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Journal of Clinical Microbiology, June 2008, p. 1930-1934, Vol. 46, No. 6
0095-1137/08/$08.00+0     doi:10.1128/JCM.02318-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Characterization of In Vitro-Generated and Clinical Optochin-Resistant Strains of Streptococcus pneumoniae Isolated from Argentina

Departamento de Bioquímica Clínica, CIBICI (CONICET), Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Medina Allende esq. Haya de la Torre, Ciudad Universitaria, X5000HUA Córdoba, Argentina,¹ Servicio de Bacteriología Clínica, Instituto Nacional de Enfermedades Infecciosas-ANLIS, Dr. Carlos Malbrán, Buenos Aires, Argentina²

Received 3 December 2007/ Returned for modification 16 January 2008/ Accepted 7 April 2008

Optochin susceptibility is a key test used for pneumococcal diagnosis, but optochin-resistant (Opt^r) pneumococci have been reported in the last 2 decades. In this work, we characterized eight Opt^r clinical strains which presented a new mutation, G47V, a predominant A49S mutation (recently reported in Brazil) and A49T. These mutations were found in the c subunit of the F₀F₁ ATPase encoded by the atpC gene, and W206C was found in the a subunit encoded by the atpA gene. The Opt^r clinical isolates were analyzed by BOX PCR, multilocus sequence typing, and serotype and antimicrobial resistance profiles, and they showed no epidemiological relationship. To characterize the Opt^r mutations that could emerge among clinical strains, we studied a pool of spontaneous Opt^r colonies obtained in vitro from the virulent D39 strain. We compared the atpAC mutations of these Opt^r pneumococci (with or without passage through C57BL/6 mice) with those described in the clinical isolates. This analysis revealed three new mutations, G47V and L26M in the c subunit and L184S in the a subunit. Most of the mutations identified in the laboratory-generated Opt^r strains were also found in clinical strains, with the exception of the L26M and L184S mutations, and we suppose that both mutations could emerge among invasive strains in the future. Considering that atpAC are essential genes, we propose that all spontaneous mutations that confer in vitro optochin resistance would not present severe physiological alterations in S. pneumoniae and may be carried by circulating pneumococcal strains.

Published ahead of print on 16 April 2008.

This article has been cited by other articles:

• Cortes, P. R., Pinas, G. E., Albarracin Orio, A. G., Echenique, J. R. (2008). Subinhibitory concentrations of penicillin increase the mutation rate to optochin resistance in Streptococcus pneumoniae. J Antimicrob Chemother 62: 973-977 [Abstract] [Full Text]