Assessment of a regulatory sanitization process in Egyptian dairy plants in regard to the adherence of some food-borne pathogens and their biofilms

Abstract

Food-borne pathogens may develop certain strategies that enable them to defy harsh conditions such as chemical sanitization. Biofilm formation represents a prominent one among those adopted strategies, by which food-borne pathogens protect themselves against external threats. Thus, bacterial biofilm is considered as a major hazard for safe food production. This study was designed to investigate the adherence and the biofilm formation ability of some food-borne pathogens on stainless steel and polypropylene surfaces using chip assay, and to validate regular sanitizing process (sodium hypochlorite 250 mg/L) for effective elimination of those pathogens. Sixteen pathogenic bacterial strains, previously isolated from raw milk and dairy products at Zagazig city, Egypt (9 Staphylococcus aureus, 4 Cronobacter sakazakii and 3 Salmonella enterica serovar Typhimurium), were chosen for this study. Strains showed different patterns of adherence and biofilm formation on tested surfaces with minor significance between surfaces. The ability of sodium hypochlorite to completely eradicate either adhered or biofilm-embedded pathogens varied significantly depending on the strain and type of surface used. Whilst, sodium hypochlorite reduced tested pathogens counts per cm² of produced biofilms, but it was not able to entirely eliminate neither them nor adherent Cronobacter sakazakii to stainless steel surface. This study revealed that biofilm is considered as a sustainable source of contamination of dairy products with these pathogens, and also emphasized the need of paying more attention to the cleaning and sanitizing processes of food contact surfaces.

Introduction

Biofilm production is a natural mechanism by which some microorganisms try to protect themselves from unfavorable environments. Simply, after adhering to a wet surface, microorganisms begin to secrete a complex extracellular matrix and get embedded inside it (Simões et al., 2009). Microbial biofilms may be defined as microbial aggregates, embedded in matrices of exopolymers, which attached to either biotic or abiotic surfaces (Costerton and Lewandowski, 1995). Since the first reported incidence (Zobell, 1943), the ability of some microorganisms to form biofilms continues to constitute a major challenge to different industries (Maukonen et al., 2003, Veran, 2002). Nearly all branches of food industry, including dairy sectors are being challenged by biofilms problem (Chen et al., 2007, Frank et al., 2003, Jessen and Lammert, 2003, Somers and Wong, 2004).

In dairy plants, biofilms can be developed everywhere; tanks, pipes, working surfaces and even walls and floors (Sinde and Carballo, 2000). These biofilms are certainly resistant to antimicrobials and it is extremely difficult to remove them eventually from food contact surfaces (Simões et al., 2006). Such biofilms constitute major sources of contamination for dairy products either directly or indirectly (Gibson et al., 1999, Holah, 1992), and subsequently constitute serious threats for consumers' health. Biofilms may represent sources of contamination with many microorganisms rather than biofilm producers as certain microorganisms may embed themselves in preformed biofilms exploiting the protective nature of those biofilms (Lapidot et al., 2006, Lehner et al., 2005, Lomander et al., 2004, Møretrø and Langsrud, 2004). In addition to the hygienic and safety issues, biofilms may destroy or impair the function of the food contact surface leading to economic losses (Bremer et al., 2006, Gram et al., 2007). Biofilm development was found to induce corrosion of metallic food surfaces due to catalytic reaction beneath biofilms' areas (Vieira et al., 1993) and significantly reduce heat transfer efficacy of surfaces, rendering the microbiological quality of the final products very poor (Mittelman, 1998).

Many food-borne outbreaks have been associated with dairy products as main vehicles for transmission. Among those outbreaks, Staphylococcus aureus (Staph. aureus), Salmonella enterica serovar Typhimurium (S. Typhimurium) and Coronobacter sakazakii (Cron. sakazakii) were well documented as major causative agents (Durango et al., 2004, Kandhai et al., 2010, Seifu et al., 2004).

While, the majority of dairy processing plants often use stainless steel to construct the dairy equipment for its advantages as a durable, non-corroded, easily cleaned and sanitized surface, polypropylene is recently widely spread in dairy industry as a main material for pipe work, tanks and cutting surfaces (Pompermayer and Gaylarde, 2000). Sanitization of food processing equipment is an indispensable process for ensuring control of cross contamination between different batches of production (Rossoni and Gaylarde, 2000). Egyptian by-laws stated that sodium hypochlorite has to be used as the main sanitizer that all dairy plants and facilities should use for sanitization.

This study was aimed to assess the biofilm developing abilities of some strains of Staph. aureus, Cron. sakazakii and S. Typhimurium, isolated from raw milk and dairy products on two routinely adopted food contact surfaces (stainless steel and polypropylene). Additionally, the ability of sodium hypochlorite to eventually eradicate the adhered or biofilm-embedded pathogens was investigated.