Contrasting patterns of longitudinal population dynamics and antimicrobial resistance mechanisms in two priority bacterial pathogens over 7 years in a single center

Background. Two of the most important pathogens contributing to the global rise in antimicrobial resistance (AMR) are Klebsiella pneumoniae and Enterobacter cloacae. Despite this most of our knowledge about the changing patterns of disease caused by these two pathogens is based on studies with limited timeframes that provide few insights into their population dynamics or the flux in AMR elements that they can carry.

Results. We investigated the flux in population of two priority AMR pathogens over seven years between 2007-12 in a major UK hospital, spanning changes made to UK national antimicrobial prescribing policy in 2007. Between 2006-12 K. pneumoniae showed epidemiological cycles of multi-drug resistant (MDR) lineages being replaced approximately every two-years. This contrasted E. cloacae where there was no correlation between acquired drug resistance and the success of specific lineages.

Conclusions. The differing patterns of clonal replacement and acquisition of mobile elements showed that the flux in the K. pneumoniae population was linked to the introduction of globally recognised MDR clones carrying drug resistance markers on mobile elements into the hospital. However, E. cloacae carries a chromosomally encoded ampC confering resistance to front-line treatments and showed that MDR plasmid acquisition in E. cloacae was not indicative of success in the hospital, with local clones dominating. This led to markedly different dynamics in the AMR populations of these two pathogens, and shows that the mechanism of the resistance and its location in the genome or mobile elements is crucial to predict population dynamics of opportunistic pathogens in clinical settings.