Antibiotic and heavy metal resistance of cacteria isolated from diseased Mud Crab (Scylla serrata)

A total of 320 bacteria isolated from marketable size and diseased mud crab (Scylla
serrata) at a commercial farm. The isolated bacteria were Aeromonas spp. n = 70,
Edwardsiella tarda n = 50, Vibrio alginolyticus n = 40, Vibrio parahaemolyticus n = 20,
Salmonella spp. n = 70 and Klebsiella spp. n = 70. All the bacterial isolates were tested
for antibiotic susceptibility against 16 types of antibiotics by using disk diffusion
method. The antibiotics tested in this study were nalidixic acid (30 µg/disk), oxolinic
acid (2 µg/disk), compound sulphonamides (300 µg/disk), doxycycline (30 µg/disk),
tetracycline (30 µg/disk), novobiocin (30 µg/disk), chloramphenicol (30 µg/disk),
kanamycin (30 µg/disk), sulphamethoxazole (25 µg/disk), flumequine (30 µg/disk),
erythromycin (15 µg/disk), ampicillin (10 µg/disk), spiramycin (100 µg/disk),
oxytetracycline (30 µg/disk), amoxycillin (25 µg/disk) and fosfomycin (50 µg/disk).
Heavy metal resistance pattern of the present bacterial isolates was also characterized
against mercury (Hg2+), chromium (Cr6+), copper (Cu2+), and Zinc (Zn2+) by using
two fold agar dilution method. The percentage of antibiotic sensitivity of the present
bacterial isolates was ranged from 12.5 % to 100 % in which most of the present
bacteria isolates were not sensitive to ampicillin whereas all the bacteria isolates were
sensitive to nalidixic acid, flumequine and oxytetracycline. Overall, the total of
antibiotic sensitive case was reported as 72.7% whereas antibiotic resistance and
intermediate sensitive case was recorded as 19.7% and 7.4 %, respectively. The
Multiple Antibiotic Resistance (MAR) values were range of 0.03 to 0.29 in which
Aeromonas spp (0.29) showed the highest value of MAR. This was followed by
Salmonella spp. (0.21) and Klebsiella spp. (0.21), Edwardsiella tarda (0.20), Vibrio
alginolyticus (0.09) and Vibrio parahaemolyticus (0.03). The MAR value indicated that
the commercial S. serrata were not contaminated to the test antibiotics. Furthermore,
low resistance activity of the present bacterial isolates to the tested heavy metals (Cr6+:
20.7 % to 30.8 %, Zn2+: 0 % to 40 %, Cu2+: 18.8 % to 25 % and Hg2+: 30 % to 33.3
%) was observed.