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Journal of Clinical Microbiology, March 2009, p. 554-559, Vol. 47, No. 3
0095-1137/09/$08.00+0     doi:10.1128/JCM.01919-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

PCR-Based Quantitation and Clonal Diversity of the Current Prevalent Invasive Serogroup 6 Pneumococcal Serotype, 6C, in the United States in 1999 and 2006 to 2007{triangledown}

Maria da Gloria Carvalho,1 Fabiana C. Pimenta,1 Robert E. Gertz Jr.,1 Hari Har Joshi,1 Alma A. Trujillo,1 Logan E. Keys,1 Joy Findley,1 Iaci S. Moura,1 In H. Park,2 Susan K. Hollingshead,3 Tamara Pilishvili,1 Cynthia G. Whitney,1 Moon H. Nahm,2,3 Bernard W. Beall,1* for the Active Bacterial Core Surveillance Team

Respiratory Diseases Branch, Centers for Disease Control & Prevention, Atlanta, Georgia 30333,1 Department of Pathology,2 Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 352943

Received 3 October 2008/ Returned for modification 25 November 2008/ Accepted 23 December 2008

Following introduction of the 7-valent pneumococcal conjugate vaccine to the United States, rates of invasive pneumococcal disease (IPD) caused by serotype 6A declined among all age groups, while rates of IPD caused by newly identified serotype 6C increased slightly among persons 5 years of age and older. Conventionally serotyped 6A isolates (CS6As) from active population-based surveillance during 1999 and 2006 to 2007 were classified as serotypes 6A and 6C by an expedient and highly accurate serotype 6C-specific PCR assay developed during this study. PCR testing of 636 year 1999, 2006, and 2007 CS6As revealed 6C proportions of 35/214 (16.4%), 141/218 (64.7%), and 141/204 (69.1%), respectively. These results agreed with those from a previously devised monoclonal antibody-based serotyping system (346 CS6As compared). Type 6C IPD incidence significantly increased during 2006 and 2007 compared to during 1999 (0.57 to 0.58 cases per 100,000 and 0.22 cases per 100,000, respectively; 164% increase from 1999 to 2007 [95% confidence interval, 87 to 270%]), while rates of IPD due to types 6A and 6B markedly decreased. In 2007, 31.2% of 6C isolates were not susceptible to penicillin. Serotype 6C is now the predominant serotype associated with serogroup 6 IPD in the United States and is often penicillin nonsusceptible. We performed multilocus sequence typing (MLST) on a limited sampling of 6C isolates with different antimicrobial susceptibility profiles. MLST of 42 6C isolates revealed 12 genotypes distributed among six distinct genetic groups. Fifteen 6C isolates shared one of four different MLST types with 6C-negative CS6As. MLST results suggest 6C strains arose from independent recombination events involving only serotype 6A and 6C parental strains.

* Corresponding author. Mailing address: Respiratory Diseases Branch, Division of Bacterial Diseases, 1600 Clifton Rd. NE, Mailstop C02, Atlanta, GA 30329. Phone: (404) 639-1237. Fax: (404) 639-4215. E-mail: BBeall{at}CDC.gov

{triangledown} Published ahead of print on 30 December 2008.

Journal of Clinical Microbiology, March 2009, p. 554-559, Vol. 47, No. 3
0095-1137/09/$08.00+0     doi:10.1128/JCM.01919-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Jin, P., Xiao, M., Kong, F., Oftadeh, S., Zhou, F., Liu, C., Gilbert, G. L. (2009). Simple, Accurate, Serotype-Specific PCR Assay To Differentiate Streptococcus pneumoniae Serotypes 6A, 6B, and 6C. J. Clin. Microbiol. 47: 2470-2474 [Abstract] [Full Text]  


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