Microbiological examination of salad served with takeaway meals K Williamson, G Allen, F J Bolton FEMS, North West, Preston Date of report: September 2006 Survey Code: 604006 Introduction Mixed salad is frequently served as an accompaniment to Indian meals, doner kebabs, pizzas, burgers and other takeaway meals. The salad may be served from an open container and added to the meal or prepacked and served in a separate bag/container. Ready to eat salad vegetables are generally considered safe to eat by consumers 1 however Environmental Health Officers in Lancashire and Greater Manchester have expressed concern relating to salad handling and storage in takeaway premises. Outbreaks of food poisoning have been caused by the consumption of salad vegetables including two recent outbreaks of Salmonellosis caused by lettuce served with fast foods 2. It was decided to carry out this study with a focus on Campylobacter because of the frequent handling and storage of raw meats including poultry by staff that may also prepare the mixed salads in the same environment. The study was timed so as to include the seasonal May/June Campylobacter epidemiological peak and summer months (May August 2006). Materials and Methods Sample collection This study was carried out as part of the Greater Manchester/Lancashire FOG/FEMS- NW, Preston sampling programme during May September 2006. Samples of mixed salad bagged or loose served as an accompaniment to a main meal were collected by local authority sampling officers from any type of takeaway outlet which also handles raw products. Loose samples were aseptically transferred and prepacked samples packed into food grade bags and transported to the laboratory at 0-8 C. Samples collected in the evening were stored overnight at 0-8 C and transported to the laboratory the following day so as to enable examination within 24 hours of collection. Information relating to the salad including type of meal served with, and whether loose or packaged on the premises, was recorded onto a modified FEMS-NW request form (Appendix 1). Sample Examination A total of 297 samples were submitted by 26 North West local authorities (Appendix 2) to their FEMS-NW testing laboratory (Preston or Carlisle). Samples were examined for aerobic colony count/g (ACC), Enterobacteriaceae/g, E. coli/g, Staphylococcus aureus/g, Listeria spp/g and for the detection of Salmonella/25g and Campylobacter/25g using UKAS accredited FEMS-NW food test methods. KW/KLM (26/06) Page 1 of 7
Microbiology Results Table 1 Microbiology results (n = 297) Detected Not detected <10,<20 10, 10 2 -<10 3 10 3 -<10 4 10 4-10 5 10 5-10 6 10 6-10 7 >10 7 <10 2 20-<10 2 ACC/g 30 C 48h 1 1 11 23 85 93 83 Enterobacteriaceae/g 45 15 44 57 64 49 21 2 E. coli/g 268 11 9 9 0 0 0 0 S. aureus/g 290 5 2 0 0 0 0 0 Listeria monocytogenes/g 296 5 2 0 0 0 0 0 Listeria spp (total)/g 295 1 1 0 0 0 0 0 Salmonella in 25g 0 297 Campylobacter in 25g 0 297 Table 2 Relevant parameters in category 4 of PHLS guidelines 3 Microbiological quality (cfu/g) unless stated Satisfactory Acceptable Unsatisfactory Unacceptable/ Potentially Hazardous Aerobic colony count <10 6 10 6 - <10 7 =10 7 N/A Enterobacteriaceae* <100 100 10 4 =10 4 N/A E.coli <20 20 - <100 =100 N/A S.aureus <20 20 - <100 100 - <10 4 =10 4 Listeria monocytogenes <20 20 - <100 N/A =100 Listeria spp (total) <20 20 - <100 =100 N/A Salmonella Not detected in 25g Detected in 25g Campylobacter Not detected in 25g Detected in 25g * Not applicable to fruit and salad vegetables Table 3 Microbiology results according to Cateogry 4 PHLS RTE food guidelines 3 (excluding Enterobacteriaceae) Satisfactory Acceptable Unsatisfactory Unacceptable/ potentially hazardous Loose salad (n=271) 94 (35%) 96 (35%) 80 (30%) 1 (<1%) Prepacked salad (n=26) 12 (46%) 6 (23%) 8 (31%) 0 TOTAL (N=297) 106 (36%) 102 (34%) 88 (30%) 1 (<1%) KW/KLM (26/06) Page 2 of 7
Table 1 demonstrates that the pathogens Salmonella and Campylobacter were not detected in any of the 297 samples examined. Only 2 samples (0.7%) produced unsatisfactory Staphylococcus aureus counts, but 18/297 (6%) E. coli counts were unsatisfactory. Only one sample (0.3%) produced an unsatisfactory Listeria spp count (100/g) which was L. monocytogenes Serotype 1/2a, and therefore of an unacceptable/ potentially hazardous quality. Table 1 also demonstrates a wide range of ACC and particularly Enterobacteriaceae results with 83/297 of the ACC s (28%) being unsatisfactory. Enterobacteriaceae were present at 10 4 cfu/g or more in 136/297 (46%) of samples tested (Table 1). There are however no guidelines for Enterobacteriaceae in salad vegetables because salad including lettuce often carry high levels of these organisms as part of their normal flora. Table 3 indicates more prepacked salad (46%) attained the satisfactory microbiological category compared with 35% of loose salad samples. Discussion Cross contamination of fresh produce can occur in food premises. Open foods such as loose salad served from trays are at a greater risk of contamination from the environment than bagged salads which are sometimes served with Indian meals. Although only 26 samples in this study were prepacked, 46% attained the satisfactory microbiological quality using category 4 of the PHLS guidelines 3 compared with 35% of the loose salad samples. Table 3 indicates no difference between the incidence of unsatisfactory results from loose or prepacked samples but the number of prepacked samples was low. Unsatisfactory results due to Staphylococcus aureus (2), E. coli (18), Listeria (1) were found in 19/271 loose (7%) samples and 2/26 (7.6%) prepacked samples. However because bagged salads are prepared in