Genetic Characterization of Optochin-Susceptible Viridans Group Streptococci

Abstract

Two clinical isolates of viridans group streptococci (VS) with different degrees of susceptibility to optochin (OPT), i.e., fully OPT-susceptible (Opt s ) VS strain 1162/99 (for which the MIC was equal to that for Streptococcus pneumoniae, 0.75 g/ml) and intermediate Opt s VS strain 1174/97 (MIC, 6 g/ml) were studied. Besides being OPT susceptible, they showed characteristics typical of VS, such as bile insolubility; lack of reaction with pneumococcal capsular antibodies; and lack of hybridization with rRNA (AccuProbe)-, lytA-, and pnl-specific pneumococcal probes. However, these VS Opt s strains and VS type strains hybridized with ant, a gene not present in S. pneumoniae. A detailed characterization of the genes encoding the 16S rRNA and SodA classified isolates 1162/99 and 1174/97 as Streptococcus mitis. Analysis of the atpCAB region, which encodes the c, a, and b subunits of the F 0 F 1 H ؉ -ATPase, the target of optochin, revealed high degrees of similarity between S. mitis 1162/99 and S. pneumoniae in atpC, atpA, and the N terminus of atpB. Moreover, amino acid identity between S. mitis 1174/97 and S. pneumoniae was found in ␣ helix 5 of the a subunit. The organization of the chromosomal region containing the atp operon of the two Opt s VS and VS type strains was spr1284-atpC, with spr1284 being located 296 to 556 bp from atpC, whereas in S. pneumoniae this distance was longer than 68 kb. In addition, the gene order in S. pneumoniae was IS1239-74 bp-atpC. The results suggest that the full OPT susceptibility of S. mitis 1162/99 is due to the acquisition of atpC, atpA, and part of atpB from S. pneumoniae and that the intermediate OPT susceptibility of S. mitis 1174/97 correlates with the amino acid composition of its a subunit.Streptococcus pneumoniae (the pneumococcus) remains a major etiological agent of community-acquired pneumonia, meningitis, and acute otitis media (6). Four phenotypic characteristics are classically used in the diagnostic laboratory for the identification of the pneumococcus: colony morphology on blood agar plates, optochin (OPT) susceptibility, bile solubility, and immunological reaction with type-specific antisera (23). Although their colony morphologies can be very similar, the alpha-hemolytic oral streptococci (known as viridans group streptococci [VS]), notably, Streptococcus mitis and Streptococcus oralis, are classically OPT resistant (Opt r ) and bile insoluble (23).Genetic and biochemical evidence supports that fact that the typical OPT susceptibility of the pneumococcus resides in the characteristics of the F 0 complex of its F 0 F 1 H ϩ -ATPase, an enzyme that is essential for the viability of this organism (10). The primary roles of this enzyme are to create a proton gradient with the energy provided by ATP hydrolysis and to maintain the intracellular pH via proton extrusion (25), as in other related bacteria (18). However, in bacteria with a respiratory chain, the role of the F 0 F 1 H ϩ -ATPase is the synthesis of ATP from the proton gradient of the respiratory chain. Hydr...

Accuracy of Phenotypic and Genotypic Testing for Identification of Streptococcus pneumoniae and Description of Streptococcus pseudopneumoniae sp. nov

“…The instructions are based on opposing recommendations published in the Manual of Clinical Microbiology (49) and a study published in 1971 by Ragsdale and Sanford (48). Ragsdale and Sanford recommended incubation in ambient air, on the basis of the reduced zone sizes obtained when tests were incubated in CO 2 , whereas the Manual of Clinical Microbiology recommends incubation in CO 2 to enhance the growth of isolates that will not grow aerobically.Bile-insoluble strains of S. pneumoniae have also been reported (39,43,44), as have atypical OPT-resistant, BS-negative strains of S. pneumoniae (15,19,26,31,41,43,66). …”

“…Bile-insoluble strains of S. pneumoniae have also been reported (39,43,44), as have atypical OPT-resistant, BS-negative strains of S. pneumoniae (15,19,26,31,41,43,66).…”

“…Molecular techniques such as PCR tests for the virulence genes of S. pneumoniae (autolysin [lytA] and pneumolysin [ply]) (9,10,15,23,26,29,30,31,39,40,50,52,59,61,62,65,66,67) and penicillin binding protein genes are beginning to gain popularity, as are probe hybridization tests for specific regions of the 16S rRNA gene (16S rDNA) (8,11,13,19,31,39,41,53,64,65).…”

Characteristic Signatures of the lytA Gene Provide a Basis for Rapid and Reliable Diagnosis of Streptococcus pneumoniae Infections

“…These two tests are usually sufficient with samples obtained from sterile locations; but isolates in samples from nonsterile sites, such as pharyngeal swabs, frequently provide conflicting results for one (or both) of these tests (see reference 1 for a recent review). Besides, nonpneumococcal, Optsusceptible (Opt s ) streptococci have also been reported (24). Isolates that are putatively identified as pneumococci on the basis of other analyses (4,18,33) but that give negative results in one or more of the classical assays are usually referred to as "atypical" pneumococci.…”

Empyema caused by optochin sensitive Streptococcus mitis in the course of varicella

“…[2][3][4][5] Hence, speciation of viridans streptococci when isolated in pure culture is a must for precise diagnosis. This case report is important that it shows a case of post-varicella empyema due to Streptococcus mitis and provides contribution to the literature regarding optochin sensitive Streptococcus mitis.…”