Chemical Agents of Control: Chemotherapeutic Agents Chemical Agents of Control: Disinfectants and Antiseptics

bacitracin

(Cell wall)

Kirby- Bauer Antibiotic sensitivity test

*The Kirby -Bauer disk-diffusion method is used to determine the drug sensitivity/susceptibility of microorganisms isolated from an infected patient. *The medium of choice is Muller-Hinton agar. *Filter paper discs are impregnated with specified concentrations of different antibiotics and placed on the surface of an agar plate that has been seeded with the organism to be tested *The size of zone of inhibition around the disk varies with the antibiotic. *The susceptibility of an organism to a drug is assessed by the size of this zone(mm), which is affected by other variables such as -The ability and rate of diffusion of the antibiotic into the medium and its interaction with the test organism -The number of organism inoculated. -The growth rate of the organism. *The size is compared to the standardized chart

Phenol

1. Germicidal effect caused by alteration of protein structure resulting in protein denaturation. 2. Surface-active agent (surfactant) precipitates cellular proteins and disrupts cell membranes. (Phenol has been replaced by better disinfectants that are less irritating, less toxic to tissues, and better inhibitors of microorganisms.)

Surface-Active Agents Wetting agents: Emulsifiers, soaps, and detergents

1. Lower surface tension and aid in mechanical removal of bacteria and soil. 2. If active portion of the agent carries a negative electric charge, it is called an anionic surface-active agent. If active portion of the agent carries a positive electric charge, it is called a cationic surface-active agent. 3. Exert bactericidal activity by interfering with or by depressing metabolic activities of microorganisms. 4. Disrupt cell membranes. 5. Alter cell permeability.

Iodine compounds: Tincture of iodine Povidone-iodine solution (Betadine ® )

1. Mechanism of action is not entirely known, but it is believed that it precipitates proteins. 2. Surface-active agent.

Silver compounds: Silver nitrate

1. Precipitate cellular proteins. 2. Interfere with metabolic activities of microbial cells. 3. Inorganic salts are germicidal.

Thymol

1. Related to the cresols. 2. More effective than phenol.

Cresols

1. Similar to phenol. 2. Poisonous and must be used externally. 3. 50% solution of cresols in vegetable oil, known as Lysol ®

Halogens Chlorine compounds: Sodium hypochlorite (Dakin's fluid): NaOCl Chloramine: CH3C6H4SO2NNaCl

1.Germicidal effect resulting from rapid combination with proteins. 2. Chlorine reacts with water to form hypochlorous acid, which is bactericidal. 3. Oxidizing agent. 4. Noncompetitively inhibits enzymes, especially those dealing with glucose metabolism, by reacting with SH and NH2 groups on the enzyme molecule.

Alcohols Ethyl: CH 3 CH 2 OH Isopropyl: (CH3)2CHOH 1.

1.Lipid solvent. 2. Denaturation and coagulation of proteins. 3. Wetting agent used in tinctures to increase the wetting ability of other chemicals. 4. Germicidal activity increases with increasing molecular weight.

You have a 200 mg/ml antibiotic solution. You prepare serial dilutions (1:2, 1:4, etc.) of the antibiotic; the first tube contains 100 mg/ml. You then inoculate each tube with Salmonella. Bacteria grow in tubes 4, 5, and 6. You subculture bacteria from tubes 1 through 3 to nutrient broth. Growth occurs in the tube 3 subculture. You can conclude that the MIC is __________. 12.5 mg/ml 25 mg/ml 50 mg/ml 200 mg/ml none of the listed choices End of Question 1

25 mg/ml

monobactam (mon'ō-bak'tam),

A class of antibiotic that has a monocyclic β-lactam nucleus and is structurally different from other β-lactams; for example, aztreonam If you are allergic to penicillin. aztreonam [az´tre-o-nam″] a narrow-range antibiotic effective against aerobic gram-negative bacteria; used for the treatment of infections caused by susceptible organisms. Administered intravenously or intramuscularly.

vancomycin

A glycopeptide antibiotic effective against coccal bacteria, especially in recalcitrant staphylococcal infections-eg, MRSA, unresponsive to penicillins or cephalosporins Adverse effects Ototoxicity, nephrotoxicity (Cell wall)

quinolones

A group of antimicrobial agents (e.g., norfloxacin, ciprofloxacin, levofloxacin) that block bacterial (DNA synthesis).

polymyxin

A group of five POLYPEPTIDE antibiotic drugs active against various GRAM NEGATIVE bacteria. They are used almost exclusively as external applications in ointments and eye and ear drops because of their toxicity if taken internally. (Cell membrane)

rifampin [rif-am´pin]

A semisynthetic antibiotic, C43H58N4O12, that is derived from a form of rifamycin and interferes with bacterial (RNA synthesis), used to treat tuberculosis and other bacterial infections.

essential metabolite

A substance that closely resembles an essential metabolite and therefore inhibits physiological reactions involving that metabolite.

