the use of antimicrobial (antibiotics) in the treatment of infections [ch9]

Question 1

what are the characteristics of antibiotics.

Answer 1

Selective toxicity
Highly soluble - contact 
Effective concentration
Immune system –not affected
Target isolated species
Prevent resistant strains
No side effects
Not bind to host proteins/ inactivated

Question 2

what is the general mode of action of antibiotics

Answer 2

Inhibiting the synthesis of cell walls;
• Inhibiting the synthesis of proteins;
• Inhibiting the synthesis of nucleic acids;
• Damaging cell membranes;
• Or by inhibiting of specific enzyme systems by antimetabolites.

Question 3

Classify antibiotics according to the class
that they belong.

Answer 3

Note that penicillin ,cephalosporins, carbapenems and monobactams are b-lactam agents.

1) Penicillin’s :ends with cillin
2) cephalosporins: Starts with cef or cep
3) monobactams: Ends with am
4) carbapenems :ends with penem
5) Glycopeptides: ends with in
6) aminoglycosides:end with cin
7) Tetracycline:cycline
8) chloramphenicol-phenicol
9) macrolides:ends with romycin
10) lincomycins:mycin
11) quinolones/fluoroquinolones: ends with oxacin
12) ansamycin:starts with rifa
13) nitroimidazole:ends with idazole
14) sulphonamides:
15) polyenes
16) polypeptides

Question 4

describe the mode of action of B-lactam agents

Answer 4

are bactericidal, and act by inhibiting the synthesis of the peptidoglycan layer of bacterial cell walls.

Question 5

describe the mode of action of aminoglycosides

Answer 5

Inhibition of protein synthesis. Once inside the bacterial cell, aminoglycosides bind to the 30s ribosomal sub-unit and cause a misreading of the genetic code. This subsequently leads to the interruption of normal bacterial protein synthesis.

Question 6

describe the mode of action of tetracycline

Answer 6

Inhibition of protein synthesis. Once tetracyclines have been transported into the cell, this class of antibiotic reversibly binds to receptors on the 30S ribosomal subunit of the bacteria, preventing attachment of aminoacyl-tRNA to the RNA-ribosome complex.

Question 7

describe the mode of action of macrolides

Answer 7

inhibition of bacterial protein biosynthesis, and they are thought to do this by preventing peptidyltransferase from adding the growing peptide attached to tRNA to the next amino acid (similarly to chloramphenicol) as well as inhibiting bacterial ribosomal translation.

Question 8

describe the mode of action of Chloramphenicol

Answer 8

Chloramphenicol is a bacteriostatic by inhibiting protein synthesis. It prevents protein chain elongation by inhibiting the peptidyl transferase activity of the bacterial ribosome

Question 9

describe the mode of action of Quinolones

Answer 9

mode of action is by inhibition of DNA replication. Quinolones bind to the topoisomerase IV/DNA gyrase–DNA complexes and this results in the inhibition of DNA replication.

Question 10

describe the mode of action of Lincosamides

Answer 10

Lincomycin inhibits bacterial protein synthesis by binding to the 23S RNA of the 50S subunit of the bacterial ribosome. Lincomycin is predominantly bacteriostatic in vitro.

Question 11

describe the mode of action of Sulphonamides

Answer 11

antimetabolite -Inhibition of other metabolic processes. Sulfonamides interfere with folic acid synthesis by preventing addition of para-aminobenzoic acid (PABA) into the folic acid molecule through competing for the enzyme dihydropteroate synthetase.

Question 12

What types of infections do the different class of antibiotics treat ?

Answer 12

1)Penicillins are used in the treatment of infections affecting skin, teeth, ears, urinary tract and
respiratory tract infections, as well as gonorrhoea.

2)Cephalosporins :Pneumonia, Streptococcal throat, Staphylococcal infections, tonsillitis, bronchitis, otitis media, various types
of skin infections and gonorrhoea may be treated with Cephalosporins which are bactericidal. (note they differ with the types of generations )

3)Glycopeptides:It is used in the treatment of infections
caused by oxacillin-resistant staphylococci and other gram-positive bacteria.

