title: Correlates between models of virulence for Mycobacterium tuberculosis among isolates of the Central Asian lineage: a case for lysozyme resistance testing?
abstract: Virulence factors (VFs) contribute to the emergence of new human Mycobacterium tuberculosis strains, are lineage dependent, and are relevant to the development of M. tuberculosis drugs/vaccines. VFs were sought within M. tuberculosis lineage 3, which has the Central Asian (CAS) spoligotype. Three isolates were selected from clusters previously identified as dominant in London, United Kingdom. Strain-associated virulence was studied in guinea pig, monocyte-derived macrophage, and lysozyme resistance assays. Whole-genome sequencing, single nucleotide polymorphism (SNP) analysis, and a literature review contributed to the identification of SNPs of interest. The animal model revealed borderline differences in strain-associated pathogenicity. Ex vivo, isolate C72 exhibited statistically significant differences in intracellular growth relative to C6 and C14. SNP candidates inducing lower fitness levels included 123 unique nonsynonymous SNPs, including three located in genes (lysX, caeA, and ponA2) previously identified as VFs in the laboratory-adapted reference strain H37Rv and shown to confer lysozyme resistance. C72 growth was most affected by lysozyme in vitro. A BLAST search revealed that all three SNPs of interest (C35F, P76Q, and P780R) also occurred in Tiruvallur, India, and in Uganda. Unlike C72, however, no single isolate identified through BLAST carried all three SNPs simultaneously. CAS isolates representative of three medium-sized human clusters demonstrated differential outcomes in models commonly used to estimate strain-associated virulence, supporting the idea that virulence varies within, not just across, M. tuberculosis lineages. Three VF SNPs of interest were identified in two additional locations worldwide, which suggested independent selection and supported a role for these SNPs in virulence. The relevance of lysozyme resistance to strain virulence remains to be established.
authors.affiliation: Clinical TB and HIV Group, Centre for Immunology and Infectious Disease, Queen Mary University of London, London, United Kingdom c.pardieu@qmul.ac.uk f.drobniewski@qmul.ac.uk.
authors.forename: Claire
authors.initials: C
authors.lastname: Pardieu
authors.affiliation: Clinical TB and HIV Group, Centre for Immunology and Infectious Disease, Queen Mary University of London, London, United Kingdom Department of Infectious Diseases and Immunity, Hammersmith Hospital, Imperial College, London, United Kingdom.
authors.forename: Nicola
authors.initials: N
authors.lastname: Casali
authors.affiliation: Porton Down, Public Health England, Salisbury, United Kingdom.
authors.forename: Simon O
authors.initials: SO
authors.lastname: Clark
authors.affiliation: Centre for Primary Care and Public Health, Queen Mary University of London, London, United Kingdom.
authors.forename: Richard
authors.initials: R
authors.lastname: Hooper
authors.affiliation: Porton Down, Public Health England, Salisbury, United Kingdom.
authors.forename: Ann
authors.initials: A
authors.lastname: Williams
authors.affiliation: Clinical TB and HIV Group, Centre for Immunology and Infectious Disease, Queen Mary University of London, London, United Kingdom.
authors.forename: Preya
authors.initials: P
authors.lastname: Velji
authors.affiliation: Clinical TB and HIV Group, Centre for Immunology and Infectious Disease, Queen Mary University of London, London, United Kingdom Department of Infectious Diseases and Immunity, Hammersmith Hospital, Imperial College, London, United Kingdom.
authors.forename: Ximena
authors.initials: X
authors.lastname: Gonzalo
authors.affiliation: Clinical TB and HIV Group, Centre for Immunology and Infectious Disease, Queen Mary University of London, London, United Kingdom Department of Infectious Diseases and Immunity, Hammersmith Hospital, Imperial College, London, United Kingdom National Mycobacterium Reference Laboratory, Public Health England, London, United Kingdom c.pardieu@qmul.ac.uk f.drobniewski@qmul.ac.uk.
authors.forename: Francis
authors.initials: F
authors.lastname: Drobniewski
mesh_terms: D000328:Adult; D000995:Antitubercular Agents / Q000494:pharmacology*; D001208:Asia / Q000453:epidemiology; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D024881:Drug Resistance, Bacterial; D005260:Female; D015964:Gene Expression Regulation, Bacterial; D006801:Humans; D008297:Male; D008875:Middle Aged; D009113:Muramidase; D009169:Mycobacterium tuberculosis / Q000145:classification / Q000187:drug effects / Q000472:pathogenicity*; D020641:Polymorphism, Single Nucleotide; D014376:Tuberculosis / Q000453:epidemiology / Q000382:microbiology*; D014774:Virulence; D037521:Virulence Factors / Q000378:metabolism; D055815:Young Adult
chemical_list: D000995:Antitubercular Agents; D001426:Bacterial Proteins; D037521:Virulence Factors; D009113:Muramidase