Detection of biofilm-producing and methicillin resistance genes in Staphylococcus epidermidis isolated from healthy humans and in blood culture tests.

The detection of biofilm-producing (ica AB) and methicillin resistance genes (mec A) was investigated in 70 blood culture isolates of Staphylococcus epidermidis and in 66 and 51 isolates from human hands and the vestibules of the nose, respectively, of 77 healthy subjects who gave consent. Of the 70 strains isolated from blood culture testing, both ica AB and mec A were detected in 36 (51.4%), and neither was detected in 4 (5.7%). The mec A gene only was detected in 30 (42.9%), but no isolate from blood culture testing possessed the ica AB gene alone. In contrast, of the 66 isolates from healthy hands, only one isolate (1.5%) possessed both genes, whereas neither was detected in 56 (84.8%), but the mec A gene was detected in 9 (13.6%). Of the 51 isolates from the nasal vestibules, both genes were detected in 12 (23.5%), and neither in 15 (29.4%). Moreover, the mec A gene was detected in 17 (33.3%). Thus, S. epidermidis strains that normally inhabit the nasal vestibule were found to carry the ica AB and mec A genes more frequently than those that inhabit the fingers. The ica AB and mec A genes were detected in S. epidermidis isolated in blood culture tests from patients diagnosed with sepsis associated with catheter-related bloodstream infection (CR-BSI). Both genes were detected in 7 (70.0%) of 10 isolates, and the mec A gene alone was detected in 3 (30.0%). In fact, we could not detect any strain carrying only the ica AB gene from S. epidermidis, an infecting organism of CR-BSI. This suggests that surviving strains carrying the mec A gene cause severe infection on empirical administration of an antibacterial drug, although biofilm formation by the ica AB gene is also important for CR-BSI. Based on these findings, most strains of S. epidermidis causing CR-BSI are biofilm-producing beta-lactam-resistant (methicillin-resistant) bacteria. When S. epidermidis is isolated from blood culture testing, the identification of both ica AB and mec A genes may be significant with regard to judging whether the detected strain is the etiologic agent of CR-BSI.

Apoptotic pathway induced by transduction of RUNX3 in the human gastric carcinoma cell line MKN-1.

The human runt-related transcription factor 3 gene (RUNX3) is considered to be a candidate tumor suppressor gene in gastric carcinoma. However, the role of RUNX3 in the regulation of cell proliferation remains unclear. In the present study, we constructed an adenoviral vector encoding human RUNX3 cDNA under the control of a Tet-responsive promoter (Ad-Tet-FLAG-RUNX3), which regulates the expression of RUNX3 in the presence or absence of doxycycline. A recombinant adenoviral expression vector encoding LacZ (Ad-Tet-LacZ) was used as a negative control. The effect of the transduction of RUNX3 on cell growth was examined using the Tet-On system in a human gastric carcinoma cell line, MKN-1. Exogenous RUNX3 expression was induced successfully by Ad-Tet-FLAG-RUNX3, but not Ad-Tet-LacZ, in the presence of doxycycline in the MKN-1 cells. At 72 h after infection, the proliferative activity in RUNX3-expressing cells was 55% or less of that of the control cells. Flow cytometry revealed that the sub-G(1) peak was increased in cells expressing RUNX3 (34.11%), indicating that the inhibition of cell growth was due to apoptosis, which was confirmed based on Hoechst 33258 staining, the release of cytochrome c from mitochondria into the cytosol, and detection of cleaved caspase-3 by western blotting in MKN-1 cells. Comprehensive analysis using a cDNA microarray showed that RUNX3 upregulated 17 apoptosis-related genes (including FADD, TRAF6, caspase-2, ING1, ING4, Calpain 10, and DNase1) and downregulated 135 apoptosis-related genes (including FLIP, PEA15, TXN2, HSPD1, IKK, and TIAL1) in MKN-1 cells. Pathway analyses to generate functional networks of the genes suggested that promotion of the formation of the death-inducing signaling complex and activation of the mitochondria-mediated pathway were associated with RUNX3-induced apoptosis. In conclusion, our findings suggest that exogenous RUNX3 expression suppressed cell proliferation by inducing apoptosis via the death-receptor mitochondria-mediated pathway in MKN-1 cells.