RESUMO
The mechanism underlying antimicrobial activity of conjugated bile acids against strains of lactic acid bacilli is not well understood. The purpose of this study was to investigate two typical conjugated bile acids (glycochenodeoxycholic acid and taurochenodeoxycholic acid) for their mechanisms of antimicrobial activity against four strains of different species of lactic acid bacilli at the physiological pH of the small intestine of humans. The bacterial cell membrane integrity, transmembrane potential, and transmembrane pH gradient were examined using the fluorescence probes SYTO 9 plus propidium iodide, 3,3'-dipropylthiadicarbocyanine iodide, and 5(6)-carboxyfluorescein diacetate N-succinimidyl ester, respectively. The intracellular ATP levels were measured by the firefly luciferase-based bioluminescence method. It was found that the antimicrobial activity of conjugated bile acids against the strains of lactic acid bacilli is strain-specific, and glycochenodeoxycholic acid showed significantly greater antimicrobial activity than taurochenodeoxycholic acid against the strains of lactic acid bacilli. The conjugated bile acids inhibited the growth of strains of lactic acid bacilli by disrupting membrane integrity, dissipating transmembrane potential, reducing the transmembrane pH gradient, and depleting intracellular ATP. In conclusion, the antimicrobial activity of conjugated bile acids against lactic acid bacilli is a multifactorial phenomenon. This study will provide valuable information for developing strategies to improve the ability of lactic acid bacilli to tolerate bile in vivo.
RESUMO
The purpose of this study is to explore the effects of the HA sequence variation on the pathogenicity and antigenicity of avian influenza virus(AIV). Haemagglutinin (HA) genes from, 6 of 25 avian influenza viruses (AIVs) H9N2 strains with different pathogenicity isolated in central China during last 10 years were amplified by reverse transcriptase PCR (RT-PCR), completely sequenced and phylogenetically analyzed. The purpose of this study was to explore the effects of the HA sequence variation on the pathogenicity and antigenicity of AIV. The results showed that all 6 representative H9N2 isolates belong to low pathogenic AIVs, since none of the amino acid sequences at the cleavage site of the HA of the isolates possessed the basic motif required for highly pathogenic viruses (R-X-R/K-R). There were eight potential glycosylation sites in HA of the isolates, except that 3# and 12# had an extra one. The higher pathogenicity of 3# and 12# was probably due to the extra glycosylation site (145aa-147aa) in HA1, which might alter the conformational structure of HA resulting in the mutation or deletion of the binding sites of anti-HA antibody, and has effects on receptor binding sites thus changed the antigenicity of the virus. Our results suggested that attention should be paid to the transmission and natural evolution of H9N2 AIV in order to control AIV H9N2.