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Antimicrobial Agents and Chemotherapy, July 2009, p. 2871-2878, Vol. 53, No. 7
0066-4804/09/$08.00+0     doi:10.1128/AAC.01542-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Novel Anion Liposome-Encapsulated Antisense Oligonucleotide Restores Susceptibility of Methicillin-Resistant Staphylococcus aureus and Rescues Mice from Lethal Sepsis by Targeting mecA{triangledown}

Jingru Meng,1 Hui Wang,1 Zheng Hou,1 Tao Chen,2 Jingguo Fu,2 Xue Ma,1 Gonghao He,1 Xiaoyan Xue,1 Min Jia,1 and Xiaoxing Luo1*

Department of Pharmacology, School of Pharmacy, Fourth Military Medical University, Xi'an 710032,1 Xi'an Libang Pharmaceutical Company, Xi'an 710075, People's Republic of China2

Received 19 November 2008/ Returned for modification 10 February 2009/ Accepted 1 May 2009

β-Lactam resistance in methicillin (meticillin)-resistant Staphylococcus aureus (MRSA) is caused by the production of an additional low-affinity penicillin-binding protein 2a, which is encoded by the mecA gene. The disruption of mecA may inhibit mecA expression and thereafter lead to the restoration of MRSA susceptibility to β-lactams. In this study, we developed a novel anionic liposome for encapsulating and delivering the complexes of a specific anti-mecA phosphorothioate oligodeoxynucleotide (PS-ODN833) and polycation polyethylenimine (PEI). The efficiencies of liposome encapsulation of the complexes were around 79.7% ± 2.7%. The liposomes showed sustained release of PS-ODN833 at 37°C but very low levels of release at 4°C and room temperature. The addition of the encapsulated anti-mecA PS-ODN833-PEI complex to cultures of MRSA strains caused 45, 76, 82, and 93% reductions in mecA expression, accompanied by the inhibition of MRSA growth on Mueller-Hinton agar containing oxacillin (6 µg/ml) in a concentration-dependent manner. The encapsulated-PS-ODN833 treatment also reduced the MICs of five of the most commonly used antibiotics for MRSA clinical isolates to values within the sensitivity range and rescued mice from MRSA-caused septic death by downregulating mecA. The survival rates of septic mice increased from 0% for the control group to 53% for the PS-ODN833-treated group. The results were associated with reductions of bacterial titers in the blood of surviving mice. The findings of the present study indicate that an antisense oligodeoxynucleotide targeted to mecA can significantly restore the susceptibility of MRSA to existing β-lactam antibiotics, providing an apparently novel strategy for treating MRSA infections.

* Corresponding author. Mailing address: Department of Pharmacology, School of Pharmacy, Fourth Military Medical University, Xi'an, 710032, China. Phone: 86-29-84776813. Fax: 86-29-84774591. E-mail: xxluo3{at}fmmu.edu.cn

{triangledown} Published ahead of print on 11 May 2009.

Antimicrobial Agents and Chemotherapy, July 2009, p. 2871-2878, Vol. 53, No. 7
0066-4804/09/$08.00+0     doi:10.1128/AAC.01542-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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