1. Antimicrob Agents Chemother. 2012 Dec;56(12):6166-74. doi: 10.1128/AAC.01031-12. 
Epub 2012 Sep 17.

Influence of the Protein Kinase C Activator Phorbol Myristate Acetate on the
Intracellular Activity of Antibiotics against Hemin- and Menadione-Auxotrophic
Small-Colony Variant Mutants of Staphylococcus aureus and Their Wild-Type
Parental Strain in Human THP-1 Cells.

Garcia LG, Lemaire S, Kahl BC, Becker K, Proctor RA, Tulkens PM, Van Bambeke F.

Pharmacologie cellulaire et moléculaire and Louvain Drug Research Institute,
Université catholique de Louvain, Brussels, Belgium.

In a previous study (L. G. Garcia et al., Antimicrob. Agents Chemother.
56:3700-3711, 2012), we evaluated the intracellular fate of menD and hemB mutants
(corresponding to menadione- and hemin-dependent small-colony variants,
respectively) of the parental COL methicillin-resistant Staphylococcus aureus
strain and the pharmacodynamic profile of the intracellular activity of a series 
of antibiotics in human THP-1 monocytes. We have now examined the phagocytosis
and intracellular persistence of the same strains in THP-1 cells activated by
phorbol 12-myristate 13-acetate (PMA) and measured the intracellular activity of 
gentamicin, moxifloxacin, and oritavancin in these cells. Postphagocytosis
intracellular counts and intracellular survival were lower in PMA-activated
cells, probably due to their higher killing capacities. Gentamicin and
moxifloxacin showed a 5- to 7-fold higher potency (lower static concentrations)
against the parental strain, its hemB mutant, and the genetically complemented
strain in PMA-activated cells and against the menD strain in both activated and
nonactivated cells. This effect was inhibited when cells were incubated with
N-acetylcysteine (a scavenger of oxidant species). In parallel, we observed that 
the MICs of these drugs were markedly reduced if bacteria had been preexposed to 
H(2)O(2). In contrast, the intracellular potency of oritavancin was not different
in activated and nonactivated cells and was not decreased by the addition of
N-acetylcysteine, regardless of the phenotype of the strains. The oritavancin MIC
was also unaffected by preincubation of the bacteria with H(2)O(2). Thus,
activation of THP-1 cells by PMA may increase the intracellular potency of
certain antibiotics (probably due to synergy with reactive oxygen species), but
this effect cannot be generalized to all antibiotics.

PMID: 22985883  [PubMed - in process]