Carriage studies published by EMGM members

• Bennett JS, Griffiths DT, McCarthy ND, Sleeman KL, Jolley KA, Crook DW, Maiden MC. Genetic diversity and carriage dynamics of Neisseria lactamica in infants. Infect Immun. 2005 Apr;73(4):2424-32.
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  • Neisseria lactamica, a harmless human commensal found predominantly in the upper respiratory tracts of infants, is closely related to Neisseria meningitidis, a pathogen of global significance. Colonization with N. lactamica may be responsible for the increase in immunity to meningococcal disease that occurs during childhood, when rates of meningococcal carriage are low. This observation has led to the suggestion that N. lactamica whole cells or components are potential constituents of novel meningococcal vaccines. However, the dynamics of carriage and population diversity of N. lactamica in children are poorly understood, presenting difficulties for the choice of representative isolates for use in vaccine development. This problem was addressed by the multilocus sequence typing of N. lactamica isolates from two longitudinal studies of bacterial carriage in infants. The studies comprised 100 and 216 subjects, with N. lactamica carriage monitored from age 4 weeks until age 96 weeks and from age 2 weeks until age 24 weeks, respectively. The maximum observed carriage rate was 44% at 56 weeks of age, with isolates obtained on multiple visits for the majority (54 of 75, 72%) of carriers. The N. lactamica isolates were genetically diverse, with 69 distinct genotypes recovered from the 75 infants. Carriage was generally long-lived, with an average rate of loss of under 1% per week during the 28 weeks following acquisition. Only 11 of the 75 infants carried more than one genotypically unique isolate during the course of the study. Some participants shared identical isolates with siblings, but none shared identical isolates with their parents. These findings have implications for the design of vaccines based on this organism.
• Bille E, Ure R, Gray SJ, Kaczmarski EB, McCarthy ND, Nassif X, Maiden MC, Tinsley CR. Association of a bacteriophage with meningococcal disease in young adults. PLoS One. 2008;3(12):e3885.
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  • Despite being the agent of life-threatening meningitis, Neisseria meningitidis is usually carried asymptomatically in the nasopharynx of humans and only occasionally causes disease. The genetic bases for virulence have not been entirely elucidated and the search for new virulence factors in this species is hampered by the lack of an animal model representative of the human disease. As an alternative strategy we employ a molecular epidemiological approach to establish a statistical association of a candidate virulence gene with disease in the human population. We examine the distribution of a previously-identified genetic element, a temperate bacteriophage, in 1288 meningococci isolated from cases of disease and asymptomatic carriage. The phage was over-represented in disease isolates from young adults indicating that it may contribute to invasive disease in this age group. Further statistical analysis indicated that between 20% and 45% of the pathogenic potential of the five most common disease-causing meningococcal groups was linked to the presence of the phage. In the absence of an animal model of human disease, this molecular epidemiological approach permitted the estimation of the influence of the candidate virulence factor. Such an approach is particularly valuable in the investigation of exclusively human diseases.
• Blackwell CC, Tzanakaki G, Kremastinou J, Weir DM, Vakalis N, Elton RA, Mentis A, Fatouros N. Factors affecting carriage of Neisseria meningitidis among Greek military recruits. Epidemiol Infect. 1992 Jun;108(3):441-8.
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  • Greek military recruits (993) were examined for carriage of meningococci during July 1990. Blood, saliva and throat swab specimens were obtained and each recruit answered a questionnaire providing information on age, education (a measure of socioeconomic level), place of residence, smoking habits and recent infections. The overall carriage rate was 25% but differed between the two camps: 79/432 (18%) in Camp A and 168/561 (30%) in Camp B (P less than 0.0005). In Camp B, there were significantly higher proportions of recruits who were non-secretors (P less than 0.0005), and/or heavy smokers (P less than 0.0005). They were also younger (less than 19 years old) (P less than 0.001), and on the whole had fewer years of education (P less than 0.0005). By univariate analysis, carriage was significantly associated with smoking. By multiple logistic regression analysis, carriage was associated with smoking (P less than 0.001), age (P less than 0.01) and the camp in which the recruits were based (P less than 0.01). Among recruits in Camp B, 15/38 (40%) of those with recent viral infections were carriers compared with 30% for the camp in general.
