GTC Microbiology Test 4 Questions &
Answers
Define antibiotic - ANSWERSchemical agent that kills microorganisms or stops them from
growing
Define antimicrobial - ANSWERSagent that stops the growth of microorganisms
Chemotherapeutic index (formula) - ANSWERSmaximum dose patient can handle/kg
------------------------------------------------------
minimum dose that will cure/kg
Define bacteriocidal - ANSWERSkill microbes directly. Usually the antibiotic of choice if available
Define bacteriostatic - ANSWERSprevent microbes from growing. Still rely on immune system to
get rid of bacteria
The best agent would have these characteristics - ANSWERSsolubility, selective toxicity, stable,
non-allergenic, not cause resistance, cheap
What do we call antibiotics that kill gram negative and gram positive bacteria? - ANSWERSBroad
spectrum drugs (antibiotics) are effective against both gram negative and gram positive
bacteria.
Why do they give broad spectrum antibiotics? - ANSWERSGiven when the pathogen is
unknown.
,What do we call it when we give the patient 2 or 3 different antibiotics at once? Why would we
do that? - ANSWERSCombination chemotherapy. Pathogens are capable of becoming resistant
to a single agent, but combination chemotherapy (using more than one drug) makes it more
difficult for the pathogen to develop resistance.
What is chemotherapeutic index? - ANSWERSThe relationship between toxicity of a compound
for the body and the toxicity for parasites.
If a drug has a low chemotherapeutic index, what does that mean? Is that good or bad? -
ANSWERSDrugs that have a low chemotherapeutic index often inhibit pathways or attack
structures found in the host cells. For example, cancer cells closely resemble normal body cells,
therefore, it is difficult to poison the cancer cells without poisoning the body. A low
chemotherapeutic is bad. The larger the therapeutic index, the better the chemotherapeutic
agent, and the less toxic it is to the host. Drugs often have high therapeutic indexes if the target
of the drug is a structure or pathway not found in the host organism.
A drug has a low selective toxicity. Is that a good or bad thing? - ANSWERSSelective toxicity is
the ability of a chemical or drug to kill a microorganism without harming its host, therefore, a
low selective toxicity is a bad thing.
Name four major methods by which antibiotics work: - ANSWERS1) inhibit cell wall synthesis
2) inhibit protein synthesis
3) inhibitor of nucleic acid synthesis
4) inhibit folic acid synthesis
Penicillin is made by a ______? - ANSWERSfungus (mold/penicillium)
Who discovered penicillin? - ANSWERSFleming
,How does penicillin harm bacteria? - ANSWERSPenicillin is in a group of "beta-lactam" drugs
that work by inhibiting the cross-linkages between the NAM-NAG layers of the peptidoglycan
cell wall. Results in faulty cell wall and lysis of bacteria: bacteriocidal.
What are three problems with penicillin? - ANSWERS1) overuse has led to resistance. Many
bacteria have beta-lactamase (penicillinase), an enzyme which inactivates the penicillin.
2) narrow spectrum
3) anaphylactic reaction: many people allergic
What types of microorganisms are affected by pencillin? - ANSWERSprimarily for staph and
strep infections- also syphilis
What do we mean by semisynthetic penicillin? Are they only good for gram positive
microorganisms? - ANSWERSAltered natural beta-lactams create semisynthetic derivatives of
penicillin. These are synthetic and more expensive. They have a broader spectrum than
penicillin due to their modified chemical structures.
Why do they add clavulinic acid to penicillin? - ANSWERSThis inactivates the penicillinase made
by bacteria.
What is beta-lactamase? - ANSWERSA bacterial enzyme that catalyzes the hydrolysis of the
lactam ring in some penicillin antibiotics, rendering them ineffective. Also known as
penicillinase.
Cephalosporins are described as first generation, second generation, and third generation. What
is the difference? - ANSWERSfirst generation are generally used for gram positives. They are
narrow spectrum. second generation are more broad. They kill enterics (gram - and some gram
+). Third generation kills pseudomonas and is broad spectrum killing gram - and even more
gram +.
, How do cephalosporins work? - ANSWERSThey work like penicillin by inhibiting cell wall
synthesis. They do this by inhibiting the cross linkages between the NAM and NAG layers of the
peptidoglycan cell wall. They are resistant to beta lactamase enzyme.
Why are these drugs better for some people than penicillin? - ANSWERSThey are active against
more organisms and do not cause as many allergic reactions as penicillin.
How do carbapenems work? - ANSWERSbroad spectrum : modified beta-lactam structure, often
effective in nosocomial infections
Name two non-beta lactam drugs that inhibit the synthesis of the cell wall, are they broad or
narrow spectrum, and how they are used : - ANSWERS1. Bacitracin - gram positives; topical
application (ointments.)
2. Vancomycin - gram positives; toxic drug and the last in the line of drugs against MRSA -
parenteral administration.
Name two drugs that inhibits the cell wall synthesis (mycolic acid) in Mycobacteria. What are
they affective against? - ANSWERSisoniazid and ethambutol inhibit the synthesis of
_____________.
These drugs are first-line drugs for tuberculosis
Review the antibiotics that inhibit cell wall synthesis: - ANSWERSbeta-lactam: penicillin,
cephalosporins, carbapenems
non beta-lactam: bacitracin, vancomycin
inhibit mycolic acid synthesis: isoniazid, ethambutol
Why can we give drugs that disrupt ribosomes? Wouldn't that also affect human ribosomes? -
ANSWERSThe drugs only affect the 30s ribosomes in prokaryotic cells. Human cells are not
affected because they have 40s ribosomes since they are eukaryotic.
