Combatting mobile colistin-resistant (MCR), metallo-β-lactamase (MBL)-producing Klebsiella pneumoniae persisters.

OBJECTIVES: Therapeutic modalities for pan-drug-resistant Gram-negatives co-expressing mobile colistin resistance and metallo-β-lactamases have not been defined. Here, we devised novel strategies involving aztreonam and ceftazidime/avibactam together with polymyxin B to combat persisters of a pan-drug-resistant Klebsiella pneumoniae strain (bla (NDM-5), bla (CTX-M-55) and mcr-1). METHODS: A hollow fibre infection model was utilized to profile the clinical combination of aztreonam + ceftazidime/avibactam + polymyxin B against a pan-drug-resistant K. pneumoniae clinical isolate over 168†h with reversion experiments conducted until a 216†h endpoint. The evolutionary profiles of the total and resistant subpopulations were assessed using real-time population analysis profiles. Scanning electron microscopy imaging was utilized to visualize time courses of salient structural alterations. RESULTS: The clinical combination of aztreonam + ceftazidime/avibactam demonstrated initial activity with a total count reduction of 2.69 log(10) CFU/mL over 24†h. Reversion experiments demonstrated complete regrowth to 10.2 log(10) CFU/mL by 216†h. In contrast, the addition of polymyxin B to the β-lactam/β-lactamase inhibitor combination resulted in marked bactericidal activity (4.19 log(10) CFU/mL) within 24†h and eventually below the limit of detection by 174†h. SEM imaging revealed filamentous persister cells under aztreonam selective pressure. However, with polymyxin B combinations, there was an absence of viable cells with no evidence of long filamentous persister cells, despite polymyxin resistance. CONCLUSIONS: Despite intrinsic mcr-1 and bla (NDM-5) resistance mechanisms, the proposed novel combination holds vast promise to maximally suppress the development of persisters and amplification of resistance in 'nightmare' pan-drug-resistant Gram-negative urgent threats.