An Outbreak of tet(X6)-Carrying Tigecycline-Resistant Acinetobacter baumannii Isolates with a New Capsular Type at a Hospital in Taiwan.

Yu-Chia Hsieh,Jia-Wen Wu,Yin-Cheng Chen,Yi-Jiun Pan,Yi-Yin Chen,Wei-Chao Liao,Tran Lam Tu Quyen,Shiao-Wen Li

doi:10.3390/antibiotics10101239

Abstract

Dissemination of multidrug-resistant, particularly tigecycline-resistant, Acinetobacter baumannii is of critical importance, as tigecycline is considered a last-line antibiotic. Acquisition of tet(X), a tigecycline-inactivating enzyme mostly found in strains of animal origin, imparts tigecycline resistance to A. baumannii. Herein, we investigated the presence of tet(X) variants among 228 tigecycline-non-susceptible A. baumannii isolates from patients at a Taiwanese hospital via polymerase chain reaction using a newly designed universal primer pair. Seven strains (3%) carrying tet(X)-like genes were subjected to whole genome sequencing, revealing high DNA identity. Phylogenetic analysis based on the PFGE profile clustered the seven strains in a clade, which were thus considered outbreak strains. These strains, which were found to co-harbor the chromosome-encoded tet(X6) and the plasmid-encoded blaOXA-72 genes, showed a distinct genotype with an uncommon sequence type (Oxford ST793/Pasteur ST723) and a new capsular type (KL129). In conclusion, we identified an outbreak clone co-carrying tet(X6) and blaOXA-72 among a group of clinical A. baumannii isolates in Taiwan. To the best of our knowledge, this is the first description of tet(X6) in humans and the first report of a tet(X)-like gene in Taiwan. These findings identify the risk for the spread of tet(X6)-carrying tigecycline- and carbapenem-resistant A. baumannii in human healthcare settings.

Highlights

The emergence of multidrug-resistant Gram-negative bacteria poses a serious threat to global health
We screened 228 non-repetitive clinical tigecycline-non-susceptible A. baumannii isolates in Taiwan for the presence of tet(X) variants via polymerase chain reaction (PCR) using a universal primer pair designed in this study
We further determined that the minimum inhibitory concentration (MIC) of tigecycline for the seven strains was 4–8 mg/L (Table 1)

Summary

Introduction

The emergence of multidrug-resistant Gram-negative bacteria poses a serious threat to global health. Acinetobacter baumannii is a troublesome nosocomial pathogen that causes pneumonia, sepsis, and wound and urinary tract infections, and leads to severe disease and death in intensive care unit (ICU) patients [1,2,3,4,5,6]. The spread of multidrug-resistant A. baumannii (MDRAB) has increased rapidly, and A. baumannii strains resistant to carbapenem, which has been used to treat MDRAB infections, has emerged [7,8,9,10,11,12,13]. Colistin and tigecycline are the two last-resort antibiotic options for treatment of infections caused by carbapenem-resistant A. baumannii. Cases of colistin- or tigecycline-resistant A. baumannii infections have been reported worldwide [14,15,16,17]

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Results