Department of Veterinary Science and Microbiology, The University of Arizona, 1117 E Lowell Street, Tucson, AZ 85721, USA.
BMC Microbiol. 2011 Oct 26;11:239. doi: 10.1186/1471-2180-11-239.
Arcanobacterium haemolyticum is an emerging human pathogen that causes pharyngitis, wound infections, and a variety of occasional invasive diseases. Since its initial discovery in 1946, this Gram positive organism has been known to have hemolytic activity, yet no hemolysin has been previously reported. A. haemolyticum also displays variable hemolytic activity on laboratory blood agar that is dependent upon which species the blood is derived.
Here we describe a cholesterol-dependent cytolysin (CDC) secreted by A. haemolyticum, designated arcanolysin (aln), which is present in all strains (n = 52) tested by DNA dot hybridization. Among the known CDCs, ALN is most closely related to pyolysin (PLO) from Trueperella (formerly Arcanobacterium) pyogenes. The aln probe, however, did not hybridize to DNA from T. pyogenes. The aln open reading frame has a lower mol %G+C (46.7%) than the rest of the A. haemolyticum genome (53.1%) and is flanked by two tRNA genes, consistent with probable acquisition by horizontal transfer. The ALN protein (~ 64 kDa) contains a predicted signal sequence, a putative PEST sequence, and a variant undecapeptide within domain 4, which is typically important for function of the toxins. The gene encoding ALN was cloned and expressed in Escherichia coli as a functional recombinant toxin. Recombinant ALN had hemolytic activity on erythrocytes and cytolytic activity on cultured cells from human, rabbit, pig and horse origins but was poorly active on ovine, bovine, murine, and canine cells. ALN was less sensitive to inhibition by free cholesterol than perfringolysin O, consistent with the presence of the variant undecapeptide.
ALN is a newly identified CDC with hemolytic activity and unique properties in the CDC family and may be a virulence determinant for A. haemolyticum.
海氏肠球菌是一种新兴的人类病原体，可引起咽炎、伤口感染和各种偶发性侵袭性疾病。自 1946 年首次发现以来，这种革兰氏阳性菌已被证明具有溶血活性，但以前没有报道过任何溶血素。海氏肠球菌在实验室血琼脂上的溶血活性具有可变性，这取决于血液来自哪种物种。
在这里，我们描述了一种由海氏肠球菌分泌的胆固醇依赖性细胞溶解素（CDC），命名为海氏溶血素（aln），通过 DNA 点杂交检测，所有测试菌株（n=52）均存在 aln。在已知的 CDCs 中，ALN 与来自 Trueperella（以前的 Arcanobacterium）pyogenes 的 pyolysin（PLO）最为密切相关。然而，aln 探针与 T. pyogenes 的 DNA 不杂交。aln 开放阅读框的 mol%G+C（46.7%）低于海氏肠球菌基因组的其余部分（53.1%），并且两侧是两个 tRNA 基因，这与可能通过水平转移获得一致。ALN 蛋白（~64 kDa）包含一个预测的信号序列、一个推定的 PEST 序列和结构域 4 内的一个变体十一肽，这通常对毒素的功能很重要。编码 ALN 的基因在大肠杆菌中克隆并表达为功能性重组毒素。重组 ALN 在人、兔、猪和马来源的培养细胞上具有溶血活性和细胞溶解活性，但对绵羊、牛、鼠和犬来源的细胞活性较差。ALN 对游离胆固醇的抑制作用不如产气荚膜梭菌毒素 O 敏感，这与存在变体十一肽一致。
ALN 是一种新发现的具有溶血活性和独特性质的 CDC，可能是海氏肠球菌的毒力决定因素。