• Buckee CO, Jolley KA, Recker M, Penman B, Kriz P, Gupta S, Maiden MC. Role of selection in the emergence of lineages and the evolution of virulence in Neisseria meningitidis. Proc Natl Acad Sci U S A. 2008 Sep 30;105(39):15082-7.
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  • Neisseria meningitis is a human commensal bacterium that occasionally causes life-threatening disease. As with a number of other bacterial pathogens, meningococcal populations comprise distinct lineages, which persist over many decades and during global spread in the face of high rates of recombination. In addition, the propensity to cause invasive disease is associated with particular "hyperinvasive" lineages that coexist with less invasive lineages despite the fact that disease does not contribute to host-to-host transmission. Here, by combining a modeling approach with molecular epidemiological data from 1,108 meningococci isolated in the Czech Republic over 27 years, we show that interstrain competition, mediated by immune selection, can explain both the persistence of multiple discrete meningococcal lineages and the association of a subset of these with invasive disease. The model indicates that the combinations of allelic variants of housekeeping genes that define these lineages are associated with very small differences in transmission efficiency among hosts. These findings have general implications for the emergence of lineage structure and virulence in recombining bacterial populations.
• Callaghan MJ, Buckee C, McCarthy ND, Ibarz Pavón AB, Jolley KA, Faust S, Gray SJ, Kaczmarski EB, Levin M, Kroll JS, Maiden MC, Pollard AJ. Opa protein repertoires of disease-causing and carried meningococci. J Clin Microbiol. 2008 Sep;46(9):3033-41.
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  • The meningococcal Opa proteins play an important role in pathogenesis by mediating invasion of human cells. The aim of this investigation was to determine whether carried and disease-associated meningococci possess different Opa repertoires and whether the diversity of these proteins is associated with clinical severity of disease. Opa repertoires in 227 disease-associated meningococci, isolated in the United Kingdom over a period of 6 years, were compared to the repertoires in 190 asymptomatically carried meningococci isolated in the United Kingdom from a contemporary, nonepidemic period. Multidimensional scaling (MDS) was employed to investigate the association between Opa repertoires and multilocus sequence typing (MLST) genotypes. Associations with clinical severity were also analyzed statistically. High levels of diversity were observed in opa alleles, variable regions, and repertoires, and MDS revealed that MLST genotypes were strongly associated with particular Opa repertoires. Individual Opa proteins or repertoires were not associated with clinical severity, though there was a trend toward an association with the opaD locus. Meningococcal Opa repertoire is strongly linked to MLST genotype irrespective of epidemiological sampling and therefore correlates with invasiveness. It is not, however, strongly associated with severity of meningococcal disease.
• Caugant DA, Tzanakaki G, Kriz P. Lessons from meningococcal carriage studies. FEMS Microbiol Rev. 2007 Jan;31(1):52-63.
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  • Neisseria meningitidis, an obligate commensal of humans, normally colonizes the mucosa of the upper respiratory tract without affecting the host, a phenomenon known as carriage. In Europe, as much as 35% of young adults are carriers at a given time. Recent studies using molecular methods for clone identification have demonstrated the extensive genetic diversity of the strains isolated from carriers, in comparison with a limited number of hypervirulent strains associated with invasive disease. Published studies and new data generated through the framework of the EU-MenNet clearly indicated significant differences in pathogenicity between meningococcal clones and in the distribution of multilocus sequence types among isolates from asymptomatic carriers among European countries; simultaneous carriage of more than one meningococcal strain in the throat is rare, but occasionally occurs; and the commensal association of particular clones with a host is a long-term relationship, often lasting several months. Further investigations of the carrier state are warranted to improve our understanding of the epidemiology and pathogenesis of meningococcal disease, as well as to support the introduction and to measure the impact of mass vaccination.
• Claus H, Maiden MC, Maag R, Frosch M, Vogel U. Many carried meningococci lack the genes required for capsule synthesis and transport. Microbiology. 2002 Jun;148(Pt 6):1813-9.
