Accuracy of phenotypic methods for identification of Streptococcus pneumoniae isolates included in surveillance programs.
Similarities between Streptococcus pneumoniae and viridans group streptococci may result in misidentification of these organisms. In surveillance programs which assess antimicrobial resistance rates among respiratory tract pathogens, such identification errors could lead to overestimates of pneumococcal resistance rates. DNA probe analysis (Gen-Probe, San Diego, CA), the bile solubility test, optochin susceptibility, colony morphology, and the capsular swelling reaction with Omni serum (Staten Serum Institut, Copenhagen, Denmark) were used to characterize 1,733 organisms provisionally identified as S. pneumoniae in a 2004 to 2005 antimicrobial resistance surveillance program. These organisms were obtained in 41 U.S. medical centers. Among these, 1,647 (95%) were determined to be S. pneumoniae by DNA probe. Elimination of those isolates found not to be S. pneumoniae resulted in 1 to 2% decreases in resistance rate estimates with penicillin, erythromycin, tetracycline, and trimethoprim-sulfamethoxazole. With AccuProbe as a reference standard, the sensitivities and specificities of each phenotypic method for the identification of S. pneumoniae were, respectively, 98.8% and 82.6% for bile solubility, 99.3% and 74.4% for the capsular swelling reaction with Omni serum, and 87.9% and 59.3% for optochin susceptibility. Colony morphology was of limited value, as 391 (23.7%) isolates lacked the typical button or mucoid colony appearance of S. pneumoniae.
Richter
Sandra S
SS
Department of Pathology, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242-1009, USA.
Heilmann
Kristopher P
KP
Dohrn
Cassie L
CL
Riahi
Fathollah
F
Beekmann
Susan E
SE
Doern
Gary V
GV
D000046:Academic Medical Centers; D001431:Bacteriological Techniques / Q000379:methods*; D005838:Genotype; D006801:Humans; D010641:Phenotype; D011008:Pneumococcal Infections / Q000382:microbiology*; D012680:Sensitivity and Specificity; D013296:Streptococcus pneumoniae / Q000302:isolation & purification*; D014481:United States