Meningococcal serotypes and serogroup B disease in north-west Europe

Meningococcal carriage in close contacts of cases

Between 1 October 1986 and 31 March 1987, 55 cases of meningococcal disease were identified in the South-West of England, an attack rate of 1.54 per 100,000 during the study period. Antibiotics used in the treatment of the disease successfully eliminated nasopharyngeal carriage of meningococci in 13 out of 14 cases without use of rifampicin. The overall meningococcal carriage rate in 384 close contacts was 18.2% and the carriage rate of strains indistinguishable from the associated case strain was 11.1%. The carriage rate of indistinguishable strains in household contacts (16.0%) was higher than the carriage rate in contacts living at other addresses (7.0%, P less than 0.05). A 2-day course of rifampicin successfully eradicated meningococci from 46 (98%) of 47 colonized contacts. In one third of cases groupable meningococci were isolated from at least one household contact; 92% of these isolates were of the same serogroup as the associated case strain. When a meningococcus is not isolated from a deep site in a clinical case of meningococcal disease, culture of serogroup A or C strains from nasopharyngeal swabs of the case or of household contacts is an indication that the close contact group should be offered meningococcal A + C vaccine in addition to chemoprophylaxis. The failure in this and other studies to isolate meningococci from any household contact in the majority of cases may be due either to the relative insensitivity of nasopharyngeal swabbing in detecting meningococcal carriage or to the acquisition of meningococci by most index cases from sources outside the household.

Genetic relationships among strains of Neisseria meningitidis causing disease in Italy, 1984-7

Since 1984 a change in the epidemiological pattern of meningococcal disease in Italy has occurred with a predominance of Neisseria meningitidis of serogroup C (76%), serotype 2a and a high proportion of strains resistant to sulphonamides (71%). In order to understand better the epidemiology of the group C N. meningitidis strains responsible for the disease over the last years in Italy, we studied the genetic features of phenotypically closely related strains, by enzyme electrophoresis. The results showed that the genetic and the phenotypic characteristics of the 57 strains studied were similar, suggesting that spread of a single clone during recent years in our country. This result is in agreement with the circulation of strains typical of epidemic situations, despite the decreasing incidence of meningococcal disease in Italy.

Epidemiology of meningococcal disease in Denmark 1980-1988

Based on epidemiological data of notified cases of meningococcal disease (MD) in Denmark during the period 1980-88 the recommendations for prophylaxis are evaluated. In 1986 the incidence of MD increased about 60% to 5.5 per 100,000 population. The clinical diagnosis of MD was verified by culture of Neisseria meningitidis in 79% of notified cases. About 40% of all patients were less than 4 years of age. The mortality in 1988 was found to be 10%. Serogroup B disease accounted for about 80% of the cases. Two co-primary and 28 secondary cases were registered. Two major outbreaks of serogroup C disease occurred in 1984 and 1986, respectively. In small clusters of 2-3 cases within socially well-defined groups the recommendations for prophylaxis are sufficient. But for the new pattern of clusters spread over months to years in certain geographical areas or open social groups, especially among teenagers, the existing recommendations are insufficient. The occurrence of localized clusters of serogroup B disease emphasises the need for a vaccine against serogroup B disease.

Clonal properties of meningococci from epidemic meningitis

Methods from the field of population genetics now enable the classification of epidemic strains of Neisseria meningitidis and have resolved the relationships between apparently distinct epidemics. The diversity of serogroup A bacteria seems quite limited and only a few strains have been responsible for the epidemics of recent decades. Meningococci express both constant and highly variable antigens, the variability of which is determined by the clonal background of the epidemic strain. The development of an improved vaccine is being pursued but still faces technical problems.

