The influence of some probiotic supernatants on the growth and virulence features expression of several selected enteroaggregative E. coli clinical strains.
The purpose of this study was the assessment of the influence of three probiotic supernatants (Bifidobacterium breve ATCC 15700, Enterococcus faecium ATCC 19434, Lactobacillus casei subsp. casei ATCC 393) on the growth (quantified by viable cell counts) and virulence features expression (adherence ability to HEp-2 cells and inert substratum- slime test) of several selected EAggEC diarrhoeagenic strains as well as the cytotoxicity of the respective supernatants on HEp-2 cells.


RESULTS
Our in vitro studies are demonstrating that the selected supernatants, when added simultaneously with the bacterial culture are generally opposing to the adherence to the cellular substratum by the EAggEC strains. When added after the pre-adherence period, the supernatants did not change the adherence indexes of the EAggEC strains, but induced slight changes in the adherence pattern, reducing the frequency and size of bacterial aggregates. Only in few cases, the bacterial growth rate was slightly increased or sustained by the probiotic supernatants, a possible explanation being that we used supernatants obtained from 24 hrs fresh cultures, which are probably still containing some nutrients and probably also other growth factors.


CONCLUSIONS
Our results are demonstrating that soluble probiotic metabolites accumulated in culture supernatants may interfere with the first step of adherence and colonization of the cellular and inert substrata by EAggEC strains, probablyby the cross-talk between probiotic soluble molecules and quorum-sensing mediators of opportunistic strains; so, direct contact between the probiotic and pathogenic bacteria are not always necessary for the occurrence of a protective effect, that could be partly mediated by the soluble molecules secreted by specific probiotic strains.
Lazăr
Veronica
V
Department of Microbiology & Immunology, Faculty of Biology, University of Bucharest, Romania.
Miyazaki
Yoshibumi
Y
Hanawa
Tomoko
T
Chifiriuc
Mariana-Carmen
MC
Diţu
Lia-Mara
LM
Măruţescu
Luminita
L
Bleotu
Coralia
C
Kamiya
Shigeru
S
D001422:Bacterial Adhesion; D001644:Bifidobacterium / Q000254:growth & development; D002460:Cell Line; D015169:Colony Count, Microbial; D017077:Culture Media, Conditioned / Q000737:chemistry / Q000494:pharmacology*; D003967:Diarrhea / Q000382:microbiology; D016984:Enterococcus faecium / Q000254:growth & development; D004847:Epithelial Cells / Q000382:microbiology; D004926:Escherichia coli / Q000187:drug effects / Q000254:growth & development* / Q000472:pathogenicity*; D004927:Escherichia coli Infections / Q000382:microbiology; D006801:Humans; D007780:Lacticaseibacillus casei / Q000254:growth & development; D019936:Probiotics; D014774:Virulence
D017077:Culture Media, Conditioned