Evaluation of a Medium (STGG) for Transport and Optimal Recovery of Streptococcus pneumoniae from Nasopharyngeal Secretions Collected during Field Studies

Abstract

Field studies of Streptococcus pneumoniae (pneumococci) nasopharyngeal (NP) colonization are hampered by the need to directly plate specimens in order to ensure isolate viability. A medium containing skim milk, tryptone, glucose, and glycerin (STGG) has been used to transport and store NP material, but its ability to preserve pneumococci has not been evaluated. Our objective was to qualitatively and semiquantitatively evaluate the ability of STGG to preserve pneumococci in NP secretions. Entwined duplicate calcium alginate NP swab samples were obtained from children. One swab was plated directly onto a gentamicin blood agar plate; the other was placed in STGG. Growth from the directly plated specimen was compared with growth from an STGG aliquot immediately cultured or stored at ؊70°C for 9 weeks, ؊20°C for 9 weeks, or 4°C for 5 days. Of 186 specimens, 96 (52%) were positive for pneumococci from the direct plating; 94 (98%) of these were positive from the fresh STGG specimen. Pneumococci were recovered from all 38 positive specimens frozen at ؊70°C, all 18 positive specimens frozen at ؊20°C, and 18 of 20 positive specimens stored at 4°C. Recovery of pneumococci after storage of NP material in STGG medium at ؊70°C is at least as good as that from direct plating. Storage at ؊20°C is also acceptable. Storage at 4°C for 5 days is not ideal.Streptococcus pneumoniae (pneumococci) is the most important cause of bacterial otitis media, pneumonia, bacteremia, and meningitis among children worldwide (12,15,17). Pneumococci are also important because the rate of nonsusceptibility to various classes of antimicrobial agents, such as penicillins and cephalosporins, is rising throughout the United States and worldwide (4,18,19). Prevention efforts have been hampered by the lack of a vaccine which is immunogenic for important serotypes in children younger than 2 years of age. A seven-valence pneumococcal conjugate vaccine (Prevnar; Wyeth Lederle Vaccines) which is immunogenic and efficacious in this age group recently has been licensed in the United States for use among children through 9 years of age and is recommended routinely for those under 2 years of age (1, 3, 16). The effect of this and other conjugate pneumococcal vaccines on nasopharyngeal (NP) colonization is a subject of intense investigation.It is well known that pneumococci are spread from person to person via the respiratory route. NP colonization studies have shown that people acquire pneumococci at a young age, carry these organisms for various periods of time, may carry more than one serotype at a time, and transmit these organisms to others with whom they are in close contact (2,5,(9)(10)(11)14). Many studies of the dynamics and ecology of pneumococcal NP carriage, particularly in the setting of new conjugate pneumococcal vaccines, will be performed in settings where microbiologic facilities are not readily available.An optimal medium has not been validated for the transport, preservation, and recovery of pneumococci from NP material. One medium, STGG (skim m...

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