Answers
Define antibiotic - ANSWERSchemical agent that kills microorganisms or stops them from
growing
Define antimicrobial - ANSWERSagent that stops the growth of microorganisms
Chemotherapeutic index (formula) - ANSWERSmaximum dose patient can handle/kg
------------------------------------------------------
minimum dose that will cure/kg
Define bacteriocidal - ANSWERSkill microbes directly. Usually the antibiotic of choice if available
Define bacteriostatic - ANSWERSprevent microbes from growing. Still rely on immune system to
get rid of bacteria
The best agent would have these characteristics - ANSWERSsolubility, selective toxicity, stable,
non-allergenic, not cause resistance, cheap
What do we call antibiotics that kill gram negative and gram positive bacteria? - ANSWERSBroad
spectrum drugs (antibiotics) are effective against both gram negative and gram positive
bacteria.
Why do they give broad spectrum antibiotics? - ANSWERSGiven when the pathogen is
unknown.
,What do we call it when we give the patient 2 or 3 different antibiotics at once? Why would we
do that? - ANSWERSCombination chemotherapy. Pathogens are capable of becoming resistant
to a single agent, but combination chemotherapy (using more than one drug) makes it more
difficult for the pathogen to develop resistance.
What is chemotherapeutic index? - ANSWERSThe relationship between toxicity of a compound
for the body and the toxicity for parasites.
If a drug has a low chemotherapeutic index, what does that mean? Is that good or bad? -
ANSWERSDrugs that have a low chemotherapeutic index often inhibit pathways or attack
structures found in the host cells. For example, cancer cells closely resemble normal body cells,
therefore, it is difficult to poison the cancer cells without poisoning the body. A low
chemotherapeutic is bad. The larger the therapeutic index, the better the chemotherapeutic
agent, and the less toxic it is to the host. Drugs often have high therapeutic indexes if the target
of the drug is a structure or pathway not found in the host organism.
A drug has a low selective toxicity. Is that a good or bad thing? - ANSWERSSelective toxicity is
the ability of a chemical or drug to kill a microorganism without harming its host, therefore, a
low selective toxicity is a bad thing.
Name four major methods by which antibiotics work: - ANSWERS1) inhibit cell wall synthesis
2) inhibit protein synthesis
3) inhibitor of nucleic acid synthesis
4) inhibit folic acid synthesis
Penicillin is made by a ______? - ANSWERSfungus (mold/penicillium)
Who discovered penicillin? - ANSWERSFleming
,How does penicillin harm bacteria? - ANSWERSPenicillin is in a group of "beta-lactam" drugs
that work by inhibiting the cross-linkages between the NAM-NAG layers of the peptidoglycan
cell wall. Results in faulty cell wall and lysis of bacteria: bacteriocidal.
What are three problems with penicillin? - ANSWERS1) overuse has led to resistance. Many
bacteria have beta-lactamase (penicillinase), an enzyme which inactivates the penicillin.
2) narrow spectrum
3) anaphylactic reaction: many people allergic
What types of microorganisms are affected by pencillin? - ANSWERSprimarily for staph and
strep infections- also syphilis
What do we mean by semisynthetic penicillin? Are they only good for gram positive
microorganisms? - ANSWERSAltered natural beta-lactams create semisynthetic derivatives of
penicillin. These are synthetic and more expensive. They have a broader spectrum than
penicillin due to their modified chemical structures.
Why do they add clavulinic acid to penicillin? - ANSWERSThis inactivates the penicillinase made
by bacteria.
What is beta-lactamase? - ANSWERSA bacterial enzyme that catalyzes the hydrolysis of the
lactam ring in some penicillin antibiotics, rendering them ineffective. Also known as
penicillinase.
Cephalosporins are described as first generation, second generation, and third generation. What
is the difference? - ANSWERSfirst generation are generally used for gram positives. They are
narrow spectrum. second generation are more broad. They kill enterics (gram - and some gram
+). Third generation kills pseudomonas and is broad spectrum killing gram - and even more
gram +.
, How do cephalosporins work? - ANSWERSThey work like penicillin by inhibiting cell wall
synthesis. They do this by inhibiting the cross linkages between the NAM and NAG layers of the
peptidoglycan cell wall. They are resistant to beta lactamase enzyme.
Why are these drugs better for some people than penicillin? - ANSWERSThey are active against
more organisms and do not cause as many allergic reactions as penicillin.
How do carbapenems work? - ANSWERSbroad spectrum : modified beta-lactam structure, often
effective in nosocomial infections
Name two non-beta lactam drugs that inhibit the synthesis of the cell wall, are they broad or
narrow spectrum, and how they are used : - ANSWERS1. Bacitracin - gram positives; topical
application (ointments.)
2. Vancomycin - gram positives; toxic drug and the last in the line of drugs against MRSA -
parenteral administration.
Name two drugs that inhibits the cell wall synthesis (mycolic acid) in Mycobacteria. What are
they affective against? - ANSWERSisoniazid and ethambutol inhibit the synthesis of
_____________.
These drugs are first-line drugs for tuberculosis
Review the antibiotics that inhibit cell wall synthesis: - ANSWERSbeta-lactam: penicillin,
cephalosporins, carbapenems
non beta-lactam: bacitracin, vancomycin
inhibit mycolic acid synthesis: isoniazid, ethambutol
Why can we give drugs that disrupt ribosomes? Wouldn't that also affect human ribosomes? -
ANSWERSThe drugs only affect the 30s ribosomes in prokaryotic cells. Human cells are not
affected because they have 40s ribosomes since they are eukaryotic.