Serotype-specific outbreak of group B meningococcal disease in Iquique, Chile

From 1979 to August 1987, there have been 178 cases of meningococcal disease in Iquique, Chile, a city of about 140,000. The attack rate for the last 5 years has been in excess of 20/100,000 per year, more than 20 times greater than for the country overall. The mortality rate was 6%. The disease occurred in patients with ages from 4 months to 60 years, but 89% of cases were in patients less than 21 years. The largest number of cases were in the age group 5-9 years (n = 54), but the highest incidence occurred in children less than 1 year of age (72.8/100,000 per year). The male/female ratio was 1.2. Cases occurred all year round with little seasonal variation. Of the 178 cases, 173 were biologically confirmed. Serogroup analysis of strains from 135 patients revealed A = 1, B = 124, C = 10. Forty-four group B strains from 1985-7 were serotyped: 15:P1.3 = 36, 15:NT = 4, 4:P1.3 = 2, NT:NT = 2. Ten of 11 of the outbreak strains tested were sulfadiazine-resistant. This is the first recognized outbreak caused by a Gp B:15 strain in South America. It shares many of the characteristics of outbreaks caused by closely related strains in Europe, such as a predilection for older children and adolescents, sulfadiazine-resistance, and sustained high attack rates. The Iquique strain (B:15:P1.3) belongs to the same genetic clone (ET-5 complex) as the Norway (B:15:P1.16) and the Cuban (B:4:P1.15) strains.

Identification of a UK outbreak strain of Neisseria meningitidis with a DNA probe

To investigate the epidemiology of meningococcal disease, a specific DNA probe pUS210 (carrying insert DNA which is repeated in the meningococcal genome) was isolated. The ability of this probe to hydridise with multiple polymorphic fragments in Southern blots was exploited to examine genetic relations within strains. Two geographically distinct foci of prolonged meningococcal disease (Gloucester and Plymouth, UK) are due to a clonal population of virulent strains that are distinct from those found elsewhere in the UK.

Changes in bacterial meningitis

In 1964, one of us (WHG) undertook a retrospective study of bacterial meningitis in childhood in the north east of Scotland during the period 1946-61. We have recently carried out a similar review of cases occurring during 1971-86, to compare the incidence, mortality, and bacteriological patterns. During the earlier period 285 cases occurred, a total incidence of 16.9/100,000 children per year. In the later period 274 children were affected, an annual incidence of 17.8/100,000. The overall mortality rate fell dramatically from 11.9% to 1.8%, the latter figure comparing favourably with recent published studies from Scandinavia and the United States. There was a change in the bacteriological profile in the second period with a significant rise in cases due to Haemophilus influenzae at all ages. A fall in cases of meningococcal meningitis was significant in infants under 1 year of age only. Possible reasons for the change in the bacteriological pattern are discussed.

Use of DNA fingerprinting in an epidemiologic study of outbreak-specific and non-specific strains of group C Neisseria meningitidis

DNA fingerprints of nine group C isolates of Neisseria meningitidis were obtained by digestion with three restriction endonucleases, BamHI, EcoRI, and HindIII. Identical restriction profiles were displayed by five strains isolated from two patients and three contacts during a localized outbreak of meningococcal disease in the area served by our laboratory. A slight difference, appreciable only in the fingerprints obtained with EcoRI, was observed between these isolates and a sixth one isolated from a clinical case occurring in the same area one year later. In contrast, three additional strains, recently isolated from patients in separate areas in Italy, gave restriction profiles differing strikingly from one another and from those produced by the strains isolated in our area.

Comparative evaluation of potential components for group B meningococcal vaccine by passive protection in the infant rat and in vitro bactericidal assay

Seventeen monoclonal antibodies to one of three main cell surface antigens of Neisseria meningitidis group B were tested for protective efficacy in the infant rat using as challenge seven strains of different class 2/3 protein serotypes, class 1 protein (P1) subtypes and LPS immunotypes. Type-specific protection indicated both by a reduction of bacteraemia and meningitis and survival of the animals was regularly obtained with antibodies to the P1 protein and to LPS. By contrast, only one of seven antibodies to the serotype-specific class 2/3 protein was protective, even though four of them were highly bactericidal. The animal protection test and in vitro bactericidal assay were otherwise concordant. These data form important guidelines for the design of vaccines to prevent group B meningococcal infections.

