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Antimicrobial Agents and Chemotherapy, September 2009, p. 3799-3802, Vol. 53, No. 9
0066-4804/09/$08.00+0     doi:10.1128/AAC.00647-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Lipoprotein Processing Is Essential for Resistance of Mycobacterium tuberculosis to Malachite Green{triangledown}

Niaz Banaei,1* Eleanor Z. Kincaid,1 S.-Y. Grace Lin,4 Edward Desmond,4 William R. Jacobs Jr.,5 and Joel D. Ernst1,2,3

Departments of Medicine (Division of Infectious Diseases),1 Pathology,2 Microbiology, NYU School of Medicine, New York, New York 10016,3 California Department of Health Services, Richmond, California 94804,4 Howard Hughes Medical Institute and Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York 104615

Received 12 May 2009/ Returned for modification 12 June 2009/ Accepted 5 July 2009

Malachite green, a synthetic antimicrobial dye, has been used for over 50 years in mycobacterial culture medium to inhibit the growth of contaminants. The molecular basis of mycobacterial resistance to malachite green is unknown, although the presence of malachite green-reducing enzymes in the cell envelope has been suggested. The objective of this study was to investigate the role of lipoproteins in resistance of Mycobacterium tuberculosis to malachite green. The replication of an M. tuberculosis lipoprotein signal peptidase II (lspA) mutant ({Delta}lspA::lspAmut) on Middlebrook agar with and without 1 mg/liter malachite green was investigated. The lspA mutant was also compared with wild-type M. tuberculosis in the decolorization rate of malachite green and sensitivity to sodium dodecyl sulfate (SDS) detergent and first-line antituberculosis drugs. The lspA mutant has a 104-fold reduction in CFU-forming efficiency on Middlebrook agar with malachite green. Malachite green is decolorized faster in the presence of the lspA mutant than wild-type bacteria. The lspA mutant is hypersensitive to SDS detergent and shows increased sensitivity to first-line antituberculosis drugs. In summary, lipoprotein processing by LspA is essential for resistance of M. tuberculosis to malachite green. A cell wall permeability defect is likely responsible for the hypersensitivity of lspA mutant to malachite green.

* Corresponding author. Mailing address: Stanford University School of Medicine, Department of Pathology, 3375 Hillview Avenue, Room 1602, Palo Alto, CA 94304. Phone: (650) 736-8052. Fax: (650) 725-5671. E-mail: niazbanaei{at}stanford.edu

{triangledown} Published ahead of print on 13 July 2009.

Antimicrobial Agents and Chemotherapy, September 2009, p. 3799-3802, Vol. 53, No. 9
0066-4804/09/$08.00+0     doi:10.1128/AAC.00647-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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