Tracing and inhibiting growth of Staphylococcus aureus in barbecue cheese production after product recall

Abstract

Staphylococcal food poisoning is one of the most prevalent causes of foodborne intoxication worldwide. It is caused by ingestion of enterotoxins formed by Staphylococcus aureus during growth in the food matrix. Following a recall of barbecue cheese due to the detection of staphylococcal enterotoxins in Switzerland in July 2015, we analyzed the production process of the respective dairy. Although most cheese-making processes involve acidification to inhibit the growth of pathogenic bacteria, barbecue cheese has to maintain a pH >6.0 to prevent undesired melting of the cheese. In addition, the dairy decided to retain the traditional manual production process of the barbecue cheese. In this study, therefore, we aimed to (1) trace Staph. aureus along the barbecue cheese production process, and (2) develop a sustainable strategy to inhibit growth of Staph. aureus and decrease the risk of staphylococcal food poisoning without changing the traditional production process. To this end, we traced Staph. aureus in a step-wise blinded process analysis on 4 different production days using spa (Staphylococcus protein A gene) typing, DNA microarray profiling, and pulsed-field gel electrophoresis analysis. We subsequently selected a new starter culture and used a model cheese production including a challenge test assay to assess its antagonistic effect on Staph. aureus growth, as well as its sensory and technological implications. We detected Staph. aureus in 30% (37/124) of the collected samples taken from the barbecue cheese production at the dairy. This included detection of Staph. aureus in the final product on all 4 production days, either after enrichment or using quantitative detection. We traced 2 enterotoxigenic Staph. aureus strains (t073/CC45 and t282/CC45) colonizing the nasal cavity and the forearms of the cheesemakers to the final product. In the challenge test assay, we were able to show that the new starter culture inhibited growth of Staph. aureus while meeting the sensory and technological requirements of barbecue cheese production.

Methicillin-Resistant Staphylococcus aureus (MRSA) in Artisanal Cheeses in México

“…The occurrence of S. aureus in this study was 56.4%, which is higher in relation to the studies in Turkey (12.5%) [13] and Iran (16%) [10]; and it is a low frequency in relation to studies in Italy and Serbia, which reports frequencies of 80% [14, 15]. The high frequencies of the bacteria in this study, as well as the others are consistent with a previous study [16], where it is shown that the microorganism can enter the artisanal cheese-making process at different stages of the manual production, with colonized cheese makers representing a likely source of S. aureus , as well as studies in Italy [14] and Poland [17], where they described that many strains were present in samples from multiple dairies from different regions and years, highlighting the spread of S. aureus in small-scale cheese production plants. The frequency data obtained in this study are important because currently only one study has been carried out for the research of S. aureus in Cotija cheese in Mexico in 2014 [18].…”

Staphylococcus aureus Entrance into the Dairy Chain: Tracking S. aureus from Dairy Cow to Cheese

“…FTIR analysis of the 187 S. aureus strains (119 originating from dairy farms and 68 from cheese production at the dairy plant) isolated in frame of this study, revealed the bovine udder as an important S. aureus contamination source for the dairy production chain (Figure 1 ). Generally, the three major clusters revealed by FTIR are linked to CCs (CC97, CC8, CC705) typically found in bovine S. aureus (Smith et al, 2005 ; Johler et al, 2016b ). Only two strains, representing the subclusters A7 and B2 as singeltons, were assigned to the human STs (Table 2 ).…”

“…This study provides a comprehensive analysis of the potential of primary production as source for S. aureus contaminations in the dairy production and processing chain. The dairy chain opens various entrance points for the human pathogen S. aureus , including the primary production environment and people involved in the dairy production and processing (Haveri et al, 2008 ; Johler et al, 2016b ). Recent molecular studies as well as reports from food borne dairy associated outbreak linked to S. aureus indicate a potential, yet not sufficiently explored, role of dairy cows as entrance point of S. aureus into the dairy production chain (Schmid et al, 2009 ; Hummerjohann et al, 2014 ; Walcher et al, 2014 ; Johler et al, 2015 ).…”

Staphylococcal Enterotoxin C—An Update on SEC Variants, Their Structure and Properties, and Their Role in Foodborne Intoxications

“…Lactic acid bacteria or their metabolites could impact quorum sensing of S. aureus and therefore influence agr-regulated SEs. In another trial, Staphylococcus vitulinus was used as a starter culture to successfully inhibit SEC-producing S. aureus growth in a barbeque cheese production facility [119].…”