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  • Of 830 Neisseria meningitidis isolates obtained from healthy carriers in Bavaria, Germany, 136 (16.4%) lacked the operons necessary for the synthesis, lipid modification, and transport of capsular polysaccharide. These operons were replaced by a non-coding intergenic region either 113 or 114 bp in length, termed here the capsule null locus (cnl). Comparisons of the nucleotide sequence of this region in the meningococcus and its acapsulate relatives, Neisseria gonorrhoeae and Neisseria lactamica, revealed six distinct sequence variants (cnl-1 to cnl-6), with a total of 10 nucleotide substitutions and three indels. With the exception of one 4 bp insertion, which was unique to a gonococcal isolate, all of the individual sequence changes were present in the N. lactamica isolates examined. The meningococcal isolates with a cnl belonged to one of four otherwise genetically diverse genetic groupings: the ST-53 and ST-1117 complexes (75 isolates); the ST-845 complex (12 isolates); the ST-198 and 1136 complexes (46 isolates), and the ST-44 complex (one isolate). These data demonstrated that a substantial proportion of carried meningococci were incapable of capsule production, that the cnl circulated within Neisseria populations by horizontal genetic exchange, and that the expression of a polysaccharide capsule was not a requirement for person-to-person transmission of certain meningococcal lineages.
• Claus H, Maiden MC, Wilson DJ, McCarthy ND, Jolley KA, Urwin R, Hessler F, Frosch M, Vogel U. Genetic analysis of meningococci carried by children and young adults. J Infect Dis. 2005 Apr 15;191(8):1263-71.
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  • BACKGROUND: Neisseria meningitidis is a diverse commensal bacterium that occasionally causes severe invasive disease. The relationship between meningococcal genotype and capsular polysaccharide, the principal virulence factor and vaccine component, was investigated in carried meningococci isolated from 8000 children and young adults in Bavaria, Germany.

    METHODS: Of the 830 meningococci isolated (carriage rate, 10.4%) by microbiological techniques, 822 were characterized by serogrouping, multilocus sequence typing, and genetic analysis of the capsule region. Statistical and population genetic analyses were applied to these data.

    RESULTS: The rapid increase in carriage rates with age of carrier, the low prevalence of hyperinvasive meningococci, and the relative prevalence of the 4 disease-associated serogroups were consistent with earlier observations. There was no genetic structuring of the meningococcal population by age of carrier or sampling location; however, there was significant geographic structuring of the meningococci isolated in civil, but not military, institutions. The rate of capsule gene expression did not vary with age of carrier or meningococcal genotype, except for serogroup C, for which increased expression was associated with ST-11 (formerly ET-37) complex meningococci. CONCLUSIONS: Serogroup C capsule expression during carriage may contribute to the invasive character of ST-11 complex meningococci and to the high efficacy of meningococcal serogroup C conjugate polysaccharide vaccine.

• Jolley KA, Kalmusova J, Feil EJ, Gupta S, Musilek M, Kriz P, Maiden MCJ. Carried Meningococci in the Czech Republic: a Diverse Recombining Population. J Clin Microbiol 2000; 38(12):4492-4498
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  • Population and evolutionary analyses of pathogenic bacteria are frequently hindered by sampling strategies that concentrate on isolates from patients with invasive disease. This is especially so for the gram-negative diplococcus Neisseria meningitidis, a cause of septicemia and meningitis worldwide. Meningococcal isolate collections almost exclusively comprise organisms originating from patients with invasive meningococcal disease, although this bacterium is a commensal inhabitant of the human nasopharynx and very rarely causes pathological effects. In the present study, molecular biology-based techniques were used to establish the genetic relationships of 156 meningococci isolated from healthy young adults in the Czech Republic during 1993. None of the individuals sampled had known links to patients with invasive disease. Multilocus sequence typing (MLST) showed that the bacterial population was highly diverse, comprising 71 different sequence types (STs) which were assigned to 34 distinct complexes or lineages. Three previously identified hyperinvasive lineages were present: 26 isolates (17%) belonged to the ST-41 complex (lineage 3); 4 (2.6%) belonged to the ST-11 (electrophoretic type [ET-37]) complex, and 1 (0.6%) belonged to the ST-32 (ET-5) complex. The data were consistent with the view that most nucleotide sequence diversity resulted from the reassortment of alleles by horizontal genetic exchange.
• Kremastinou J, Blackwell C, Tzanakaki G, Kallergi C, Elton R, Weir D. Parental smoking and carriage of Neisseria meningitidis among Greek schoolchildren. Scand J Infect Dis. 1994;26(6):719-23.
