title: Diversity and characterization of oxytetracycline-resistant bacteria associated with non-native species, white-leg shrimp (Litopenaeus vannamei), and native species, black tiger shrimp (Penaeus monodon), intensively cultured in Thailand.
abstract: OBJECTIVE
  This study aimed at surveying prevalence of oxytetracycline (OTC)-resistant bacteria in the white-leg shrimp Litopenaeus vannamei, and the black tiger shrimp Penaeus monodon, intensively cultured in Thailand. We investigated the phylogenetic diversity of the bacterial isolates, as well as the minimum inhibitory concentration (MIC) of OTC, the occurrence of major OTC-resistant genes and multiple-antibiotic resistance in the isolates.
  
  
  RESULTS
  Shrimps were collected from culture ponds, and the homogenates of whole bodies were plated on tryptic soy agar supplemented with or without OTC. Percentages of OTC-resistant bacteria were 0·3-52·1% in white-leg samples and 0·008-22·3% in black tiger samples. Analyses of 16S rDNA sequences indicated that most OTC-resistant isolates were closely related to Aeromonas spp. and Lactococcus garvieae. MICs of OTC were 4-128 μg ml(-1) in the OTC-resistant aeromonads and 128-256 μg ml(-1) in OTC-resistant L. garvieae. OTC resistance was found to be conferred by the genes tet(A), tet(C), tet(D), tet(E), tet(M) and tet(S), detected either singly or in pairs. No resistance to ceftazidime, imipenem or chloramphenicol was observed in any isolate.
  
  
  CONCLUSIONS
  Both species of shrimp are associated with OTC-resistant bacteria, occasionally at high densities exceeding 10(6) cfu g(-1). The associated bacteria, predominantly Lactococcus and Aeromonas genera, are potential pathogens and are reservoirs of a variety of OTC-resistant genes.
  
  
  CONCLUSIONS
  Cultured shrimps can be vehicle to carry OTC-resistant bacteria to domestic and foreign consumers via the food chain. Very low populations of OTC-resistant bacteria observed in the several ponds suggest that levels of the resistant bacteria are artificially high and should be reduced in farmed shrimps.
authors.affiliation: National Research Institute of Fisheries Science, Fisheries Research Agency, Yokohama, Japan. yanoya@affrc.go.jp
authors.forename: Y
authors.initials: Y
authors.lastname: Yano
authors.forename: K
authors.initials: K
authors.lastname: Hamano
authors.forename: M
authors.initials: M
authors.lastname: Satomi
authors.forename: I
authors.initials: I
authors.lastname: Tsutsui
authors.forename: D
authors.initials: D
authors.lastname: Aue-umneoy
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001419:Bacteria / Q000145:classification* / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D044822:Biodiversity; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics; D008826:Microbial Sensitivity Tests; D010118:Oxytetracycline / Q000494:pharmacology*; D033561:Penaeidae / Q000382:microbiology*; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D013753:Tetracycline Resistance / Q000235:genetics; D013785:Thailand
chemical_list: D000900:Anti-Bacterial Agents; D012336:RNA, Ribosomal, 16S; D010118:Oxytetracycline