Distribution, prevalence and persistence of Cronobacter (Enterobacter sakazakii) in the nonprocessing and processing environments of five milk powder factories.

AIMS: To characterise the occurrence of Cronobacter in milk powder factories. METHODS AND RESULTS: Cronobacter was isolated from 32% of 298 environmental samples from five factories. More isolations occurred in nonprocessing (49%) than processing areas (29%), although the greatest occurrence was in a single milk powder area during shutdown maintenance (81%) and the lowest after reinstatement of production hygiene practices (6%). Clonal analysis using PFGE placed 129 isolates into 49 groups. Most clones (45) were unique to each factory and seven were isolated in both milk powder and other areas of the same factory including tanker bays, evaporator rooms, an employee's shoes and external roofs. Cronobacter was not isolated from raw milk processing areas. Within powder areas, 17 clones occurred at more than one and up to eight locations and six occurred more than once at the same location. Between four and seven clones were in the powder areas at each factory. The most prevalent and persistent clones were isolated from external roofs above spray driers, in air treatment areas and where high foot traffic occurs. CONCLUSIONS: Cronobacter is dispersed widely at milk powder factories. This study suggests that distribution is assisted by movement of air, milk powder and personnel and that new hygiene strategies will be needed to reduce prevalence. SIGNIFICANCE AND IMPACT OF THE STUDY: Knowledge of occurrence is essential for the development of strategies to control dissemination of Cronobacter within factories and reduce risk of entry into powdered milk products.

A model system for evaluating surface disinfection in dairy factory environments.

A model system was developed for evaluating the efficacy of disinfectants for inactivating bacteria present in biofilms on surfaces within dairy factory environments. Mixed culture biofilms of six dairy factory isolates (pseudomonads, coliforms and presumptive staphylococci) were generated on factory floor tiles and subjected to up to three fouling and cleaning (FC) cycles. Disinfectants (hypochlorite, peroxyacetic acid-, acid anionic- and quaternary ammonium compound (QUAT)-based products) were applied after cleaning at the supplier's recommended concentrations. Bacterial groups were enumerated using selective agar media. All disinfectants significantly (p<0.05) reduced surface counts of the three bacterial groups. The peroxyacetic acid-based product applied at 3.0% (v/v) achieved the greatest overall reductions in counts. In some cases, disinfectants were more biocidal towards particular bacterial groups. For example, hypochlorite demonstrated greater biocidal activity towards coliforms and staphylococci while the QUAT- and acid anionic-based disinfectants demonstrated greater biocidal activity towards staphylococci. The selective biocidal activity of hypochlorite and the acid anionic-based disinfectant was maintained over at least three FC cycles. The results demonstrate that disinfectants can alter the composition of the surface microflora and can be used to selectively reduce or eliminate particular bacterial groups from production environments. The model system was adapted to assess biofilm development and inactivation on a range of floor materials used in dairy factory environments. Clear differences were observed between surface materials at the end of the inoculation stage and following one FC cycle. For example, after one FC cycle, the highest bacterial counts were obtained for extruded floor tiles and the lowest for stainless steel and the polyurethane surface coating. The model system is versatile and there is scope to employ it to investigate a range of factors influencing the efficacy of cleaning and disinfection procedures towards biofilms. In addition, other microorganisms, such as pathogenic bacteria, may be added to the model biofilm and the influence of disinfectants on these investigated.

Inactivation of Bacillus spores in reconstituted skim milk by combined high pressure and heat treatment.

AIMS: To determine the resistance of a variety of Bacillus species spores to a combined high pressure and heat treatment; and to determine the affect of varying sporulation and treatment conditions on the level of inactivation achieved. METHODS AND RESULTS: Spores from eight Bacillus species (40 isolates) were high pressure-heat treated at 600 MPa, 1 min, initial temperature 72 degrees C. The level of inactivation was broad (no inactivation to 6 log10 spores ml(-1) reduction) and it varied within species. Different sporulation agar, high pressure equipment and pressure-transmitting fluid significantly affected the response of some isolates. Varying the initial treatment temperature (75, 85 or 95 degrees C) shifted the relative order of isolate high pressure-heat resistance. CONCLUSIONS: The response of Bacillus spores to combined high pressure-heat treatment is variable and can be attributed to both intrinsic and extrinsic factors. The combined process resulted in a high level of spore inactivation for several Bacillus species and is a potential alternative treatment to traditional heat-only processes. SIGNIFICANCE AND IMPACT OF THE STUDY: Sporulation conditions, processing conditions and treatment temperature all affect the response of Bacillus spores to the combined treatment of high pressure and heat. High levels of spore inactivation can be achieved but the response is variable both within and between species.