To assess the relatedness of Streptococcus pneumoniae isolates recovered concurrently from blood and respiratory tract specimens from patients with pneumonia, we analyzed 24 paired isolates by pulsed-field gel electrophoresis (PFGE), serotyping, and antimicrobial susceptibility testing. PFGE, serotype, and/or susceptibility patterns were identical for 22 of 24 pairs. Susceptibility results for blood isolates should guide therapy.Streptococcus pneumoniae often colonizes the nasopharynx, and one or more serotypes can be found as normal throat flora in 5 to 10% of adults and 20 to 40% of children (6). However, this microorganism commonly causes community-acquired pneumonia and also is an important cause of more invasive infections, including bacteremia. As many as 25% of untreated patients with pneumococcal pneumonia may also have bacteremia (7). For patients who have both pneumonia and bacteremia, the respiratory isolates may be more resistant due to prior therapy for respiratory tract infections (2, 4).To assess genetic and phenotypic relatedness, we analyzed paired blood and respiratory isolates of S. pneumoniae to determine if they had the same pulsed-field gel electrophoresis (PFGE) profile, serotype, and antimicrobial susceptibility pattern. In total, 24 pairs of S. pneumoniae isolates recovered concurrently from both blood and respiratory tract cultures between April 1998 and November 2003 were tested. Most of the isolates were from patients at Duke University-affiliated hospitals (23 pairs); 1 pair was from a patient at a nearby hospital. The patients comprised 18 males and 6 females with an age range of 1 month to 73 years. There were 2 pediatric patients (aged 1 month and 6 years), but most (20/24) of the patients were more than 40 years old. The respiratory isolates were obtained by sputum collection (n ϭ 9), endotracheal suction (ETS) (n ϭ 11), bronchial washing (n ϭ 3), and sinus aspiration (n ϭ 1). Isolates were identified by standard microbiological methods (10), including alpha-hemolysis on sheep blood agar, Gram staining, and the bile solubility test. Isolates were frozen at Ϫ70°C until further testing.DNA preparation and restriction were done with the BioRad universal module and GenePath group I reagent kit as specified in the manufacturer's package insert (Bio-Rad Laboratories, Hercules, CA). Briefly, isolates were grown overnight (16 to 18 h) at 37°C on sheep blood agar plates, and colonies were suspended in 1.0 ml of sterile water. This suspension was centrifuged, and the pellet was resuspended in lysis buffer and placed in agarose to form plug molds. The agarose-embedded cells were lysed, after which the DNA was extracted, deproteinized, and restricted with SmaI enzyme. PFGE was performed with the Bio-Rad GenePath system using program 12, which separates DNA in the size range of 25 to 300 kb. Gels were stained with ethidium bromide and photographed under UV transillumination. Gels were visually inspected and interpreted by the criteria of Tenover et al. (11).Serotyping was performed by the que...