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  • In December 1990 and January 1991, primary (320) and secondary (697) pupils in 2 areas of Athens were screened to determine the rate of carriage of Neisseria meningitidis and to determine if the genetic and environmental factors associated with carriage of meningococci in Greece were similar to those observed for northern European populations. In 1 area, socioeconomic indicators were significantly lower than in the other (p < 0.0005), but the isolation rates from pupils in the areas were similar, 5.3% and 6.3%. In contrast to studies in northwest Europe, carriage was not associated with lower socioeconomic conditions, sex, numbers of individuals per household, upper respiratory tract infection, or secretor status. By univariate analysis, carriage was associated with age (15-18 years) (p < 0.05) and mother's or other carer's smoking habits (p < 0.05)--but not father's smoking. Although the proportion of fathers who smoked was greater in the area where socioeconomic indicators were lower (61%) vs. (47%) (p < 0.0005), the proportions of women smokers were similar (33% vs. 38%). By multiple regression analysis, the only significant factors were age (p < 0.01) and carer's smoking (p < 0.05).
• Kremastinou J, Tzanakaki G, Velonakis E, Voyiatzi A, Nickolaou A, Elton RA, Weir D, Blackwell C. Carriage of Neisseria meningitidis and Neisseria lactamica among ethnic Greek school children from Russian immigrant families in Athens. FEMS Immunol Med Microbiol. 1999;23(1):13-20.
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  • During February and March 1995, a survey of meningococcal carriage in 625 school children was carried out in a suburb of Athens in which there was a large number of ethnic Greeks who had immigrated from Russia beginning in the early 1990s. The objectives of the study were: (1) to determine if factors associated with carriage of meningococci observed in a previous study of Greek school children were similar for the immigrant population; (2) to compare phenotypic characteristics of meningococci from the immigrant population with those isolated from children in Athens. Overall isolation rate for meningococci was 82/625 (13.1%), significantly higher than that found for school children in Athens (5.8%) during the winter of 1990 1991 (5.8%) (chi=25.98, P=0.0000003). By univariate analysis, carriage was not associated with sex, number of individuals per household, blood group, secretor status, socioeconomic level or maternal smoking; however, it was associated with fathers' smoking. The high proportion of men who smoked compared with the low proportion of women smokers might contribute to this finding. The main serogroup of meningococci isolated from this population was A (28%). While serogroup A appears to be more prevalent among Russian and Kurdish immigrants (14%) than among Greek school children or military recruits (4%), there has not been an increase in group A meningococcal disease in Greece. The isolation rate for N. lactamica was high 105/625 (17.3%). A few of these strains bound some of the monoclonal antibodies used for meningococcal serotyping and subtyping, and they are being examined in greater detail.
• Kremastinou J, Tzanakaki G, Levidiotou S, Markou F, Themeli E, Voyiatzi A, Psoma E, Theodoridou M, Blackwell CC. Carriage of Neisseria meningitidis and Neisseria lactamica in northern Greece. FEMS Immunol Med Microbiol. 2003; 39(1):23-9.
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  • In response to an increase in the number of cases of invasive meningococcal disease (IMD) in northern regions of Greece, a survey was carried out to determine if there was an increase in carriage of Neisseria meningitidis, particularly in areas where there have been increases in immigrant populations from neighbouring countries. The second objective was to determine if there was an increase in the serogroup C:2a:P1.5,2 a phenotype associated with recent outbreaks or changes in antibiotic sensitivities. As carriage of Neisseria lactamica is associated with development of natural immunity to IMD, the third objective was to determine the carriage rate of N. lactamica in this population. Among 3167 individuals tested, meningococci were isolated from 334 (10.5%). Compared with our previous studies, the proportion of meningococcal carriers was significantly increased among children in secondary education (11.3%) (chi2=9.67, P<0.005) and military recruits (37.4%) (chi2=21.11, P<0.000). Only 5/334 (1.5%) isolates expressed the phenotype associated with the increase in IMD in Greece. N. lactamica was isolated from 146/3167 (4.6%) participants. It was isolated from 71/987 (7.2%) children attending primary or nursery schools; however, the highest proportion of carriers (11.3%) was found in the boarding school for young Albanian men. In the 21-59-year age range, the majority of N. lactamica isolates (22/25, 88%) were from women, probably due to closer or more prolonged contact with children in the primary school age range. Smoking was significantly associated with isolation of meningococci from men but not from women. Penicillin-insensitive strains (25/334, 7.5%) were identified in all four regions examined; the majority (14/25, 56%) were obtained from military personnel. We conclude that there was a higher proportion of carriers in the population of northern Greece; however, the increase in carriage rate was not associated with the influx of immigrants from neighbouring countries, and there was not a higher incidence of the C:2a:P1.5,2 strain responsible for increased disease activity in Greece in either the immigrant or local populations.