Human immune response to meningococcal outer membrane protein epitopes after natural infection or vaccination

Antibody levels in 41 sets of human acute- and convalescent-phase meningococcal sera were compared with those in 23 sets of human prevaccination and 2-week postvaccination sera. We used a modification of a solid-phase radioimmunoassay (SPRIA) technique to test each of the human serum samples as inhibitors of monoclonal antibodies (MAbs) that bind (HIMSPRIA) to the outer membrane complex from a 2a:P1.2:P5.1 strain. We used three murine MAbs specific for the 2a, P1.2, and P5.1 epitopes on meningococcal class 1, 2, and 5 proteins, respectively, to detect antibodies with similar specificities in human sera. Each of 40 available matching strains from patients were also screened with the three MAbs in a nitrocellulose spot blot assay. A total of 37 (92%) were positive for the 2a epitope, 36 (90%) were positive for the P1.2 epitope, and 16 (40%) were positive for the P5.1 epitope. Of 38 available convalescent-phase sera, 27 (71%) matched with these strains and had detectable inhibiting antibody for each of the MAb-defined protein epitopes of the infecting strain. Three convalescent-phase sera had no HIMSPRIA activity for MAb-defined epitopes that were present on the infecting strain; others had activity for one or two of the epitopes. The results were similar for pre- and postvaccination sera. The average level of HIMSPRIA activity for the P1.2 epitope was greater than fivefold higher in postvaccination sera compared with that in convalescent-phase sera. Sera with distinct patterns of HIMSPRIA activity also were tested by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot analysis and showed a correlation between the HIMSPRIA activity for particular epitopes and the level of antibody binding to the immunoblotted proteins possessing those epitopes. A comparison of the HIMSPRIA and the bactericidal activity of selected postvaccination sera indicated a possible correlation between HIMSPRIA and bactericidal activity, but it also suggested the presence of bactericidal antibodies with specificities other than those defined by the MAbs.

Endotoxin release from neisseria meningitidis. Relationship between key bacterial characteristics and meningococcal disease

A method was established in order to measure total and filtrable (CF) endotoxin in cultures of Neisseria meningitidis strains. The Limulus lysate (LAL) test gave results which paralleled those of the standard rabbit pyrogen test and of gas chromatography (GLC), concerning detection of different CF endotoxin levels. Meningococci varied in their ability to produce CF endotoxin. Cultures of similar bacterial densities, whether with a high (E+) or a low (E-) release of endotoxin in CF, had both high yields of endotoxin in sonicated culture suspensions determined by the LAL test. GLC demonstrated only small differences in total LPS contents between E+ and E- strains. This suggests that strains with similar cell wall endotoxin contents may vary in CF endotoxin. Electron microscopy revealed that E+ strains presented a high number of free, outer cell wall fragments (blebs, tubuli, membranes and aggregates of such structures) in surroundings. Few such free, small structures were found around E- strains. The amount of CF endotoxin of E+ strains was in part a function of the number of colony forming units (CFU/ml), and generally followed the growth curve. Because of its moment of appearance, and also based on electron microscopy findings, CF endotoxin appeared mainly to be released from living bacteria. The CF level of endotoxin was low or not detected at all in cultures of E- strains although their cultures reached higher mean CFU-levels than the niveaus required for the detection of CF endotoxin in the E+ strains. The E+ property was strain dependent. Meningococci isolated from CSF or blood had a significantly higher proportion of E+ strains (88.2%) and a higher CF endotoxin titre (greater than or equal to 10(3); 34.5%), than isolates from carriers (32.3% and 10.8%, respectively) (p less than 0.001 and p less than 0.001, respectively). A high mean CFU/ml in cultures seemed to be more often associated with isolates from patients than from carriers, more often with the presence than abscence of capsular polysaccharide (p less than 0.05), and more often with the presence than absence of the E+ property (p = 0.002). E+ strains were mostly serogroupable (i.e. encapsulated), regardless of source of the isolate (99% case and 80% carrier isolates). In contrast, serogroupable bacteria were not necessarily E+ when isolated from carriers (54.8%). The serogroup most apt to cause disease tended to have the highest proportion of E+ strains and the highest level of CF endotoxin.(ABSTRACT TRUNCATED AT 400 WORDS)

