Related Experiment Videos
Hospital green salads and the effects of washing them
E Houang1, P Bodnaruk, Z Ahmet
1Department of Microbiology, Queen Charlotte's and Chelsea Hospital, London.
Abstract:
Each week from April 1989 to February 1990, a plate of green salad prepared in the hospital kitchen was examined microbiologically. Of the 256 plates examined, 51% had total viable counts (TVCs) of greater than or equal to 10(5) colony forming units (cfu) g-1. Staphylococcus aureus was present in 13 samples and Escherichia coli in one sample. No Listeria monocytogenes, Clostridium perfringens or Salmonella spp. were isolated. The effect of washing mustard and cress, cucumber and the different layers of lettuce leaves was examined. Washing the salad by agitating it under running tap water in a colander for 2 min reduced the total bacterial counts by 10-fold. The inner leaves of a lettuce had TVCs less than 10(4)cfu g-1, at least 10-100-fold less than the outer leaves. Cucumber after washing had similar TVCs as after peeling. Five of six samples of mustard and cress had TVCs of at least 10(6)cfu g-1 before washing. As a consequence, mustard and cress was no longer used in our salads.
Insights
Hospital salads frequently exceeded safe microbial limits, with 51% showing high total viable counts (TVCs). Washing reduced bacteria, but inner lettuce leaves and peeled cucumbers were safest, leading to the removal of mustard and cress.
Area of Science:
- Microbiology
- Food Safety
- Hospital Hygiene
Background:
- Microbial contamination of hospital food is a significant concern.
- Ready-to-eat salads can harbor high levels of bacteria.
- Assessing the microbiological quality of hospital-prepared salads is crucial for patient safety.
Purpose of the Study:
- To evaluate the microbiological quality of hospital-prepared green salads.
- To determine the effectiveness of washing procedures on bacterial load reduction.
- To identify salad components with the highest microbial contamination.
Main Methods:
- Weekly microbiological examination of 256 green salad plates over 11 months.
- Quantification of total viable counts (TVCs) and isolation of specific pathogens.
- Assessment of bacterial load before and after washing for lettuce, cucumber, and mustard/cress.
Main Results:
- 51% of salads had TVCs ≥ 10(5) cfu/g; Staphylococcus aureus found in 13 samples, E. coli in one.
- Washing reduced bacterial counts by 10-fold; inner lettuce leaves had significantly lower TVCs than outer leaves.
- Mustard and cress consistently showed high TVCs (≥ 10(6) cfu/g) even after washing, leading to its removal from salads.
Conclusions:
- Hospital-prepared salads frequently present a microbiological risk.
- Standard washing procedures offer partial bacterial reduction.
- Mustard and cress pose a significant contamination risk and should be excluded from hospital salads.