Transcript Microbial physiology

Antibiotics
楊倍昌
Antibiotics and vaccines are among the biggest
medical advances since 1000. (Culver Pictures)
A brief history of antibiotics
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1495, mercury to treat syphilis.
1630, quinine (cinchona tree) for malarial fever by South American
Indians.
1889, Buillemin defined antibiosis.
1910, Paul Ehrlich developed arsenical compound (Salvarsan) for syphilis,
term: the chemical knife.
1929, Alexander Fleming found penicillin.
1935, Gerhard Domagk showed the value of sulfonamides.
1940, Ernst Chain and Howard Flory demonstrated the effect of penicillin.
1940-1970, then searching for new antibiotics
~ recent year: modifying old drugs, finding new discipline in antibacterial
combats
Early time in war: thanks penicillin, we can go home now
Now a day……….Oh eh?!
Thanks to work by Alexander Fleming (1881-1955), Howard
Florey ( 1898-1968) and Ernst Chain (1906-1979), penicillin
was first produced on a large scale for human use in 1943. At
this time, the development of a pill that could reliably kill
bacteria was a remarkable development and many lives
were saved during World War II because this medication
was available.
A. Fleming
E. Chain
H. Florey
A tale by A. Fleming
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He took a sample of the mold
from the contaminated plate. He
found that it was from the
penicillium family, later specified
as Penicillium notatum. Fleming
presented his findings in 1929, but
they raised little interest. He
published a report on penicillin
and its potential uses in the British
Journal of Experimental Pathology.
Scenario of penicillin action on E. coli
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1: ordinary appearance
2-4: globular extrusions emerge
5: rabbit-ear forms
6: Ghost form
Evaluation by BUSINESS COMMUNICATIONS COMPANY, INC.,
year
By 2001, in developed countries, as many as 60% of hospital-acquired
infections are caused by drug-resistant microbes. These infections are no
longer found only in hospital or nursing home wards but are active in the
community at large.
An ideal antibiotics
• Broad-spectrum
• Did not induce resistance
• Selective toxicity, low side effects
• Preserve normal microbial flora
Susceptibility test
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Tube dilution method
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Minimal inhibitory
concentration (MIC): the
smallest amount of
chemotherapeutic agent
required to inhibit the
growth of organism in vitro
Disk diffusion method
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Zone of inhibition (ZOI):
the correlation of ZOI and
MIC has been established
by FAD
ETest. This commerciallyprepared strip creates a gradient
of antibiotic concentration when
placed on an agar plate
Guidance of antimicrobial therapy
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Minimum inhibitory concentration: lowest concentration of
antibiotic that inhibits visible growth (難用)
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Minimum bactericidal concentration: lowest concentration of
antibiotic that kills 99.9% of the inoculum
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Serum bactericidal title: dilution of serum that kills 99.9% of
the inoculum
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Synergy test: synergistic activity of multiple antibiotics
In vitro: Factors for optimal antibiotic action
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pH of environment:
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Nitrofurantoin is more active in acid pH; sulfonamides and aminoglycoside
are more active in alkaline pH.
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Components of medium:
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Anionic detergents inhibit aminoglycosides, serum proteins bind to
penicillin in varying degrees.
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Stability of drug:
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Aminoglycosides and chloramphenicol are stable for long period in vivo.
Size of inoculums:
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The larger the bacterial inoculum, the greater the chance for resistant
mutant to emerge.
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Metabolic activity of microorganisms:
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Actively and rapidly growing organisms are more susceptible to drug
action
Affecting factors in vivo
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Abscess: circulation is blocked off.
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Foreign bodies: obstruction of the urinary,
biliary or respiratory tracts etc.
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Immunity.
Sites of action
Modes of action (1)
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Penicillins, cephalosporin, bacitracin, carbapenems and
vancomycin.
vancomycin
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Tetracyclines
Inhibitors of Cell Membrane.
Polyenes - Amphotericin B, nystatin, and condicidin.
Imidazole - Miconazole, ketoconazole and clotrimazole.
Polymixin E and B.
Amphotericin
Aminoglycosides
Inhibitors of cell wall synthesis.
Inhibitors of Protein Synthesis.
Aminoglycosides - Streptomycin, gentamicin,
neomycin and kanamycin.
Tetracyclines - Chlortetracycline, oxytetracycline,
doxycycline and minocycline.
Erythromycin, lincomycin, chloramphenicol and
clindamycin.
Modes of action (2)
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Inhibitors of metabolites
(Antimetabolites).
Sulfonamides - Sulfanilamide, sulfadiazine silver and
sulfamethoxazole.
Trimethoprim, ethambutol, isoniazid.
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Inhibitors of nucleic acids (DNA/RNA
polymerase).
Quinolones - Nalidixic acid, norfloxacin and ciprofloxacin.
Rifamycin and flucytosine.
rifamycin
Penicillin: an extensively
studied example
Action mechanism of penicillin
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Action target: cell wall
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on penicillin binding proteins (PBPs)
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Transpeptidases (form cross-links in peptidoglycan)
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Beta-lactam ring attached to 5-membered
thiazolidine ring
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Accessibility of PBPs differ in gram+ and gram- bacteria
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Amino acyl side chain groups determine spectrum,
adsorption, susceptibility to lactamase
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Bactericidal inhibitors
Resistance
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Failure to bind to PBPs
Cannot penetrate porins (gram-)
Production of lactamase (penicillinase)
Lack autolytic enzyme
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B-lactamase
• Types:
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Different substrate specificity
Penicillinases
cephalosporinases
Metallo-b-Lactamase
Location:
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Gram+: extracellularly
Gram-: periplasmic space
Serine-b-Lactamase
By Dr. Osnat Herzberg
University of Maryland Biotechnology Institute (UMBI)
Drug resistance in general
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Natural (inherent) resistance
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Structural barrel
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Lack of target
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Transport system
Acquired resistance
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Mutation
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Gene exchange (conjugation in most)
Transferable antibiotic resistance in bacteria
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Reduced uptake into cell (chloramphenicol)
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Active efflux from cell (tetracycline)
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Modification of antibiotic targets (b-lactam, erythromycin)
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Inactivation of antibiotic by enzyme modification: hydrolysis
(b-lactam, erythromycin); derivatization (aminoglycosides)
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Sequestration of antibiotic by protein binding (b-lactam)
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Metabolic bypass (sulfonamides)
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Overproduction of antibiotic target (titration: sulfonamides)
Some probable overuse/misuse of
antibiotics
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Prophylactic use before surgery
Empiric use (blinded use)
Increased use of broad spectrum
agents
Pediatric use for viral infections
Patients who do not complete course
(chronic disease, e.g. TB, AIDS)
Antibiotics in animal feeds
Policy to deal drug resistance (1)
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Ideally, bacteriological management of clinical
infection should involve:
• Identification of causative organism
• Sensitivity test
• Follow-up the drug effect
• Monitor antibiotic level to avoid toxicity.
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In reality, most patients requiring antimicrobial
therapy are treated empirically. In serious infections
immediate chemotherapy may be life-saving.
Policy to deal drug resistance (2)
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Periodic changes of antibiotics used might change selective
pressure and thus avoid the emergence of resistance and retain
the therapeutic value of antibiotics over a longer period.
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The unnecessary prophylactic or animal feeds use should be
discouraged.
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Distribution of information on current/updated infectious
microbes (consult microbiologists): use more targeted antibiotics
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Patient education (不隨便吃藥, 停藥)