Optochin Resistance in Streptococcus Pneumoniae: Mechanism, Significance, and Clinical Implications
582 Optochin Resistance in Streptococcus pneumoniae: Mechanism, Significance, and Clinical Implications Andreas Pikis,1,2 Joseph M. Campos,3,4,5,6 1Vaccine and Therapeutic Development Section, Oral Infection William J. Rodriguez,2,4,a and Jerry M. Keith1 and Immunity Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland; Departments of 2Infectious Diseases and 3Laboratory Medicine, Children’s National Medical Center, and Departments of 4Pediatrics, 5Pathology, and 6Microbiology/Tropical Medicine, George Washington University Medical Center, Washington, DC Downloaded from https://academic.oup.com/jid/article/184/5/582/808236 by guest on 23 September 2021 Traditionally, Streptococcus pneumoniae is identified in the laboratory by demonstrating susceptibility to optochin. Between 1992 and 1998, 4 pneumococcal isolates exhibiting op- tochin resistance were recovered from patients at Children’s National Medical Center. Three of the 4 isolates consisted of mixed populations of optochin-resistant and -susceptible organ- isms. Both subpopulations had identical antibiograms, serotypes, and restriction fragment profiles. The other isolate was uniformly resistant to optochin. Resistant strains had MICs of optochin 4–30-fold higher than susceptible strains, belonged to different serotypes, and had dissimilar restriction fragment profiles, indicating clonal unrelatedness. Resistance arose from single point mutations in either the a-subunit (W206S) or the c-subunit (G20S, M23I, and A49T) of H+-ATPase. There is speculation of a possible association between exposure to antimalarial drugs and evolution of optochin resistance. a-Hemolytic streptococci resistant to optochin, particularly invasive isolates, should be tested for bile solubility or with an S. pneumoniae DNA probe before identification as viridans streptococci.
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