Antimicrobial Activity, Antibiotic Resistance and the Safety of Lactic Acid Bacteria in Raw Milk Valtellina Casera Cheese

Abstract

The study involved 75 autochthonous lactic acid bacteria (LAB) obtained from Valtellina Casera Protected Designation of Origin cheese and provides data on their antibiotic resistance (AR), antimicrobial activity and safety aspects. High biodiversity was revealed, assigning the isolates to 16 species. In the curd Streptococcus thermophilus was predominant, while Enterococcus and the Lactobacillus casei group prevailed in ripened cheese. One Lactobacillus rhamnosus was resistant to penicillin G. The presence of 19 tetracycline‐resistant strains indicates that tetracycline resistance is emerging in dairy sources. Seven Enterococcus faecalis, one Lactococcus garvieae and one Lactoc. lactis subsp. lactis showed the presence of the int gene that is responsible for the transfer of tetracycline resistance. Six En. faecalis inhibited Listeria monocytogenes and closely related LAB, and four of these harbored the entAS48 gene. Genes associated with virulence factors were detected in En. faecalis but not in En. faecium. A low spread of AR in wild LAB and a low occurrence of safety hazards in enterococci strains were highlighted. Practical Application In recent years, raw milk cheese have received increasing attention for their microbial biodiversity and as a source of food bio‐preservatives, but they could also provide a vehicle for antibiotic resistance. The results of this study showed that wild microbiota of Valtellina Casera cheese is characterized by an important activity inhibiting growth of Listeria monocytogenes. These probably actively contribute to ensure the safety and quality of this cheese. The presence of tetracycline resistance among En. faecalis and Str. thermophilus may indicate that this resistance is emergent in dairy sources, a point that needs further investigation. En. faecium from artisanal Valtellina Casera cheese did not show antibiotic resistance and did not harbor any of the virulence genes associated to the hospital‐associated clade according to European Food Safety Authority.

Lactic acid bacteria with cholesterol-lowering properties for dairy applications: In vitro and in situ activity

“…Recently, the assessment of E. faecium for qualified presumption of safety was performed, and this led to the conclusion that strains associated with clinical infections could be differentiated from commensal strains (EFSA Panel on Biological Hazards, 2013). The 2 strains used in this research did not harbor genes encoding for virulence factors, and antibiotic resistance was established by EFSA criteria for the safety assessment of E. faecium for intentional use in feed or food (Morandi et al, 2013(Morandi et al, , 2015, thus supporting possible use of these strains as probiotics.…”

“…lactis, 1 E. faecium, and 1 Enterococcus lactis (Supplemental Table S1; https: / / doi .org/ 10 .3168/ jds .2018 -15096). The strains were previously identified by partial 16S ribosomal DNA sequence analysis as described by Morandi et al (2015). The 2 enterococci strains had previously been tested for antibiotic resistance and did not harbor any of the virulence genes reported by the European Food Safety Authority (EFSA) for the safety assessment of E. faecium (EFSA Panel on Additives and Products or Substances Used in Animal Feed, 2012; Morandi et al, 2013Morandi et al, , 2015.…”

Evaluation of antimicrobial resistance and virulence of enterococci from equipment surfaces, raw materials, and traditional cheeses

“…In this study, a collection of 40 strains of dairy origin was characterized phenotypically and genotypically in order to explore their safety aspects. Contrarily to previous studies (Martín-Platero et al, 2009;Nieto-Arribas et al, 2011;Morandi et al, 2015) carried out on the characterization of the antibiotic resistance and virulence determinants of cheese Enterococcus, our collection was composed of strains isolated along the entire production chain of three traditional raw milk cheeses. In this manner, we investigated not only the enterococci from final (fresh and ripened) cheeses but also those from raw materials (bulk milks and animal rennets) and from the contaminating sources (wooden surfaces of the vats used from milk transformation).…”

Gida Kaynakli Enterokoklarin Potansi̇yel Ri̇sk Faktörleri̇

“…Tetrasiklin direnci klinik kaynakl› enterokok izolatlar›nda s›kl›kla karfl›lafl›lan bir antibiyotik direnci olmakla birlikte, çeflitli hayvansal g›dalarda da dirençli sufllar›n varl›¤› tespit edilmifltir (4,9). Enterokoklarda tetrasiklin direnci genellikle ribozomal koruma sa¤layan tet(M) geni ile iliflkilidir.…”

“…Yap›lan çal›flmalar hayvansal g›dalardan s›kl›kla izole edilen enterokok türlerinin Enterococcus faecalis, E. faecium ve E. durans oldu¤unu göstermifltir (4,(7)(8)(9)(10). Hayvansal g›dalardan izole edilen enterokok türleri aras›nda E. faecalis'in görülme s›kl›¤›n›n di¤er türlere nazaran daha yüksek oldu¤u yap›lan çal›flmalarda gösterilmifltir (4,7). Enterokoklar›n baz› teknolojik ve probiyotik özelliklere sahip olduklar› bilinmesine ra¤men, bu bakterilerin sahip olduklar› virülens özellikleri ve artan antibiyotik dirençleri f›rsatç› patojen olarak kabul edilmelerine neden olmufltur.…”