Singh Kavindra V, Nallapareddy Sreedhar R, Nannini Esteban C, Murray Barbara E
Division of Infectious Diseases, Center for the Study of Emerging and Re-emerging Pathogens, University of Texas Medical School at Houston, 6431 Fannin, 2.112 MSB, Houston, TX 77030, USA.
Infect Immun. 2005 Aug;73(8):4888-94. doi: 10.1128/IAI.73.8.4888-4894.2005.
An Enterococcus faecalis gelE insertion disruption mutant (TX5128), which produces neither gelatinase (GelE) nor the cotranscribed (in the wild type) serine protease (SprE), was found to be attenuated in a rat endocarditis model with a significant decrease in the endocarditis induction rate versus wild-type E. faecalis OG1RF (GelE(+), SprE(+)). TX5266, which has a nonpolar deletion in fsrB and, like TX5128, is phenotypically GelE(-) under usual conditions, was also studied; fsrB is a homologue of agrB of staphylococci and participates in regulation of gelE-sprE expression. Unexpectedly, TX5266 approximated wild-type OG1RF in the endocarditis model and was significantly less attenuated than TX5128. This is in contrast to other models which have found fsr mutants to be as or more attenuated than TX5128. Further study found that the fsrB mutant produced very low levels of gelatinase activity after prolonged incubation in vitro versus no gelatinase activity with TX5128 and did not show the extensive chaining characteristic of TX5128. Reverse transcription-PCR confirmed that gelE was expressed in TX5266 at a very low level versus wild-type OG1RF and was not expressed at all in TX5128. Possible explanations for the increased induction of endocarditis by TX5266 versus TX5128 include the production of low levels of protease(s) or some other effect(s) of the inactivation of the E. faecalis fsr regulator. The equivalent ability of OG1RF and its fsr mutant to initiate endocarditis may explain why we did not find naturally occurring fsr mutants, which account for ca. 35% of E. faecalis isolates, unrepresented in endocarditis versus fecal isolates.
粪肠球菌gelE插入破坏突变体(TX5128)既不产生明胶酶(GelE),也不产生(野生型中)共转录的丝氨酸蛋白酶(SprE),在大鼠心内膜炎模型中被发现毒力减弱,与野生型粪肠球菌OG1RF(GelE(+),SprE(+))相比,心内膜炎诱导率显著降低。还研究了TX5266,它在fsrB中有一个非极性缺失,并且像TX5128一样,在通常条件下表型为GelE(-);fsrB是葡萄球菌agrB的同源物,参与gelE-sprE表达的调控。出乎意料的是,TX5266在心内膜炎模型中接近野生型OG1RF,并且毒力减弱程度明显低于TX5128。这与其他发现fsr突变体与TX5128一样或更弱毒的模型形成对比。进一步研究发现,与TX5128无明胶酶活性相比,fsrB突变体在体外长时间孵育后产生的明胶酶活性非常低,并且没有表现出TX5128广泛的成链特征。逆转录PCR证实,与野生型OG1RF相比,gelE在TX5266中以非常低的水平表达,而在TX5128中根本不表达。TX5266相对于TX5128心内膜炎诱导增加的可能解释包括低水平蛋白酶的产生或粪肠球菌fsr调节因子失活的一些其他效应。OG1RF及其fsr突变体引发心内膜炎的同等能力可能解释了为什么我们没有发现天然存在的fsr突变体,其约占粪肠球菌分离株的35%,在心内膜炎分离株中与粪便分离株相比没有代表性。