• MacLennan J, Kafatos G, Neal K, Andrews N, Cameron JC, Roberts R, Evans MR, Cann K, Baxter DN, Maiden MC, Stuart JM; United Kingdom Meningococcal Carriage Group. Social behavior and meningococcal carriage in British teenagers. Emerg Infect Dis. 2006;12(6):950-7.
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  • Understanding predisposing factors for meningococcal carriage may identify targets for public health interventions. Before mass vaccination with meningococcal group C conjugate vaccine began in autumn 1999, we took pharyngeal swabs from approximately 14,000 UK teenagers and collected information on potential risk factors. Neisseria meningitidis was cultured from 2,319 (16.7%) of 13,919 swabs. In multivariable analysis, attendance at pubs/clubs, intimate kissing, and cigarette smoking were each independently and strongly associated with increased risk for meningococcal carriage (p<0.001). Carriage in those with none of these risk factors was 7.8%, compared to 32.8% in those with all 3. Passive smoking was also linked to higher risk for carriage, but age, sex, social deprivation, home crowding, or school characteristics had little or no effect. Social behavior, rather than age or sex, can explain the higher frequency of meningococcal carriage among teenagers. A ban on smoking in public places may reduce risk for transmission.
• Maiden MC, Stuart JM; UK Meningococcal Carriage Group. Carriage of serogroup C meningococci 1 year after meningococcal C conjugate polysaccharide vaccination. Lancet. 2002;359(9320):1829-31.
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  • The UK was the first place to introduce meningococcal serogroup C conjugate (MCC) vaccines. From November, 1999, all people younger than 18 years, about 14 million individuals, were offered MCC immunisation. The uptake rate was more than 70% by November, 2000. We compared the carriage of meningococci in isolates we obtained from 14,064 students aged 15-17 years during vaccination in 1999, with those from 16,583 students of the same age surveyed 1 year later. Carriage of serogroup C meningococci was reduced by 66% (p=0.004). Our results show that MCC vaccines protect against carriage of meningococci that express serogroup C polysaccharide capsules.
• Maiden MC, Ibarz-Pavón AB, Urwin R, Gray SJ, Andrews NJ, Clarke SC, Walker AM, Evans MR, Kroll JS, Neal KR, Ala'aldeen DA, Crook DW, Cann K, Harrison S, Cunningham R, Baxter D, Kaczmarski E, Maclennan J, Cameron JC, Stuart JM. Impact of meningococcal serogroup C conjugate vaccines on carriage and herd immunity. J Infect Dis. 2008;197(5):737-43.
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  • BACKGROUND: In 1999, meningococcal serogroup C conjugate (MCC) vaccines were introduced in the United Kingdom for those under 19 years of age. The impact of this intervention on asymptomatic carriage of meningococci was investigated to establish whether serogroup replacement or protection by herd immunity occurred.

    METHODS: Multicenter surveys of carriage were conducted during vaccine introduction and on 2 successive years, resulting in a total of 48,309 samples, from which 8599 meningococci were isolated and characterized by genotyping and phenotyping.

    RESULTS: A reduction in serogroup C carriage (rate ratio, 0.19) was observed that lasted at least 2 years with no evidence of serogroup replacement. Vaccine efficacy against carriage was 75%, and vaccination had a disproportionate impact on the carriage of sequence type (ST)-11 complex serogroup C meningococci that (rate ratio, 0.06); these meningococci also exhibited high rates of capsule expression.

    CONCLUSIONS: The impact of vaccination with MCC vaccine on the prevalence of carriage of group C meningococci was consistent with herd immunity. The high impact on the carriage of ST-11 complex serogroup C could be attributed to high levels of capsule expression. High vaccine efficacy against disease in young children, who were not protected long-term by the schedule initially used, is attributed to the high vaccine efficacy against carriage in older age groups.

