TY - JOUR
T1 - Prolonged exposure of methicillin-resistant Staphylococcus aureus (MRSA) COL strain to increasing concentrations of oxacillin results in a multidrug-resistant phenotype
AU - Martins, Ana
AU - Couto, Isabel
AU - Aagaard, Lone
AU - Martins, Marta
AU - Viveiros, Miguel
AU - Kristiansen, Jette E
AU - Amaral, Leonard
PY - 2007/3/1
Y1 - 2007/3/1
N2 - Our previous studies demonstrated that exposure of a bacterium to increasing concentrations of an antibiotic would increase resistance to that antibiotic as a consequence of activating efflux pumps. This study utilises the same approach; however, it employs the methicillin-resistant Staphylococcus aureus (MRSA) COL strain, which is highly resistant to oxacillin (OXA). MRSA COL was adapted to 3200 mg/L of OXA. Changes in resistance to other antibiotics were evaluated and efflux pump activity during the adaptation process was determined. MRSA COL was exposed to stepwise two-fold increases of OXA. At the end of each step, minimum inhibitory concentration determination for erythromycin (ERY) and other antibiotics was conducted. Reserpine (RES) was employed to evaluate whether resistance to ERY was dependent on efflux pump activity. Efflux pump activity was also evaluated using the ethidium bromide (EB) assay. DNA typing of the products of each culture step was conducted to assess purity. Serial exposure of MRSA COL to increasing concentrations of OXA resulted in increased resistance to ERY, which could be eliminated with RES. Evaluation of efflux pump activity by the EB method indicated increased efflux activity. Resistance to ERY was accompanied by resistance to kanamycin, amikacin, ofloxacin, norfloxacin, ciprofloxacin and rifampicin. This is the first time that a multidrug-resistant phenotype has been experimentally produced as a consequence of exposure of the organism to an antibiotic to which it is initially highly resistant.
AB - Our previous studies demonstrated that exposure of a bacterium to increasing concentrations of an antibiotic would increase resistance to that antibiotic as a consequence of activating efflux pumps. This study utilises the same approach; however, it employs the methicillin-resistant Staphylococcus aureus (MRSA) COL strain, which is highly resistant to oxacillin (OXA). MRSA COL was adapted to 3200 mg/L of OXA. Changes in resistance to other antibiotics were evaluated and efflux pump activity during the adaptation process was determined. MRSA COL was exposed to stepwise two-fold increases of OXA. At the end of each step, minimum inhibitory concentration determination for erythromycin (ERY) and other antibiotics was conducted. Reserpine (RES) was employed to evaluate whether resistance to ERY was dependent on efflux pump activity. Efflux pump activity was also evaluated using the ethidium bromide (EB) assay. DNA typing of the products of each culture step was conducted to assess purity. Serial exposure of MRSA COL to increasing concentrations of OXA resulted in increased resistance to ERY, which could be eliminated with RES. Evaluation of efflux pump activity by the EB method indicated increased efflux activity. Resistance to ERY was accompanied by resistance to kanamycin, amikacin, ofloxacin, norfloxacin, ciprofloxacin and rifampicin. This is the first time that a multidrug-resistant phenotype has been experimentally produced as a consequence of exposure of the organism to an antibiotic to which it is initially highly resistant.
KW - Anti-Bacterial Agents
KW - Bacterial Proteins
KW - Dose-Response Relationship, Drug
KW - Drug Resistance, Multiple, Bacterial
KW - Ethidium
KW - Humans
KW - Membrane Transport Proteins
KW - Methicillin Resistance
KW - Microbial Sensitivity Tests
KW - Oxacillin
KW - Phenotype
KW - Staphylococcal Infections
KW - Staphylococcus aureus
U2 - 10.1016/j.ijantimicag.2006.10.012
DO - 10.1016/j.ijantimicag.2006.10.012
M3 - Journal article
C2 - 17276037
SN - 0924-8579
VL - 29
SP - 302
EP - 305
JO - International Journal of Antimicrobial Agents
JF - International Journal of Antimicrobial Agents
IS - 3
ER -