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 log₁₀ CFU/mL over 24 h. Reversion experiments demonstrated complete regrowth to 10.2 log₁₀ 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 log₁₀ 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.