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Hand washing Practical - How clean are your Hands?

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Hand washing Practical How clean are your Hands? Aims: The aim of this experiment is to gain an understanding of the theory and practical application of food safety in relation to microbiological contamination potential from ineffectual hand washing controls. Introduction: The surface tissues of humans are in constant contact with environmental organisms and they become readily colonised by various microbial organisms. The natural flora of humans is exceedingly complex and consists of approximately >200 spp. of bacteria, a few simple eukaryotic fungi and protests and some methanogenic Archaea of the gastro-intestinal tract. This make up varies depending on various factors including age, sex, stress levels and even the nutritional intake/diet of the individual as well as the usual critical factors for microbial growth including temperature and available water, &c, &c. The average human adult has an estimated 2m2 of skin tissue, with a calculated estimate of bacterial load is expected in the region of 10 x1012 bacteria1. In the whole, most of these micro organisms are non-pathogenic and can be considered as commensal, but when considering food safety it is the pathogenic, or harm causing organisms, which are in consideration for this experiment. Method: Apparatus: * Petri Dishes (plastic, disposable; dimensions:100x15ml) * Bunsen Burner * Sterile Nail Brushes * Alcohol, bactericidal liquid soap * China-graph/marker pen * Sticky tape * Hand paper towels/ hot air dryer * Incubator, 35 � 1�C * Autoclave * Circulating water bath, for tempering agar, thermostatically controlled to 45 � 1�C * Commercial sodium hypochlorite solution, about 5% NaOCl (bleach) ...read more.


In order to state that any deductions are true and accurate, the experiment would have to be repeated many times to give us greater certainty using a higher degree of confidence. This point aside, the first assumption that can be drawn from the results is that the first plate (i.e. the 'Dirty' plate) can be seen as having the greatest APC number, and therefore the highest bacteriological load. This would hold true with what our initial beliefs are, prior to the experiment, in that un-washed hands hold a great number of microbiological organisms, and as such have the greatest potential for cross-contamination and food poisoning. Reviewing the results for the hand washing, it can be seen that both methods of hand washing are effective at reducing the biological load, to a greater or lesser extent, but it is the apparent best method that is surprising. It would appear that the best method for the cleaning and drying of hands is with the use of paper towels, over the use of hot air blow-dryers. This would be initially seem counter-intuitive at first, but on further examination, is not as surprising as at once thought. When you consider the media of the two methods in question, this goes part way into explaining the difference. Firstly, the paper towel; the towel is a piece of wood-pulp paper substrate that is cut into individual sheets. Because the towel is designed to absorb water, it has a very low amount of available water (Aw) ...read more.


By selectively identifying these organisms from the initial inoculate, or future plates, it may be beneficial because certain species of bacterium can be considered as indicator species. For example, S. aureus can sometime indicate that persons have been touching their mouths/nose/skin or hair and not washing their hands after each event. E. coli may indicate that persons are not washing their hands after using the lavatory. By using these methods it is possible to monitor the effectiveness of the cleaning system that is in place, as well as the hand washing procedures. It also goes some way to help to provide a 'due-diligence' defence in relation to any alleged food poisoning incidences. Appendix: 1: Source:- The Bacterial Flora of Humans, p5/6 'The Composition of Normal Flora'; Kenneth Todar, University of Wisconsin (Dept of Biology); 2002 2: Media preparation:- Beef Extract 3g Peptone 5g Agar 15g Distilled Water 1L * Heat to boiling to dissolve ingredients * Dispense into tubes of flasks * Autoclave 15min @ 121oC * pH = 6.8 � 0.2 * Pour constant amount of sterile agar @ 60-70oC (e.g. 15ml/100mm plate) * Allow to solidify on a level surface * Place solidified agar plates into poly-bags and seal (store until use @ 0-4.4oC) * Bring to room temp, prior to inoculation Source:- M112 Nutrient Agar, Bacterial Analytical Manual (8th Ed, Revision A), FDA/CFSAN, 1998 3: Source:- Aerobic Plate Count, Bacterial Analytical Manual (8th Ed, Revision A), FDA/CFSAN, 1998 4: Source:- Micro Search Laboratories Ltd Units 3-7 Scotts Trading Complex Mytholmroyd Halifax HX7 5LH FdSc Food Manufacturing Management Unit 3: Food Microbiology Steve Norman - 1 - ...read more.

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