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Ybarra, Bio221
Microbial control
Disclaimer: these questions are what have been asked of you during lecture and or
lab. The questions may or may not be quiz or test questions and should be treated
as quick concept reviews. This is what I used to study there is extra information
here.
What are the ideal characteristic of an antibiotic?
Selective Toxicity Against Target Pathogen But Not Against Host
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Would like LD50 to be high and Minimal Inhibitory Concentration (MIC) and/or
Minimal Bactericidal Concentration (MBC) to be low
LD50 stands for Lethal Dose 50% of the time; Measure of drug
toxicity/lethality against host
MIC; Measure of the concentration of the antibiotic necessary to inhibit
growth of the target pathogen
MBC; Measure of the concentration of the antibiotic necessary to kill the
target pathogen
Favorable Pharmacokinetics: Survive in high concentration and reach the target
site (site of infection)
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Pharmacokinetics: Action of drugs in the body over a period of time
including:
Absorption
Distribution
Localization in tissues
Biotransformation through biochemical alterations
Excretion
Would Like the Drug to be:
o
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Bactericidal: Kills microbes (-cidal = death)
Bacteriostatic: Stops growth of microorganisms without killing them (-static
= stationary)
Spectrum of Activity (Broad vs. Narrow) Coordinated with Diagnosis
o
o
a broad-spectrum antibiotic would be useful against a multiple pathogens
causing an infection … an intrabdominal anaerobic infection
a narrow spectrum antibiotic would be ideal for an infection caused by a
single pathogen, e.g., a staphylococcal skin infection.
Lack of "Side Effects"
Able to Cross Outer and Cytoplasmic Membranes
No or Low Level of Antibiotic Resistance in Target Pathogen and Lack of CrossResistance in Closely Related Strains
Resistant to Inactivation by Microbial Enzymes
Ybarra, Bio221
Quick review:
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Microbial control
broad spectrum
stable long shelf life
soluble in body fluids
stable toxicity
Nonallergenic (no side effects)
reasonable cost
selectively toxic
not likely to induce bacterial resistance
Where do we get our antibiotic from anyway?
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Bacillus
Streptomyces
Cephalosporium
Penicillium
Quick Review: Mode of Action
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Cell wall synthesis
o penicillins, cephalosporins (beta-lactamase producing bacteria
resistant to both, require active cell wall synthesis in actively
growing cultures), bacitracin, vancomycin, Lysozyme (natural and in
tears)
Cell membrane function
o amphotericin B, nystatin, polymyxin E, polymyxin B
Protein Synthesis
o Aminoglycides, tetracyclines, chloramphenicol, erythromycin, neomycin,
streptomycin
How are microbes beating the antibiotics? (Mechanisms of antibiotic resistance)
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Enzymatic destruction of drug
Prevention of penetration of drug
Alteration of drug's target site
Rapid ejection of the drug
*Resistance genes are often on plasmids or transposons that can be transferred
between bacteria*
Okay, so should I prescribe several antibiotics to be sure everything is dead?
What happens when I mix them?
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Synergism occurs when the effect of two drugs together is greater than the
effect of either alone (adds)
Antagonism occurs when the effect of two drugs together is less than the
effect of either alone (cancels)
Ybarra, Bio221
Microbial control
Halogens
Iodine: combines with certain amino acids to inactivate enzymes and other
cellular proteins. Strong oxidizing agent
Chlorine: chlorine forms a strong oxidizing agent, hypochlorous acid (HOCl), when
chlorine is added to water. ~ Two drops Clorox per liter of water (four if cloudy)
and let sit 30 minutes.
Alcohols
Alcohols exert their action by denaturing proteins and dissolving lipids.
In tinctures, they enhance the effectiveness of other antimicrobial chemicals.
Heavy Metals and Their Compounds
Silver, mercury, copper, and zinc are used as germicidals.
They exert their antimicrobial action through oligo-dynamic action. When heavy
metal ions combine with sulfhydryl (—SH) groups, proteins are denatured.
Quaternary Ammonium Compounds
Quaternary Ammonium Compounds are cationic detergents attached to NH4+.
By disrupting plasma membranes, they allow cytoplasmic constituents to leak out
of the cell. They also denature proteins (inhibit enzymes) and are surface
active. Quaternary Ammonium Compounds are most effective against gram-positive
bacteria. Good against fungi, amoeba, and enveloped viruses but pseudomonads can
grow in them.
Aldehydes
Aldehydes such as formaldehydes and glutaraldehyde exert their antimicrobial
effect by inactivating proteins (denaturing).
Ethylene oxide
Penetrates most materials and kills all microorganisms (and destroys endospores)
by cross linking proteins and nucleic acids (denaturing). Sterilizes.
Disadvantage: Requires long exposure times and is explosive and toxic in pure
form but works well at low (room) temperatures.
Oxidizing Agents (peroxygens)
Peroxygens are highly reactive and exert their effect by oxidizing proteins
inside the cell.
Ybarra, Bio221
Microbial control
What is the hydrologic cycle? Can you diagram it?
Where in the hydrologic cycle do we get our drinking water? Example?
Why is there so much financial investment in water microbiology, water treatment
plants?
What obstacles prevent the creation of the ideal killing compound?
What is the antibiotic of last resort for resistance? What is the clinical
significance?
Why are there many tests designed to detect E. coli and E. aerogenes?
Why is folic acid so important?
What is PABA?
Where are extraneous populations more dangerous in a large body of water or milk?
Why is that? What is the impact?
Why is the person next to you the most dangerous person in the room?
How does water get sanitized?
What the difference is between sanitize, disinfect, and sterilize?
What is Germ Theory? Who developed it?
What are Koch’s 5 postulates?
What is the general disease cycle? Can you diagrammatically outline it? Provide
examples with each transmission.
What are the 5 causes/types of diseases?
Define: Potable, Safe, Polluted, Contaminated and how they relate to water
microbiology.
What are indigenous populations and extraneous populations as they relate to
water microbiology?
What is the Qualitative procedure to determination the presence of Escherichia
coli? What is the significance? Other organisms?
1. Presumptive Test:
2. Confirmed Test:
3. Completed Test:
What is the chlorine concentration required to kill Escherichia coli? Why is this
concentration significant? What about spores?
What is IMVC? What organisms are significant? Why are these two organisms
significant?
What are the 3 methods of pasteurization?
Ybarra, Bio221
Microbial control