• Oppermann H, Thriene B, Irmscher HM, Gräfe L, Borrmann M, Bellstedt D, Kaynak S, Hellenbrand W, Vogel U. [Meningococcal carriers in high school students and possible risk factors] [Article in German] Gesundheitswesen. 2006;68(10):633-7.
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  • From August 2004 to January 2005 a cluster of 7 cases of serogroup B meningococcal disease occurred in the state of Saxony-Anhalt in the town of Sangerhausen and the surrounding area. This led to an investigation of meningococcal carriage in 816 high school students (grades 9 to 13). The students were also asked to fill out a questionnaire regarding possible risk factors for carriage. The goal of the study was the evaluation of a possibly persistently increased risk for further cases in the region. Results of the study were to be used for a comprehensive and targeted education of the public. The percentage of students found harbouring N. meningitidis in the nasopharynx in Sangerhausen (9.0 %) was not elevated compared to that found in the two control regions of Kelbra, County of Sangerhausen (8.2 %) and Jessen, County of Wittenberg (9.9 %). The serogroup B fine type responsible for the cluster (P1.7-2,16:F3-3:PorB3-24) was found only in one student each in Sangerhausen and Kelbra. Thus, there was no evidence of an increased risk for further cases at the time of the study at the end of January, 2005. This may have been due to intensive contact tracing and provision of chemoprophylaxis in Sangerhausen. Visiting a disco or bar and smoking were identified as risk factors for meningococcal carriage. However, these factors were associated with carriage only in boys but not in girls. This may be explained by sex-specific differences in physical interaction with others. Efforts to prevent further cases during clusters of meningococcal disease should consider sex-specific risk behaviour.
• Tzanakaki G, Blackwell CC, Kremastinou J, Kallergi C, Kouppari G, Weir DM. Antibiotic sensitivities of Neisseria meningitidis isolates from patients and carriers in Greece. Epidemiol Infect. 1992;108(3):449-55.
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  • Usage of antibiotics in southern Europe is less well regulated than in northern countries. The proportion (48%) of meningococci in Spain insensitive to pencillin (MIC greater than or equal to 0.1 mg/l) prompted this investigation of antibiotic sensitivities of isolates from Greek patients with meningitis (31) and carriers (47 school-children and 472 recruits). The agar dilution method was used to determine MIC to penicillin G (PN), sulphamethoxazole (SU), rifampicin (RF), cefaclor (CF) and ciprofloxacin (CP). The proportion of isolates insensitive to PN was 48% for isolates from patients, 19% from school-children and 36.6% from recruits. Resistance to SU (MIC greater than or equal to 16 mg/l) was found in 16% of those from patients, 10.6% from children and 40% from recruits. None of the isolates from patients was resistant to RF (greater than or equal to 1 mg/l) but 6% of those from carriers were. Resistance to CF (greater than or equal to 4 mg/l) was found in 9.2% of patient isolates, 6.4% from children and 23.7% from recruits. All isolates except one were sensitive to CP (MIC range less than 0.0015-0.125 mg/l). Resistances to PN, SU and RF were analysed by serogroup, serotype and subtype of the bacteria. The proportion of resistant isolates showed some variation between different areas of Greece, but it was not statistically significant.
• Tzanakaki G, Blackwell CC, Kremastinou J, Weir DM, Mentis A, Fallon RJ. Serogroups, serotypes and subtypes of Neisseria meningitidis isolated from patients and carriers in Greece. J Med Microbiol. 1993;38(1):19-22.
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  • The increase in the number of cases of meningococcal disease reported to the Ministry of Health in Athens since 1989 prompted the present study to determine if isolates from patients or carriers expressed the same phenotypic characters as those in other parts of Europe. None of the isolates from patients (31) or carriers (547) expressed the antigenic combinations associated with outbreaks in northern Europe, i.e., B:15:P1.16 or B:4:P1.15. The majority of the Greek isolates did not react with any of the six monoclonal serotype reagents tested; however, most reacted with one or more of the 11 monoclonal subtype antibodies. The results suggest that additional serotype reagents are needed for epidemiological studies in southeastern Europe and that vaccines based on serotype antigens developed against outbreak strains in northern Europe would not be effective in Greece.
