Molecular typing of Aeromonas isolates in natural mineral waters

Abstract

A total of 103 isolates of Aeromonas spp. were obtained over a 3-year period from a natural mineral water and from surface streams located within the boundaries of the watershed of the natural mineral water wells and were typed by macrorestriction analysis of genomic DNA with XbaI and by pulsed-field gel electrophoresis. All Aeromonas caviae isolates from the natural mineral water belonged to the same clone, and an analogous clonal identity was found among Aeromonas hydrophila isolates. These two clones expressed no hemolytic or cytotoxic activities. Aeromonas isolates from surface waters showed high molecular heterogeneity and were not related to the clones found in the natural mineral water. The presence of aeromonads chronically found in the natural mineral water was a likely consequence of a localized development of a biofilm, with no exogenous contamination of the aquifer. Molecular fingerprinting of drinking water isolates is a useful tool in explaining possible reasons for bacterial occurrences.

FIG. 1.

Temporal trends of Aeromonas CFU counts at the sampling points chosen for the quality control program for natural mineral water. Only values for well no. 9 and for production line no. 1 are displayed. The other wells were always free of Aeromonas spp., whereas concentrations of aeromonads in the other three production lines were not different from those observed in production line no. 1.

FIG. 2.

XbaI PFGE patterns of A. hydrophila and A. caviae isolates from the sampling points chosen for the quality control program for the natural mineral water. Lanes 1 to 5 contain A. caviae strains with PFGE pattern A₁ isolated from well no. 9 (lane 1), the mixing tank (lane 2), the entrances of the bottling lines (lanes 3 and 4), and the bottled water (lane 5). Lanes 7 and 8 contain A. hydrophila strains with PFGE pattern A isolated from well no. 9, whereas lanes 9 to 15 contain A. hydrophila strains with the same PFGE pattern, A, isolated downstream (mixing tank, entrances of the bottling lines, and bottled water). Lanes 6 and 16 contain molecular size markers (lambda ladder; values to the right are kilobases).

FIG. 3.

XbaI PFGE patterns of A. hydrophila and A. caviae isolates from natural mineral water (lanes 5 to 10) and the surface waters of the watershed (lanes 1 to 4). Lanes 1 to 4 contain A. hydrophila strains with PFGE patterns B and F (lanes 1 and 2) and A. caviae strains with PFGE patterns C and G (lanes 3 and 4). Lanes 5 to 8 and 10 contain A. caviae strains with PFGE pattern A₁, whereas lane 9 contains an A. hydrophila strain with PFGE pattern A. Lane 11 contains molecular size markers (lambda ladder; values to the right are kilobases).