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Zhen Zhang,1 Zhulan Yang,2 Xiaohong Xiang,3 Pu Liao,1 Changchun Niu1 1Department of Clinical Laboratory, Chongqing General Hospital, University of Chinese Academy of Sciences, Chongqing, People’s Republic of China; 2Department of Clinical Laboratory, Southwest Hospital, Army Medical University, Chongqing, People’s Republic of China; 3School of Pharmacy, Chongqing Medical and Pharmaceutical College, Chongqing, People’s Republic of ChinaCorrespondence: Changchun Niu; Pu Liao, Email bright_star2000@163.com; liaopu@sina.comIntroduction: Moraxella catarrhalis, which is an opportunistic pathogen and is one of the three major pathogens of community-acquired pneumonia, causes a variety of infections in clinic. In recent years, the isolation rate of Moraxella catarrhalis has gradually increased. In China, due to the clinical empirical use of antibiotics, the resistance rate of Moraxella catarrhalis isolated from children to β-lactam antibiotics has reached 99%. The non-susceptible rate of Moraxella catarrhalis to macrolide antibiotics has also increased significantly.Methods: Two isolates of Moraxella catarrhalis (R17123922_R and R18013231_R) were isolated from in-patients and were confirmed to be resistant to macrolide antibiotics using the standard disk diffusion and broth microdilution method recommended by CLSI. Whole-genome sequencing (WGS) analysis was performed in these two resistant strains.Results: A total of 696 SNVs (single nucleotide variations), and 79 indels (Insertion and Deletion) were found in R17123922_R and R18013231_R. These SNVs and indels were distributed evenly in the genome, and no centralized distribution occurred. Moreover, two isolates did not harbor any previously reported mutations in the 23S rRNA and ribosomal proteins.Conclusion: A novel indel in the MCR_0492 gene encoding TonB-dependent receptor protein was identified, and we speculated that TonB-dependent protein receptor may play an important role in macrolide resistance of Moraxella catarrhalis.Keywords: Moraxella catarrhalis, macrolides, mechanism of drug resistance, whole-genome sequencing

Ling Pu,1 Zuoyi Jian,2 Fen Pan,3 Yang Geng,4 Miao He,5 Pu Liao1,6 1Key Laboratory of Clinical Laboratory Diagnostics (Ministry of Education of China), College of Laboratory Medicine, Chongqing Medical University, Chongqing, People’s Republic of China; 2Department of Bioinformatics, Novogene Biotechnology Co., Ltd, Sichuan, People’s Republic of China; 3Department of Clinical Laboratory, Shanghai Children’s Hospital, Shanghai, People’s Republic of China; 4College of Life Sciences, Sichuan University, Sichuan, People’s Republic of China; 5Institute of Blood Transfusion, Chinese Academy of Medical Sciences, Chengdu, Sichuan, People’s Republic of China; 6Department of Clinical Laboratory, Chongqing People’s Hospital, Chongqing, People’s Republic of ChinaCorrespondence: Pu LiaoCollege of Laboratory Medicine, Chongqing Medical University, No.1, Yixueyuan Road, Chongqing 400016, People’s Republic of ChinaTel +86 0 236 848 5240Fax +86 0 236 848 5240Email liaopu2015@163.com Miao HeInstitute of Blood Transfusion, Chinese Academy of Medical Sciences, No. 26, Huacai Road, Chengdu 610052, Sichuan, People’s Republic of ChinaTel +86 0 286 164 8549Fax +86 0 286 164 8556Email messa1022@126.comIntroduction: Multidrug-resistance in Acinetobacter baumannii has emerged as a serious problem to public health. There is still a significant gap in the understanding of the multidrug-resistance and the genome diversity evolutionary process of A. baumannii in China, especially in the central and western regions.Methods: Ten A. baumannii strains were collected from three hospitals in Chongqing, China. Whole-genome re-sequencing was used to obtain differences in genomic levels among strains. The diversity were determined by multi-locus sequence typing method, and investigate the genetic relationship between the ten strains and others by phylogenetic analysis. Comparative analysis focused on resistance genes related to insertions and deletions (InDels) and single-nucleotide polymorphisms (SNPs) was performed.Results: The overall G+C% content was 39.05%∼39.43%, the average sequencing depth was 273.95∼428.99, and the alignment ratio of the sequencing data was 92.93%∼99.27%. A total of 42 InDels and 11,387 SNPs were detected in the coding sequence region of the isolates. Phylogenetic tree shows that the 10 A. baumannii isolates were divided into four relative groups, and there exist the possibility of cross-regional spread pattern. A total number of 19 drug resistance genes had been found in each strain, and efflux pump-related genes accounted for the most. Only AacA4 underwent a change in InDel. Six types of drug resistance genes were found in the SNPs resistance gene-related loci, among which gene ANT(3’’)-II and QacE mutations were found in each strain.Conclusion: In this study, the main mechanism of A. baumannii multi-drug resistance is due to the multi-drug efflux pump related genes. The point mutations at the SNPs sites of the six types of resistance genes are the main differences in A. baumannii between Chongqing and the eastern coastal areas of China.Keywords: Acinetobacter baumannii, antimicrobial resistance, genome-wide re-sequencing, MLST, phylogenetic analysis, SNP