Question

1. Interpret the following standard antibiotic test results using the interpretive chart below. Assume that the method was used correctly and that all antibiotic discs were effective (not expired): (5 marks) a. Aeromonas hydrophilia tested with Tetracycline had an average zone size of 16.5 mm b. Aeromonas hydrophilia tested with Pencillin G had an average zone size of 10 mm c. Staphylococcus aureus Patient AB tested with Pencillin G had an average zone size of 24 mm. d. Staphylococcus aureus Patient CK tested with Pencillin G had an average zone size of 11 mm. e. Escherichia coli tested with Streptomycin had an average zone size of 17 mm. Table 1:Zone Size Interpretive Chart for Kirby Bauer Test I Antibiotic Target Size of resistant Size of intermediate Size of susceptible zone (mm) zone (mm) zone (mm) Tetracycline Broad spectrum 15 - 18 Penicillin G 11 or less 12-21 Streptomycin Gm- 11 or less 12-14 14 or less 19 or more Gm + 22 or more 15 or more

Answer 1

Kirby-Bauer test is used to determine the sensitivity pathogenic aerobic and facultative anaerobic bacteria to various antimicrobial compounds. The pathogenic organism is grown on Mueller-Hinton agar in the presence of various antimicrobial infused filter paper disks. The presence or absence of growth around the disks indicates an indirect measure of the ability of that antibiotic to inhibit the growth of the organism.

From the give Kirby Bauer test the following results can be interpreted.
a. Aeromonas hydrophilia shows an inhibition zone of size 16.5mm which is in the range of 15-18. Hence it can be concluded that Aeromonas hydrophilia is moderately susceptible to Tetracycline.

Similarly
b. Aeromonas hydrophilia is resistant to Penicillin G.
c. Staphylococcus aureus strain from Patient AB is susceptible to Penicillin G.
d. Staphylococcus aureus strain from Patient CK is resistant to Penicillin G.
e. Escherichia coli is susceptible to Streptomycin.