Antibiogram for isolated Streptococcus agalactiae from red hybrid tilapia (Oreochromis spp.) from selected wet markets in Kelantan

Freshwater aquaculture is among the fastest growing field in food chain production and it has become consumer’s best option especially in monsoon seasons. Streptococcosis has become worldwide disease and is considered as main pathogen in variable freshwater fish. In this study, Streptococcus spp. isolates are identified from red hybrid tilapia (Oreochromis spp.) collected at 12 wet markets in Kelantan. All fish are selected randomly, any physiological characteristic such as haemorrhages, tail rot, and sunken eyes are not considered. Seven isolates of S. agalactiae are isolated from 71 samples of red hybrid tilapia by direct streaking from eyes, heart, gills and liver onto blood agar. All isolates are identified through colonies morphological characteristic; and haemolysis on blood agar, catalase and oxidase test; and Gram staining. Furthermore, S. agalactiae isolates are further confirmed using 16S rDNA sequencing. Streptococcus agalactiae are tested with multiple antibiotic resistances (MAR) using 12 type of antibiotic discs which are amoxicillin-clavulanic, ampicillin, gentamicin, ciprofloxacin, erythromycin, imipenem, neomycin, nalidixic acid, norfloxacin, streptomycin, trimethoprim-sulphamethoxazole and tetracycline. The result shows that the most resistant antibiotic towards S. agalactiae is neomycin (71.4%) while sensitive antibiotics are imipenem and tetracycline (71.4%). Statistical analysis shows p-value (p > 0.05) is 0.069. This indicates that there is no association between types of antibiotics and antibiotic results. Presence of resistance antibiotic genes in 7 isolates of S. agalactiae is carried out using conventional polymerase chain reaction (PCR). Eleven resistance antibiotic genes are tetA, tetB, tetC, tetD, tetE, tetM, aadA, strA-B, blaTEM, blaSHV and sul1. There are only SA3 and SA4 of S. agalactiae that contain aadA and strA-B of resistance gene. Meanwhile, sul1 resistance genes are detected in sample SA1, SA2, SA3, and SA4 of S. agalactiae isolates. SA5, SA6 and SA7 of S. agalactiae do not contain any antibiotic resistance genes. Streptococcus agalactiae (SA3) isolated from red hybrid tilapia which contains high combination of resistance genes is chosen for experimental infection in red hybrid tilapia. Healthy juveniles of red hybrid tilapia (average weight of 50 g) are injected intraperitoneally with 0.2 ml of S. agalactiae suspension containing 10-4, 10-5, 10-6, 10-7 and 10-8 cfu/ml. Value of LD50 is 105.8 LD50/ml which is equivalent with bacterial concentration 6.1 x 10-6. The findings in this study indicate that S. agalactiae infection has become a health issue in public. Likewise, multiple antibiotics resistant of Streptococcus will lead to treatment challenge in Streptococcal infection. This study demonstrates that the presence of different combinations of the antibiotic resistance genes in S. agalactiae isolates indicating their probable roles in the pathogenesis of Streptococcal infections. Constant monitoring should be done in order to compile more information on antibiotic sensitivity of S. agalactiae.