Comparison of Phenotypic and Genotypic Approaches to Capsule Typing of Neisseria meningitidis by Use of Invasive and Carriage Isolate Collections

Abstract

e Neisseria meningitidis serogroup B (MnB) is a leading cause of bacterial meningitis; however, MnB is most commonly associated with asymptomatic carriage in the nasopharyngeal cavity, as opposed to the disease state. Two vaccines are now licensed for the prevention of MnB disease; a possible additional benefit of these vaccines could be to protect against disease indirectly by disrupting nasopharyngeal carriage (e.g., herd protection). To investigate this possibility, accurate diagnostic approaches to characterize MnB carriage isolates are required. In contrast to invasive meningococcal disease (IMD) isolates, which can be readily serogrouped, carriage isolates often lack capsule expression, making standard phenotypic assays unsuitable for strain characterization. Several antibody-based methods were evaluated for their abilities to serogroup isolates and were compared with two genotyping methods (real-time PCR [rt-PCR] and whole-genome sequencing [WGS]) to identify which approach would most accurately ascertain the polysaccharide groups associated with carriage isolates. WGS and rt-PCR were in agreement for 99% of IMD isolates, including those with coding sequences for MnB, MnC, MnW, and MnY, and the phenotypic methods correctly identified serogroups for 69 to 98% of IMD isolates. In contrast, only 47% of carriage isolates were groupable by genotypic methods, due to mutations within the capsule operon; of the isolates identified by genotypic methods, <43% were serogroupable with any of the phenotypic methods tested. These observations highlight the difficulties in the serogrouping and capsular genogrouping of meningococcal carriage isolates. Based on our findings, WGS is the most suitable approach for the characterization of meningococcal carriage isolates. N eisseria meningitidis, a Gram-negative bacterium that causes both epidemic and endemic life-threatening disease, is also an obligate human commensal organism that colonizes the nasopharyngeal mucosa with no or minimal harm to the host, a phenomenon known as carriage (1). Asymptomatic pharyngeal colonization with N. meningitidis in young adults is relatively common, and these asymptomatic carriers represent a potential reservoir for the transmission of pathogenic isolates in the community (2, 3). The rates of asymptomatic carriage in the United States and Europe are highest among adolescents and young adults, peaking at the age of 19 years, and are estimated to be 10% to 35% (4-6). Rates of transmission and carriage are higher in closed and semiclosed populations, such as university students living in dormitories and military recruits housed in barracks (7). Higher rates of carriage are also found among people in close contact with patients with active meningococcal infections (8). For the majority of people, carriage is an immunizing process that results in systemic, serogroup-specific, protective antibody responses (9, 10). Invasive meningococcal disease (IMD) usually occurs shortly after the onset of colonization of a susceptible host, when the bacteria ...

Observational study of nasopharyngeal carriage of Neisseria meningitidis in applicants to a military academy in the Russian Federation

“…This study was also only conducted at 3 time points and was not a continuous longitudinal sampling study, and so provides only a limited understanding of the dynamics of carriage changes in this population, and cannot provide information on transmission patterns. Additionally, many of the isolates were ungroupable, which has been seen before in carrier studies (Caugant et al, 2006;Celal Basustaoglu et al, 2011;Glitza et al, 2008;Korzeniewski et al, 2015;Tyski et al, 2001) and previous evidence has shown challenges in serogrouping of isolates from carriage studies due to reduced or no capsule expression in the carriage state (Jones et al, 2016). Similarly genetic plasticity of the capsule can effect PCR assay sensitivity (Jones et al, 2016) and may have resulted in some of the discrepancy seen between the assays.…”

“…Additionally, many of the isolates were ungroupable, which has been seen before in carrier studies (Caugant et al, 2006;Celal Basustaoglu et al, 2011;Glitza et al, 2008;Korzeniewski et al, 2015;Tyski et al, 2001) and previous evidence has shown challenges in serogrouping of isolates from carriage studies due to reduced or no capsule expression in the carriage state (Jones et al, 2016). Similarly genetic plasticity of the capsule can effect PCR assay sensitivity (Jones et al, 2016) and may have resulted in some of the discrepancy seen between the assays. MLST and whole genome sequencing (WGS) are more precise methods for characterizing isolates, however they were not used in this study to characterize all of the positive samples.…”

Neisseria meningitidis carriage in Swedish teenagers associated with the serogroup W outbreak at the World Scout Jamboree, Japan 2015

“…Grouping of carriage isolates is challenging whether using phenotypic or genotypic approaches. High percentages of isolates recovered from healthy carrier's displays low level or complete absences of expression of the genes required for capsule production during carriage, this due to phase variation, deletions or insertion of genetic mobile elements or a complete absence of the capsule genes .…”

Commentary: Unveiling New Aspects of Meningococcal Carriage and Disease Prevention

“…It would be of interest to analyze the data from this study with respect to the presence of the genes encoding NHBA, NadA, and fHbp. Similarly, the data of Jones et al (11) could also provide clues as to why MenB strains, in particular, seem to express their polysaccharide capsule less avidly during carriage. This could be the result of a combination of phase variation and deletions or insertions in the cps locus.…”

“…This lack of sensitivity has potential implications for the surveillance of meningococcal carriage following vaccination with the novel MenB vaccines. In this issue, Jones and coworkers present the results of their comparative study of phenotypic and genotypic approaches to N. meningitidis capsule typing (11). The investigators looked at invasive (n ϭ 97) and carriage (n ϭ 93) isolates from different populations, geographic locations, and time periods.…”