15/16: antibiotics and microbes

Question 1

according to the joint committee in 1969 what is the definition of a “true antibiotic”?

Answer 1

“a chemical substance produced wholly or partially by a microorganism (bacterium or fungus) which has the capacity in dilute solution to inhibit the growth of, or to destroy, bacteria and other microorganisms”

Question 2

how do antibiotics differ from disinfectants/antiseptics?

Answer 2

antibiotics are substances that kill/damage pathogens but do not harm host cells, whilst antiseptics/disinfectants are poisonous for both microbes and mammals

Question 3

what are streptomyces?

Answer 3

• most important bacteria for antibiotic production
• source of 75% of antibiotics
  -> chloramphenicol, kanamycin, erythromycin, rifamycin, streptomycin, neomycin, tetracycline & venomycin.

Question 4

what % of antibiotics come from fungi or moulds?

Answer 4

20%

Question 5

what are examples of fungi/mould antibiotics?

Answer 5

penicillin, cephalosporin n fusidic acid

Question 6

what % of bacteria do true bacteria produce?

Answer 6

5%

Question 7

what genus of bacteria is the primary source of antibiotics?

Answer 7

bacillus

Question 8

what are examples of sources for microbes?

Answer 8

soil (especially uncultivated or tropical), sewage, excreta, rotten food or feed, hospital isolates, the sea, and others

Question 9

name the steps taken to prepare antibiotic microbes

Answer 9

1. sample, grow n isolate microbes
2. test isolates as antimicrobials, by adding a purified growth sample to pathogen plate
   -> clear zone around sample indicates inhibition zone -> antimicrobial activity

Question 10

what does MIC stand for? what does it mean?

Answer 10

minimum inhibitory concentration: lowest antibiotic dose requires to stop pathogen growth

Question 11

how do you determine the MIC using liquid?

Answer 11

1. prepare liquid media and add various amounts of antibiotic
2. inoculate media with test microbes (pathogen) and incubate
   -> turbid culture: pathogen growth (no inhibition)
   -> clear culture: no pathogen growth
3. the lowest dose resulting in clear culture = MIC.
4. further tests using nutrient agar plates to confirm the MIC

Question 12

how can gene technology be used to enhance the yield of antibiotics?

Answer 12

gene mutation methods
-x-ray
- UV radiation
- chemicals

Question 14

what are the key steps in preparing n testing antibiotics from microbes

Answer 14

• isolate microbes
• identifying microbes, conditions: sterile agar, pH, time, temperature)
• isolate colonies and test MIC
• test anti-bacterial chemicals against pathogens
• purify chemicals using solvent extract, precipitate, chromatograph)
• re-test in vitro and in vivo for antimicrobial activity and toxicity
• mass produce using fermenting vessels, mix w carriers & binders, conduct final tests for potency, toxicity, safety & efficacy for approval

Question 15

what are the 5 groups of antibiotics, based on their target sites when attacking bacteria? name an example for each

Answer 15

• cell walls: eg penicillin
• cell membrane: eg polymyxin, vallomycin
• nucleic acid replication: eg actinomycine
• protein synthesis (ribosomes): eg streptomycin, tetracycline, chloramphenicol
• cell metabolism: eg sulphonamide

Question 16

what is the difference between bactericidal and bacteriostatic antibiotics?

Answer 16

bactericidal: kill or dissolve pathogens/bacteria by breaking cell wall, eg penicillin, cephalosporin, and vencomycin
bacteriostatic: suppress/stop bacterial growth
- disrupt the cell membrane
- distort DNA replication
- interfere w protein synthesis (ribosomes)
- stop folic acid synthesis
some bacteriostatic antibiotics can become bactericidal if dose is increased, eg tetracyclines, chloramphenicol, macrolides

Question 17

what is ß-Lactam?

Answer 17

• Structurally similar to Penicillin
• Lactam molecule with an Amide bond within a four member ring
• Involve an amide N & Carbonyl carbon

Question 18

how do aminoglycosides work?

Answer 18

• bind to the 30S ribosomal sub-unit causing misreading by tRNA
  -> prevents bacteria from synthesising vital protein for growth - treat serious bacterial infections via intravenous or intramuscular routes, sometimes orally or topically for intestinal or eye infections

Question 19

what are macrolides chemically characterised by?

Answer 19

• lactone ring with 1 or more deoxy sugars (Cladinose & Desosamine).
• lactone ring may have 14, 15, or 16 members

Question 20

when should antimicrobials be used?

Answer 20

• natural defence fails -> injury
• microbes invade -> infection

Question 21

what is the therapeutic use of antimicrobials?

Answer 21

high/safe doses for short periods to treat existing infections and diseases
- bacterial enteritis in swine
- anaplasmosis in cattle
- respiratory diseases in young animals
- Diarrhoea
- Cholera
- Typhoid & Blisters in Poultry
- local injuries
- stress-related problems

Question 22

what is the sub-therapeutic/prophylactic use of antimicrobials?

Answer 22

small doses in feed/water to prevent diseases
- diarrhoea
- rhinitis
- abscessed liver

Question 23

what are benefits of antimicrobial use in animals?

Answer 23

• Disease control and Animal Welfare
• Nutrient sparing, Improved Feed & Water intake
• Metabolic (Gut absorbable antimicrobials)
  Reduced Toxic waste products
  Better Digestion and Absorption
• Better Growth & Production
• Quality Food for Consumers
• Better Profits for Producers