1. Antimicrob Agents Chemother. 2013 May;57(5):2310-8. doi: 10.1128/AAC.02609-12.
Epub 2013 Mar 11.

Pharmacodynamic Evaluation of the Intracellular Activity of Antibiotics towards
Pseudomonas aeruginosa PAO1 in a Model of THP-1 Human Monocytes.

Buyck JM, Tulkens PM, Van Bambeke F.

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

Pseudomonas aeruginosa invades epithelial and phagocytic cells, which may play an
important role in the persistence of infection. We have developed a 24-h model of
THP-1 monocyte infection with P. aeruginosa PAO1 in which bacteria are seen
multiplying in vacuoles by electron microscopy. The model has been used to
quantitatively assess antibiotic activity against intracellular and extracellular
bacteria by using a pharmacodynamic approach (concentration-dependent experiments
over a wide range of extracellular concentrations to calculate bacteriostatic
concentrations [Cs] and maximal relative efficacies [Emax]; Hill-Langmuir
equation). Using 16 antipseudomonal antibiotics (three aminoglycosides, nine
β-lactams, three fluoroquinolones, and colistin), dose-response curves were found
to be undistinguishable for antibiotics of the same pharmacological class if data
were expressed as a function of the corresponding MICs. Extracellularly, all of
the antibiotics reached a bacteriostatic effect at their MIC, and their Emax
exceeded the limit of detection (-4.5 log10 CFU compared to the initial
inoculum). Intracellularly, Cs values remained unchanged for β-lactams,
fluoroquinolones, and colistin but were approximately 10 times higher for
aminoglycosides, whereas Emax values were markedly reduced (less negative),
reaching -3 log10 CFU for fluoroquinolones and only -1 to -1.5 log10 CFU for all 
other antibiotics. The decrease in intracellular aminoglycoside potency (higher
Cs) can be ascribed to the acid pH to which bacteria are exposed in vacuoles. The
decrease in the Emax may reflect a reversible alteration of bacterial
responsiveness to antibiotics in the intracellular milieu. The model may prove
useful for comparison of antipseudomonal antibiotics to reduce the risk of
persistence or relapse of pseudomonal infections.

PMCID: PMC3632903 [Available on 2013/11/1]
PMID: 23478951  [PubMed - in process]