to or penetrate
pathogen
bacterial decrease in
permeability
(4) pump drug out
Figure 34.18
Origin and spread of
resistance genes
„
chromosomal genes
„
„
R plasmids
„
„
„
„
spontaneous mutations
in the drug target
can be transferred by
conjugation, transduction
and transformation
can carry multiple
resistance genes
transposons
Integrons: may be > 100 kb
Figure 34.19
Preventing drug resistance
„
„
„
„
give drug in high concentrations
give two or more drugs at same time
use drugs only when necessary
possible future solutions
„
„
continued development of new drugs
use of bacteriophages
Antibiotic misuse and drug resistance
„
Overuse and misuse of antibiotics
Over 90% of colds and upper respiratory infections
are caused by viruses
„ Many patients always do not complete their
course of medication
„
„
The use of antibiotics in animal feeds
„
As much as 70% of the antibiotics are added to
livestock feed in USA
„ Increase the number of drug resistant bacteria
in animal intestinal tracts
Box 34.2
Superinfection
„
development and spread of drug-resistant
pathogens
„
„
caused by drug treatment, which destroys drug
sensitive strains
pseudomembranous enterocolitis
„
caused when treatment with certain antibiotics
kills intestinal flora, leaving Clostridium difficile
to flourish and produce a toxin
Antifungal drugs
„
„
fewer effective agents because of
similarity of fungal cells and human cells
easier to treat superficial mycoses than
systemic infections
Treating superficial mycoses
Figure 34.20
polyene antibiotic from
Streptomyces
disrupts
mitotic spindle;
may inhibit protein
and DNA
synthesis
disrupt
membrane
permeability
and inhibit
sterol
synthesis
Treating systemic infections
binds sterols in membranes
5FC
disrupts RNA function
Figure 34.20
Antiviral Drugs„
relatively few because
difficult to specifically
target viral replication
-used to prevent
influenza infections
-blocks penetration
and uncoating of
influenza virus
Figure 34.21
Tamiflu 克流感
„
„
„
„
anti-influenza agent
a neuraminidase (NA) inhibitor
not a cure for influenza (to shorten course of illness)
Emerging resistant strain
inhibits herpes virus enzymes
involved in DNA and RNA
synthesis and function
Figure 34.21
inhibits herpes
virus and
cytomegalovirus
DNA polymerase
inhibits herpes
virus DNA
polymerase
Broad-spectrum anti-DNA virus drugs
inhibits
viral DNA
polymerase
papovaviruses,
adenoviruses,
herpesviruses
iridoviruses,
and poxviruses
Anti-HIV drugs
„
Target to reverse
transcriptase
„
Target to protease
Microbial Vaccines and disease
control
Chapter 36
1-7-2009
Vaccines
„
Vaccine are non-toxic antigens
„
„
„
preparation of microbial antigens used to
induce protective immunity
may consist of killed, living, weakened
(attenuated) microbes or inactivated bacterial
toxins (toxoids), purified cell material,
recombinant vectors or DNA
the antigens injected, ingested, or inhaled to
induce specific defenses
Table 36.4
Table 36.5
Acellular or subunit vaccines
„
The use of specific,
purified macromolecules
derived from pathogenic
microbes
„
subunit vaccines
„
„
„
capsular
polysaccharides
recombinant surface
antigens
inactivated exotoxins
(toxoids)
Toxoid vaccine
Recombinant-Vector Vaccines
„
„
pathogen genes that encode major
antigens inserted into nonvirulent viruses
or bacteria which serve as vectors and
express the inserted gene
released gene products (antigens) can
elicit cellular and humoral immunity
DNA Vaccines
„
„
DNA directly introduced into
host cell via air pressure or
gene gun
when injected into muscle
cells, DNA taken into nucleus
and pathogen’s DNA fragment
is expressed
„
„
host immune system responds
to foreign proteins produced
many DNA vaccine trials are
currently being run
New directionsthe end of the dreaded syringe
„
Nasal inoculation
„
not for human trials
„
„
proximity to CNS?
Patch vaccine- applied to
skin surface
„
Edible vaccinepotato,(tobacco), banana
Scientific American 2000
http://www.sciam.com/2000
Vaccinomics- The Omics study of vaccine
To Identify molecular targets for vaccine development
Passive immunization
„
protected by injection of antibodies
„
„
„
limited duration, however, can be a lifesaver
for immunocompromised people or organ
transplant recipients
diphtheria and tetanus
multidrug resistant bacteria
Against bioterrorism
„
1984 in Dalles, OR
„
„
1996 in Texas
„
„
intentional release of Shigella dysentariae in a hospital
lab break room
2001 in seven eastern U.S. states
„
„
Salmonella typhimurium in 10 restaurant salad bars
use of weaponized Bacillus anthracis spores delivered
through U.S. postal systems
All caused hospitalizations, the anthrax episode
resulted in five deaths
Biological Weapons
„
Characteristics that favor their use
„
„
„
„
invisible, odorless and tasteless
difficult to detect
take hours or days before awareness that they
have been used
fear and panic associated with the anticipation
that they were used
Table 36.7
Table 36.9
Nosocomial Infections
„
„
„
result from pathogens that develop within
a hospital or other clinical care facility and
are acquired by patients while they are in
the facility
5-10% of all hospital patients acquire a
nosocomial infection
usually caused by bacteria that are
members of normal microbiota
Community-acquired MRSA
„
„
A recently emergent clinical problem
CA-MRSA infections (in contrast to HA-MRSA) are
acquired by persons who have not been recently
(within the past year) hospitalized or had a medical
procedure (such as dialysis, surgery, catheters)
„
The infections in the community are usually
manifested as skin infections, such as pimples and
boils, and occur in otherwise healthy people
Infection sources
„
endogenous pathogen
„
„
exogenous pathogen
„
„
brought into hospital by patient or acquired when
patient is colonized after admission
microbiota other than the patient’s
autogenous infection
„
caused by an agent derived from microbiota of patient
despite whether it became part of patient’s microbiota
following admission
Control, prevention, and surveillance
„
proper training of personnel in basic
infection control measures
„
„
handling of surgical wounds and hand
washing
monitoring of patient for signs and
symptoms of nosocomial infection
The hospital epidemiologist
„
„
individual responsible for developing and
implementing policies to monitor and
control infections and communicable
diseases
reports to infection control committee or
similar group