24We analyze the evolutionary dynamics of ninety carbapenem-resistant Acinetobacter 25 baumannii (CRAB) isolates collected between 1990 and 2015 in Chile. CRAB were 26 identified at first in an isolate collected in 2005, which harbored the ISAba1-bla OXA-69 27 arrangement. Later, OXA-58-and OXA-23-producing A. baumannii strains emerged in 28 2007 and 2009, respectively. This phenomenon was associated with variations in the 29 epidemiology of OXA-type carbapenemases, linked to nosocomial lineages belonging to 30 ST109 (CC1), ST162 (CC79), ST15 (CC15) and ST318 (CC15).31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 3Carbapenem-resistant Acinetobacter baumannii (CRAB) has been deemed a critical-47 priority pathogen by the World Health Organization (WHO) (1). It is normally involved in 48 infections acquired in the intensive care units (ICUs), and is commonly resistant to several 49 antibiotics, including carbapenems (2). Accordingly, OXA-type carbapenemases (OTCs) 50 are the main resistance mechanism to carbapenems in A. baumannii (3). While OXA-51-51 like carbapenemases are chromosomally encoded, the remaining OTCs (OXA-23-like, -24-52 like, -58-like and -143-like) are frequently plasmid encoded (4, 5). OXA-51-like enzymes 53 can mediate resistance to carbapenems if they are overexpressed when the ISAba1 element 54 is present upstream of the bla OXA-51-like gene (6). CRAB outbreaks are commonly associated 55 to the three predominant clonal complexes (CCs) CC109/1, CC118/2 and CC187/3 56 (University of Oxford/Institute Pasteur MLST schemes) (7). Although, the clonal complex 57 CC113/CC79 has been predominant in South America; CC104/CC15, CC110/ST25 and 58 CC109/CC1 are also present in this region (8).
59The aim of this study was to investigate the evolutionary dynamics of CRAB in 60 Chilean hospitals, where this pathogen has an endemic status.
61Ninety non-repetitive A. baumannii isolates recovered between 1990 and 2015 were 62 included. They were collected in hospitals from nine different cities throughout Chile, in 63 which the greatest distance between two cities is 2,433 km, representing over 50% of the 64 length of the country.
65Antibiotic susceptibility tests were performed to carbapenems, cephalosporins, 66 aminoglycosides, ampicillin/sulbactam, piperacillin/tazobactam, ciprofloxacin, and 67 tetracycline (9). Imipenem (IPM) and meropenem (MEM) MICs were determined 68 following the CLSI guidelines (9). Colistin-resistance was screened using the 69 4 SuperPolymyxin media (10). Multidrug-resistant (MDR), extensively-drug resistant (XDR) 70 and pandrug-resistant (PDR) phenotypes were defined as previously described (11, 12).
71Genetic relatedness was determined by pulsed-field gel electrophoresis (PFGE) as 72 described earlier (13). Groups with at least three genetically related isolates (>87% 73 similarity) were designated as major PFGE clusters (14). Single-locus bla OXA-51-like 74 sequence-based typing (SBT) was carried out as described previously (15). Isolates 75 101 PCR. Thus carbapenem-resistance could be...
