Antimicrobial activities of some culinary spice extracts against Streptococcus agalactiae and its prophylactic uses to prevent streptococcal infection in red hybrid tilapia (Oreochromis sp.)

The extracts of ten culinary spices were screened to identify their antimicrobial activities against Streptococcus agalactiae by using disk diffusion assay. Only Cinnamomum verum, Allium sativum Linn, Eugenia caryophyllus and Thymus vulgaris displayed antimicrobial activity. The bark C. verum extract displayed the highest antimicrobial activity with a 18 mm inhibition zone. The minimum inhibitory concentration (MIC) values for spice extracts were determined by utilizing the agar diffusion method. The lowest MIC value with high efficacy against S. agalactiae was 0.15 mg\mL, which was obtained from C. verum extract. The median lethal dose (LD50) of S. agalactiae to tilapia fingerlings was measured to be 1.56×105 CFU/mL. The in vivo antimicrobial effect of C. verum was tested by feeding tilapia fingerlings fish feed supplemented with different ratios of C. verum extract and bark powder for 17 days after experimentally injecting the fish with S. agalactiae intraperitoneally (IP). The mortality was significantly lower (p<0.05) in the fish fed on feed supplemented with bark C. verum extract with a ratio of 3:26 (w/w) compared to other groups. These results indicated that the C. verum bark extract supplement is promising as a prophylactic against tilapia streptococcosis and for fish health improvement

Streptococcus agalactiae the etiological agent of mass mortality in farmed red tilapia (Oreochromis sp.).

Streptococcal infection was reported to cause significant mortality and high economical loss in freshwater and saltwater fish species including tilapia species, worldwide. Recently, few disease outbreaks affecting cultured red tilapia in Selangor state, Malaysia was investigated. Affected fish showed loss of appetite, serpentine swimming and exophthalmia. Sick and healthy appeared fish were clinically examined and samples from brain, liver, spleen and kidney were collected for agent isolation. All isolates were gram-positive, oxidase-negative, catalase-negative, β-haemolytic cocci and were characterized as a Group B Streptococcus agalactiae (GBS) using commercial identification kits (Streptococcal grouping Kit, RapID™ STR System and BBL Crystal GP ID Kit). The isolates were sensitive to amoxicillin, ampicillin, erythromycin, chloramphenicol, linomycin, rifampicin, vancomycin, gentamicin, sulfamethoxazole + trimethoprime and tetracycline. In contrast, they were resistant to neomycin, amikacin, kanamycin and streptomycin. Specific Polymerase Chain Reaction (PCR) and 16S rRNA sequencing technique results confirmed the isolates as a GBS. Results of this current study indicated that the Streptococcus agalactiae infection started to spread and warrants focusing on ways to prevent and control the disease before it become endemi

Pathogenicity of Streptococcus agalactiae isolated from a fish farm in Selangor to Juvenile Red Tilapia (Oreochromis sp.)

The rapid increases in global aquaculture industry have exposed many diseases that were not known in aquaculture fields. Streptococcus agalactiae, one of Streptococci species that infecting both terrestrial and aquatic animals. The organisms have been isolated from numerous fish species in natural disease outbreaks and showed to be pathogenic to several fish species. Recently, few streptococcosis outbreaks affecting cultured Red tilapia in Selangor were investigated and the S. agalactiae isolate was used to study its pathogenicity on juvenile Red tilapia. The 120 h 50% endpoint (LD50) value in juvenile tilapia injected Intraperitoneally (IP) was 1.56x105 cfu mL-1. Experimental infections were carried out by bathing the fish for 30 min in water containing the bacteria and by IP injection. It was observed that IP route was more potent to cause mortality to juvenile Red tilapia and produced clear clinical signs within 5 days. It was noted that the mortality started to reduce after 5 days and fish recovered after 9 days post inoculation. In contrast, immersion route did not induce mortality but produced moderate clinical signs such as lethargy and loss of appetite and fish started to recover after 6 days. The findings of the current study would enable us to formulate a suitable measure to prevent and control future disease outbreak

Environmental factors influencing the susceptibility of red hybrid tilapia (Orechromis sp.) to Streptococcus agalactiae infection

Streptococcosis in fish refers to re-emerging diseases causing high mortality in a variety of freshwater and marine fish throughout the Asia-Pacific region. The growth of the pathogen Streptococcus agalactiae isolated from red hybrid tilapia (Oreochromis sp.) in a brain heart infusion broth was investigated under a variety of environmental conditions. The results revealed the optimal growth temperature (25 °C and 30 °C), salinity (5 and 10 ppt), and pH (7 and 7.5) values. The effects of different environmental conditions on the susceptibility of red hybrid tilapia (Oreochromis sp.) to S. agalactiae were also investigated. Oreochromis sp., which were kept under various environmental conditions, were intraperitoneally injected with 0.1 mL of 1.56 × 105 cfu/ml S. agalactiae. Two weeks after infection, the cumulative mortality of the red hybrid tilapia held at 33 °C was significantly higher (P 0.05). These results indicate that environmental conditions at 33 °C, 15 ppt, and pH 6 increased the susceptibility of red hybrid tilapia to S. agalactiae and probably adversely affected the fish's immune system

Pathogenicity of streptococcus agalactiae in juvenile red tilapia (Oreochromis sp.) from a fish farm in Selangor, Malaysia

Streptococcal infection is one of the emerging bacterial diseases that was reported to cause significant mortality and high economical loss in freshwater and saltwater fish species including Tilapia sp., worldwide. Recently, a streptococcosis outbreak affecting Red tilapia (Oreochromis sp.) farm in Selangor was investigated. Affected fish showed loss of appetite, cornea opacity and serpentine swimming. Healthy and morbid fish were clinically examined. Samples from brain, liver, spleen and kidney were collected for causal agent isolation. Pure bacteria isolates were successfully isolated on trypticase soy agar (TSA) blood agar (BA) and brain heart infusion agar (BHIA). The colonies were of grayish white color, circular, convex, pin-head size and β-haemolytic. All isolates were gram-positive cocci, oxidase-negative and catalase-negative. They were identified as group B Streptococcus agalactiae (GBS) using a commercial identification kit (Streptococcal grouping kit, RapID™ STR System and BBL Crystal GP ID kit). Specific polymerase chain reaction (PCR) and 16S rRNA sequencing technique confirmed the isolates as GBS. The isolates were sensitive to amoxicillin, ampicillin, erythromycin, chloramphenicol, linomycin,rifampicin, vancomycin, gentamicin, sulfamethoxazole + trimethoprime and tetracycline. On contrary, they were resistant to neomycin, amikacin, kanamycin and streptomycin. The 120 hours median lethal dose (LD50) value in juvenile tilapia injected intraperitoneally (IP) was 1.5×105 cfu/mL. Experimental infections were carried out by bathing the fish for 30 minutes in water containing the bacteria and by intraperitoneal (IP) injection. It was observed that IP route was more potent to cause mortality to juvenile Red tilapia and produced clear clinical signs within five days. It was noted that the mortality started to reduce after five days and fish recovered after nine days post inoculation. In contrast, immersion route did not induce mortality, but produced moderate clinical signs such as lethargy and loss of appetite, and fish started to recover after six days. The findings of the current study indicated that S. agalactiae infection started to become an issue in tilapia farms and warrants focusing to formulate a suitable measure to prevent and control the disease before it becomes endemic in the future