E. coli and K. pneumoniae are major aetiological agents of life-threatening sepsis with globally disseminated successful clones dominating the epidemiology of serious infections (1). E. coli sequence type (ST) 131 with extended spectrum beta-lactamase-type resistance (blaCTX-M-15) and highly resistant K. pneumoniae CC292 (blaKPC) can reside asymptomatically in the human gut for at least 6-12 months. Lytic bacteriophages are effective against several problematic bacterial species but clinical utility is limited by poor understanding of clinical applicability, penetration, and resistance (2). In our work, we aim to use well-characterized bacterial sets from a prospective global collection to purify high-titre lytic phages and study the kinetics of bacterial killing in vitro and in vivo in order to define optimal phage cocktails and administration protocols. To date, in our Australian clinical isolates collection, we have identified 90 E. coli ST131 with blaCTX-M-15 and 45 K. pneumoniae with blaKPC and obtained genome sequences using Illumina NGS technology (NextSeq; paired-end – 150 bp) to compare with international isolates. Six E. coli ST131 with distinct XbaI-PFGE profiles were tested against 5 virulent ds-DNA phages from a pre-existing library (prepared on E. coli lawns). Four of 5 phages lysed most test strains at high titre, and 5 of 6 strains were lysed by 2-3 phages. Most strains resisted at least one phage. Control strains of P. aeruginosa, S. aureus, Enterobacter and Serratia marcescens were resistant to all E. coli phages. Six K. pneumoniae CC292 (ST258 and ST512) were also tested. One phage only proved clearly effective. Our preliminary data indicate that more E. coli candidate phages are required to cover the target population and that direct inoculation of faecal extracts from different sources onto directly relevant bacterial lawns is needed to optimize the yield of specific lytic phage.

(1) Woodford N et al. (2011) FEMS Microbiol Rev 35:736.
(2) Ly-Chatain MH. (2014) Front Microbiol 5:51.