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.

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.

Epidemiological evaluation of Neisseria meningitidis serogroup B by pulsed-field gel electrophoresis.

Genomic DNA from 25 strains of serogroup B Neisseria meningitidis was subjected to pulsed-field gel electrophoresis (PFGE) after digestion with Spe I. N. meningitidis genomic DNA displayed considerable diversity. The diversity we observed among these strains was stable and included isolates from an outbreak that were phenotypically identical. This confirms the value of macrorestriction profiling and PFGE in providing epidemiologically stable strain markers for typing 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.

Production of a mannose-resistant fibrillar haemagglutinin by strains of Escherichia coli of EPEC serotype O111:H12.

Two strains of Escherichia coli of serotype O111:H12 produced a mannose-resistant haemagglutinin (MREHA) of Duguid's pattern 7 that reacted strongly with the red cells of ox and sheep. These strains also adhered to HEp2-epithelial cells and formed fibrillae demonstrable by negative staining and immunogold labelling.

The haemagglutinins and fimbriae of Proteus penneri.

The haemagglutinins and fimbriae produced by 18 strains of Proteus penneri were studied and compared with those formed by representative strains of other species of Proteeae. After repeated subcultures at 30 degrees C, 12 P. penneri strains formed only MR/K haemagglutinins which were associated with thin, non-channelled, type-3 fimbriae. Two strains formed simultaneously both MS and MR/K haemagglutinins associated with thick, channelled, type-1 fimbriae and type-3 fimbriae, respectively. Four strains formed simultaneously both MR/K and MR/P haemagglutinins. No P. penneri strain formed either MS or MR/P haemagglutinins alone under these conditions. The type-3 fimbriae from P. penneri strain E180 were isolated, purified and found to be protein of 19 Kda. Immunoelectronmicroscopy studies with antibody to the type-3 fimbriae of strain E180 showed that P. penneri strains at least two antigenic types of type-3 fimbriae. The type-3 fimbrial antigen of the vaccine strain E180 was shared by another eight strains of P. penneri. A further eight P. penneri strains and the strains representative of other genera within Proteeae had type-3 fimbriae of a different antigenic type. The formation of these haemagglutinins and fimbriae suggests that this organism is well endowed to be a urinary-tract pathogen.

Immunological and genetical relatedness of type-1 and type-2 fimbriae in salmonellas of serotypes Gallinarum, Pullorum and Typhimurium.

The fimbriae of 50 strains of serotype Gallinarum and 35 strains of serotype Pullorum of the genus Salmonella were compared with the type-1 fimbriae of serotype Typhimurium strains by immune electron microscopy and dot blot hybridization tests with gene probes for type-1 fimbriation in Typhimurium. The fimbriae of Gallinarum and Pullorum strains were coated with Typhimurium type-1 fimbrial antiserum and probes hybridized strongly with DNA of Gallinarum and Pullorum strains under stringent conditions. Furthermore, when Typhimurium type-1 fimbrial antiserum, that had been absorbed with fimbriate Gallinarum or Pullorum bacteria, was used in immune gold labelling experiments, it was shown that residual antibody recognized sites of possible adhesin incorporation at intervals along the length of Typhimurium type-1 fimbriae. These findings suggest that the type-2 fimbriae produced by all Gallinarum and Pullorum strains are non-adhesive forms of adhesive, type-1 fimbriae. This observation is of interest because type-1 fimbriae have never been reported in naturally occurring strains of these two avian-adapted serotypes.

Characterisation of a fimbrial, mannose-resistant and eluting haemagglutinin (MREHA) produced by strains of Salmonella of serotype Sendai.

Strains of Salmonella of serotype Sendai, producing a mannose-resistant and eluting haemagglutinin (MREHA) when cultured at 37 degrees C but not at 18 degrees C, were examined by electronmicroscopy after negative staining. Production of this MREHA, previously thought to be nonfimbrial, was correlated with the presence of thick fimbriae with an external diameter of 13.6 nm. These fimbriae were readily fragmented and, when purified, had an estimated Mr of 28 Kda. Production of fimbrial MREHA by Sendai strains was associated with the ability to adhere to a wide range of substrates and to form a fimbrial pellicle at the surface of liquid media incubated statically in air. The origin of this unusual Sendai fimbrial MREHA is unknown. Thin filamentous structures produced independently of fimbrial MREHA by Sendai strains were also described. Fimbrial MREHA was not produced by strains of the antigenically similar serotype Miami which, however, and unlike Sendai strains, formed mannose-sensitive haemagglutinin and type-1 fimbriae. The ability to differentiate strains of Miami and Sendai (serotype 1,9,12:a: 1,5) by means of their fimbriae is noted.

Some strains of Escherichia coli of putative enteroadherent-aggregative serotypes produce an unusual fibrillar haemagglutinin.

Two strains of Escherichia coli that formed on unusual kind of mannose-resistant and eluting haemagglutinin (MREHA) reacting with the red blood cells of rat and mouse, when cultured at 37 degrees C but not at 18 degrees C, were examined by electron microscopy. Production of this rare rodent-positive MREHA was correlated with the presence of fine fibrillae of estimated diameter 2.5 nm that were demonstrated by negative staining and immuno-gold labelling with MREHA-specific anti-serum. These two strains belonged to serotypes 078:H- and 078:H33; thus, it would be useful to know whether enteroadherent-aggregative strains of E. coli of these and other serotypes also possess this unusual MREHA.

A novel fimbrial haemagglutinin produced by a strain of Salmonella of serotype Salinatis.

A strain of Salmonella of serotype Salinatis, that produced a mannose-resistant and eluting haemagglutinin (MREHA) when cultured at 37 degrees C but not at 18 degrees C, was examined by electron microscopy after negative staining. Production of this MREHA, previously described as being non-fimbrial, was correlated with the presence of thin fimbriae which had an external diameter of 3.6 nm. The purified Salinatis thin fimbriae had an estimated Mr of 19 kDa. This fimbrial MREHA was not produced by strains of the antigenically related serotypes Duisburg and Sandiego.

Demonstration by immuno-electronmicroscopy of antigenic heterogeneity among P fimbriae of strains of Escherichia coli.

The identification of P fimbriae on urinary strains of Escherichia coli isolated from urine was made by observation of the patterns of mannose-resistant and eluting haemagglutination of erythrocytes of seven animal species (and including those of human p phenotype), and by haemagglutination-inhibition tests with hydatid-cyst fluid known to contain an analogue of P-fimbrial receptor. In tests with five different, pure P-fimbrial antisera prepared in rabbits, agglutinin titres of 37 P-fimbriate strains revealed differences in their reactivity; immuno-electronmicroscopy studies with the same five antisera showed that P-fimbriate strains were markedly different in the extent to which their P fimbriae were coated with antibody. The antigenic heterogeneity observed among P fimbriae is discussed with regard to the development of P-fimbrial vaccines.