Screening of Virulence Determinants in Enterococcus faecium Strains Isolated From Breast Milk

Abstract

In a previous study, the authors isolated lactic acid bacteria from breast milk of healthy mothers. Since some of the identified isolates belonged to the species Enterococcus faecium, the objective of this work was to evaluate their safety. The enterococcal strains were screened by polymerase chain reaction (PCR) and Southern hybridization for the presence of virulence determinants. The potential of the strains to acquire plasmids by conjugation was investigated by screening for genes involved in conjugation processes. Parallel, phenotypic assays were performed. Presence of genes conferring resistance to vancomycin was assessed by PCR. PCR amplifications and Southern hybridizations revealed that all the strains were clear of the majority of potential virulence determinants. None of the strains showed gelatinase activity, hemolysin production, or aggregation phenotype, and none carried the vanA or vanB genes. These findings suggest that milk of healthy mothers may be a source of avirulent E faecium isolates to the newborns.

Occurrence of enterocin genes, virulence factors, and antibiotic resistance in 3 bacteriocin-producer Enterococcus faecium strains isolated from Turkish tulum cheese

“…The E. faecium strains only exhibited intermediary resistance to erythromycin (15 µg). The resistance against antibiotics is an important factor for the evaluation of the safety of enterococci (16). These bacteria have natural and acquired resistance to antibiotics.…”

“…The primers used in this assay are listed in Table 2. PCR for virulence genes was performed as an initial cycle of denaturation at 95 °C for 5 min, followed by 35 cycles of denaturation at 95 °C for 30 s, annealing at 54 °C (56 °C for gene agg) for 30 s, and elongation at 72 °C for 1 min (16). The amplification products were analysed by electrophoresis on 1.5% agarose gel at 120 V for 1.5 h in Tris-acetate-EDTA buffer and revealed in ethidium bromide (20 µg/mL).…”

Investigation of potential virulence genes and antibiotic resistance characteristics of Enterococcus faecalis isolates from human milk and colostrum samples

“…All antibiotic discs were purchased from Oxoid (UK). Results were interpreted according to the cut-off levels proposed by Charteris et al (1998) for gentamycin and kanamycin, and CLSI (2006) (Reviriego et al, 2005). Primers were obtained from IDT (Integrated DNA Technologies, USA).…”

“…Several virulence factors such as cytolysins, serine protease, hyaluronidase, aggregation substances, extracellular surface protein and other adhesins, sex pheromone determinants, extracellular metalloendopeptidase, and hemolytic activity in enterococci, especially in Enterecoccus faecium and Enterococcus faecalis strains, have been mentioned in the literature (Franz et al, 2001;Mannu et al, 2003;Eaton and Gasson, 2005;Reviriego et al, 2005;Sanchez Valenzuela et al, 2009). Antibiotic-resistant clinical-or food-originated enterococci are widespread worldwide, and this property is transferred among bacteria by plasmids (Franz et al, 1999;Coleri et al, 2004;Oryaşın et al, 2013).…”

“…These bacteria are considered to be components of the natural microflora of breast milk (Martin et al, 2004;Albesharat et al, 2011;Jeurink et al, 2013). Among the bacteria isolated from breast milk, species such as Lactobacillus gasseri, Lactobacillus rhamnosus, or Enterococcus faecium are considered to be potential probiotic bacteria (Martin et al, 2004;Martin et al, 2005;Reviriego et al, 2005). Some Enterococcus faecium and E. faecalis strains are used as starter cultures, co-cultures, or probiotics (Franz et al, 1999;De Vuyst et al, 2003;Franz et al, 2003;Hugas et al, 2003;Klein, 2003;Foulquie Moreno et al, 2006).…”