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. 2016 Jul 8;11(7):e0158689.
doi: 10.1371/journal.pone.0158689. eCollection 2016.

ATP-Binding Cassette (ABC) Transporters of the Human Respiratory Tract Pathogen, Moraxella catarrhalis: Role in Virulence

Timothy F Murphy  1   2   3 , Aimee L Brauer  1   2 , Antoinette Johnson  1   2 , Charmaine Kirkham  1   2
Affiliations

ATP-Binding Cassette (ABC) Transporters of the Human Respiratory Tract Pathogen, Moraxella catarrhalis: Role in Virulence

Timothy F Murphy et al. PLoS One. .

Abstract

Moraxella catarrhalis is a human respiratory tract pathogen that causes otitis media (middle ear infections) in children and respiratory tract infections in adults with chronic obstructive pulmonary disease. In view of the huge global burden of disease caused by M. catarrhalis, the development of vaccines to prevent these infections and better approaches to treatment have become priorities. In previous work, we used a genome mining approach that identified three substrate binding proteins (SBPs) of ATP-binding cassette (ABC) transporters as promising candidate vaccine antigens. In the present study, we performed a comprehensive assessment of 19 SBPs of 15 ABC transporter systems in the M. catarrhalis genome by engineering knockout mutants and studying their role in assays that assess mechanisms of infection. The capacity of M. catarrhalis to survive and grow in the nutrient-limited and hostile environment of the human respiratory tract, including intracellular growth, account in part for its virulence. The results show that ABC transporters that mediate uptake of peptides, amino acids, cations and anions play important roles in pathogenesis by enabling M. catarrhalis to 1) grow in nutrient-limited conditions, 2) invade and survive in human respiratory epithelial cells and 3) persist in the lungs in a murine pulmonary clearance model. The knockout mutants of SBPs and ABC transporters showed different patterns of activity in the assay systems, supporting the conclusion that different SBPs and ABC transporters function at different stages in the pathogenesis of infection. These results indicate that ABC transporters are nutritional virulence factors, functioning to enable the survival of M catarrhalis in the diverse microenvironments of the respiratory tract. Based on the role of ABC transporters as virulence factors of M. catarrhalis, these molecules represent potential drug targets to eradicate the organism from the human respiratory tract.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Legend.
Growth curve results of M. catarrhalis wild type strain O35E and selected knockout mutants. X-axis: time (hours). Y-axis: optical density at 600 nm. The lolA and lolB mutants show slow growth (prolonged lag phase and lower growth rate) and reduced growth (lower final optical density) compared to wild type in both nutrient-rich brain heart infusion broth (panel A) and nutrient-limited chemically defined media (CDM) (panel B). The afe mutant has growth characteristics similar to those of the wild type strain in nutrient-rich brain heart infusion broth (panel C), whereas the afe mutant shows slower growth (prolonged lag phase and lower growth rate) in nutrient-limited CDM (panel D). Each point is the average of five wells, and error bars indicate standard deviations.
Fig 2
Fig 2. Legend.
Results of adherence and invasion assays with human respiratory epithelial A549 cells. Y-axis: adherence and invasion shown as a percentage of wild type values. X-axis a) wild type; knockout mutants of: b) znu c) znuA; d) mod; e) modA; f) unk; g) unkA; h) cysP; i) pst; j) met; k) sbp1; l) sbp3; m) nrt; n) nrtA; o) oppA; p) opp; q) bcaasbp12; r) bcaa; s) polysbp; t) afe. Error bars show standard deviations of three independent experiments. Asterisk indicates p< 0.05 compared to results for the wild type (two-tailed t test). Mutants noted in bold show significantly reduced invasion compared to wild type.
Fig 3
Fig 3. Legend.
Results of pulmonary clearance in mice following simultaneous aerosol challenge by equal numbers (109 cfu) of M. catarrhalis strain 035E (wild type) and individual knockout mutants. Y-axis is cfu per ml in homogenized lung tissue 3 hours following challenge. X-axis: a) wild type strain; knockout mutants of b) oppA; c) sbp1; d) sbp2; e) sbp3; f) met; g) bcaa; h) polysbp; i) cysP; j) znu; k) mod; l) pst; m) nrt; n) afe; o) unk. Results are the averages of 10 animals per group; error bars show standard deviations. Asterisks indicate clearance of mutant is significantly lower (p<0.05) compared to wild type (Student’s t test). Mutants noted in bold show significantly reduced persistence in murine lungs compared to wild type.
Fig 4
Fig 4. legend.
Diagram summarizing the results of assays of knockout mutants in nutrient uptake, human respiratory epithelial cell invasion and persistence in the mouse pulmonary clearance model noted by columns at the right. A closed circle indicates that the result of the assay with the mutant was statistically different from that of wild type. An asterisk indicates that the assay was not possible because the mutant did not reliably grow in the conditions of the assay.
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References

    1. Murphy TF, Parameswaran GI. Moraxella catarrhalis, a human respiratory tract pathogen. Clin Infect Dis. 2009;49(1):124–31. Epub 2009/06/02. 10.1086/599375 . - DOI - PubMed
    1. Su YC, Singh B, Riesbeck K. Moraxella catarrhalis: from interactions with the host immune system to vaccine development. Future Microbiol. 2012;7(9):1073–100. Epub 2012/09/08. 10.2217/fmb.12.80 . - DOI - PubMed
    1. Perez Vidakovics ML, Riesbeck K. Virulence mechanisms of Moraxella in the pathogenesis of infection. Curr Opin Infect Dis. 2009;22(3):279–85. Epub 2009/05/02. . - PubMed
    1. Murphy TF, Brauer AL, Grant BJ, Sethi S. Moraxella catarrhalis in chronic obstructive pulmonary disease. Burden of disease and immune response. Am J Respir Crit Care Med. 2005;172:195–9. - PMC - PubMed
    1. Ruckdeschel EA, Kirkham C, Lesse AJ, Hu Z, Murphy TF. Mining the Moraxella catarrhalis genome: identification of potential vaccine antigens expressed during human infection. Infect Immun. 2008;76(4):1599–607. Epub 2008/01/30. IAI.01253-07 [pii] 10.1128/IAI.01253-07 . - DOI - PMC - PubMed

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