Effect of Swab Composition and Use of Swabs versus Swab-Containing Skim Milk-Tryptone-Glucose-Glycerol (STGG) on Culture- or PCR-Based Detection of Streptococcus pneumoniae in Simulated and Clinical Respiratory Specimens in STGG Transport Medium

Abstract

To detect Streptococcus pneumoniae colonization, the nasopharynx is sampled using a swab placed in skim milk-tryptone-glucose-glycerol (STGG) transport medium, and then the swab specimen or STGG medium is cultured or subjected to PCR. We evaluated the effect of swab composition and compared the sensitivities of detection of culture and PCR using swabs and swab-containing medium. Calcium alginate, Dacron polyester, or rayon-tipped swabs were inoculated with pneumococci or were immersed in nasal wash specimens from children and then placed in STGG medium. Swabs and medium inoculated with pneumococci were cultured. Swabs grew significantly more colonies than medium. The number of colonies cultured from rayon swabs or medium was significantly higher than the number cultured from the calcium alginate swab or medium. The number of colonies from both the Dacron polyester swabs and medium were significantly lower than with either calcium alginate or rayon swabs. When DNA was separately extracted from the calcium alginate swab and medium and subjected to PCR for pneumococcal detection from either S. pneumoniae-inoculated swabs or clinical specimens that grew S. pneumoniae, the sensitivity was at least 10 times higher using the swab. With Dacron polyester or rayon-tipped swabs, there was no consistent difference between the sensitivity of PCR using swabs and that of PCR using medium. Thus, calcium alginate swabs may be superior to STGG medium for the culture and PCR-based detection of S. pneumoniae. For culture, rayon swabs are superior and Dacron polyester swabs are inferior. The sensitivity of the swab and swab-containing medium for culture or PCR detection of S. pneumoniae varies with swab composition.Streptococcus pneumoniae (pneumococcus) is an important pathogen of children and adults (15). Pneumococci frequently and asymptomatically colonize the nasopharynges of infants and young children. Colonizing bacteria are the source of respiratory tract infections such as pneumonia and acute otitis media as well as invasive pneumococcal infections and serve as the reservoir for person-to-person transmission. In 2000, a heptavalent pneumococcal conjugate vaccine (PCV7) was licensed in the United States and recommended for routine administration to all infants (4). Use of this vaccine has resulted in a large decrease in the incidence of invasive pneumococcal infections in young children and a decrease in the prevalence of colonization with vaccine serotypes. The latter fact has resulted in a decrease in invasive disease in adults (21) and in infants too young to have been directly protected by vaccination (13) via herd type immunity. This has been accompanied by an apparent increase in the prevalence of colonization with nonvaccine serotypes (7,10,12). Some of these nonvaccine serotypes may have been present prior to the use of PCV7 but were unrecognized due to limitations in the sensitivity of culture and the difficulty in detecting more than one serotype in a nasopharyngeal specimen. Thus, there is a need for sensitive test...

Detection of Streptococcus pneumoniae from Different Types of Nasopharyngeal Swabs in Children

“…Our finding, that Dacron swabs were better than rayon swabs for the recovery of pneumococcus is in contrast with the finding of Rubin et al (2008), following a similar protocol [23]. In our study, we used twice the volume of medium to inoculate swabs (20 µL vs. 10 µL) used by Rubin et al in their in-vitro assay [23].…”

“…Only one study has compared the recovery of S. pneumoniae by culture and nucleic acid amplification from Dacron, calcium alginate and rayon swabs [23]. No published study has compared the more recently available flocked swabs (Copan Italia, Brescia, Italy) with other swab types for the recovery of S. pneumoniae .…”

Trends in Asymptomatic Nasopharyngeal Colonization With Streptococcus pneumoniae After Introduction of the 13-valent Pneumococcal Conjugate Vaccine in Calgary, Canada

“…There was some variation in terms of the age distribution and number of children in childcare; however, the decrease in overall colonization was sustained when stratified separately by childcare and by age groups (results not shown). 27 However, this does not change our overall conclusions as we used consistent collection and laboratory methods throughout all surveys. Studies done in the pre-PCV7 era showed S. pneumoniae to be isolated from 28% to 35% of middle ear fluid samples from otitis media cases.…”

Optimal Sampling Sites and Methods for Detection of Pathogens Possibly Causing Community-Acquired Lower Respiratory Tract Infections

“…Since 2003, studies have been performed to evaluate the recovery of different organisms in new transport (83,87,102) and storage (20,52) media.…”