1. Front Microbiol. 2020 Nov 23;11:587364. doi: 10.3389/fmicb.2020.587364. 
eCollection 2020.

The Persister Character of Clinical Isolates of Staphylococcus aureus 
Contributes to Faster Evolution to Resistance and Higher Survival in THP-1 
Monocytes: A Study With Moxifloxacin.

Nguyen TK(1)(2), Peyrusson F(1), Dodémont M(3), Pham NH(4)(5), Nguyen HA(6), 
Tulkens PM(1), Van Bambeke F(1).

Author information:
(1)Pharmacologie Cellulaire et Moléculaire, Louvain Drug Research Institute, 
Université catholique de Louvain (UCLouvain), Brussels, Belgium.
(2)Department of Pharmaceutical Industry, Hanoi University of Pharmacy, Hanoi, 
Vietnam.
(3)Centre National de Référence des Staphylocoques, Laboratoire Hospitalier 
Universitaire de Bruxelles (LHUB-ULB) Site Anderlecht, Hôpital Erasme - 
Cliniques Universitaires de Bruxelles, Brussels, Belgium.
(4)Department of Microbiology, Bach Mai Hospital, Hanoi, Vietnam.
(5)Microbiology Department, Hanoi Medical University, Hanoi, Vietnam.
(6)The National Center for Drug Information and Adverse Drug Reactions 
Monitoring, Hanoi University of Pharmacy, Hanoi, Vietnam.

Staphylococcus aureus may cause relapsing infections. We previously showed that 
S. aureus SH1000 surviving intracellularly to bactericidal antibiotics are 
persisters. Here, we used 54 non-duplicate clinical isolates to assess links 
between persistence, resistance evolution, and intracellular survival, using 
moxifloxacin throughout as test bactericidal antibiotic. The relative persister 
fraction (RPF: percentage of inoculum surviving to 100× MIC moxifloxacin in 
stationary phase culture for each isolate relative to ATCC 25923) was determined 
to categorize isolates with low (≤10) or high (>10) RPF. Evolution to resistance 
(moxifloxacin MIC ≥ 0.5 mg/L) was triggered by serial passages at 0.5× MIC (with 
daily concentration readjustments). Intracellular moxifloxacin maximal efficacy 
(Emax) was determined by 24 h concentration-response experiments 
[pharmacodynamic model (Hill-Langmuir)] with infected THP-1 monocytes exposed to 
moxifloxacin (0.01 to 100× MIC) after phagocytosis. Division of intracellular 
survivors was followed by green fluorescence protein dilution (FACS). Most 
(30/36) moxifloxacin-susceptible isolates showed low RPF but all 
moxifloxacin-resistant (n = 18) isolates harbored high RPF. Evolution to 
resistance of susceptible isolates was faster for those with high vs. low RPF 
(with SOS response and topoisomerase-encoding genes overexpression). 
Intracellularly, moxifloxacin Emax was decreased (less negative) for isolates 
with high vs. low RPF, independently from resistance. Moxifloxacin intracellular 
survivors were non-dividing. The data demonstrate and quantitate persisters in 
clinical isolates of S. aureus, and show that this phenotype accelerates 
resistance evolution and is associated with intracellular survival in spite of 
high antibiotic concentrations. Isolates with high RPF may represent a possible 
cause of treatment failure not directly related to resistance in patients 
receiving active antibiotics.

Copyright © 2020 Nguyen, Peyrusson, Dodémont, Pham, Nguyen, Tulkens and Van 
Bambeke.

DOI: 10.3389/fmicb.2020.587364
PMCID: PMC7719683
PMID: 33329458