In vitro activities of meropenem and other antimicrobial agents against British meningococcal isolates.

The in vitro activity of meropenem was compared with those of penicillin, ampicillin, cefuroxime, cetriaxone, cefotaxime, rifampicin, chloramphenicol, sulphadiazine and ciprofloxacin against 121 British meningococcal isolates by a microdilution method in Mueller-Hinton broth and by the E test. All meningococcal strains were susceptible to the agents except for ampicillin (88.4%), penicillin (88.4%), sulphadiazine (57.9%) and rifampicin (95%). The emergence of resistance problems among meningococcal isolates stresses the need for their constant monitoring and of the development of new agents. In this study we have shown that meropenem is highly active in vitro against Neisseria meningitidis. Recent studies have indicated that meropenem is highly active clinically and bacteriologically in the treatment of bacterial meningitis. Thus, the potentials of meropenem as meningococcal prophylactic and therapeutic agent needs to be fully evaluated.

Rifampin resistance in Neisseria meningitidis due to alterations in membrane permeability.

Rifampin-resistant (Rifr) Neisseria meningitidis strains are known to have single point mutations in the central conserved regions of the rpoB gene. We have demonstrated two distinct resistance phenotypes in strains with identical mutations in this region, an intermediate level of resistance in Rifr clinical isolates and a high level of resistance in mutants selected in vitro. The possible role of membrane permeability in the latter was investigated by measuring MICs in the presence of Tween 80; values for high-level-resistance mutants were reduced to intermediate levels, whereas those for intermediate-level-resistance strains were unaffected. The highly resistant mutants were also found to have increased resistance to Triton X-100 and gentian violet. Sequencing of the meningococcal mtrR gene and its promoter region (which determine resistance to hydrophobic agents in Neisseria gonorrhoeae) from susceptible or intermediate strains and highly resistant mutants generated from them showed no mutation within this region. Two-dimensional gel electrophoresis of two parent and Rif mutant strains showed identical shifts in the pI of one protein, indicating that differences between the parent and the highly Rifr mutant are not confined to the rpoB gene. These results indicate that both permeability and rpoB mutations play a role in determining the resistance of N. meningitidis to rifampin.

Antimicrobial susceptibility of penicillin-sensitive and penicillin-resistant meningococci.

Ceftriaxone showed high in-vitro activity against 119 penicillin-sensitive, penicillin-resistant and rifampicin-resistant UK isolates of meningococci. Unlike ciprofloxacin and minocycline, ceftriaxone is suitable for use in young children or in pregnancy and should be considered for therapy or prophylaxis in an outbreak of meningococcal disease. The E test gave results comparable to those given by broth microdilution method in the determination of meningococcal susceptibility to antimicrobials. It is convenient for use in small laboratories and can be used to determine antimicrobial subgroups of meningococci.

Molecular epidemiology of recent United Kingdom isolates of Neisseria meningitidis serogroup C.

The genomes of 34 recent United Kingdom isolates of Neisseria meningitidis serogroup C were examined by restriction enzyme digestion and by conventional and pulsed-field gel electrophoresis (PFGE). Strains were assigned to groups on the basis of the Dice similarity coefficient; strains with values of > 92% were considered to be clonally related. Twelve clones were identified by PFGE. Strains of two clonal groups predominated. Restriction endonuclease analyses using the 'high frequency cleavage' endonuclease Stu I and conventional electrophoresis gave 11 groups; in general it had lower resolving power than PFGE.

Molecular characterization of rifampin-resistant Neisseria meningitidis.

Primers were designed to amplify the rpoB gene of Neisseria meningitidis. The region of the gene amplified covered clusters I and II of the rifampin resistance (Rifr) mutation sites identified in Escherichia coli. DNAs from six Rifr isolates and 21 rifampin-susceptible isolates from the United Kingdom representing a number of serogroups were amplified and sequenced. All six Rifr isolates had identical DNA sequences and the same amino acid change, a His to an Asn change at position 35 (H35N). This His residue is equivalent to the His residue at position 526 in E. coli, one of the known Rifr mutation sites. DNAs from an additional six Rifr mutations generated in vitro were amplified and sequenced. Three had H35Y changes, one had an H35R change, one had an H35N change and one had an S40F change. The predominance of mutations at the His residue at position 35 in Rifr N. meningitidis isolates suggests that it plays a critical role in the selection of antibiotic-resistant variants. All six Rifr isolates belonged to the same clonal group when analyzed by restriction enzyme analysis and pulsed-field gel electrophoresis. These data suggest that a single clone of Rifr N. meningitidis is present and widespread throughout the United Kingdom.