Antimicrobial susceptibility and minimum inhibition concentration of Vibrio parahaemolyticus, Vibrio vulnificus and Vibrio harveyi isolated from a white shrimp (Litopenaeus vannamei) pond

Abstract

Shrimp infection by Vibrio spp. has led to loss of production. To control this bacterial epidemic, people have applied antibiotics. Uncontrolled antibiotic treatments have led to Vibrio spp. pathogenic-resistance. This study aimed to determine the antimicrobial susceptibility and minimum inhibition concentration (MIC) of Vibrio parahaemolyticus, Vibrio vulnificus and Vibrio harveyi towards certain antibiotics. The trials used 10 and 100 ppm concentrations of 10 antibiotics: Chloramphenicol, Gentamicin, Amoxicillin, Co-Amoxiclay, Ciprofloxacin HCL, Azithromycin, Doxycycline, Tetracyclin, Erythromycin stearate and Ampicillin. Paper disc diffusion followed standard methods with incubation for 24 hrs. The inhibition zone was then measured. The results showed that at 100 ppm all antibiotics had activity toward all three Vibrio spp. (100 ppm). At 10 ppm, Amoxicillin and Ampicillin did not produce an inhibition zone in the V. parahaemolyticus culture. Antibacterial activity at 100 ppm resulted in inhibition zone diameters ranging from 6.930.34 mm (Ampicillin/V. parahaemolyticus) to 31.852.5 mm (Gentamicin/V. harveyi). The reduction in bacterial activity ranged from 3.89% (Doxycycline/V. harveyi) to 75.30% (Gentamicin/V. parahaemolyticus). The MIC was determined for six antibiotics. The lowest MIC was ≤0.625 ppm (Gentamicin/all Vibrio spp.), and the highest was 10 ppm (Doxycycline/V. vulnificus, V. harveyi and Ampicillin/V. vulnificus). This research revealed that some antibiotics, especially Amoxicillin and Ampicillin, were ineffective against Vibriosis, conforming that the Vibrio spp. isolates used in this research were resistant to these antibiotics.