The Sampling Food Contact Surfaces

Published Date: 02 Nov 2017

Sampling food contact surfaces is a complex problem, and the results depend on many factors, including the type of surface, the sources of contamination, the cleaning solution, and the temperature. The accuracy and reproducibility of all sampling methods are reduced when the numbers of bacteria on the surface are low. Some differences between methods are probably due to an uneven distribution of bacteria on the surface. The type of surface markedly influenced the cleaning results. For this study, nineteen selected premises were tested/studied (Ten replicate surfaces were tested; stainless steel, marble and wood, with adjacent areas being sampled before and after cleaning). The results of these studies indicate that three of ten stainless steel surfaces were contaminated before cleaning the surfaces and no surface was contaminated after cleaning, which means that stainless steel surfaces were more easily cleaned. Furthermore, three out of ten marble surfaces were contaminated before cleaning and one surface was contaminated after cleaning the surfaces, which means marble surfaces were easily cleaned but using the wrong cleaning products and the wrong cleaning techniques can damage the marble because marble is a calcium-based natural stone which is highly sensitive to acidic materials (Marble Institute of America, 2012). Stainless steel resists impact damage but is vulnerable to corrosion, while marble surfaces are exposed to deterioration and may develop surface cracks where bacteria can accumulate (Leclercq and Lalande, 1994). Wood surfaces were particularly difficult to clean. As has been found in other studies, the difficulty in cleaning wooden surfaces in comparison to stainless steel and marble surfaces is due to the physical structure of wood which can absorb moisture and retain bacteria (Carpentier, 1997). Six out of ten wood surfaces were heavily contaminated before cleaning and three surfaces remained contaminated after the cleaning methods. The difficulty in cleaning was related to the amount of surface damage and it is best to avoid this type of surface. Nowadays, there is a need to change the use of wood as a medium for food contact because it allows a high level of bacteria attachment. The cut on the edge of wood surface that occur by the knife allow food residues to accumulate, thus creating a suitable medium for biofilm adherence and making cleaning difficult. A proper surface is essential for avoiding scratched and cracks where organic material could accumulate thereby forming biofilms.

Food contact surfaces sometimes harbour foodborne pathogens (Bloomfield and Scott 1997). As a result, these surfaces may pose a constant risk of transferring contaminants. Therefore, all such surfaces should have antimicrobial treatment prior to use (Bloomfield and Scott 1997). The results of this study further confirm the necessity for using the appropriate food processing area sanitizing product for the specified food contact surface because contact surfaces may attain high levels of bacteria instead, which can contaminate food if it is not properly cleaned with a certain frequency, becoming a potential risk to cause cross contamination. Using products in a manner for which they are intended will help ensure microbial populations will be reduced to levels considered safe, and thus minimize the likelihood of foodborne illness. On the other hand, using agents with unproven antibacterial actions may lead to a false sense of safety. Hypochlorite solution, used for cleaning the surfaces in this study, was considered to be effective against the tested foodborne pathogens. With reductions reported for all organisms, it can be concluded that bleach (hypochlorite solution) is an appropriate sanitizer (Cozad and Jones 2003). Similarly, the contact surfaces that were disinfected with hypochlorite solution showed better microbiological performance. It has been found that rinsing with water and domestic chemical cleaners does not ensure total elimination of bacteria from food contact surfaces (Cogan et al. 2002). The use of hypochlorite solution to clean the surfaces has been found in other studies to be effective to reduce bacteria and pathogens that require a short to moderate contact time to acceptable limits (Williams et al. 2005). Although cleaning was carried out under observation and at times when it may not normally have been done, there was no evidence that attitudes towards cleaning methods markedly changed during the study.

Bacterial contamination of food processing areas is common. Studies of the domestic environment by Josephson et al. (1997) and Rusin et al. (1998) indicate that micro-organisms, including some pathogenic species, are commonly found in all areas of the home environment. As a result, in the domestic environment, foodborne illness caused by cross contamination is a major issue. According to a survey done by Scott et al. (2000), of 200 homes studied/tested it was found that 90% of the food processing areas were contaminated with Pseudomonas and 69% of domestic kitchens were contaminated with Enterobacteriaceae (Kagan, et al. 2002). The Enterobacteriaceae spp. isolated in this study from the three types of contact surfaces included Klebsiella, Enterobacter and Proteus. Although these species are not normally pathogenic, they must be regarded as indicators of poor hygiene. Other species which were isolated included Staphylococcus aureus and Pseudomonas aeruginosa. Staphylococcus aureus can cause food poisoning when a food handler contaminates surfaces or equipment on which food is prepared and when food not kept at the correct temperature. These bacteria multiply rapidly at room temperature to produce a toxin which is called an enterotoxin that causes inflammation or gastroenteritis of the lining of the intestinal tract. On other hand, Pseudomonas aeruginosa is widely distributed in nature and is common in moist environments in food processing areas. In many foods, Pseudomonas aeruginosa are regarded as potential spoilage microorganisms (Riemann and Cliver, 2006). To prevent the growth of this type of bacteria, proper hand washing techniques and proper sanitation of food contact surfaces must be ensured (Food Safety.gov, 2012).

Yersinia enterocolitica was also isolated from the marble surface before the cleaning stage. Although less frequently, Yersinia enterocolitica is transmitted through the fecal–oral route, resulting from improper hand washing and poor hygiene (Sreedharan et al, 2012). Failure to remove bacteria from a food contact surface can greatly increase the risk of foodborne illness by cross contamination. When bacterial colonies dry, a significant reduction of recoverable organisms results (Scott and Bloomfield, 1990).

Surface roughness and hydrophobicity can significantly affect the attachment of an organism. The roughness of a surface increases the surface area available for colonization. Organisms adhere to hydrophobic surfaces, such as plastics, better than hydrophilic surfaces, such as stainless steel (Lee, et al. 2007). This is due to the hydrophobic surface features present on the cell (Doyle, 2000).

The survival of Staphylococcus aureus and Escherichia coli on stainless steel surfaces is indicated in Table No.13. Two different contamination levels were used for the experiments with Staphylococcus aureus and Escherichia coli. The results indicated that the survival of bacteria decreased rapidly, especially when the initial numbers on the surfaces were low. Staphylococcus aureus could be detected on dry surfaces for at least 12 hours at a high level of contamination, while at low levels, the cells decreased below the detection limit (3.8 x 103 CFU/100 cm2) within 6 hours after contamination. For Escherichia coli, the viable cells could still be detected after 6 hours when a high initial level was present, but at low contamination levels, the count of Escherichia coli within 2 hours was below the detection limit.

Microorganisms can attach to the food contact surface within hours or they may take days depending on surface characteristics (Cliver and Riemann 2002). Depending on the organism, nutrient availability may play an important role in the adhesion rate of the bacteria. When surfaces are dry, minimal bacterial growth and survival can be attributed to reduced bacterial attachment and lack of available nutrients (Kusumaningrum, et al. 2003). Surface soiling then may preserve viability (Scott and Bloomfield 1990). Scott et al. (1990) found that on soiled surfaces, Gram positive and some Gram negative bacteria were recoverable in significant numbers for 4 hours and up to 24 to 48 hours in some cases. High numbers of bacteria can be transferred to hands, dish cloths and food from contact with the contaminated surface (Scott and Bloomfield 1990).

This study has highlighted that the pathogens may remain viable on dry stainless steel surfaces and presents a (re)-contamination risk for long periods of time. Moreover, cross-contamination from food contact surfaces could lead to contamination of food; therefore, attention needs to be given to supervision and training to ensure appropriate hand washing and proper cleaning procedures to reduce or eliminate cross-contamination.