Molecular epidemiology of penicillin-resistant pneumococci isolated in Nairobi, Kenya

Abstract

A total of 26% of the pneumococci isolated from an outpatient clinic in Nairobi, Kenya, during 1991 to 1992 had intermediate levels of penicillin resistance. Gene fingerprinting and DNA sequencing were used to distinguish the penicillin-binding protein (PBP) LA, 2B, and 2X genes in 23 resistant isolates. Isolates were grouped into those that had identical forms of each of the three PBP genes (fingerprint groups) and those that had identical rRNA gene restriction patterns (ribotypes). Both methods divided the isolates into 11 groups. In a few cases, horizontal gene transfer appeared to have distributed an identical altered PBP gene into different pneumococcal lineages. Eight isolates were indistinguishable by ribotyping or multilocus enzyme electrophoresis and contained identical PBP LA genes. Although these isolates were therefore members of the same clone, they were divided into two fingerprint groups which contained different PBP 2X and 2B genes. Presumably, members of this clone have acquired different altered PBP 2X and 2B genes on two separate occasions. One of these fingerprint groups contained isolates of serotype 14, whereas the other contained isolates of both serotypes 14 and 7. The identification of isolates in the latter group that are identical by all criteria, except serotype, implies the occurrence of a change in serotype. The predominant serotypes of the penicillin-resistant pneumococci from Nairobi were serotypes 14 and 19. In both cases, isolates of the same serotype which required the same MIC of penicillin were not members of a single clone, indicating that identity of serotype and MIC are not sufficient criteria for defining clones of resistant pneumococci even when the bacteria are isolated from a single clinic.

Penicillin-binding proteins and β-lactam resistance

“…Both class B PBPs, PBP2x and PBP2b, are essential in Streptococcus pneumoniae, which is consistent with the selection of variants of these proteins by b-lactams (Kell et al, 1993). PBP1b and PBP3 are not essential (Schuster et al, 1990;Hoskins et al, 1999), which is again consistent with the fact that these proteins are not involved in the resistance process.…”

Evaluation of commercial methods for determining antimicrobial susceptibility of Streptococcus pneumoniae

“…In pneumococci the rates of resistance to a variety of antimicrobial agents are increasing around the world (2,4,9,10,12,16,17,33). However, until recently, relatively few microbiologists in the United States tested pneumococci for resistance, or they limited testing to the oxacillin screen test.…”

“…Strains of Streptococcus pneumoniae, particularly those resistant to antimicrobial agents, continue to be a major cause of otitis media, pneumonia, and meningitis in the United States (2,8,10,29,32) and around the world (7,19,22,33). Therapeutic regimens for pneumococcal disease have been compromised over the last decade by the development of resistance to penicillin (9,12,16,17), extended-spectrum cephalosporins (4,13,31), and other antimicrobial agents (19,23,24,33). A recent report from Atlanta emphasized that 25% of isolates from patients with invasive pneumococcal disease were no longer susceptible to penicillin and 9% were no longer susceptible to cefotaxime (10).…”

Molecular Analysis by Pulsed-Field Gel Electrophoresis and Antibiogram of Streptococcus pneumoniae Serotype 6B Isolates from Selected Areas within the United States

“…While serotyping and antibiotic susceptibility testing have been the most common epidemiologic tools for typing pneumococci, they have relatively limited discriminatory power (2). In contrast, genotyping methods such as multilocus enzyme electrophoresis (MLEE) (8,15,22,27,32), ribotyping (19,29), and PFGE (5,12,18) have shown greater discriminatory power for isolates within a single serogroup and have provided evidence for clonality and intercontinental spread of particular drugresistant pneumococci (8,11,19,21,25,26). In this study, we utilized PFGE following ApaI and SmaI restriction digestion of chromosomal DNA to determine genetic relatedness between pneumococcal serotype 6B isolates from different geographic locations in the United States.…”