Abstract
Goat milk has become a popular item of human consumption due to its originality. Enterococci are ubiquitous bacteria, and they can also be found in traditional dairy products. This study focuses on the safety of enterococci from Slovak raw goat milk and on their susceptibility to lantibiotic bacteriocins and durancin ED26E/7, which has not previously been studied. Biofilm formation ability in enterococci, virulence factor genes, enzyme production and antibiotic profile were investigated. Samples of raw goat milk (53) were collected from 283 goats in Slovakia. MALDI-TOF mass spectrometry identified three enterococcal species: Enterococcus faecium, E. hirae and E. mundtii, with dominant occurrence of the species E. faecium. Low-grade biofilm formation ability (0.1 ≤ A570 < 1.0) was found in four strains of E. faecium. Gelatinase, hyaluronidase, aggregation substance and enterococcal surface protein genes were absent in these enterococci. Gene efaAfm (adhesin) was detected in five E. faecium strains. However, it was not detected in biofilm-forming strains. Enterococci detected in Slovak raw goat milk were found not to have pathogenic potential; four strains even produced high amounts of useful β-galactosidase. The strains were susceptible to lantibiotic bacteriocin treatment and to durancin ED26E/7 as well, which represents original information in dairy production.
Highlights
This study focuses on the safety aspects of enterococci isolated from raw goat milk, with the intention of testing properties such as biofilm formation ability, virulence-factor genes, enzyme production, antibiotic profile, as well as hemolysis and/or deoxyribonuclease activity
The species E. faecium dominated with 11 strains (Table 1), followed by one strain of E. hirae and one strain of E. mundtii
Five out of eleven E. faecium strain species were evaluated, with highly probable species identification (2.300–3.000), five E. faecium strains as well as one strain of E. hirae were identified with evaluation corresponding to secure genus identification/probable species identification (2.000–2.299)
Summary
Enterococci are widespread microorganisms which can be found in many traditional dairy products [1,2] They belong in a community of lactic acid-producing bacteria which forms part of a controversial group of dairy bacteria [3], because antibiotic-resistant enterococci or virulence-factor genes possessing enterococci can cause human health disorders [4]. Based on the previous studies, the prevalent enterococcal species in raw milk have been found to be Enterococcus faecium, E. faecalis and E. durans [3]. Knowledge of these properties is required in order to reduce the pathogenic enterococcal strains from dairy production, and to eliminate the transfer of virulence-factor genes to other strains. It is essential to find possible ways of eliminating them; the application of bacteriocins represents a promising approach, especially those with a broad antimicrobial spectrum [5,6,7]
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