Question

Select the methods of antimicrobial susceptibility testing that can be used to determine
minimal inhibitory concentrations (MIC).

Kirby-Bauer test

E-test

Tube-dilution test

Beta-lactamase testing

Answer 1

Answer: Kirby-Bauer test

Tube-dilution test

The following are the tests used for antimicrobial effectiveness.

1. Kirby-Bauer disk susceptibility test: In this antibiotic is placed in disks in nutrient media and tested for the growth of specific antibiotics. The microbe freezones surrounding the wells with antibiotic is taken as criteria to measure the effectiveness.
2. Zone of inhibition test: In a nutrient agar media containing microbial growth, the zone of inhibition is tested with the test antibiotic drug.
3. Minimum Inhibitory concentration test: This test is used to measure the lowest effective concentration of antibiotic against the growth inhibition of some specific bacteria.

Advantages of synthetic and semi-synthetic antibiotics over natural antibiotics:

1. Synthetic and semi-synthetic antibiotics (altered natural antibiotics) have broader spectrum of action than natural antibiotics.
2. It is easy to produce synthetic antibiotics on large scale than the natural antibiotics.

Beta lactum antibiotics contain beta-lactum ring in their structures, examples include penicillins, cephalosporins, carbapenems and monobactum antibiotics. They act by inhibiting the cell wall synthesis, hence they are bactericidal. These antibiotics are generally effective against Gram positive bacteria and some are also effective against gram negative bacteria. Examples include staphylococcus species, streptococcus species.