Identification of a Novel NDM Variant,NDM-13, from a Multidrug-Resistant Escherichia coli Clinical Isolate in Nepal

A novel New Delhi metallo-β-lactamase, NDM-13, was identified in a carbapenem-resistant Escherichia coli clinical isolate obtained from the urine of a patient in Nepal. The enzymatic activity of NDM-13 against β-lactams was similar to that of NDM-1. However, NDM-13 displayed significantly higher k_cat/K_m ratios for cefotaxime. The genetic environment of bla_NDM-13 was determined to be tnpA-IS30-bla_NDM-13-ble_MBL-trpF-dsbC-cutA-groES-groL, with bla_NDM-13 located within the chromosome.     

High Prevalence of blaNDM-1 Carbapenemase-Encoding Gene and 16S rRNA armA Methyltransferase Gene among Acinetobacter baumannii Clinical Isolates in Egypt

The main objective of this study was to decipher the molecular mechanism of resistance to carbapenems and aminoglycosides in a large series of 150 Acinetobacter baumannii clinical isolates collected from July 2012 to September 2013 in Egypt. We report for the first time the emergence of bla_NDM-1 and the cooccurrence of 16S rRNA methylase armA with bla_NDM-1 and bla_OXA-23 in Egyptian hospitals. Multilocus sequence typing identified 27 distinct sequence types, 11 of which were novel.     

黄芩苷对一株产NDM-1 大肠埃希菌体内外抗菌作用的研究

目的 观察黄芩苷对产NDM-1大肠埃希菌的体内外抗菌作用。方法 肉汤稀释法测定黄芩苷的最小抑菌浓度(MIC)、最小杀菌浓度(MBC); 棋盘联合药敏试验检测黄芩苷与亚胺培南的协同作用; 通过小鼠菌血症模型,观察黄芩苷对感染模型的保护作用。结果 黄芩苷的最小抑菌浓度和最小杀菌浓度相同,均为8 mg/ml; 黄芩苷与亚胺培南呈明显的协同作用(FIC=0.125),单独使用黄芩苷使菌血症小鼠死亡率降低25%。结论 黄芩苷体内、外均具有一定的抗产NDM-1大肠埃希菌活性。     

三株从新生儿标本中分离的ST 1642型产NDM-5型碳青霉烯酶 大肠埃希菌

摘要：目的 分析新生儿科3株产NDM-5型碳青霉烯耐药大肠埃希菌的分子流行特征。方法 收集2017年8-9月新生儿科病房分离的3株碳青霉烯耐药大肠埃希菌（E1、E2、E3），Vitek2-Compact系统联合K-B法、E-test法进行药物敏感性试验，PCR扩增碳青霉烯耐药基因及其他相关耐药基因，检测质粒复制子分型并进行质粒接合转移试验，多位点序列分析（MLST）和脉冲场凝胶电泳（PFGE）分析菌株同源性。结果 药敏结果提示3株细菌对绝大多数β内酰胺类药物耐药，除外氨曲南（E1、E3敏感，E2耐药），对多粘菌素B、氨基糖苷类药物均敏感。PCR及测序结果提示3株细菌均检到blaNDM-5基因，同时检测到部分超广谱β内酰胺酶基因（blaSHV、blaTEM或blaCTX-M）；质粒复制子类型均为IncX3，E1质粒接合转移试验成功；MLST结果提示3株细菌均为ST1642型，PFGE结果显示3株细菌条带一致。结论 新生儿科3株碳青霉烯耐药的细菌均产NDM-5型碳青霉烯酶，同时携带超广谱β内酰胺酶基因，MLST和PFGE提示3株细菌为同一克隆来源。     

Tetracycline Resistance in Escherichia coli Isolates from Hospital Patients

Hospital isolates of Escherichia coli resistant to tetracycline (TC) were studied to identify mechanisms which regulate TC resistance levels and ability to transfer TC resistance. Antibiotic resistance patterns, resistance levels to TC, and ability to transfer TC resistance were determined for the isolates. Similar data were obtained for the transferable plasmids after transfer to several new host strains of E. coli. Of the 110 isolates, 50% were able to transfer TC resistance by conjugation. There was a nearly linear relationship between the minimum inhibitory concentration (MIC) of TC for the hospital strains and the percentage of strains at a given MIC that could transfer TC resistance. The strains that were simultaneously resistant to tetracycline, streptomycin, and ampicillin had relatively high MICs of TC and high ability to transfer TC resistance. These results and surveys of TC-resistant E. coli by others suggest that TC resistance levels and transmissibility may be influenced by other resistance markers. The isolates which did not transfer TC resistance by conjugation were tested for the presence of TC resistance plasmids by mobilization or by transformation with deoxyribonucleic acid from the isolates. Evidence for plasmid-mediated TC resistance was found in 92 (84%) of the 110 hospital strains.     