4)Polypeptides : topically-applied drug for treating skin-infections caused by Gram-positive bacteria

5) Aminoglycosides: are used in the treatment of systemic infections caused by
Gram-negative bacteria as well as Mycobacteria.

6)Tetracycline:bacteriostatic drugs include tetracycline, doxycycline and minocycline which are used in the treatment
of infections caused by Chlamydia, Mycoplasma, Rickettsia and some Gram-positive and Gram-negative
bacteria

7). Macrolides: can also be used to treat infections caused
by gram-positive and Campylobacter bacteria in patients with allergies to penicillin.

8) Chloramphenicol is an antibiotic. It’s mainly used to treat eye infections (such as conjunctivitis) and sometimes ear infections
9) Oxazolidones :It is the drug of choice to treat infections caused by Enterococci

10)Lincosamides :It is used to treat
Staphylococcal infections as well as anaerobic gram-negative infections.

11)Quinolones:
Naladixic acid, a narrow spectrum antibiotic, was initially used for the treatment of urinary tract infections
caused by Gram-negative rods until resistance to this drug developed in these bacteria

12)Nitroimidazoles:Metronidazole belongs to this class and it is used to treat anaerobic infections as well as amoebiasis and
giardiasis.

13) Rifampin: is an antibiotic used to treat several types of bacterial infections, including tuberculosis, Mycobacterium avium complex, leprosy, and Legionnaires’ disease.
14) Sulphonamides :They may be prescribed to treat urinary tract infections (UTIs), bronchitis, eye infections, bacterial meningitis, pneumonia, ear infections, severe burns, traveler’s diarrhea, and other conditions
15) Trimethoprim: It’s used to treat urinary tract infections (UTIs), such as cystitis. Occasionally, trimethoprim is used to treat other types of infections, such as chest infections and acne.

Question 13

Discuss the type, mode of action and
function of the different types of antiviral
drugs

Answer 13

Action : Inhibit nucleic acid synthesis ,synthetic antibiotics ,nucleoside analogues
Selectivity has been a problem because viruses use the metabolic machinery of the
host
B. Antiviral drugs target specific steps of life cycle, especially enzymes that function in
the life cycle (e.g., amantadine, vidarabine, acyclovir, and azidothymidine)
C. Human interferon is used to treat some viral infections

Question 14

Differentiate between intrinsic and

acquired resistance.

Answer 14

Inherent resistance occurs as a result of lack of affinity of the drug for the bacterial
target, inaccessibility of the drug into the bacterial cell, extrusion of the drug by chromosomally encoded
active exporters and innate production of enzymes that inactivate the drug. More than one of these
mechanisms may be responsible for inherent resistance.

Acquired resistance occurs when an organism that is initially susceptible to an antibiotic, becomes resistant
to it

Question 15

Describe the strategies used by bacteria to

resist the action of antibiotics

Answer 15

refer to written book notes

Question 16

Discuss how the development of antibiotic

resistant bacteria can be prevented

Answer 16

correct dosage and that the regimenm of the antibiotic is complete
Using 2 diff antibiotics which target different sites of action
avoid broad-spectrum drugs
identification of pathogen and drug sensitivity tests so the use of the correct antibiotic is prescribed

Question 17

Differentiate between synergistic,

antagonistic and indifferent drugs.

Answer 17

Two antibiotics are said to be synergistic (fig 12.27) when a combination of the two drugs causes inhibition
or killing when used at a fourfold-lower concentration than that of either antibiotic used separately

Two antibiotics are said to be antagonistic (fig 12.27) when the one antibiotic interferes with the action of
the second antibiotic.

Two antibiotics are said to be indifferent or additive when the combination of the two antibiotics is equal to
the sum of the independent effects of each antibiotic.

Question 18

how does the transmission of drug resistance occur

Answer 18

patients not taking their full course prescription

Hospitals-Large number of patients are frequently in close contact with each
other. The transmission of airborne antibiotic resistant bacteria is facilitated by the patient coming into direct
or indirect contact with contaminated equipment, environment and contaminated hands of staff

Animals who are destined for the food market are treated with prophylactic antibiotics leading to the
development of resistant bacteria which can be transmitted via contaminated meat to humans