Activity and expression of a virulence factor, gelatinase, in dairy enterococci

• Published in: International journal of food microbiology Vol. 112; no. 3; pp. 208 - 214
• Main Authors: Lopes, Maria de Fátima Silva, Simões, Ana Patrícia, Tenreiro, Rogério, Marques, José Joaquim Figueiredo, Crespo, Maria Teresa Barreto
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-12-2006; Elsevier
• Subjects: Animals; Base Sequence; Biological and medical sciences; cheeses; Consumer Product Safety; dairies; Dairy enterococci; DNA primers; DNA, Bacterial - chemistry; DNA, Bacterial - genetics; Enterococcus; Enterococcus - enzymology; Enterococcus - genetics; Enterococcus - pathogenicity; Enterococcus dispar; Enterococcus durans; Enterococcus faecalis; Enterococcus faecium; Enterococcus hirae; enzyme activity; ewe milk; Food Contamination - analysis; Food industries; Food Microbiology; Fundamental and applied biological sciences. Psychology; Gelatinase; Gelatinases - genetics; Gelatinases - metabolism; genes; isolation; lactic acid bacteria; metalloproteinases; Milk - microbiology; Molecular Sequence Data; Operon; Phylogeny; raw milk; Sheep; Species Specificity; Virulence; Virulence - genetics; Virulence; Dairy enterococci; Gelatinase; Enterococcus; Streptococcaceae; Bacteria; Micrococcales
• ISSN: 0168-1605; 1879-3460
• DOI: 10.1016/j.ijfoodmicro.2006.09.004

In order to understand the virulence potential of dairy enterococci, 35 isolates from raw ewe's milk and traditionally fermented cheeses, identified as
Enterococcus faecalis,
Enterococcus faecium,
Enterococcus durans,
Enterococcus dispar and
Enterococcus hirae, were screened for their capacity to produce gelatinase and for the presence of the genes
gelE,
sprE,
fsrA,
fsrB and
fsrC. Studies correlating gelatinase production with maintenance and subculture of the isolates in the Laboratory environment, and growth in different media were performed. These studies were conducted with two dairy isolates identified as
E. faecalis and
E. durans, and one clinical isolate,
E. faecalis OG1-10. RT-PCR was used for detection of transcripts of the above mentioned genes. Results demonstrated that the virulence factor gelatinase is disseminated among the genus
Enterococcus and that dairy isolates are capable of producing gelatinase at comparable levels with clinical isolates, although this capacity is easily lost during conservation by freezing in the laboratory. Therefore, gelatinase production potential of dairy enterococci may be underestimated. The gene
gelE was present in all studied isolates. The same was observed for the
fsr operon, either complete or incomplete, revealing that the gelatinase genetic determinants, so far only described in
E. faecalis, are a common trait in the genus. This work describes for the first time the detection of the complete Fsr-GelE operon in other species than
E. faecalis, namely
E. faecium and
E. durans. The loss of expression of this virulence factor under laboratory culture conditions correlated with the loss of one or more genes of the regulatory
fsr operon, although the gene
gelE was maintained, demonstrating that a complete
fsr operon is required for a positive GelE phenotype. Independent of the detection of any gelatinase activity, if both
gelE and the complete
fsr operon are present in the cell, all genes are transcribed, as revealed by RT-PCR, suggesting that regulation of gelatinase activity can also be post-transcriptional. The silent behavior of
gelE was only observed in
E. faecalis, but not in
E. durans, suggesting different modulation mechanisms of gelatinase activity in these two species. Overall, these findings reopen the issue of food safety of enterococci and reinforce the need to further study the mechanisms responsible for triggering the virulence factor gelatinase in non-pathogenic enterococcal environmental isolates.