Sero- and subtypes of group B meningococci causing invasive infections in Finland in 1976-87

Neisseria meningitidis group B (MenB) strains isolated from 1976 to 1987 in Finland in 339 patients with invasive infection were sero/subtyped by whole cell enzyme immunoassay using monoclonal antibodies to class 1 and 2/3 outer membrane proteins. 66.7% of the strains could be serotyped (class 2/3) and 70.2% subtyped (class 1). No single phenotype was clearly predominant. The most common serotypes were 4 (18.6%) and 14 (17.4%) and the most common subtypes P1.16 (20.1%) and P1.2 (12.1%). The Norwegian phenotype B:15:P1.16 was seen only rarely (a total of 18 strains). Strains from Northern Finland did not differ from those from Southern Finland: no single phenotype caused the slight increase seen in the incidence of MenB infections in the end of 1970s in the North.

Serological study of meningococcal isolates in Switzerland and France 1980-1986

A study was performed of 342 disease-related strains of meningococci isolated in Switzerland and France between 1980 and 1986, including more than 50% of all strains isolated in Switzerland in 1986. Using a newly developed spot-blot enzyme-linked immunoassay and a panel of monoclonal anti-meningococcal antibodies, 96% of all strains were shown to react with at least one antibody. In both countries more than 50% of the strains were group B. In France serotype 2a was the prevalent serotype and was often associated with subtype P1.2. In Switzerland serological markers of epidemic strains recently described in Northern Europe (serotype 15 and subtype P1.16) were observed with increasing frequency in 1986. However, serotype 4 has been prevalent in Switzerland since 1980 and no clonal population was seen to emerge.

Meningococcal serogroups in New South Wales, 1977-1987

Data are presented on serogroups of meningococci (Neisseria meningitidis) that were submitted to Westmead Hospital and The Children's Hospital, Camperdown, from patients in Sydney and in rural areas of New South Wales, from January 1, 1977 to December 31, 1987. One hundred and ten organisms that were isolated from cerebrospinal fluid or from blood were examined. All organisms were isolated from sporadic cases of meningococcal disease. Patients in the zero-to-two-years' age-group were affected most commonly, but 36.3% of isolates were from older children and adults. The distribution of serogroups was as follows: serogroup B, 43.6; serogroup A, 28.2%; serogroup C, 10.0%; serogroup W135, 8.2%; serogroup Y, 4.5%; and serogroup Z, 0.9%. The isolates that were serogrouped by us represented approximately half the cases of meningococcal meningitis that were notified in New South Wales during this period. Serogrouping of meningococcal isolates is very important in order to follow epidemiological trends in the disease and to monitor the serogroups that cause outbreaks, where vaccination of contacts may be indicated. Our laboratories are prepared to receive isolates for serogrouping and antibiotic sensitivity testing from across New South Wales.

Electromorphic characterization and description of conserved epitopes of the lipooligosaccharides of group A Neisseria meningitidis