Microbes that produce antimicrobial chemicals that inhibit the growth of other microorganisms in the same habitat are exhibiting what type of behavior? Synergism Mutualism Antagonism Parasitism Commensalism

Antagonism

nystatin (nī-stat'in)

Antibiotic substance isolated from cultures of Streptomyces noursei, effective in treatment of all forms of candidiasis, particularly candidal infections of intestine, skin, and mucous membranes. (Anti-fungal) (Cell membrane)

How are drugs that block the synthesis of folic acid able to maintain selective toxicity? A) Humans do not need folic acid while bacteria do. B) Bacteria must synthesize folic acid, while humans acquire it from their diet. C) Eucaryotic enzymes involved in folic acid synthesis differ from the prokaryotic enzymes involved in folic acid synthesis. D) Eucaryotic cells do not transport this class of antibiotics into the cytoplasm, while prokaryotes do. E) Such metabolic analogs only recognize prokaryotic enzymes involved in the synthesis of folic acid.

Bacteria must synthesize folic acid, while humans acquire it from their diet.

Why are viral infections especially difficult to treat? A) Because they rely upon their host cells for the majority of their metabolic functions B) Because they can have RNA as their nucleic acid C) Because some viruses are naked while others are enveloped D) Because there are many types of viral structures E) Because viruses can halt their metabolism when in the presence of

Because they rely upon their host cells for the majority of their metabolic functions

*Chloramphenicol*

Binds to 50S portion and inhibits formation of peptide bond

erythromycin (topical)

Binds with 50S subunit of susceptible bacterial ribosomes, suppressing protein synthesis in bacterial cells and causing cell death. (Protein synthesis)

Cycloserine inhibits A. alanine racemase B. D-alanyl - D-alanine synthetase C. Both (a) and (b) D. amidase

Both (a) and (b)

Which of the following statements is true regarding the properties of benzylpenicillin? a) It is a bacteriostatic agent. b) It is active over a wide range of bacterial species. c) It is resistant to β-lactamases. d) Certain individuals may have an allergic response to it.

Certain individuals may have an allergic response to it. Penicillins are bactericidal agents and not bacteriostatic agents. Benzylpenicillin has good activity against certain types of bacterial species, but not all. It is also susceptible to attack by bacterial β-lactamases which makes it ineffective against these bacterial strains. It is true to say that certain individuals can be allergic to benzylpenicillin.

*Streptomycin*

Changes shape of 30S portion, causing code on mRNA to be read incorrectly

Which of the following is the general mechanism of action for erythromycin? a) Inhibition of a metabolic enzyme b) Inhibition of cell wall synthesis c) Disruption of protein synthesis d) Inhibition of nucleic acid transcription and replication

Disruption of protein synthesis

Which of the following antibiotics is a tetracycline? a) Chloramphenicol b) Doxycycline c) Erythromycin d) Streptomycin

Doxycycline Chloramphenicol does not belong to any general class of antibiotics. Doxycycline is a tetracycline. Erythromycin is a macrolide. Streptomycin is an aminoglycoside. Page reference: 454-455, 457

Which of the following statements is accurate in explaining why Gram negative bacteria are generally more resistant to penicillins than Gram positive bacteria? a) Gram negative bacteria have a thicker cell wall b) Gram negative bacteria have an outer hydrophilic membrane that acts as an extra barrier c) Gram negative bacteria can concentrate β-lactamase enzymes in the periplasmic space d) Gram negative bacteria produce smaller quantities of transpeptidase enzyme

Gram negative bacteria can concentrate β-lactamase enzymes in the periplasmic space

isoniazid [i″so-ni´ah-zid] .

Inhibits cell-wall biosynthesis by interfering with lipid and nucleic acid DNA synthesis in tubercle bacilli cells (Cell wall)

*Tetracyclines*

Interfere with attachment of tRNA to mRNA-ribosome complex

carbapenem (kahr-bă-pen'em),

Member of a class of antibiotic drugs that works by inhibiting cell wall synthesis. If you are allergic to penicillin. imipenem [im″ĭ-pen´em] a β-lactam antibiotic with a broad spectrum of activity against gram-positive and gram-negative organisms. Because it is metabolized in the kidneys, it is administered with the enzyme inhibitor cilastatin in order to decrease the amount of it that is degraded by an enzyme in the kidneys.

