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Prevalence and phase variable expression status of two autotransporters, NalP and MspA, in carriage and disease isolates of Neisseria meningitidis

Oldfield, Neil J.; Matar, Suzan; Bidmos, Fadil A.; Alamro, Mohammed; Neal, Keith R.; Turner, David P.J.; Bayliss, Christopher D.; Ala'Aldeen, Dlawer A.A.


Suzan Matar

Fadil A. Bidmos

Mohammed Alamro

Keith R. Neal

David P.J. Turner

Christopher D. Bayliss

Dlawer A.A. Ala'Aldeen


Neisseria meningitidis is a human nasopharyngeal commensal capable of causing life-threatening septicemia and meningitis. Many meningococcal surface structures, including the autotransporter proteins NalP and MspA, are subject to phase variation (PV) due to the presence of homopolymeric tracts within their coding sequences. The functions of MspA are unknown. NalP proteolytically cleaves several surface-located virulence factors including the 4CMenB antigen NhbA. Therefore, NalP is a phase-variable regulator of the meningococcal outer membrane and secretome whose expression may reduce isolate susceptibility to 4CMenB-induced immune responses. To improve our understanding of the contributions of MspA and NalP to meningococcal-host interactions, their distribution and phase-variable expression status was studied in epidemiologically relevant samples, including 127 carriage and 514 invasive isolates representative of multiple clonal complexes and serogroups. Prevalence estimates of .98% and .88% were obtained for mspA and nalP, respectively, with no significant differences in their frequencies in disease versus carriage isolates. 16% of serogroup B (MenB) invasive isolates, predominately from clonal complexes ST-269 and ST-461, lacked nalP. Deletion of nalP often resulted from recombination events between flanking repetitive elements. PolyC tract lengths ranged from 6–15 bp in nalP and 6–14 bp in mspA. In an examination of PV status, 58.8% of carriage, and 40.1% of invasive nalP-positive MenB isolates were nalP phase ON. The frequency of this phenotype was not significantly different in serogroup Y (MenY) carriage strains, but was significantly higher in invasive MenY strains (86.3%; p,0.0001). Approximately 90% of MenB carriage and invasive isolates were mspA phase ON; significantly more than MenY carriage (32.7%) or invasive (13.7%) isolates. This differential expression resulted from different mode mspA tract lengths between the serogroups. Our data indicates a differential requirement for NalP and MspA expression in MenB and MenY strains and is a step towards understanding the contributions of phase- variable loci to meningococcal biology.


Oldfield, N. J., Matar, S., Bidmos, F. A., Alamro, M., Neal, K. R., Turner, D. P., …Ala'Aldeen, D. A. (2013). Prevalence and phase variable expression status of two autotransporters, NalP and MspA, in carriage and disease isolates of Neisseria meningitidis. PLoS ONE, 8(7), Article e69746.

Journal Article Type Article
Publication Date Jul 25, 2013
Deposit Date Mar 25, 2014
Publicly Available Date Mar 25, 2014
Journal PLoS ONE
Electronic ISSN 1932-6203
Publisher Public Library of Science
Peer Reviewed Peer Reviewed
Volume 8
Issue 7
Article Number e69746
Public URL
Publisher URL


journal.pone.0069746.pdf (645 Kb)

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