We studied the lipooligosaccharides (LOS) of 28 group A Neisseria meningitidis of epidemiologically diverse origins to investigate whether each of the LOS serotypes found in serogroup A could be identified physically as well as antigenically. Using a dot blot assay with LOS-specific monoclonal antibodies (MAbs), we identified four epitopes that were serotype specific. The LOS from strains of each serotype were electromorphically and antigenically distinct when analyzed by silver-stained sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting. The LOS of L8 strains contained a 3,600-Mr component that bound the L8 MAb. The LOS of L9 strains contained two major components of 4,500 and 4,200 Mr. They bound the L9 MAb to the larger component. The LOS of L10 strains had a single major component of 4,000 Mr that bound the L10 MAb. The LOS of L11 strains contained a major 3,600-Mr component that could not be distinguished from the 3,600-Mr LOS of L8 strains by SDS-PAGE but that bound the L11 MAb. LOS of group A strains contained a highly conserved epitope in addition to a serotype-specific epitope. This was identified by a MAb that bound to all the strains on dot-blots and to multiple LOS components of various Mrs on immunoblots. We conclude that the LOS which bear the L9, L10, and L11 determinants are physically distinct and can be identified by SDS-PAGE or MAb binding or both. L8 and L11 are both borne on a 3.6-kilodalton LOS and can only be distinguished serologically.

Carriage of Neisseria meningitidis: investigations in a military establishment

A prevalence study of personnel on a Royal Naval Air Station revealed that 23.0% of 2479 personnel were carrying a meningococcus. Selected groups of personnel were subsequently swabbed monthly for a year. We have shown that it is only by repeated swabbing and the use of optimal methods including enrichment media that one can have a hope of identifying the 'true' carriage rate. A presumed virulent strain of Neisseria meningitidis B15 P1.16 was repeatedly isolated from three personnel who remained well, as did their colleagues both at their work place and socially. The study served to emphasize our lack of knowledge of the virulence factors associated with N. meningitidis.

Outer membrane protein serosubtyping of Neisseria meningitidis

A system for typing Neisseria meningitidis has been developed which uses monoclonal antibodies against two separate classes of outer membrane proteins (class 1 and class 2/3) in addition to capsular polysaccharide serogrouping. It was shown that class 1 outer membrane protein subtypes are common to meningococcal reference strains of different serotypes. Application of the system to 50 group B meningococcal patient isolates revealed that 75% could be categorized as class 1 subtypes. The typing system has potential usefulness in epidemiological surveillance and vaccine development.

Two monoclonal antibodies specific for serotype 4 antigen of Neisseria meningitidis

Two new monoclonal antibodies (MN14G21.17 and MN14E9.15) specific for the serotype 4 antigen of meningococci were isolated. The antibodies were raised against a previously non-typable serogroup B strain from the Netherlands and were shown to react with the serotype antigen of the prototype reference strains for serotype 4 and serogroup A as well as with that of the homologous strain. Further screening of 290 serogroup A and B case isolates with the monoclonal antibodies indicated that the serotype 4 epitope was present on all 100 serogroup A strains tested, including representative isolates from 28 epidemics, and on most isolates from a recent serogroup B epidemic (1981-1983) in Cuba. In addition, 68 isolates from recent sporadic cases (1980-1986) and/or clusters of cases of serogroup B disease in many parts of Europe, the USA, the USSR and Australia were also of this serotype.

Experimental meningococcal meningitis in the infant rat

Experimental infection of the infant rat could be established with intraperitoneal challenge with strains of all three meningococcal groups A, B, and C tested. 5-day-old rats were challenged with 3 different doses (10(2), 10(4), and 10(6) bacteria/animal) and the development of peritonitis, bacteraemia and meningitis detected as a function of time at 3, 6, and 9 h. Mortality was followed up to 24 h. Group B strains caused a rapidly developing and sustained high level bacteraemia and meningitis with all challenge doses. Bacteraemia and meningitis following challenge with MenA and MenC were of somewhat shorter duration and reached lower peak levels. Repeated 'rat passages' of meningococcal strains that had been kept stored for long periods markedly increased their virulence. This study shows that the infant rat model can be applied for studying pathogenesis of meningococcal bacteraemia and meningitis. Previous work from this laboratory has shown it to be suited also for studying antibody-mediated protection from this disease.