Which of the following statements does not characterize the ideal antimicrobial drug? A)Microbistatic B)Selectively toxic C)Safely and easily broken down and excreted by the body D)Remain active in the body as long as is needed E)Not excessively costly

Microbistatic

*Semisynthetic penicillins*

Oxacillin:Narrow spectrum, only gram-positives, but resistant to penicillinase Ampicillin:Extended spectrum, many gram-negatives.

The golden age of antibiotics began in 1928 with Sir Alexander Fleming's discovery of an antibacterial compound he called what? A)Arsenic B)Salvarsan C)Sulfonamide D)Penicillin E)Tetracycline

Penicillin

Which antibacterial drug does not inhibit protein synthesis? A) Aminoglycoside B) Tetracycline C) Penicillin D) Chloramphenicol E) Erythromycin

Penicillin

Which antibiotic has a beta-lactam ring? A. Cephalosporin B. Penicillin C. Tetracycline D. Streptomycin

Penicillin

*Natural penicillins*

Penicillin G (requires injection) Penicillin V (can be taken orally)

Aminoglycoside drugs are products of what group of microorganisms? A) Soil actinomycetes B) Aerobic, Gram positive cocci C) Penicillium chrysogenum D) Cephalosporium acrimonium E) Bacillus subtilis

Soil actinomycetes

What microorganism has the distinction of being one of nature's most prolific antibiotic producers? A) Penicillium chrysogenum B) Bacillus subtilis C) Streptomyces sp. D) Cephalosporium acrimonium E) Micromonospora sp.

Streptomyces sp.

What was the first disease to be treated with a specific chemical? A) Tuberculosis B) Syphilis C) Bacterial meningitis D) Whooping cough E) Scarlet fever

Syphilis

You are reviewing the following results of a disk- diffusion antibiotic susceptibility test on an isolate of Staphylococcus aureus: Antibiotic A: ZI (zone of inhibition) = 0 millimeters Antibiotic B: ZI = 23 millimeters Antibiotic C: ZI = 16 millimeters Antibiotic D: ZI = 19 millimeters Which antibiotic is bactericidal? Antibiotic A Antibiotic B Antibiotic C Antibiotic D The correct answer cannot be determined from the information provided.

The correct answer cannot be determined from the information provided.

What portion of penicillin is responsible for its microbicidal activity? A) The peptidoglycan B) The thiazolidine ring C) The beta-lactam ring D) The variable side chain E) The carboxyl group

The variable side chain

Which of the following is untrue of the cephalosporin group of drugs? A) Their structure is similar to that of the penicillins. B) Their spectrum of activity is extremely narrow. C) There are three generations of these drugs. D) They cause fewer allergic reactions than the penicillins. E) They have two possible sites for placement of variable side chains.

Their spectrum of activity is extremely narrow.

Antimicrobials that block nucleic acid synthesis may act in all but which of the following manners? A) They can cross-link the DNA and prevent DNA replication. B) They can inhibit DNA helicases and prevent unwinding. C) They can block DNA transcription. D) They can block the synthesis of DNA and RNA nucleotides. E) They can inhibit the action of tRNA

They can inhibit the action of tRNA.

Which of the categories of antimicrobial drugs exhibits the least degree of selective toxicity? A) Those that disrupt cell membrane function B) Those that affect the cell wall C) Those that inhibit nucleic acid function D) Those that inhibit protein synthesis E) Those that inhibit nucleic acid synthesis

Those that disrupt cell membrane function

which of the following is not a category of antimicrobial drugs? A) Those that inhibit cell wall synthesis B) Those that inhibit DNA and RNA structure and function C) Those that inhibit protein synthesis D) Those that interfere with cell membrane structure and function E) Those that inhibit mRNA processing in the nucleus

Those that inhibit mRNA processing in the nucleus

The drug Flagyl is commonly used to treat an STD caused by __________. Neisseria gonorrhoeae Treponema pallidum Trichomonas vaginalis herpesvirus HIV

Trichomonas vaginalis

Drugs that affect the bacterial cell wall are active only against what type of cells? A) Gram negative B) Dormant C) Young, actively growing D) Endospore-forming E) Gram variable

Young, actively growing

Streptomyces

a genus of nonpathogenic soil bacteria, but occasionally parasitic on plants and animals. Notable as the source of various antibiotics, e.g. the tetracyclines, erythromycin (S. erythreus), lincomycin (S. lincolnensis), tylosin (S. fradiae), rifampin (S. mediterranei), amphotericin B (S. nodosus) and monensin (S. cinnamonensis).

