Frequency and Expression of Antibiotic Resistance in Luminous Vibrio harveyi

Abstract

In-vitro activities of chloramphenicoi, ciprofloxacin, nalidixic acid and oxytetra-cycline were evaluated against penaeid shrimp larval pathogen, luminous Vibrio harveyi. The frequency at which three strains of luminous V. harveyi strains can mutate to develop resistance to these antibiotics was also estimated. Resistant mutants developed at lower frequencies to chloramphenicol (<9.43 x lO"10) and ciprofloxacin (<1.14 x lO"10 - 1.61 x lO"9) than to nalidixic acid (6.61 x lO"5 - 8.87 x lO"5) and oxytetracycline (6.82 x lO"6 - 4.74 x lO"4) at 10 times the respective minimal inhibitory concentration (MIC). Low concentration of antibiotics (5 x MIC and 2 x MIC), however, induced more of mutant strains. Although ciprofloxacin was effective in terms of MIC and induction of low level of mutants, chloramphenicol was more effective in its ability to kill both resistant and sensitive strains of luminous V. harveyi