Identification of multiple clones of extended-spectrum cephalosporin-resistant Streptococcus pneumoniae isolates in the United States

Abstract

We characterized 12 isolates of Streptococcus pneumoniae with various levels of susceptibility to penicillin and extended-spectrum cephalosporins by antimicrobial susceptibility patterns, serotypes, ribotypes, chromosomal DNA restriction patterns by pulsed-field gel electrophoresis, multilocus enzyme electrophoresis patterns, penicillin-binding protein (PBP) profiles, and DNA restriction endonuclease cleavage profiles of pbp1a, pbp2x, and pbp2b. Seven cefotaxime-resistant (MIC, >2 g/ml) serotype 23F isolates were related on the basis of ribotyping, pulsed-field gel electrophoresis, and multilocus enzyme electrophoresis, but they had two slightly different PBP patterns: one unique to strains for which the MIC of penicillin is high (4.0 g/ml) and one unique to strains for which the MIC of penicillin is low (0.12 to 1.0 g/ml). The pbp1a and pbp2x fingerprints were identical for the seven isolates; however, the pbp2b fingerprints were different. An eighth serotype 23F isolate with high-level resistance to cephalosporins was not related to the other seven isolates by typing data but was a variant of the widespread, multiresistant serotype 23F Spanish clone. The PBP profiles and fingerprints of pbp1a, pbp2x, and pbp2b were identical to those of the Spanish clone isolate. An additional serotype 6B isolate with high-level resistance to cephalosporins had unique typing profiles and was unrelated to the serotype 23F cephalosporin-resistant isolates but was related on the basis of genetic typing methods to a second serotype 6B isolate that was cephalosporin susceptible. The serotype 6B isolates had different PBP profiles and fingerprints for pbp1a, but the fingerprints for pbp2x and pbp2b were the same.Penicillin-resistant strains of Streptococcus pneumoniae, first isolated in the late 1960s in Australia, are now prevalent throughout the world and are often associated with resistance to other antimicrobial agents (1, 25). In the United States, previous surveys revealed only sporadic occurrences of penicillin-resistant pneumococcal isolates (prevalence, Յ5% [23,46]); however, more recent surveys show much higher rates of infection caused by resistant pneumococci (14,16,47). Although the optimal therapy for infections caused by penicillinintermediate or -resistant strains of pneumococci has not been established, several reports indicate that cefotaxime or ceftriaxone is the drug of choice for initial empiric therapy for meningitis and sepsis caused by this pathogen (7,14,31).Most pneumococcal isolates that are resistant to penicillin also have increased resistance to extended-spectrum cephalosporins, including cefotaxime and ceftriaxone. The MICs of penicillin are generally equal to or two to four times higher than the MICs of the cephalosporins. Recently, we (45) and others (3, 14, 22) reported on infections caused by pneumococcal isolates that have not responded to cephalosporin therapy and for which the MICs of cefotaxime and ceftriaxone are 2 to 32 g/ml. These MICs are in excess of the MICs of penicillin for these isolat...

Emergence of a high-level cefotaxime-resistant Streptococcus pneumoniae strain in New Zealand

“…The Sma I restriction pro®le was shared with several isolates that were more susceptible to cefotaxime, suggesting that the strain with high-level cefotaxime resistance had evolved from a pre-existing strain. In contrast, isolates of S. pneumoniae from the USA that were resistant to extended-spectrum cephalosporins appear to have emerged on several occasions in different pneumococcal clones [9].…”

“…Pneumococci with high-level resistance to extended-spectrum cephalosporins have been reported from the USA [9] , UK [10] and Spain [11]. The spread of such strains would compromise the use of extended-spectrum cephalosporins in serious pneumococcal infections.…”

Nomenclature of Major Antimicrobial-Resistant Clones of Streptococcus pneumoniae Defined by the Pneumococcal Molecular Epidemiology Network

“…Genomic DNA was prepared in situ in agarose blocks as described previously (28,33) and was digested with SmaI (Life Technologies, Gaithersburg, Md.). The fragments were resolved by PFGE in 1% agarose (SeaKem GTG agarose; BioWhittaker Molecular Applications, Rockland, Maine) in 0.5ϫ Trisborate-EDTA buffer at 14°C and 6 V/cm in a CHEF-DR III system (Bio-Rad Laboratories, Hercules, Calif.).…”

Genetic Relatedness of Levofloxacin-Nonsusceptible Streptococcus pneumoniae Isolates from North America

“…This Spain 23F -1 clone is already responsible for an estimated 38.7% of penicillin-resistant S. pneumoniae respiratory tract isolates in the United States (6). While there have been many studies that address the epidemiology of S. pneumoniae with reduced susceptibility to macrolides and ␤-lactams (2,6,8,12,15,25,28,31), much remains unknown about the epidemiology of fluoroquinolone resistance in S. pneumoniae, since it has been documented only within the past few years and relatively small numbers of clinical isolates are available for study. It is important to assess the characteristics of these organisms to gain a better understanding of their clonal relationships and their potential for clonal dissemination and to aid in the selection of appropriate antimicrobials for empirical therapy.…”