An antibiotic that disrupts the normal flora can cause A) the teeth to turn brown B) aplastic anemia C) a superinfection D) hepatotoxicity

a superinfection

Microbial resistance to drugs is acquired through A) conjugation B) transformation C) transduction D) all of these

all of these

When a patient's immune system becomes reactive to a drug, this is an example of A) superinfection B) drug resistance C) allergy D) toxicity

allergy

trimethoprim

an oral antibacterial closely related to pyrimethamine, almost always administered in combination with a sulfonamide, primarily for treatment of urinary tract infections.

*A compound synthesized by bacteria or fungi that destroys or inhibits the growth of other microbes is a/an* A) synthetic drug B) antibiotic C) antimicrobic drug D) competitive inhibitor

antibiotic a substance produced by a microbe that, in small amounts, inhibits another microbe

Cephalosporins

are similar in structure and antimicrobial action to penicillin. The cephalosporins have been classified by "generations" according to general features of antimicrobial activity, with successive generations having increasing activity against gram-negative organisms and decreasing activity against gram-positive organisms.

Antibiotics

are synthesized and secreted by some true bacteria, actinomycetes, and fungi that destroy or inhibit the growth of other microorganisms. some antibiotics are laboratory synthesized or modified; however, their origins are living cells. actinomycetes: branched gram-positive bacteria, often found in soil, some of which are pathogenic for humans and animals.

The most selective antibiotics are those that interfere with the synthesis of A. bacterial DNA B. bacterial RNA C. bacterial cell walls D. bacterial plasma membrane

bacterial cell walls

Which statement is not an aim in the use of drugs in antimicrobial chemotherapy? The drug should: A) have selective toxicity B) be active even in high dilutions C) be broken down and excreted rapidly D) be microbicidal

be broken down and excreted rapidly

Drugs that prevent the formation of the bacterial cell wall are A) quinolones B) beta-lactams C) tetracyclines D) aminoglycosides

beta-lactams

An example of an antiviral drug that can prevent a viral nucleic acid from being replicated is A) azidothymidine B) acyclovir C) amantadine D) both a and b

both a and b

Which of the following types of antibiotics is most likely to be associated with the development of a superinfection? broad-spectrum antibiotics bactericidal antibiotics narrow-spectrum antibiotics bacteriostatic antibiotics β-lactam antibiotics

broad-spectrum antibiotics

tetracycline

broad-spectrum antiinfective; action: antimicrobial effect related to inhibition of (protein synthesis); decreases incidence of postsurgical inflammation and edema; suppresses bacteria and acts as a barrier to bacterial entry; acts on cementum or fibroblasts to enhance periodontal ligament regeneration; (Bacteriostatic)

Inhibition of protein synthesis:

chloramphenicol, erythryomycin, tetracyclines, streptomycin

Which of the following is the drug of choice for the treatment of malaria? quinacrine chloroquine Flagyl nifurtimox iodoquinol

chloroquine

Which drug would be used to treat athlete's foot? polymyxin B chloroquine clotrimazole neomycin amantadine

clotrimazole

Which of the following antibiotics is a common choice to treat streptococcal infections in children? neomycin tetracycline rifampin erythromycin trimethoprim

erythromycin

Which of the following antibiotics is frequently used as an alternative for those who are allergic to penicillin? streptomycin erythromycin vancomycin amoxicillin ethambutol

erythromycin

*Sulfonamide drugs initially disrupt which process?* A) folic acid synthesis B) transcription C) PABA synthesis D) protein synthesis

folic acid synthesis (Competitive inhibitors)

Tetracyclines are effective against all of the following EXCEPT __________. fungi intracellular rickettsias intracellular chlamydias gram-positive bacteria gram-negative bacteria

fungi

An antimicrobial drug that inhibits peptidoglycan synthesis is most likely to be effective against __________. protozoan parasites viruses fungi gram-positive bacteria gram-negative bacteria

gram-positive bacteria

An antimicrobic drug with a ______ therapeutic index is a better choice than one with a ______ therapeutic index. A) low, high B) high, low

high, low

Which of the following mechanisms is antifungal? inhibit ergosterol synthesis cause muscle spasms inhibit 70S ribosomes inhibit peptidoglycan synthesis interfere with anaerobic metabolism

inhibit ergosterol synthesis

competitive inhibition

inhibition of enzyme activity by an inhibitor (a substrate analogue) that competes with the substrate for binding sites on the enzymes.

