Factors affecting the viability of Staphylococcus aureus and production of enterotoxin during processing and storage of white-brined cheese

Abstract

Staphylococcus aureus is a major foodborne pathogen that causes severe disease in humans. It is commonly found in milk and dairy products, particularly in fresh brined cheese. Our aim was to investigate the behavior of Staph. aureus and enterotoxin production during the storage of white-brined cheese prepared with or without a starter culture and stored in a 10 or 15% NaCl brine at 10°C and 25°C for 28 d. NaCl concentration, water activity, pH, and number of Staph. aureus and lactic acid bacteria were determined in cheese and brine. Only 1 of 4 Staph. aureus strains (ATCC 439) was positive for enterotoxin production, and its production was detected in unsalted UHT milk, but not in salted milk or in any of the cheese treatments held at 37°C for 1, 3, or 7 d. Staphylococcus aureus grew in the cheese stored in both brines at 10°C and 25°C, regardless of the presence of a starter culture, although the latter significantly reduced Staph. aureus growth in cheese or its brine at 10°C. Staphylococcus aureus numbers were increased by 2.26 and 0.47 log 10 cfu/g in cheese stored in 10 and 15% NaCl brine, respectively, in the presence of starter culture, and by 2.78 and 2.96 log 10 cfu/g, respectively, in the absence of starter culture at 10°C. Nonetheless, the pathogen grew, but at a lower number in the brines. The salt concentration of cheese stored in 10% brine remained at approximately 5% during storage; however, in 15% brine, the salt concentration increased to almost 8% (wt/wt) by 28 d. The addition of a starter culture, high salt concentration, low tem-perature, and pH (~5.2) had inhibitory effects on the growth of Staph. aureus. Moreover, lactic acid bacterial numbers increased considerably in cheese and brine by d 28. The use of starter cultures, salt (15%), and low storage temperature (10°C) reduced the growth of Staph. aureus, and salt may have prevented enterotoxin production in white-brined cheese.

The Use of Unique, Environmental Lactic Acid Bacteria Strains in the Traditional Production of Organic Cheeses from Unpasteurized Cow’s Milk

“…This contamination is most common among unpasteurized dairy products, which is especially true of products manufactured largely by hand [ 31 ]. Moreover, it has been observed that the number of staphylococci increases during the storage of products [ 32 ] which was also observed in our research. This is due to the ability of S. aureus to grow rapidly in milk and dairy products, and also due to the contamination of cheese makers’ skin.…”

Lactic Starter Dose Shapes S. aureus and STEC O26:H11 Growth, and Bacterial Community Patterns in Raw Milk Uncooked Pressed Cheeses

“…These results were consistent with those from previous studies in Saint-Nectaire-model cheese made from cows’ raw milk [ 15 ], similar to our cheese models, in which no staphylococcal enterotoxin was detected, although coagulase-positive staphylococci counts were around 5 Log CFU/g at D0.25, a propitious condition to SE accumulation. The increase in the S. aureus counts with the 10-fold reduced lactic starter dose are similar to those reported by Al-Nabulsi et al [ 53 ] in white brined cheeses manufactured without a lactic starter. Using standard brine (10% of NaCl) and a storage temperature of 25 °C, the authors showed reductions by 1.17 Log [CFU/g] and by 0.56 Log [CFU/g] at D1 and at D28, respectively, between the cheeses manufactured without and with a lactic starter.…”

Metataxonomic Mapping of the Microbial Diversity of Irish and Eastern Mediterranean Cheeses

“…The family Enterobacteriaceae includes some severe foodborne pathogens, including toxin producing Shigella spp., Salmonella spp., and some serotypes of E. coli , such as E. coli O157:H7 [ 64 ]. Among the Staphylococcus spp., S. aureus , which is commonly detected in cheeses, is an important foodborne pathogen and disease-causing bacterium in humans [ 65 ]. Moreover, two cheeses had low relative abundance of the species C. perfringens .…”