Related Experiment Videos
Molecular epidemiology of penicillin-resistant pneumococci isolated in Nairobi, Kenya
C M Kell1, J Z Jordens, M Daniels
1Microbial Genetics Group, School of Biological Sciences, University of Sussex, Falmer, Brighton, United Kingdom.
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) 1A, 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 1A 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.
Insights
Penicillin resistance in pneumococci from Kenya was studied using gene fingerprinting. Results show that identical serotypes and penicillin resistance levels do not always indicate a single bacterial clone.
Area of Science:
- Microbiology
- Genetics
- Epidemiology
Background:
- Penicillin resistance in Streptococcus pneumoniae is a growing public health concern.
- Understanding the genetic diversity and clonal evolution of resistant strains is crucial for effective treatment strategies.
Purpose of the Study:
- To investigate the genetic relatedness and clonal structure of penicillin-resistant pneumococci isolated from Nairobi, Kenya.
- To determine if serotype and penicillin resistance levels are sufficient to define bacterial clones.
Main Methods:
- Gene fingerprinting and DNA sequencing of penicillin-binding protein (PBP) genes (1A, 2B, 2X).
- Ribotyping and multilocus enzyme electrophoresis for bacterial strain typing.
- Analysis of serotypes and minimum inhibitory concentrations (MICs) of penicillin.
Main Results:
- 26% of pneumococci isolates exhibited intermediate penicillin resistance.
- Both gene fingerprinting and ribotyping identified 11 distinct groups among the resistant isolates.
- Horizontal gene transfer of altered PBP genes was observed.
- Identical clones could possess different PBP genes, and isolates of the same serotype with similar penicillin resistance levels did not always belong to the same clone.
- Serotype switching was implied in some isolates.
Conclusions:
- Serotype and penicillin resistance levels alone are insufficient to define clones of resistant pneumococci.
- The genetic diversity and complex evolutionary dynamics of penicillin-resistant pneumococci necessitate advanced molecular typing methods for accurate clonal identification.