Drug Resistance and Transferable R Plasmids in Edwardsiella tarda from Fish Culture Ponds

Abstract

One hundred sixty eight strains of Edwardsiella tarda collected from cultured eel (Anguilla japonica), tilapia (Tilapia nilotica) and channel catfish (Ictalurus punctatus), and from water and plankton of culture ponds were studied for their sensitivities to 10 chemotherapeutic agents: chloramphenicol (CM), tetracycline (TC), streptomycin (SM), kanamycin (KM), aminobenzyl penicillin (ABP), cefazolin (CEZ), nalidixic acid (NA), furazolidone (NF), sulfamonomethoxine (SA) and trimethoprim (TMP). All strains were highly sensitive to CEZ and TMP. Only 32 of 168 strains were sensitive to all the drugs tested. The remaining 136 strains were resistance to various combinations of the 8 drugs (CM, TC, SM, KM, ABP, NA, NF and/or SA). The most common types of drugs resistance were to combinations of CM, TC, NF and/or SA.Transferable R plasmids were detected in 38 out of 136 resistant strains. The most common type of resistance markers of R plasmid was CM, TC and SA. Other R plasmids had markers for resistance to TC, SA, TC SA and CM TC SM KM SA.Cryptic plasmids were also detected in all strains E.. tarda tested by agarose gel electrophoresis.