Genomic and Molecular Characterization of Clinical Isolates of Enterobacteriaceae Harboring mcr-1 in Colombia, 2002 to 2016

ABSTRACT Polymyxins are last-resort antimicrobial agents used to treat infections caused by carbapenem-resistant Enterobacteriaceae. Due to the worldwide dissemination of polymyxin resistance in animal and human isolates, we aimed to characterize polymyxin resistance associated with the presence of mcr-1 in Enterobacteriaceae and nonfermenter Gram-negative bacilli, using isolates collected retrospectively in Colombia from 2002 to 2016. A total of 5,887 Gram-negative clinical isolates were studied, and 513 were found to be resistant to the polymyxins. Susceptibility to colistin was confirmed by broth microdilution for all mcr-1-positive isolates, and these were further subjected to whole-genome sequencing (WGS). The localization of mcr-1 was confirmed by S1 pulsed-field gel electrophoresis (S1-PFGE) and CeuI-PFGE hybridization. Transferability was evaluated by mating assays. A total of 12 colistin-resistant isolates recovered after 2013 harbored mcr-1, including 8 Escherichia coli, 3 Salmonella enterica serovar Typhimurium, and 1 Klebsiella pneumoniae isolate. E. coli isolates were unrelated by PFGE and belonged to 7 different sequence types (STs) and phylogroups. S. Typhimurium and K. pneumoniae isolates belonged to ST34 and ST307, respectively. The mcr-1 gene was plasmid borne in all isolates but two E. coli isolates which harbored it on the chromosome. Conjugation of mcr-1 was successful in 8 of 10 isolates (8.2 × 10−5 to 2.07 × 10−1 cell per recipient). Plasmid sequences showed that the mcr-1 plasmids belonged to four different Inc groups (a new IncP-1 variant and the IncFII, IncHI1, and IncH families). Our results indicate that mcr-1 is circulating in clinical isolates of colistin-resistant Enterobacteriaceae in Colombia and is mainly harbored in transferable plasmids.

Modeling ratios of phenotypic classes in wheat hybrids of introgressive origin for glume color trait

Aim. Develop inheritance model for glume color in hybrid generations considering introgressive origin of crossing components. Methods. Phenotypic assessment of the trait, cytological study of chromosome conjugation in meiosis, methods determining statistical significance of the results. Results. Twelve cross combinations of wheat introgressive with one another and with recurrent genotype Aurora were studied. Selected for the crosses introgressive lines had contrasting glume color trait. Characteristics of wheat introgressive lines and its hybrids which would be important in hybrid analysis for the development of the inheritance model were identified. Genetic analysis of the introgressive lines was done as for the number of glume color genes for which lines differed from one another and from the Aurora genotype. Conclusions. In case the critical gene in localized in a chromosome that do not conjugate with hom(e)olog of the cross partner, F1 hybrids developed with introgressive lines form gametes and zygotes with frequencies differing from theoretically expected for the cross of homozygous lines. Keywords: wheat introgression lines, Aegilops, glume colour, aneuploidy gametes and zygotes, meiotic drive.