Molecular identification of a Stenotrophomonas species used in the bioassay for erythromycin in aquaculture samples.

A bacterial strain isolated from aquaculture pond slurry, which was extremely sensitive to erythromycin, was used to detect erythromycin at levels as low as 0.05 micrograms ml-1 in aquaculture water, sediments and soil samples. Identification of the indicator organism was attempted by 16S rRNA sequencing, biochemical profile, fatty-acid analysis and polymerase chain reaction (PCR). GenBank comparison showed that the 16S rRNA sequence of the strain was similar to those of more than 20 copies of Xanthomonas and Stenotrophomonas. The position of the strain in a phylogenetic tree based on the 16S rRNA gene sequence comparison is in a cluster of Stenotrophomonas. The fatty-acid analysis also showed that the strain is similar to Stenotrophomonas maltophilia. However, the biochemical profile of the strain is most similar to Xanthomonas campestris, except that it can utilize maltose, which is similar to S. maltophilia. Polymerase chain reaction results showed that the strain is different from X. campestris, S. maltophilia and other Xanthomonas species tested. Based on these results, the authors named this strain as Stenotrophomonas sp. strain NCTR.