Analysis of Cytotoxicity and Invasiveness of Heterotrophic Plate
Count Bacteria Isolated from Drinking Water on Blood Media
THE ISSUE
An issue affecting all drinking water but in particular
importance to bottled
water, is the possible adverse health effects of naturally occurring
microbes,
collectively called heterotrophic plate count (HPC). HPC, are present
in all bot-
tled waters, even though the water may be subject to ozonation. The
small
numbers of HPC that survive ozonation multiply within the bottle
to achieve
concentrations in the thousands per ml. Tap water has fewer HPC per
ml
because it generally has a disinfection residual. In the late 1980's,
Dr. Pierre
Payment (University of Quebec) presented data to indicate that HPC
bacteria is
responsible for gastroenteritis.
RESEARCH STRATEGY
A laboratory based study was conducted by Dr. Stephen Edberg (Yale
University) to isolate HPC from tap water and bottled water products.
The HPC
were isolated on blood agar and then subjected to a large battery
of tests to
determine if they possessed characteristics associated with human
infection.
These characteristics are known as virulence factors.
MAJOR FINDINGS AND SIGNIFICANCE
HPC bacteria are naturally present in all aqueous environments.
These bacte-
ria undergo multiplication cycles in drinking water, especially
in closed con-
tainers (bottled water) or in tap water when chlorine levels
are dissipated, such
as in dead ends in water mains or household plumbing. A study
was under-
taken to estimate the health risk from these naturally occurring
bacteria by the
determination of cytotoxicity and invasiveness in a human
enterocyte cell
line. HPC bacteria were isolated from bottled and tap water
samples by enu-
merating them under physical and chemical conditions analogous
to human
physiology. All HPC bacteria were examined at both log and
lag phase of their
growth cycles. Bacterial broth supernatants were also tested
to serve as criti-
cal negative controls. Naturally occurring HPC bacteria demonstrated
low
invasiveness and cytotoxicity with more than 95 of isolates
showing equiv-
alency to broth supernatant. When showing either invasiveness
or cytotoxici-
ty, only a small number of cells from the culture were positive.
Edberg, S.C., Kops, S., Kontnick, C., and Escarzaga, M.,
Analysis of Cytotoxicity and
Invasiveness of Heterotrophic Plate Count Bacteria (HPC)
Isolated from Drinking Water on
Blood Media, Journal of Applied Microbiology, 82:445-461
(1997).
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