[Phenotyping and antibiotic susceptibility's study of Neisseria meningitidis strains isolated at the "Hôpital d'Enfants" of Tunis]. / Typage phenotypique et etude de la sensibilite aux antibiotiques des souches de neisseria meningitidis isolees a l'Hopital d'Enfants de Tunis (mars 1998 - fevrier 2004).

A total of 23 invasive strains of Neisseria meningitidis were isolated between March 1998 and February 2004. 19 strains were recovered from cerebrospinal fluid (CSF) and 4 from blood. The majority of these strains were recovered from children with an age less to 4 years (86.9%). The antigenic formula'study (serogroup:serotype:serosubtype) of the strain's collection have shown there great diversity. The sero-group B was the most frequent (83%) followed by serogroup C (17%). The B:NT:NST phenotype was major among strains of the serogroup B and the C:4:P1-14 phenotype among strains of the serogroup C. No beta-lactamase activity was detected. 30.4% of the strains were of diminished susceptibility to penicillin G (CM190 = 0.38 Ig/ml). No resistance to amoxicillin (CMI90 = 0.19 microg/ml), to cefotaxime (CMI90 = 0.016 microg/ml) and to rifampin (CMI90-0.125 microg/ml) was detected; whereas 8.7% of strains-were resistant to chloramphenicol (CMI90=2 Ig/ml) and 65.2% to spiramycin.

Target gene sequencing to characterize the penicillin G susceptibility of Neisseria meningitidis.

Clinical isolates of Neisseria meningitidis with reduced susceptibility to penicillin G (intermediate isolates, Pen(I)) harbor alterations in the penA gene encoding the penicillin binding protein 2 (PBP2). A 402-bp DNA fragment in the 3' half of penA was sequenced from a collection of 1,670 meningococcal clinical isolates from 22 countries that spanned 60 years. Phenotyping, genotyping, and the determination of MICs of penicillin G were also performed. A total of 139 different penA alleles were detected with 38 alleles that were highly related, clustered together in maximum-likelihood analysis and corresponded to the penicillin G-susceptible isolates. The remaining 101 penA alleles were highly diverse, corresponded to different genotypes or phenotypes, and accounted for 38% of isolates, but no clonal expansion was detected. Analysis of the altered alleles that were represented by at least five isolates showed high correlation with the Pen(I) phenotype. The deduced amino acid sequence of the corresponding PBP2 comprised five amino acid residues that were always altered. This correlation was not complete for rare alleles, suggesting that other mechanisms may also be involved in conferring reduced susceptibility to penicillin. Evidence of mosaic structures through events of interspecies recombination was also detected in altered alleles. A new website was created based on the data from this work (http://neisseria.org/nm/typing/penA). These data argue for the use of penA sequencing to identify isolates with reduced susceptibility to penicillin G and as a tool to improve typing of meningococcal isolates, as well as to analyze DNA exchange among Neisseria species.