LAUSR

Abstract Background Resistance to colistin, the last line therapy for infections caused by multidrug-resistant Gram-negative bacteria, represents a major public health threat. Citrobacter freundii B9-C2 which was isolated from the stool of preterm neonate on the first week of life, displayed resistance to almost all major antibiotics, including colistin. Through whole genome sequencing (WGS), we characterised the genome features that underline the antibiotic-resistance phenotype of this isolate. Methods Genome of C. freundii B9-C2 was sequenced on an Illumina MiSeq platform. The assembled genome was annotated and deposited into GenBank under the accession number CP027849. Results Multiple antimicrobial resistance genes including blaCMY-66 were identified. Further, the presence of 15 antibiotic efflux pump-encoding resistance genes, including crp, baeR, hns, patA, emrB, msbA, acrA, acrB, emrR, mdtC, mdtB, mdtG, kdpE, mdfA and msrB, were detected and likely to account for the observed cephalosporins, carbapenems, aminoglycosides and monobactams resistance in C. freundii B9-C2. The isolate also presented unique virulence genes related to biofilm formation, motility and iron uptake. The genome was compared to publicly available genomes and it was closely related to strains with environmental origins. Conclusion To the best of our knowledge, this is the first report of intestinal carriage of colistin-resistant C. freundii from the stool of a neonate in Malaysia. Using genomic analysis, we have contributed to the understanding of the potential mechanism of resistance and the phylogenetic relationship of the isolates with draft genomes available in the public domain.