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Appl. Environ. Microbiol., Jul 1997, 2708-2715, Vol 63, No. 7
I Kuhn, G Allestam, G Huys, P Janssen, K Kersters, K Krovacek and T Stenstrom
The Aeromonas populations in 13 Swedish drinking water distribution
systems, representing different treatments, were investigated. From each
system, water samples were collected four times during the period from May
to September 1994 from raw water and water after treatment and at two to
five sites within the distribution system. In total, 220 water samples were
collected. From samples containing presumptive Aeromonas, up to 32 colonies
were analyzed by the PhenePlate Aeromonas (PhP-AE) system, which is a
highly discriminating biochemical fingerprinting method. Selected isolates
from different phenotypes (PhP types) were further identified by the API 20
NE system and by gas-liquid chromatography analysis of fatty acid methyl
esters (FAMEs). Selected isolates were also assayed for their potential to
produce hemolysin and cytotoxin and for their ability to adhere to human
intestinal cells. In total, 117 water samples (53%) contained presumptive
Aeromonas which numbered up to 10(sup6) CFU/100 ml in raw water and up to
750 CFU/100 ml in tap water. Among the 2,117 isolates that were subjected
to typing by the PhP-AE system, more than 300 distinct PhP types were
found, of which the majority occurred only sporadically. Raw (surface)
water samples usually contained many different PhP types, showing high
diversity indices (Di) (median Di = 0.95). The Aeromonas populations in
samples collected from within the distribution systems were less diverse
(median Di = 0.58) and were often dominated by one major PhP type that was
found on several sampling occasions. Seventeen such major PhP types could
be found and were represented in 1,037 isolates (49%). Identification by
API 20 NE and FAME analysis revealed that most of the major PhP types were
Aeromonas hydrophila or belonged to unidentified Aeromonas species.
Hemolysin and cytotoxin production was observed in most major PhP types
(representing 87 and 54% of the assayed isolates, respectively), and
adherence was found in 89% of the isolates that produced cytotoxin. Thus,
the data presented here show that although raw water may contain very
diverse Aeromonas populations, the populations seemed to be remarkably
stable within the studied water distribution systems, and that some
potentially pathogenic Aeromonas strains could persist for several months
in drinking water.
Copyright © 1997, American Society for Microbiology
Diversity, Persistence, and Virulence of Aeromonas Strains Isolated from Drinking Water Distribution Systems in Sweden
Microbiology and Tumor Biology Centre, Karolinska Institute, S-171 77 Stockholm, Swedish Institute for Infectious Disease Control, S-105 21 Stockholm, and Department of Veterinary Microbiology, Swedish University of Agricultural Sciences Biomedical Centre, S-751 23 Uppsala, Sweden, and Laboratorium voor Microbiologie, Universiteit Gent, B-9000 Ghent, Belgium
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