Genomic Epidemiology of Escherichia coli Isolates from a Tertiary Referral Center in Lilongwe, Malawi

Antimicrobial resistance (AMR) is a global threat, including in sub-Saharan Africa. However, little is known about the genetics of resistant bacteria in the region. In Malawi, there is growing concern about increasing rates of antimicrobial resistance to most empirically used antimicrobials. The highly drug resistant Escherichia coli sequence type (ST) 131, which is associated with the extended spectrum B-lactamase blaCTX-M-15, has been increasing in prevalence globally. Previous data from isolates collected between 2006-2013 in Southern Malawi have shown the presence of ST131 and the blaCTX-M-15 gene in the country. We performed whole genome sequencing (WGS) of 58 clinical E. coli isolated from 2012-2018 at Kamuzu Central Hospital, a tertiary care center in central Malawi to increase our understanding of the genomic epidemiology. We used , Oxford Nanopore Technologies (ONT) sequencing, which was performed in Malawi.. During the study period, ST131 has become more prevalent (14.9% increasing to 32.8%) and the blaCTX-M-15 gene is occurring at a higher frequency (21.3% increasing to 44.8%). Phylogenetics show isolates are highly related between the Central and Southern geographic regions and confirm that ST131 isolates are contained in a single group consistent with recent expansion. All AMR genes, including blaCTX-M-15, were widely distributed across sequence types. We also identified a large number of ST410 isolates, not previously seen in Malawi, which carry the blaCTX-M-15 gene at a higher frequency than ST131 as a plasmid mediated copy. This study confirms the expanding nature of ST131 and the wide distribution of the blaCTX-M-15 gene in Malawi. We highlight the feasibility of conducting longitudinal genomic epidemiology studies of important bacteria with the sequencing done on site using a nanopore platform that requires minimal infrastructure.