4. Discussion
The purpose of our study was to verify our hypothesis that in order to obtain clean crockery, it is important to get the crockery mechanically clean.[11.] We used international standard test soils (A, [4.] B, [4.] C [5. and 6.]) and test soils with increased adherence (I, II, III). The choice of soil with increased adherence was also based on suggestions from other international standards. [12. and 13.] Test soils A and C were easily removed in dishwashers. Test soil B was more difficult and demanded a larger flux of water in the cleaning process, which is obvious from our results ( Figure 4). [14. and 15.]
In the professional kitchen the soil is more adhesive as in test soils I, II and III. These types of soil will not be removed in a dishwashing process for normally soiled crockery, (Figure 5). There is always a risk of cross-contamination with soil residues. [8. and 14.] In test soil C, the bacteria were moved from the metal test plates to the wash-water in the dishwater tank of the machine. [15.] Wash-water samples from other dishwashing machines in hospital kitchens and restaurant kitchens have shown bacterial concentrations in the order of 103–10[4.] cfu/mL.[16.]
From the experiment with test soil C, the result showed that no bacteria remained on the metal test plates after a normal dishwashing process. However, using test soils I and II with the bacterial load, there was hardly any decrease in bacterial activity due to the dishwashing process (Table I). This suggests that if the soil contains bacteria and is not properly removed, bacteria survive and are still viable in spite of the high temperature, of the dishwashing process. The dishwater used in these tests has comparable data concerning temperatures and cycle times to other dishwashers used in hospital kitchens. [3., 7., 8. and 17.] The thermal resistance test verifies that E. faecium can survive at much higher temperatures than is achieved in dishwashers.[3., 7. and 15.] Several other types of bacteria survive the temperatures produced by standard dishwashers and could cause serious infections in hospitals. [1., 14. and 17. J. Francis and S.W.B. Newsom, Evaluation of dishwashing machines in four hospitals. J Hosp Infect 9 (1987), pp. 294–297. Article | PDF (250 K) | View Record in Scopus | Cited By in Scopus (5)17.]
Another risk is cross-contamination from wash-water to crockery. Our results show, that in all test soils I, II and III cross-contamination was detected (Figure 6). However, on the plates that were visually clean, no cross-contamination was found. There is an obvious risk for the spread of infection through improperly cleaned crockery. Having survived, the kitchen provides suitable temperature and humidity for bacterial growth. [3.]
Porcelain plates and other types of crockery are used in wards and staff canteens all over the hospital. If the crockery is contaminated by bacteria from any ward, cross-contamination can occur in the cleaning process of the dishwashers. Bacteria could then be spread to other wards. To reduce the risk of spread, it is necessary to ensure that the crockery is mechanically cleaned.