Transduction of Enteric Escherichia coli Isolates with a Derivative of Shiga Toxin 2-Encoding Bacteriophage φ3538 Isolated from Escherichia coli O157:H7

We investigated the ability of a detoxified derivative of a Shiga toxin 2 (Stx2)-encoding bacteriophage to infect and lysogenize enteric Escherichia coli strains and to develop infectious progeny from such lysogenized strains. The stx(2) gene of the patient E. coli O157:H7 isolate 3538/95 was replaced by the chloramphenicol acetyltransferase (cat) gene from plasmid pACYC184. Phage φ3538(Δstx(2)::cat) was isolated after induction of E. coli O157:H7 strain 3538/95 with mitomycin. A variety of strains of enteropathogenic E. coli (EPEC), enteroinvasive E. coli (EIEC), Stx-producing E. coli (STEC), enterotoxigenic E. coli (ETEC), enteroaggregative E. coli (EAEC), and E. coli from the physiological stool microflora were infected with φ3538(Δstx(2)::cat), and plaque formation and lysogenic conversion of wild-type E. coli strains were investigated. With the exception of one EIEC strain, none of the E. coli strains supported the formation of plaques when used as indicators for φ3538(Δstx(2)::cat). However, 2 of 11 EPEC, 11 of 25 STEC, 2 of 7 EAEC, 1 of 3 EIEC, and 1 of 6 E. coli isolates from the stool microflora of healthy individuals integrated the phage in their chromosomes and expressed resistance to chloramphenicol. Following induction with mitomycin, these lysogenic strains released infectious particles of φ3538(Δstx(2)::cat) that formed plaques on a lawn of E. coli laboratory strain C600. The results of our study demonstrate that φ3538(Δstx(2)::cat) was able to infect and lysogenize particular enteric strains of pathogenic and nonpathogenic E. coli and that the lysogens produced infectious phage progeny. Stx-encoding bacteriophages are able to spread stx genes among enteric E. coli strains.

本研究探究了编码志贺毒素2（Stx2）的大肠杆菌噬菌体的脱毒衍生物感染肠道大肠杆菌菌株、使其发生溶原化，并从这类溶原化菌株中产生感染性子代噬菌体的能力。研究人员将患者来源的大肠杆菌O157:H7分离株3538/95中的stx(2)基因替换为源自质粒pACYC184的氯霉素乙酰转移酶（cat）基因。通过丝裂霉素诱导大肠杆菌O157:H7菌株3538/95后，成功分离得到噬菌体φ3538(Δstx(2)::cat)。本研究使用该噬菌体感染多种肠道大肠杆菌菌株，涵盖肠致病性大肠杆菌（EPEC）、肠侵袭性大肠杆菌（EIEC）、产志贺毒素大肠杆菌（STEC）、产肠毒素大肠杆菌（ETEC）、肠聚集性大肠杆菌（EAEC）以及来自生理粪便菌群的大肠杆菌，并对其噬菌斑形成情况与野生型大肠杆菌菌株的溶原性转换现象进行了考察。除1株EIEC菌株外，其余所有受试大肠杆菌菌株作为φ3538(Δstx(2)::cat)的指示菌时，均无法支持噬菌斑形成。不过，11株EPEC分离株中的2株、25株STEC分离株中的11株、7株EAEC分离株中的2株、3株EIEC分离株中的1株，以及6株来自健康个体粪便菌群的大肠杆菌分离株中的1株，可将该噬菌体整合至自身染色体基因组中，并表现出对氯霉素的抗性。经丝裂霉素诱导后，这些溶原菌株可释放具有感染性的φ3538(Δstx(2)::cat)颗粒，该颗粒可在大肠杆菌实验室菌株C600的菌苔上形成噬菌斑。本研究结果表明，φ3538(Δstx(2)::cat)能够感染特定的致病性与非致病性肠道大肠杆菌菌株并使其发生溶原化，且此类溶原菌可产生具有感染性的噬菌体子代。编码志贺毒素的噬菌体可在肠道大肠杆菌菌株间传播stx基因。