Neisseria meningitidis group B serosubtyping using monoclonal antibodies in whole-cell ELISA

Meningococci can be classified by the presence of serotype and subtype antigens on the class 2/3 and class 1 outer membrane proteins, respectively. A typing system employing monoclonal antibodies and a WCE for detection of such antigens enabled us to sero- and/or subtype 255 out of 268 group B meningococci from 19 countries collected from 1959 till 1987. The combination of a comprehensive collection of antibodies and a sensitive, specific, large-scale screening technique greatly facilitates the assignment of bacterial isolates to their sero- or subtype. This will then allow definitive, bass-line information on the epidemiology of meningococci and on the possible construction of outer membrane protein vaccines.

Comparison of clonal analysis and DNA restriction analysis for typing of Neisseria meningitidis

We have formerly described a clonal analysis of 423 serogroup A isolates of Neisseria meningitidis which distinguished 21 clones and 34 electrophoretic types. The clones were found to be uniform within distinct epidemiological situations and distinct between different sets of epidemics. Strains representative of the 34 electrophoretic types have now been analyzed by restriction endonuclease digestion of their genomic DNA's. The results correlated partially with the clonal assignments; the discrepancies were epidemiologically more consistent with the interpretation of the clonal analysis than with that of the restriction endonuclease analysis.

Cloning of an outer membrane protein of Neisseria meningitidis in Escherichia coli

A gene bank of chromosomal DNA of Neisseria meningitidis group B was constructed in phage lambda EMBL3, and screened by rabbit polyclonal antibodies to major outer membrane (OM) proteins of the meningococcus. Several clones expressing a 28 kDa protein were found. The gene coding for the 28 kDa protein was subcloned into plasmid pUC18 in Escherichia coli. The protein was expressed in E. coli and located in the OM. Rabbit antibodies were raised to the 28 kDa protein purified from E. coli and used to localize the protein in the meningococcus. The antiserum recognized a minor protein of similar electrophoretic mobility in the outer membrane complex (OMC) of the meningococcus. The 28 kDa protein was found to be common to different Neisseria species; it was expressed by both pathogenic and nonpathogenic Neisseria.

An outbreak of meningococcal disease in Stonehouse: planning and execution of a large-scale survey

In November 1986 a large-scale survey was undertaken in the Gloucestershire town of Stonehouse during an outbreak of meningococcal disease due to group B type 15 subtype P1.16 sulphonamide-resistant strains. There were 15 cases in Stonehouse residents during the 4 years from April 1983, an annual attack rate of 56.5 per 100,000. Four secondary cases occurred despite rifampicin prophylaxis. The objectives of this community survey were to investigate patterns of meningococcal carriage, transmission and immunity and to determine the proportion of non-secretors of blood group antigens in the Stonehouse population and amongst meningococcal carriers. A total of 6237 subjects participated including 75% of the 6635 Stonehouse residents. Over 97% of the participants provided all three of the requested specimens-nasopharyngeal swabs, saliva and blood samples. The co-operation between the many organizations involved in the detailed preliminary planning was instrumental in the success of the survey; in particular the value of effective collaboration between Departments of Community Medicine and Microbiology and of the Public Health Laboratory Service network of laboratories in undertaking investigations of this size and type was clearly demonstrated.

The Stonehouse survey: nasopharyngeal carriage of meningococci and Neisseria lactamica

A total of 6234 nasopharyngeal swabs was collected during a survey of the population of Stonehouse, Gloucestershire in November 1986 as part of an investigation into an outbreak of meningococcal disease. The overall meningococcal carriage rate was 10.9%. The carriage rate rose with age from 2.1% in the 0- to 4-year-olds to a peak of 24.5% in the 15- to 19-year-olds, and thereafter declined steadily with age. Male carriers outnumbered female carriers of meningococci by 3:2. Group B (or non-groupable) type 15 sulphonamide-resistant strains which had caused the outbreak were isolated from 1.4% of subjects. The age distribution of carriers of these strains was similar to that of other meningococci apart from an additional peak in the 5-9-year age group and a more rapid decline in carriage with increasing age. Variations in the carriage rates of the outbreak strain were seen in children attending different schools and in the residents of different areas of the town. The low carriage rate of these strains in a community during a prolonged outbreak supports the hypothesis that these organisms are less transmissible but more virulent than other strains of pathogenic meningococci. Carriage of Neisseria lactamica, which is thought to be important in the development of meningococcal immunity, was most frequent in children under the age of 5 years and was six times commoner in this age group than carriage of Neisseria meningitidis. In older children and adults female carriers of N. lactamica increasingly outnumbered males in contrast to the male preponderance observed with meningococcal carriage.

