Carrasco Letícia Dias de Melo, Dabul Andrei Nicoli Gebieluca, Boralli Camila Maria Dos Santos, Righetto Gabriela Marinho, Carvalho Iago Silva E, Dornelas Janaína Valerini, Martins da Mata Camila Pacheco Silveira, de Araújo César Augusto, Leite Edna Mariléa Meireles, Lincopan Nilton, Camargo Ilana Lopes Baratella da Cunha
Laboratory of Molecular Epidemiology and Microbiology, Department of Physics and Interdisciplinary Science, São Carlos Institute of Physics, University of São Paulo, São Paulo, Brazil.
Hospital Risoleta Tolentino Neves, Belo Horizonte, Brazil.
Front Microbiol. 2021 Mar 26;12:622704. doi: 10.3389/fmicb.2021.622704. eCollection 2021.
is an opportunistic pathogen primarily associated with multidrug-resistant nosocomial infections, for which polymyxins are the last-resort antibiotics. This study investigated carbapenem-resistant strains exhibiting an extensively drug-resistant (XDR) phenotype, including four isolates considered locally pan drug-resistant (PDR), isolated from inpatients during an outbreak at a teaching hospital in Brazil. ApaI DNA macrorestriction followed by PFGE clustered the strains in three pulsotypes, named A to C, among carbapenem-resistant strains. Pulsotypes A and B clustered six polymyxin-resistant strains. MLST analysis of representative strains of pulsotypes A, B, and C showed that they belong, respectively, to sequence types ST1 (clonal complex, CC1), ST79 (CC79), and ST903. Genomic analysis of international clones ST1 and ST79 representative strains predicted a wide resistome for β-lactams, aminoglycosides, fluoroquinolones, and trimethoprim-sulfamethoxazole, with and genes encoding carbapenem resistance. Amino acid substitutions in PmrB (Thr232Ile or Pro170Leu) and PmrC (Arg125His) were responsible for polymyxin resistance. Although colistin MICs were all high (MIC ≥ 128 mg/L), polymyxin B MICs varied; strains with Pro170Leu substitution in PmrB had MICs > 128 mg/L, while those with Thr232Ile had lower MICs (16-64 mg/L), irrespective of the clone. Although the first identified polymyxin-resistant strain belonged to ST79, the ST1 strains were endemic and caused the outbreak most likely due to polymyxin B use. The genome comparison of two ST1 strains from the same patient, but one susceptible and the other resistant to polymyxin, revealed mutations in 28 ORFs in addition to . The ORF codifying an acyl-CoA dehydrogenase has gained attention due to its fatty acid breakdown and membrane fluidity involvement. However, the role of these mutations in the polymyxin resistance mechanism remains unknown. To prevent the dissemination of XDR bacteria, the hospital infection control committee implemented the patient bathing practice with a 2% chlorhexidine solution, a higher concentration than all chlorhexidine MICs. In conclusion, we showed the emergence of polymyxin resistance due to mutations in the chromosome of the carbapenem-resistant ST1, a high-risk global clone spreading in this hospital.
是一种机会致病菌，主要与多重耐药的医院感染相关，针对此类感染，多粘菌素是最后的抗生素选择。本研究调查了表现出广泛耐药（XDR）表型的耐碳青霉烯菌株，包括从巴西一家教学医院疫情期间住院患者中分离出的4株被认为是本地全耐药（PDR）的菌株。ApaI DNA宏观限制性内切酶消化后进行脉冲场凝胶电泳（PFGE），将耐碳青霉烯菌株分为三个脉冲型，命名为A至C。脉冲型A和B包含6株耐多粘菌素菌株。对脉冲型A、B和C的代表性菌株进行多位点序列分型（MLST）分析表明，它们分别属于序列类型ST1（克隆复合体，CC1）、ST79（CC79）和ST903。对国际克隆ST1和ST79代表性菌株的基因组分析预测，其对β-内酰胺类、氨基糖苷类、氟喹诺酮类和甲氧苄啶-磺胺甲恶唑具有广泛的耐药组，有编码耐碳青霉烯的 和 基因。PmrB（Thr232Ile或Pro170Leu）和PmrC（Arg125His）中的氨基酸替换导致了多粘菌素耐药。尽管所有菌株的黏菌素最低抑菌浓度（MIC）都很高（MIC≥128mg/L），但多粘菌素B的MIC有所不同；PmrB中发生Pro170Leu替换的菌株MIC>128mg/L，而发生Thr232Ile替换的菌株MIC较低（16 - 64mg/L），与克隆无关。尽管最早鉴定出的耐多粘菌素菌株属于ST79，但ST1菌株是本地流行菌株，很可能是由于使用多粘菌素B导致了疫情爆发。对来自同一患者的两株ST1菌株进行基因组比较，其中一株对多粘菌素敏感，另一株耐药，结果显示除了 外，还有28个开放阅读框（ORF）发生了突变。编码酰基辅酶A脱氢酶的ORF因其参与脂肪酸分解和膜流动性而受到关注。然而，这些突变在多粘菌素耐药机制中的作用尚不清楚。为防止XDR细菌传播，医院感染控制委员会实施了用2%洗必泰溶液给患者洗澡的措施，该浓度高于所有洗必泰的MIC。总之，我们发现耐碳青霉烯的ST1（一种在该医院传播的高风险全球克隆）染色体突变导致了多粘菌素耐药的出现。
