Clinical Unit of Infectious Diseases, Clinical Microbiology and Preventive Medicine, Institute of Biomedicine of Seville (IBiS), University Hospital Virgen del Rocío/CSIC/University of Seville, Seville, Spain.
Department of Medicine, University of Seville, Seville, Spain.
J Antimicrob Chemother. 2018 Nov 1;73(11):2960-2968. doi: 10.1093/jac/dky289.
Acinetobacter baumannii is intrinsically resistant to fosfomycin; however, the mechanisms underlying this resistance are poorly understood.
To identify and characterize genes that contribute to intrinsic fosfomycin resistance in A. baumannii.
More than 9000 individual transposon mutants of the A. baumannii ATCC 17978 strain (fosfomycin MIC ≥1024 mg/L) were screened to identify mutations conferring increased susceptibility to fosfomycin. In-frame deletion mutants were constructed for the identified genes and their susceptibility to fosfomycin was characterized by MIC determination and growth in the presence of fosfomycin. The effects of these mutations on membrane permeability and peptidoglycan integrity were characterized. Susceptibilities to 21 antibiotics were determined for the mutant strains.
Screening of the transposon library identified mutants in the ampD and anmK genes, both encoding enzymes of the peptidoglycan recycling pathway, that demonstrated increased susceptibility to fosfomycin. MIC values for in-frame deletion mutants were ≥42-fold (ampD) and ≥8-fold (anmK) lower than those for the parental strain, and growth of the mutant strains in the presence of 32 mg/L fosfomycin was significantly reduced. Neither mutation resulted in increased cell permeability; however, the ampD mutant demonstrated decreased peptidoglycan integrity. Susceptibility to 21 antibiotics was minimally affected by mutations in ampD and anmK.
This study demonstrates that AmpD and AnmK of the peptidoglycan recycling pathway contribute to intrinsic fosfomycin resistance in A. baumannii, indicating that inhibitors of these enzymes could be used in combination with fosfomycin as a novel treatment approach for MDR A. baumannii.
鲍曼不动杆菌对磷霉素具有固有耐药性；然而，其耐药机制尚不清楚。
鉴定和表征导致鲍曼不动杆菌固有磷霉素耐药的基因。
筛选了超过 9000 个鲍曼不动杆菌 ATCC 17978 株（磷霉素 MIC≥1024mg/L）的转座子突变体，以鉴定增加对磷霉素敏感性的突变。对鉴定的基因进行框内缺失突变体构建，并通过 MIC 测定和在磷霉素存在下的生长来表征其对磷霉素的敏感性。还对这些突变对膜通透性和肽聚糖完整性的影响进行了表征。测定了突变株对 21 种抗生素的敏感性。
转座子文库筛选发现了编码肽聚糖回收途径中酶的 ampD 和 anmK 基因的突变体，这些突变体对磷霉素的敏感性增加。框内缺失突变体的 MIC 值比亲本株至少低 42 倍（ampD）和 8 倍（anmK），并且突变株在 32mg/L 磷霉素存在下的生长显著减少。这两种突变都没有导致细胞通透性增加；然而，ampD 突变体显示出肽聚糖完整性降低。ampD 和 anmK 突变对 21 种抗生素的敏感性影响最小。
本研究表明，肽聚糖回收途径中的 AmpD 和 AnmK 有助于鲍曼不动杆菌固有磷霉素耐药，表明这些酶的抑制剂可与磷霉素联合用于治疗 MDR 鲍曼不动杆菌。