Protective efficacy of monoclonal antibodies to class 1 and class 3 outer membrane proteins of Neisseria meningitidis B:15:P1.16 in infant rat infection model: new prospects for vaccine development

The protective efficacy of monoclonal antibodies to class 1 and class 3 outer membrane proteins of Neisseria meningitidis B:15:P1.16 was tested in an infant rat infection model. Four monoclonal antibodies to class 1 protein had bactericidal titres exceeding 20,000 and they protected infant rats completely against bacterial challenge with meningococci carrying the same class 1 protein, P1.16. One monoclonal antibody to class 3 protein was highly bactericidal (titer greater than 20,000), whereas two others had no bactericidal activity. All these antibodies gave some protection from infection, resulting in mortalities varying from 66 to 83% as compared to 100% in control rats who had received either unrelated monoclonal antibody or saline. These results strongly speak for class 1 outer membrane protein as a vaccine candidate for meningococcus group B.

Genetic relationships and clonal population structure of serotype 2 strains of Neisseria meningitidis

Two hundred and thirty-four strains of Neisseria meningitidis, including 94 serotype 2a, 111 serotype 2b, and 19 serotype 2c isolates, together with 10 isolates that were serotyped as 2 with polyvalent antiserum but did not react with monoclonal antibodies, were characterized by the electrophoretic mobilities of 15 metabolic enzymes. Of these enzymes, 14 were polymorphic, and 56 distinctive combinations of alleles at the enzyme loci (electrophoretic types) were identified, among which the mean genetic diversity per locus was 0.413, or about 75% of that recorded for the species N. meningitidis as a whole. Mean genetic diversity among electrophoretic types of the same serotype (2a, 2b, or 2c) was, however, on average, less than half the total species diversity, and no multilocus genotypes were shared between isolates of the different serotypes, which belong to distinctive clonal lineages. Recent temporal changes in the frequencies of recovery of pathogenic strains of serotypes 2a and 2b in South Africa and North America resulted from clone replacement in these populations rather than evolutionary modification of the serotype protein of the initially dominant clones.

Opsonisation and phagocytosis of group B meningococci by polymorphonuclear leucocytes: comparison of sulphonamide sensitive and resistant strains

A large proportion of disease caused by sulphonamide resistant strains of group B type 15 meningococci affects patients 10-24 years. In contrast, disease caused by sulphonamide sensitive strains conforms to the usual pattern, and most infection occurs in early childhood. In an attempt to explain this phenomenon possible differences in susceptibility of resistant and sensitive strains to phagocytosis by polymorphonuclear leucocytes were investigated, using radioactively labelled bacteria. In initial experiments a group B resistant strain required higher concentrations of normal human serum and longer opsonisation times for phagocytosis than an ungroupable non-pathogenic meningococcus. Comparison of sulphonamide resistant and sensitive group B meningococci showed that with either heat inactivated serum or agammaglobulinaemic serum, phagocytosis did not occur with any of the strains, whereas if these two sera were used together, phagocytosis was restored to the level seen with normal human serum. Thus both antibody and complement are required for phagocytosis. Furthermore, opsonisation depended on an intact classical pathway of complement for each group B strain. In all the experiments there was no significant difference between the phagocytosis of sulphonamide sensitive and resistant group B strains neither with regard to the efficiency of opsonisation by normal human serum nor the exact requirements for antibody and complement.