Department of Microbiology, Faculty of Biology, A. Mickiewicz University, Poznań, Poland.
Microb Pathog. 2010 Sep;49(3):83-9. doi: 10.1016/j.micpath.2010.04.003. Epub 2010 May 6.
Strains of the Enterobacter cloacae complex are becoming increasingly important human pathogen. The aim of the study was to identify, by sequencing the hsp60 gene, the species of clinical isolates phenotypically identified as E. cloacae and to examine them for virulence-associated properties: the ability of adhesion, invasion to HEp-2 cells and the induced apoptosis of infected epithelial cells. The majority of the strains were identified as Enterobacter hormaechei with E. hormaechei subsp. steigerwaltii being the most frequent subspecies. Other strains belonged to E. hormaechei subsp. oharae, E. cloacae cluster III, and E. cloacae cluster IV. The strains were examined for virulence-associated properties: the ability to adhesion and invasion to HEp-2 cells and the apoptosis induction of infected epithelial cells. All strains revealed adherence ability and most of them (71%) were invasive to epithelial cells. Analyses of cellular morphology and DNA fragmentation in the HEp-2 cells exhibited typical features of cells undergoing apoptosis. We observed morphological changes, including condensation of nuclear chromatin, formation of apoptotic bodies and blebbing of cell membrane. The lowest apoptotic index did not exceed 6%, whereas the highest reached 49% at 24h and 98% at 48 h after infection. Forty strains (73%) induced fragmentation of nuclear DNA and characteristic intranucleosomal pattern with the size of about 180-200 bp in DNA extracted from infected cells at 48 h after infection. The results indicated that the bacteria of the E. cloacae complex may adhere to and penetrate into epithelial cells and induce apoptosis, which could be an important mechanism contributing to the development diseases.
肠杆菌科 cloacae 复合菌株正日益成为重要的人类病原体。本研究的目的是通过 hsp60 基因测序鉴定表型鉴定为 cloacae 的临床分离株的物种，并检查其与毒力相关的特性：粘附能力、侵袭 HEp-2 细胞的能力以及感染上皮细胞的诱导凋亡。大多数菌株被鉴定为霍氏肠杆菌，其中 steigerwaltii 亚种最为常见。其他菌株属于 oharae 亚种、cloacae 簇 III 和 cloacae 簇 IV。这些菌株被检查与毒力相关的特性：粘附和侵袭 HEp-2 细胞的能力以及感染上皮细胞的凋亡诱导。所有菌株均显示出粘附能力，其中大多数（71%）能够侵袭上皮细胞。对 HEp-2 细胞中细胞形态和 DNA 片段化的分析显示出典型的凋亡细胞特征。我们观察到形态学变化，包括核染色质的浓缩、凋亡小体的形成和细胞膜的起泡。凋亡指数最低不超过 6%，而最高在感染后 24 小时达到 49%，感染后 48 小时达到 98%。40 株（73%）在感染后 48 小时从感染细胞中提取的 DNA 中诱导核 DNA 片段化和特征性核小体模式，大小约为 180-200bp。结果表明，cloacae 复合细菌可能粘附并穿透上皮细胞并诱导凋亡，这可能是导致疾病发展的重要机制。
