Growth and Biocontrol of Listeria monocytogenes in Greek Anthotyros Whey Cheese without or with a Crude Enterocin A-B-P Extract: Interactive Effects of the Native Spoilage Microbiota during Vacuum-Packed Storage at 4 °C

Abstract

Effective biopreservation measures are needed to control the growth of postprocess Listeria monocytogenes contamination in fresh whey cheeses stored under refrigeration. This study assessed growth and biocontrol of inoculated (3 log10 CFU/g) L. monocytogenes in vacuum-packed, fresh (1-day-old) or ‘aged’ (15-day-old) Anthotyros whey cheeses, without or with 5% of a crude enterocin A-B-P extract (CEntE), during storage at 4 °C. Regardless of CEntE addition, the pathogen increased by an average of 2.0 log10 CFU/g in fresh cheeses on day 15. Gram-negative spoilage bacteria also increased by an average of 2.5 log10 CFU/g. However, from day 15 to the sell-by date (days 35–40), L. monocytogenes growth ceased, and progressively, the populations of the pathogen declined in most cheeses. This was due to an unmonitored, batch-dependent natural acidification by spoilage lactic acid bacteria, predominantly Leuconostoc mesenteroides, which reduced the cheese pH to 5.5, and finally to ≤5.0. The pH reductions and associated declines in pathogen viability were greater in the CEntE-treated samples within each batch. L. monocytogenes failed to grow in cheeses previously ‘aged’ in retail for 15 days. Overall, high population levels (>7.5 log10 CFU/g) of lactose-fermenting Enterobacteriaceae, particularly Hafnia alvei, were associated with an extended growth and increased survival of L. monocytogenes during storage.

Characterization and Antibiotic Resistance of Listeria monocytogenes Strains Isolated from Greek Myzithra Soft Whey Cheese and Related Food Processing Surfaces over Two-and-a-Half Years of Safety Monitoring in a Cheese Processing Facility

“…Most dairy products (e.g., cheese and yogurt) are the result of microbial activity (fermentation) of the native microbiota contained in milk, albeit in the food and cheese production process in particular, microbial pathogens may gain access to the final product and represent a threat to the consumer [ 29 ], given their growth potential and survivability in cheese and its products thereof [ 30 , 31 , 32 , 33 , 34 , 35 ]. L. monocytogenes cannot grow in the traditional Greek soft acid-curd cheeses, such as Galotyri and Katiki [ 35 , 36 ], or hard ripened cheeses like traditional Greek Graviera cheese [ 32 , 37 ], although effective control of post-processing listerial cross-contamination is needed in Greek Myzithra, Anthotyros, and Manouri soft whey cheeses [ 38 , 39 , 40 ]. Thankfully, to the best of the authors’ knowledge, the last documented survey conducted in the Greek retail market, although published a decade ago, indicated a low prevalence of Listeria spp.…”