house in the same environment as the handling of raw products including chicken HACCP principles must be adhered to. Fifteen (58%) of the bagged samples were served with Indian takeaway meals. The lack of any heating step prior to consumption places the emphasis on high quality ingredients, hygiene preparation, appropriate shelf life, and correct storage for maintaining product safety. In particular, food businesses must ensure that working surfaces are clearly defined for handling raw products and ready to eat foods. Overall the results from this study indicate that 70% of the samples were of acceptable microbiological quality according to category 4 of the PHLS guidelines, the ACC was the parameter often associated with unsatisfactory results accounting for 83 of the 297 (28%) unsatisfactory samples. Although a high ACC does not constitute a risk to health, it may sometimes indicate a general lack of hygiene, and may also reflect the effect of the high seasonal temperatures during the study sampling period. Improving temperature control, shelf life, or prewashing may be factors to be considered in order to control potential microbiological risks highlighted by a unsatisfactory ACC. Salad vegetables carry a natural non-pathogenic epiphytic microflora, the majority of which consists of Gram-negative bacteria belonging to either the Enterobacteriaceae or Pseudomonas group. The level of these organisms depends on seasonal and climatic variation and may range from 10 4 10 8 4. The findings from this study (46% KW/KLM (26/06) Page 3 of 7
of samples >10 4 /g Enterobacteriaceae) support previous studies 5,6 and show that high levels of Enterobacteriaceae are normal in salad vegetables although as with the ACC, Enterobacteriaceae levels of >10 7 /g must indicate a risk factor needing control. Levels of faecal indicator organisms such as E. coli are therefore a better indication of contamination and hygienic quality. The incidence of E. coli in this study (10%) is similar to the findings in a US study of vegetable salads collected from food service facilities (12%) 7. Levels of E. coli in ready to eat salad however should be kept to a minimum and it is of concern that 6% of samples in this study had levels of >100/g, compared to 3% in a recent LACORS study of ready to eat prepared salad from catering and retail 6. Although only sample produced a unacceptable/potentially hazardous result (L. monocytogenes 100/g) it must be emphasised that transmission of pathogenic bacteria such as Salmonella, Campylobacter and Listeria monocytogenes to salad vegetables remains a risk. Contamination may occur at production and washing the salad before serving is recommended to control this risk. Contamination may also occur in the kitchen during washing/preparation/storage/serving and the necessary food safety controls need to be in place and adhered to. Conclusion Based on category 4 of the PHLS guidelines for some ready to eat foods 3, 30% of samples examined in this study were unsatisfactory, predominantly caused by high ACC s. High ACC s may reflect poor temperature control, shelf life problems or the need to wash the salad before serving/prepackaging. Salmonella spp and Campylobacter spp were not detected in any of the samples. Only one sample produced a unacceptable/potentially hazardous result due to L. monocytogenes. However it is of concern that 6% of samples had unsatisfactory levels of E. coli further emphasising the need for risk assessment. A wide range of Enterobacteriaceae count results with 46% of samples being >10 4 /g support previous study findings, and indicate that high levels of Enterobacteriaceae are normal in minimally processed salads. Therefore Enterobacteriaceae should not be used as an indication of microbiological quality in the examination of salad vegetables. Salad prepackaged on the premises produced more results (46%) of satisfactory microbiological quality than loose salad (35%). However the number of prepacked salads examined was too low (26) to draw meaningful conclusions. KW/KLM (26/06) Page 4 of 7
References 1 Consumer attitudes to Food Standards, FSA, Final Report. London: Taylor Nelson Sofres pce, 2001. 2 Long SM, Adak GK, O Brien, General outbreaks of infectious intestinal disease linked with salad vegetables and fruit, England and Wales, 1992-2000. Comm Dis Pub Health 2002; 5: 101-105. 3 Guidelines for microbiological quality of some ready to eat foods sampled at the point of sale, PHLS ACFDP Working Group CDPH, Sept 2000, Vol 3, No3: 163-167. 4 Lund BM. Ecosystems in vegetables foods. J. Appl. Bact 1992; 73 (Supp 21): 1155-1355. 5 Nguyen C and Carlin 1994. The microbiology of minimally processed fresh fruits and vegetables. Crit Rev Food Sci Nutr 34: 371-401. 6 SK Sagoo, CL Little and RT Mitchell. The microbiology of open ready to eat prepared salad vegetables from Catering and Retail Premises. LACORS/PHLS Report 2002. 7 Lin C-M, Fernando SY. Occurrence of L. monocytogenes, Salmonella, E. coli in vegetables salads. Food Control 1996; 7: 135-140. KW/KLM (26/06) Page 5 of 7
APPENDIX 1 Modified FEMS-NW request form for Survey 604006 KW/KLM (26/06) Page 6 of 7
APPENDIX 2 List of Participants Authority Number of samples Allerdale 7 Carlisle City 0 Copeland 0 Eden 4 CUMBRIA TOTAL 11 Barrow 12 Blackburn 4 Blackpool 14 Burnley 11 Chorley 17 Fylde 8 Hyndburn 0 Lancaster 19 Pendle 0 Preston 14 Ribble Valley 4 Rossendale 7 South Lakes 15 South Ribble 3 West Lancs 8 Wyre 20 LANCASHIRE TOTAL 156 Bolton 14 Bury 3 Manchester 18 Oldham 18 Rochdale 3 Salford 16 Stockport 16 Tameside 16 Trafford 5 Wigan 21 GT MANCHESTER 130 TOTAL TOTAL FOR CUMBRIA, LANCASHIRE AND MANCHESTER 297 KW/KLM (26/06) Page 7 of 7