Combatting mobile colistin-resistant (MCR), metallo-β-lactamase (MBL)-producing 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 strain ( , and ).

METHODS

A hollow fibre infection model was utilized to profile the clinical combination of aztreonam + ceftazidime/avibactam + polymyxin B against a pan-drug-resistant 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 CFU/mL over 24 h. Reversion experiments demonstrated complete regrowth to 10.2 log 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 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 and 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.