title: Co-occurrence of resistance to different antibiotics among aquatic bacteria.
abstract: BACKGROUND
  Antibiotic resistance is not confined to pathogens, but is also widespread in various natural environments. In nature the microbes producing antibiotic compounds have been around for millions of years. Heavy use of antibiotics in medicine and veterinary practice may lead to the accumulation of resistance genes in microbial populations, followed by a rise in multiresistant bacteria.
  
  
  RESULTS
  To test the extent of resistance among aquatic bacteria, we have collected 760 isolates resistant to at least one antibiotic. The phylogeny of the isolates covers a wide range of Proteobacteria, Actinobacteria and Bacteroidetes. In order to determine the extent of multiresistance, the isolates were tested on six antibiotics. As the growth rate of the different bacteria was highly variable, the classical medical resistance tests could not be used, and an alternative method considering the full growth curve was developed. In general, the overall resistances to different antibiotics could be explained by random, independent distribution. An exception to this was the resistances against tetracycline and chloramphenicol, which tended to occur in pairs.
  
  
  CONCLUSIONS
  We conclude that there is no massive spread of multiresistance determinants in the studied environment, although some specific cases can be found, awaiting for molecular characterization of the resistance mechanisms.
authors.affiliation: University of Tartu Institute of Technology, Nooruse St 1, Tartu, 50411, Estonia.
authors.forename: Veiko
authors.initials: V
authors.lastname: Voolaid
authors.forename: Arvi
authors.initials: A
authors.lastname: Jõers
authors.forename: Veljo
authors.initials: V
authors.lastname: Kisand
authors.forename: Tanel
authors.initials: T
authors.lastname: Tenson
mesh_terms: D039903:Actinobacteria / Q000187:drug effects* / Q000302:isolation & purification; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D059001:Aquatic Organisms / Q000187:drug effects* / Q000302:isolation & purification; D041963:Bacteroidetes / Q000187:drug effects* / Q000302:isolation & purification; D016000:Cluster Analysis; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004275:DNA, Ribosomal / Q000737:chemistry / Q000235:genetics; D024881:Drug Resistance, Bacterial; D008826:Microbial Sensitivity Tests / Q000379:methods; D010802:Phylogeny; D020560:Proteobacteria / Q000187:drug effects* / Q000302:isolation & purification; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D017422:Sequence Analysis, DNA; D014871:Water Microbiology
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D004275:DNA, Ribosomal; D012336:RNA, Ribosomal, 16S