Open Hint for Question 5 in a new window Which antimicrobial works by inhibiting the synthesis of mycolic acid? vancomycin methicillin penicillin chloramphenicol isoniazid

isoniazid

Which of the following effects do antiviral drugs not have? A) killing extracellular viruses B) stopping virus synthesis C) inhibiting virus maturation D) blocking virus receptors

killing extracellular viruses

*Selective toxicity*

killing harmful microbes without damaging the host

All of the following are antiprotozoan drugs EXCEPT __________. mefloquine chloroquine quinacrine mebendazole metronidazole

mebendazole

Which drug is NOT a nucleoside analog? zidovudine acyclovir ribavirin lamivudine nevirapine

nevirapine

Which of the following is used for treating influenza infections? acyclovir indinavir oseltamivir pentamidine isethionate interferon

oseltamivir

Inhibition of cell wall synthesis:

penicillins, cephalosporins, bacitracin, vancomycin

R factors are ______ that contain a code for ______. A) genes, replication B) plasmids, drug resistance C) transposons, interferon D) plasmids, conjugation

plasmids, drug resistance

Injury to plasma membrane:

polymyxin B nystatin

Which antifungal drug was recently introduced to treat systemic fungal infections? tolnaftate miconazole amphotericin B clotrimazole posaconazole

posaconazole

Which of the following modes of action would be most selectively toxic? A) interrupting ribosomal function B) dissolving the cell membrane C) preventing cell wall synthesis D) inhibiting DNA replication

preventing cell wall synthesis

Inhibition of nucleic acid replication and transcription:

quinolones, rifampin

Which of the following drugs inhibits the synthesis of mRNA in bacteria? ampicillin polymyxin B trimethoprim rifampin ethambutol

rifampin

The MIC is the ______ of a drug that is required to inhibit growth of a microbe. A) largest concentration B) standard dose C) smallest concentration D) lowest dilution

standard dose

Which of the following antibiotics inhibits protein synthesis? vancomycin cephalosporin isoniazid streptomycin rifampin

streptomycin

Which of the following antibiotics inhibits folic acid synthesis? ampicillin neomycin sulfanilamide chloramphenicol tetracycline

sulfanilamide

Inhibition of essential metabolite synthesis:

sulfanimide, trimethoprim

Most antihelminth drugs function by A) weakening the worms so they can be flushed out by the intestine B) inhibiting worm metabolism C) blocking the absorption of nutrients D) inhibiting egg production

weakening the worms so they can be flushed out by the intestine

A nucleoside analog used to treat HIV infection is __________. acyclovir praziquantel ribavirin zidovudine amantadine

zidovudine

Which of the antibiotic is not used as a food preservative ? A. Pimaricin B. Nisin C. Tylosin D. β-lactam antibiotic

β-lactam antibiotic

What crucial feature of a penicillin is involved in its mechanism of action? a) Carboxylic acid b) β-lactam ring c) Acyl side chain d) Thiazolidine ring

β-lactam ring

Chemical Agents for the Control of Microbial Growth

●Antiseptics: Chemical substances used on the living tissue that kill or inhibit the growth of vegetative microbial forms ●Disinfectants: chemical substances that kill or inhibit the growth of vegetative microbial forms on nonliving materials ●Chemotherapeutic agents: Chemical substances that destroy or inhibit the growth of microorganisms in living tissues

Antimicrobial Drugs

●Chemotherapy: the use of drugs to treat a disease ●Antimicrobial drugs: interfere with the growth of microbes within a host ●Antibiotic: a substance produced by a microbe that, in small amounts, inhibits another microbe ●Synthetic drugs: are synthesized in the laboratory ●Sulfadiazine (a sulfonamide) is the best example - mode of action is competitive inhibition. ●Semisynthetic drugs: part nature made, part man made ●Selective toxicity: killing harmful microbes without damaging the host

Mode of Actions of Chemotherapeutic Agents

●Inhibition of cell wall synthesis ●Inhibition of protein synthesis ●Inhibition of nucleic acid replication ●Injury to plasma membrane ●Inhibition of essential metabolite synthesis