Campylobacter was isolated in 44 (80%) of the water samples and 10 (11%) of the watercress
samples. All of the sites had Campylobacter present in the growing waters and except for
Manaia Road Drain, Campylobacter was present in the growing waters at each site on three or
more occasions. Campylobacter appeared to be uniformly present in waters in rural and semi�urban and urban catchments. Although the Golf Course site had the consistently lowest E. coli
levels, Campylobacter was still present in three out of five samples. All sites were considered
unsuitable for gathering watercress for consumption (unless boiled) due to the presence of
Camplyobacter in the growing waters.
The presence of Campylobacter on 11% of the watercress samples is of public health
significance. Campylobacter has been shown to survive long enough on Ready To Eat (RTE)
produce to cause infection (Beuchat, 1996). The Microbiological Reference Criteria for Food
(5.8a) for cooked ready-to-eat foods is 0/10gm Campylobacter.
As Campylobacter was found in growing waters at all the sites it appeared to have a wide
distribution across all catchment types. This would be expected as Campylobacter is excreted
in the faeces of a wide range of mammals (e.g. humans, sheep, cattle, goats), and birds
(poultry often being implicated) (MfE, 1999).
For example, in a survey conducted by Gill and Harris (1982) in New Zealand,
Campylobacter fetus subsp. Jejuni were detected in the faeces of calves and sheep. Calves
were more likely to be infected with Campylobacter than adult cattle with 50% of the 50
faeces samples from unweaned calves containing between 100 - 5,000 (mean 1.6x103
) cfu
Campylobacter/g faeces whereas the organism was not isolated from any of the 75 faecal
specimens from adult cattle. Conversely, adult sheep were infected more than lambs with
respective isolation rates of 14% (10/71) and 2.4% (1/42). Thermophilic Campylobacter
species were recovered from 22% of 273 dairy cows, with the highest incidence in autumn
(Fakir, 1986).
4.1.2 E. coli
All the watercress and growing water samples at each site showed variable levels of E. coli
contamination. Although there are no applicable standards to determine safety of growing
waters, most sites showed high levels of E. coli in the water with only the Golf course site not
30
exceeding 103
(MPN/100ml) on any occasion. High E. coli counts would be expected in slow
moving streams where watercress grows in sufficient quantities for collection.
Although in this study the Microbiological Reference Criteria (salads) are only used as a
comparison and not as a measure of suitability for safe consumption, of the ten sites
(excluding Waiwhetu Stream), none of the watercress samples were acceptable on all
occasions, six sites were non-complying and four were marginally acceptable. Little et al.,
(1997) describes the results of a large salad survey in England and Wales in which 2552
samples were examined. The survey used the same limits that were used in this study (i.e. E.
coli, n=5, c=2, m=102
, M=103
). The survey found only 1% of salads had E. coli counts of 102
cfu or more per g. In this study, 46% of watercress samples had E. coli counts of 102
cfu or
more per g. This indicates significant faecal contamination of watercress from contaminated
growing waters.
While it is not possible from the tests used to know whether E. coli are of human, animal or
avian origin, all of these species can act as carriers of micro-organisms that can cause human
disease. If faecal contamination (as indicated by E. coli results) is present on watercress then
human pathogens may also be present posing a risk of infection. The presence of any enteric
pathogen on Ready To Eat (RTE) vegetables is a major food safety concern. Pathogens such
as Salmonella, Campylobacter, Giardia, Cryptosporidium and specific human viruses are
potential contaminants of watercress especially in rural situations, where livestock can carry
and excrete these pathogens.
Giardia and Cryptosporidium are protozoan pathogens widespread in the environment and
New Zealand surface waters (Ball and Till, 1998). Humans and a wide range of domestic and
feral animals can carry these parasites and when infected can excrete high numbers of
cysts/oocysts. Water transmission of infection to humans is well recognised (Ball and Till,
1998). However, E. coli concentrations do not correlate well with the more persistent
protozoan pathogens and therefore have limited use for predicting health risk from these
groups of organisms, especially when faecal indicator concentrations are low (Ball & Till,
1998b). The large numbers of protozoan parasites in New Zealand surface waters may
increase this problem (Ball & Till, 1998b).
Viruses such as Adenoviruses, Enteroviruses, Rotaviruses, and Norwalk viruses can cause a
wide range of diseases including respiratory infections, skin rashes, conjunctivitis and gastro�enteritis. They can be transmitted via ingestion or contact with polluted water (Ball and Till,
1998). write the main points only from the above infofrmation
- Campylobacter was found in 80% of water samples and 11% of watercress samples, making all sites unsuitable for watercress consumption without boiling
- Campylobacter is excreted in the feces of mammals and birds, indicating widespread distribution in all catchment types
- E. coli contamination was present in all watercress and growing water samples, with high levels in most sites except the Golf course site
- Faecal contamination on watercress poses a risk of human pathogen presence and infection
- Giardia, Cryptosporidium, and other protozoan pathogens are widespread in New Zealand surface waters and can be transmitted to humans via water
- Viruses such as Adenoviruses, Enteroviruses, Rotaviruses, and Norwalk viruses can cause various diseases and can be transmitted via polluted water