Background
Nongroupable (NG) Neisseria meningitidis are typically unencapsulated and are more often associated with asymptomatic carriage rather than causing invasive disease, although clinically significant infections causing IMD have been reported worldwide. In India, meningococcal surveillance is sparse and predominantly relies on conventional culturing and serogrouping is very limited resulting in under-detection of meningococcal isolate and systematically misses NG meningococci, limiting their epidemiology and clinical significance.
Objective
To report the first documented ST-175 nongroupable N. meningitidis in India, recovered from a clinical respiratory specimen.
Methods
A 30-year-old patient with chronic bronchiectasis presented with acute exacerbation and was treated with amoxicillin-clavulanate for 10 days. Sputum culture grew Neisseria meningitidis. The isolate was identified by MALDI-TOF and confirmed by Real-time PCR targeting SodC. Serogrouping was performed using Real-time PCR and was found negative for all six major serogroups A,W135, X, B, C and Y and the isolate was therefore classified as nongroupable.
Results
Molecular typing assigned the isolate to Clonal complex ST-175, with a cgMLST v3 LIN profile of 13_1_0_0_1_0_7_14_0_0_0_0_0. Genomic analysis showed absence of ctrA with retention of ctrB, ctrC, and ctrD, consistent with a ctrA-deficient nongroupable phenotype and a partial capsule null locus genotype. Vaccine antigen profiling identified fHbp allele 111, PorA VR types 22-11 and 15-25, and NHBA allele 9, while nadA was absent. Antimicrobial susceptibility testing showed susceptibility to minocycline, meropenem, ciprofloxacin, rifampicin, chloramphenicol, cefotaxime, and azithromycin, with resistance to trimethoprim-sulfamethoxazole.
Public Health Statement:
Geographic Expansion: ST 175, a well-known globally distributed lineage, is documented for the first time in India, suggesting international transmission and/or undetected circulation. As a non-groupable strain, this isolate escapes protection by current capsular meningococcal vaccines (MenA/C/W/Y) and may demonstrates only partial coverage by MenB vaccine, representing vaccine-escape strains not captured in Indian surveillance.
Conclusion
This report documents a nongroupable ST-175 N. meningitidis isolate with ctrA deficiency in India and expands the known molecular diversity of meningococci isolates in India . The finding highlights the limitations of surveillance systems and supports the need for molecular characterization of unusual meningococcal isolates, including those recovered from respiratory specimens