199. LytA Positive Streptococcus mitis/oralis Confound Interpretation of Pneumococcal Colonization Studies
Session: Poster Abstract Session: Diagnostics: Bacteriology, Sequencing, and Resistance
Thursday, October 27, 2016
Room: Poster Hall
  • IDSA 2016 Pneumo Poster.pdf (743.9 kB)
  • Background: Streptococcus pneumoniae is a significant cause of respiratory illness in older adults and colonization is considered a necessary precursor to invasive disease. Carriage studies may provide insights about the effects of vaccination in adults. The lytA PCR assay developed by the Center for Disease Control (CDC) has been used to screen samples and is felt to be sensitive and specific for S. pneumoniae.  However, unless pneumococcal isolates are recovered from lytA + samples, there is a theoretical concern that results reflect Streptococcus mitis/oralis carrying homolog genes. As part of an ongoing longitudinal surveillance study in older adults assessing cumulative incidence of colonization, we assessed lytA + samples for the presence of S. pneumoniae and lytA + Streptococcus mitis/oralis.

    Methods: Nasopharynx [NP] and oropharynx [OP] swabs obtained from 150 adults ³55 years old were collected bimonthly in skim milk-tryptone-glucose-glycerol (STGG) medium. OP and NP samples were combined and processed with a sequential broth enhancement method and subjected to PCR using the lytA gene assay. lytA + (Ct value <40) samples were cultured on gentamicin blood agar plates and S. pneumoniae identified by morphology and susceptibility to optochin. In a subset of 25 broth samples from which pneumococcus could not be recovered, 2-3 optochin resistant alpha-hemolytic streptococci with distinct colony morphology were screened for the lytA gene by PCR.

    Results: From January 2015 – May 2016, 217 positive lytA + samples were detected in 64 subjects for a cumulative incidence of pneumococcal carriage of 42% based on PCR. Pneumococcal isolates could be recovered from only 8% of lytA + samples which were cultured. One of approximately50 optochin resistant alpha-hemolytic streptococcal colonies tested was lytA positive. This organism was confirmed as Streptococcus mitis/oralis by MALDI-TOF.

    Conclusion: We have confirmed the presence of lytA + Streptococcus mitis/oralis. The majority of lytA +, culture negative samples likely reflect low titers of pneumococci that autolyse prior to culture. Although lytA + Streptococcus mitis/oralisappear to be relatively uncommon, their presence will confound carriage studies based on PCR without culture confirmation.

    Angela Branche, MD, Department of Medicine, Division of Infectious Diseases, University of Rochester Medical Center, Rochester, NY, Edward Walsh, MD, FIDSA, Medicine, Division of Infectious Diseases, University of Rochester Medical Center, Rochester, NY; Infectious Diseases, Rochester General Hospital, Rochester, NY, Edna Yellamatty, B.S., Department of Pathology and Laboratory Medicine, Rochester General Hospital, Rochester, NY and Ann R. Falsey, MD, Medicine, Division of Infectious Diseases, Rochester General Hospital, Rochester, NY; Medicine, Division of Infectious Diseases, University of Rochester School of Medicine and Dentistry, Rochester, NY


    A. Branche, None

    E. Walsh, None

    E. Yellamatty, None

    A. R. Falsey, None

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