Two Multidrug-Resistant Clinical Isolates of Bacteroides fragilis Carry a Novel Metronidazole Resistance nim Gene (nimJ)

Two multidrug-resistant Bacteroides fragilis clinical isolates contain and express a novel nim gene, nimJ, that is not recognized by the “universal” nim primers and can confer increased resistance to metronidazole when introduced into a susceptible strain on a multicopy plasmid. HMW615, an appendiceal isolate, contains at least two copies of nimJ on its genome, while HMW616, an isolate from a patient with sepsis, contains one genomic copy of nimJ. B. fragilis NimJ is phylogenetically closer to Prevotella baroniae NimI and Clostridium botulinum NimA than to the other known Bacteroides Nim proteins. The predicted protein structure of NimJ, based on fold recognition analysis, is consistent with the crystal structures derived for known Nim proteins, and specific amino acid residues important for substrate binding in the active site are conserved. This study demonstrates that the “universal” nim primers will not detect all nim genes with the ability to confer metronidazole resistance, but nimJ alone cannot account for the very high metronidazole MICs of these resistant clinical isolates.     

Molecular Characterization of Multidrug-Resistant Mycobacterium tuberculosis Isolates from China

To investigate the molecular characterization of multidrug-resistant tuberculosis (MDR-TB) isolates from China and the association of specific mutations conferring drug resistance with strains of different genotypes, we performed spoligotyping and sequenced nine loci (katG, inhA, the oxyR-ahpC intergenic region, rpoB, tlyA, eis, rrs, gyrA, and gyrB) for 128 MDR-TB isolates. Our results showed that 108 isolates (84.4%) were Beijing family strains, 64 (59.3%) of which were identified as modern Beijing strains. Compared with the phenotypic data, the sensitivity and specificity of DNA sequencing were 89.1% and 100.0%, respectively, for isoniazid (INH) resistance, 93.8% and 100.0% for rifampin (RIF) resistance, 60.0% and 99.4% for capreomycin (CAP) resistance, 84.6% and 99.4% for kanamycin (KAN) resistance, and 90.0% and 100.0% for ofloxacin (OFX) resistance. The most prevalent mutations among the MDR-TB isolates were katG315, inhA15, rpoB531, -526, and -516, rrs1401, eis-10, and gyrA94, -90, and -91. Furthermore, there was no association between specific resistance-conferring mutations and the strain genotype. These findings will be helpful for the establishment of rapid molecular diagnostic methods to be implemented in China.     

Outbreak Caused by NDM-1- and RmtB-Producing Escherichia coli in Bulgaria

Twelve consecutive carbapenem-resistant Escherichia coli isolates were recovered from patients (infection or colonization) hospitalized between March and September 2012 in different units at a hospital in Bulgaria. They all produced the carbapenemase NDM-1 and the extended-spectrum-β-lactamase CTX-M-15, together with the 16S rRNA methylase RmtB, conferring high-level resistance to all aminoglycosides. All those isolates were clonally related and belonged to the same sequence type, ST101. In addition to being the first to identify NDM-producing isolates in Bulgaria, this is the very first study reporting an outbreak of NDM-1-producing E. coli in the world.     

Inhibitor-Resistant TEM- and OXA-1-Producing Escherichia coli Isolates Resistant to Amoxicillin-Clavulanate Are More Clonal and Possess Lower Virulence Gene Content than Susceptible Clinical Isolates

In a previous prospective multicenter study in Spain, we found that OXA-1 and inhibitor-resistant TEM (IRT) β-lactamases constitute the most common plasmid-borne mechanisms of genuine amoxicillin-clavulanate (AMC) resistance in Escherichia coli. In the present study, we investigated the population structure and virulence traits of clinical AMC-resistant E. coli strains expressing OXA-1 or IRT and compared these traits to those in a control group of clinical AMC-susceptible E. coli isolates. All OXA-1-producing (n = 67) and IRT-producing (n = 45) isolates were matched by geographical and temporal origin to the AMC-susceptible control set (n = 56). We performed multilocus sequence typing and phylogenetic group characterization for each isolate and then studied the isolates for the presence of 49 virulence factors (VFs) by PCR and sequencing. The most prevalent clone detected was distinct for each group: group C isolates of sequence type (ST) 88 (C/ST88) were the most common in OXA-1 producers, B2/ST131 isolates were the most common in IRT producers, and B2/ST73 isolates were the most common in AMC-susceptible isolates. The median numbers of isolates per ST were 3.72 in OXA-1 producers, 2.04 in IRT producers, and 1.69 in AMC-susceptible isolates; the proportions of STs represented by one unique isolate in each group were 19.4%, 31.1%, and 48.2%, respectively. The sum of all VFs detected, calculated as a virulence score, was significantly higher in AMC-susceptible isolates than OXA-1 and IRT producers (means, 12.5 versus 8.3 and 8.2, respectively). Our findings suggest that IRT- and OXA-1-producing E. coli isolates resistant to AMC have a different and less diverse population structure than AMC-susceptible clinical E. coli isolates. The AMC-susceptible population also contains more VFs than AMC-resistant isolates.