g. subdominant 1, subdominant 2 in order of prevalence). This allows for collection of information regarding possible multiple serotype
carriage, albeit in a biased fashion. If there is only one morphology present, and it is later identified as non-pneumococcus, return to the primary culture plate and repeat colony selection at least once to verify that pneumococci are not present. Traditionally, identification of pneumococci has focused on isolates cultured from normally sterile sites that tend to display a classical phenotype, in particular being optochin susceptible and bile soluble. These identification criteria are generally satisfactory for clinical application and are widely applied in diagnostic microbiology. However, alternative pneumococcal forms are frequently cultured from NP specimens [58] and [59]. find more These non-classical forms may give test results normally expected for other members of the viridans group of streptococci [60] and [61] and some other viridans group streptococci have been
reported to give test results normally associated with pneumococci [62], [63] and [64]. For example, the original description of Streptococcus pseudopneumoniae was optochin susceptible when grown in ambient air conditions, and resistant when incubated in 5% CO2 atmosphere [62]. However, recent studies have found that these phenotypic characteristics are not universal for S. pseudopneumoniae selleckchem [65]. These issues create difficulties for identification and differentiation between
pneumococci and other oral streptococci in carriage studies. Although optochin susceptibility and bile solubility are still considered key tests, we recommend extending the criteria for presumptive identification of pneumococci to encompass non-classical forms of pneumococci (Fig. 2). Further testing by a reference laboratory may be needed if the research question requires a more definitive identification than this algorithm provides. We now recommend that all α-hemolytic enough colonies growing on selective media are potentially analyzable, rather than just those with ‘typical pneumococcal colony morphology’ [66], and reiterate that the optochin test culture plate is incubated in 5% CO2 atmosphere, rather than ambient air. Further work is needed to more clearly differentiate pneumococci, particularly the non-classical forms, from other oral microbes. As a clearer understanding of how to fully define the species is achieved, a revised pragmatic definition of pneumococci will be needed for use in carriage studies. Non-culture based techniques have some advantages in detecting pneumococci from NP samples: they do not require viable organisms, preserve the original composition of the NP sample and, depending on the methods used, provide a detailed characterization and quantification of the pneumococci within a sample.
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