• Vogel U, Morelli G, Zurth K, Claus H, Kriener E, Achtman M, Frosch M. Necessity of molecular techniques to distinguish between Neisseria meningitidis strains isolated from patients with meningococcal disease and from their healthy contacts. J Clin Microbiol. 1998;36(9):2465-70.
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  • Serogroup C strains of Neisseria meningitidis were isolated from a Germany patient with severe meningococcal disease after a trip to the Czech Republic. These strains (case isolates) were characterized by classical and molecular techniques, as were other strains (carrier isolates) isolated from healthy contacts. Five of 10 carrier isolates had switched off the expression of capsular polysaccharide, as demonstrated by a serogroup-specific PCR. The two case isolates were indistinguishable by multilocus sequence typing and belonged to the ET-37 complex. The carrier isolates belonged to four different sequence types, all unrelated to that of the case strains. Pulsed-field gel electrophoresis showed that the case isolates differed from reference ET-37 complex strains from the Czech Republic and Canada as well as from all the carrier isolates. The isolate from the patient's nasopharynx was indistinguishable from the blood isolate except for a 40,000-bp chromosomal deletion that had occurred during systemic spread.
• Weber MV, Claus H, Maiden MC, Frosch M, Vogel U. Genetic mechanisms for loss of encapsulation in polysialyltransferase-gene-positive meningococci isolated from healthy carriers. Int J Med Microbiol. 2006;296(7):475-84.
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  • Encapsulated Neisseria meningitidis expressing serogroups A, B, C, W-135, or Y remain a major cause of morbidity and mortality globally. This bacterium is, however, a common commensal inhabitant of the human nasopharynx that causes disease infrequently. Isolates obtained from healthy carriers are frequently unencapsulated and therefore essentially avirulent. The lack of capsule can be due to inactivation of capsule synthesis genes by a variety of genetic mechanisms, or the absence of capsule synthesis genes. Analysis of inactivation mechanisms was undertaken in a diverse but representative set of 166 acapsulate meningococci isolated from carriage that possessed capsule synthesis genes. Slipped strand mispairing in the siaA and siaD genes of the capsule synthesis locus was observed in 39 isolates. Insertion sequence (IS) elements (IS1016-like, IS1106 and IS1301) were responsible for the loss of encapsulation in 46 isolates. Irreversible gene silencing events (insertions, deletions, base exchanges) were found in 47 isolates. Two non-synonymous mutations were identified in close vicinity of the putative active site of the UDP-N-acetylglucosamine 2-epimerase encoded by the siaA gene. The mechanisms for loss of encapsulation were not associated with particular meningococcal genotypes. There was no evidence for successive gene silencing events in the capsule genes, suggesting that the irreversible inactivation events observed were the result of short-term, within-host evolution. These observations are consistent with the postulate that particular meningococcal clonal complexes are associated with possession of a capsule and that this association is important for transmission success.
• Yazdankhah SP, Caugant DA. Neisseria meningitidis: an overview of the carriage state. J Med Microbiol. 2004;53(Pt 9):821-32.
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  • During periods of endemic disease, about 10 % of the general population harbour Neisseria meningitidis in the nasopharynx. Since N. meningitidis is a strict human pathogen and most patients have not been in contact with other cases, asymptomatic carriers are presumably the major source of the pathogenic strains. Most carrier isolates are shown to lack capsule production. The capsule deficient state of meningococcal strains in the nasopharynx may aid evasion of the human immune defence and hence be selected to survive nasopharyngeal colonization. Carriage itself can be an immunizing process resulting in systemic protective antibody responses. Frequent nasopharyngeal colonization with related bacteria like Neisseria lactamica improves natural immunity to meningococci by the formation of cross-reacting antibodies. While most meningococcal strains recovered from patients belong to a limited number of clonal groups worldwide, strains isolated from carriers comprise numerous genotypes, with only a small proportion of the strains representing invasive clones. During the carriage state, co-colonization with other pathogenic and non-pathogenic bacteria may lead to genetic exchange, which may result in the emergence of new meningococcal clones. The high diversity of meningococcal carrier strains, compared with hypervirulent strains, supports the idea that transmissibility, not invasion, is essential in the life cycle of N. meningitidis.