The occurrence, growth, and biocontrol of Listeria monocytogenes in fresh and surface‐ripened soft and semisoft cheeses

Abstract

Listeria monocytogenes continues to pose a food safety risk in ready‐to‐eat foods, including fresh and soft/semisoft cheeses. Despite L. monocytogenes being detected regularly along the cheese production continuum, variations in cheese style and intrinsic/extrinsic factors throughout the production process (e.g., pH, water activity, and temperature) affect the potential for L. monocytogenes survival and growth. As novel preservation strategies against the growth of L. monocytogenes in susceptible cheeses, researchers have investigated the use of various biocontrol strategies, including bacteriocins and bacteriocin‐producing cultures, bacteriophages, and competition with native microbiota. Bacteriocins produced by lactic acid bacteria (LAB) are of particular interest to the dairy industry since they are often effective against Gram‐positive organisms such as L. monocytogenes, and because many LAB are granted Generally Regarded as Safe (GRAS) status by global food safety authorities. Similarly, bacteriophages are also considered a safe form of biocontrol since they have high specificity for their target bacterium. Both bacteriocins and bacteriophages have shown success in reducing L. monocytogenes populations in cheeses in the short term, but regrowth of surviving cells can commonly occur in the finished cheeses. Competition with native microbiota, not mediated by bacteriocin production, has also shown potential to inhibit the growth of L. monocytogenes in cheeses, but the mechanisms are still unclear. Here, we have reviewed the current knowledge on the growth of L. monocytogenes in fresh and surface‐ripened soft and semisoft cheeses, as well as the various methods used for biocontrol of this common foodborne pathogen.

Assessment of the Spoilage Microbiota during Refrigerated (4 °C) Vacuum-Packed Storage of Fresh Greek Anthotyros Whey Cheese without or with a Crude Enterocin A-B-P-Containing Extract

“…Conversely, at abusive (>7–12 °C) temperatures L. lactis and other Bac+ mesophilic dairy LAB strains affect the desirable sensory quality characteristics of high-pH ready-to-eat (RTE) whey cheeses by a simultaneous high production of organic acids during retail storage. To overcome low-pH defects, bioprotective strains of non-aciduric LAB species/genera or Nis+/Bac+ mutant lactose-negative dairy LAB strains may be applied [ 28 , 29 , 30 ]. An alternate option is the addition of commercial nisin (Nisaplin ® ), pediocins or various crude LAB bacteriocin concentrates in fresh whey cheeses [ 3 , 10 , 28 , 30 ].…”

“…To overcome low-pH defects, bioprotective strains of non-aciduric LAB species/genera or Nis+/Bac+ mutant lactose-negative dairy LAB strains may be applied [ 28 , 29 , 30 ]. An alternate option is the addition of commercial nisin (Nisaplin ® ), pediocins or various crude LAB bacteriocin concentrates in fresh whey cheeses [ 3 , 10 , 28 , 30 ]. However, Nisaplin ® added as an antilisterialbiopreservative to the whey (100 or 500 IU/g) before heating, or to the fresh cheese curd (500 IU/g) before VP, reversed the natural predominant spoilage microbiota of traditional Anthotyros from Gram-positive LAB in the control cheeses without nisin to Gram-negative bacteria during storage at 4 °C for up to 45 days, particularly in the most effective Nisaplin ® treatments [ 3 ].…”

“…The best candidates are selected safe Ent+ strains of Enterococcus faecium , Enterococcus durans and Enterococcus faecalis without β-hemolytic activity, virulence genes, vancomycin resistance genes and other undesirable traits. An increasing number of promising experimental applications of Ent+ strains or enterocin preparations in dairy foods, particularly active against L. monocytogenes , are summarized in recent reviews [ 28 , 30 , 31 ], including a few studies on fresh whey cheeses [ 32 ]. Most enterococci are naturally non-aciduric LAB, which is advantageous for Ent+ strain applications in fresh RTE whey cheeses.…”

“…Most enterococci are naturally non-aciduric LAB, which is advantageous for Ent+ strain applications in fresh RTE whey cheeses. Moreover, apart from L. monocytogenes , the antimicrobial spectrum of several enterocins and/or Ent+ strains has been reported to include a wide range of Gram-positive sporoforming as well as Gram-negative bacteria [ 28 , 29 , 30 , 31 , 33 ]. On the other hand, most enterococci promote negligible or poor growth at refrigeration temperatures [ 33 ], which is against outnumbering other psychrotrophic spoilage or pathogenic bacteria with sufficient in situ enterocin production in fresh cold-stored whey cheeses [ 14 ].…”

Monitoring by a Sensitive Liquid-Based Sampling Strategy Reveals a Considerable Reduction of Listeria monocytogenes in Smeared Cheese Production over 10 Years of Testing in Austria

“…Although milk is usually subjected to a heating process prior to processing, cheese can become contaminated during several process steps such as pressing, curing, ripening, and during cutting and packaging [22,23].…”