Department of Bacteriophage Therapeutics, Bacterial Diseases Branch, Walter Reed Army Institute of Research, Silver Spring, Maryland, USA.
Department of Bacteriophage Therapeutics, Bacterial Diseases Branch, Walter Reed Army Institute of Research, Silver Spring, Maryland, USA
Appl Environ Microbiol. 2019 Oct 30;85(22). doi: 10.1128/AEM.01209-19. Print 2019 Nov 15.
Staphylococci are frequent agents of health care-associated infections and include methicillin-resistant (MRSA), which is resistant to first-line antibiotic treatments. Bacteriophage (phage) therapy is a promising alternative antibacterial option to treat MRSA infections. -specific phage Sb-1 has been widely used in Georgia to treat a variety of human infections. Sb-1 has a broad host range within , including MRSA strains, and its host range can be further expanded by adaptation to previously resistant clinical isolates. The susceptibilities of a panel of 25 genetically diverse clinical MRSA isolates to Sb-1 phage were tested, and the phage had lytic activity against 23 strains (92%). The adapted phage stock (designated Sb-1A) was tested in comparison with the parental phage (designated Sb-1P). Sb-1P had lytic activity against 78/90 strains (87%) in an expanded panel of diverse global isolates, while eight additional strains in this panel were susceptible to Sb-1A (lytic against 86/90 strains [96%]). The Sb-1A stock was shown to be a mixed population of phage clones, including approximately 4% expanded host range mutants, designated Sb-1M. In an effort to better understand the genetic basis for this host range expansion, we sequenced the complete genomes of the parental Sb-1P and two Sb-1M mutants. Comparative genomic analysis revealed a hypervariable complex repeat structure in the Sb-1 genome that had a distinct allele that correlated with the host range expansion. This hypervariable region was previously uncharacterized in Twort-like phages and represents a novel putative host range determinant. Because of limited therapeutic options, infections caused by methicillin-resistant represent a serious problem in both civilian and military health care settings. Phages have potential as alternative antibacterial agents that can be used in combination with antibiotic drugs. For decades, phage Sb-1 has been used in former Soviet Union countries for antistaphylococcal treatment in humans. The therapeutic spectrum of activity of Sb-1 can be increased by selecting mutants of the phage with expanded host ranges. In this work, the host range of phage Sb-1 was expanded in the laboratory, and a hypervariable region in its genome was identified with a distinct allele state that correlated with this host range expansion. These results provide a genetic basis for better understanding the mechanisms of phage host range expansion.
葡萄球菌是常见的医疗保健相关感染的病原体，包括耐甲氧西林金黄色葡萄球菌（MRSA），它对一线抗生素治疗有耐药性。噬菌体（噬菌体）治疗是一种有前途的替代抗菌选择，可用于治疗 MRSA 感染。-特异性噬菌体 Sb-1 已在格鲁吉亚广泛用于治疗各种人类感染。Sb-1 在 内具有广泛的宿主范围，包括 MRSA 菌株，并且可以通过适应以前耐药的临床分离株进一步扩大其宿主范围。测试了一组 25 种遗传上不同的临床 MRSA 分离株对 Sb-1 噬菌体的敏感性，噬菌体对 23 株（92%）具有裂解活性。与亲本噬菌体（命名为 Sb-1P）相比，适应性噬菌体库存（命名为 Sb-1A）进行了测试。在扩展的多样化全球 分离株面板中，Sb-1P 对 78/90 株（87%）具有裂解活性，而该面板中的另外 8 株对 Sb-1A 敏感（裂解对 86/90 株 [96%]）。显示 Sb-1A 库存是噬菌体克隆的混合群体，包括大约 4%的扩大宿主范围突变体，命名为 Sb-1M。为了更好地理解这种宿主范围扩展的遗传基础，我们对亲本 Sb-1P 和两个 Sb-1M 突变体的完整基因组进行了测序。比较基因组分析显示，Sb-1 基因组中存在一个超可变的复杂重复结构，该结构具有一个独特的等位基因，与宿主范围扩展相关。这个超可变区域在 Twort 样噬菌体中以前没有被描述过，代表了一个新的潜在的宿主范围决定因素。由于治疗选择有限，耐甲氧西林 引起的感染在民用和军事医疗保健环境中都是一个严重的问题。噬菌体作为替代抗菌剂具有潜力，可以与抗生素药物联合使用。几十年来，噬菌体 Sb-1 在前苏联国家一直用于人类抗葡萄球菌治疗。通过选择具有扩大宿主范围的噬菌体突变体，可以增加 Sb-1 的治疗谱。在这项工作中，噬菌体 Sb-1 的宿主范围在实验室中得到了扩展，并在其基因组中确定了一个具有独特等位基因状态的超可变区域，该区域与这种宿主范围扩展相关。这些结果为更好地理解噬菌体宿主范围扩展的机制提供了遗传基础。
