REPORT OF THE GREATER MANCHESTER/LANCASHIRE/PHLS LIAISON GROUP
SURVEY ON THE MICROBIOLOGICAL EXAMINATION OF LOOSE POTATOES AT
RETAIL
K. Williamson, G. Allen, F. J. Bolton, PHLS North West FESL – Preston PHL
Date of Report June, 2001
Survey Code No. 104004
Introduction
Potatoes may be contaminated with any of the organisms present in the soil in which they are grown.
The cleanliness of irrigation water also plays an important part in the extent of contamination. In
countries where polluted water is used for irrigation and animal and human excreta used for
fertilisation, there is an increased risk of contamination with enteric pathogens including bacteria,
viruses and parasites.
Potatoes either imported or local are often available as a self service loose product from retail outlet
displays or direct from the sack.
Hence, the purpose of this survey was to determine whether the handling of loose soiled potatoes at
retail could be a potential risk to health.
Additionally the survey aimed to determine the extent to which retail outlets provide some form of
hand protection for the handling of potatoes.
Materials and Methods
Sample Collection
This survey was carried out as part of the Greater Manchester FLG/Lancashire FOG/Preston PHL
sampling programme during January – May 2001. The samples comprised loose soiled potatoes of
any type. The samples were collected from various retail outlets and placed directly into food grade
plastic bags, from the sack or display unit. Information relating to the premises, sample details and in
particular the country of origin and availability of gloves or other form of hand protection at the point
of service was recorded onto a modified PHL food request form.
Sample Examination
A total of 267 potato samples were submitted from 25/26 authorities in Greater Manchester and
Lancashire as detailed in Appendix 1.
Samples were rinsed in a standard volume of diluent so as to remove soil deposits and to produce a
well mixed suspension.
The suspension was examined for the presence of Salmonella,
Campylobacter, E. coli O157 and enumerated for Listeria spp and E. coli using UKAS accredited
106751348
Page 1 of 4
PHLS NW FESL food methods. A standard volume of suspension was also concentrated for parasites
and examined microscopically for the presence of ova and cysts (parasites) by the enteric section of
Preston PHL.
Results
Table 1.
Microbiology results of loose potato (n = 267)
<20
20-<102
102-<103
E. coli/ml
261
5
1
Listeria monocytogenes/ml
265
2
0
Listeria spp (total)/ml
264
3
0
Not
detected
Detected
Salmonella spp/25ml
267
0
Campylobacter spp/25ml
267
0
E. coli O157/25ml
267
0
Cysts, ova, parasites
267
0
Results expressed per ml/25ml of standardised volume of potato rinse fluid.
Table 2.
Table 1 demonstrates that E. coli was isolated from only 6/267 (2.2%) and Listeria spp from 5/267
(1.9%) of which only 2/267 (0.7%) were Listeria monocytogenes. Salmonella, Campylobacter,
E. coli O157 or parasites were not detected from any of the samples examined.
Discussion
Previous research has indicated that the survival period of Salmonella in soil on the surface of
potatoes is 40 days, whereas survival in the soil is 72 weeks (1).
It is therefore possible because the majority of samples examined in this study were ‘old potatoes’ that
the exposure time to atmospheric conditions may be well in excess of 40 days and therefore the
viability of organisms may have been lost. It is interesting to note that 5/6 E. coli counts were derived
from new potatoes which were imported from Egypt. Hence a survey of new potatoes, particularly
local new potatoes with a minimum transport and storage time before retail, may prove to be a useful
supplementary study. It may also be useful to carry out such a survey in relation to the seasonal
trends of Campylobacter and E. coli O157
From the microbiological results of this survey no evidence was established to enforce the provision
of gloves for handling loose potatoes.
106751348
Page 2 of 4
Questionnaire Results
(1)
Is hand protection available for handling potatoes?
Yes
No
Not answered
157 (60%)
103 (40%)
7
Of the 157 premises providing hand protection for the customer at the point of service, 148
provided bags to be used on the hand, 8 gloves and 1 metal scoop.
(2)
What is the country of origin?
UK
Imported
177 (66%)
90 (34%)
The countries of origin are available as raw data but not considered of significance in this
study.
Conclusion

Salmonella, Campylobacter, E. coli O157 and parasites were not detected from any of the samples
examined.

The very low recovery and numbers of the indicator organisms E. coli and Listeria spp and the
absence of pathogens suggest loss of viability which may be related to time period between
harvesting and retail. The time period is longer for imported and ‘old potatoes’ hence a study of
fresh local ‘new potatoes’ may prove to be of interest.

The 60% of premises providing some form of hand protection at the point of service indicates
good basic hygiene education. The availability of hand protection is considered a good practice
and should be encouraged because of the potential association of enteric pathogens with soil.
Future work

Further survey of fresh local and imported new soiled potatoes.
References
(1)
The Microbiology of Safe Food, Stephen J Forsythe, Blackwell 2000.
106751348
Page 3 of 4
Appendix 1 - Survey Participants
Authority
Number of samples
tested
Barrow
8
Blackburn
0
Blackpool
12
Bolton
11
Burnley
9
Bury
9
Chorley
15
Fylde
12
Hyndburn
9
Lancaster
12
Manchester
12
Oldham
3
Pendle
6
Preston
9
Ribble Valley
11
Rochdale
6
Rossendale
11
Salford
9
South Lakes
16
South Ribble
9
Stockport
15
Tameside
12
Trafford
12
West Lancs
15
Wigan
12
Wyre
12
TOTAL
267
106751348
Page 4 of 4