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An Investigation of Histophilus Somni Virulence Factors in Pathogenesis and 1

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An Investigation of Histophilus Somni Virulence Factors in Pathogenesis and 1 An Investigation of Histophilus somni Virulence Factors in Pathogenesis and 1 Diagnosis 2 3 Yu Pan 4 Dissertation submitted to the faculty of the Virginia Polytechnic Institute and State University in 5 partial fulfillment of the requirements for the degree of 6 7 Doctor of Philosophy 8 In 9 Biomedical and Veterinary Sciences 10 11 Thomas J. Inzana, Chair 12 Stephen M. Boyle 13 Stephen B. Melville 14 Sharon G. Witonsky 15 16 9/24/2014 17 Blacksburg, Virginia 18 19 20 Keywords: Histophilus somni, ELISA, diagnosis, luxS, uspE, regulation, phagocytosis, ibpA, 21 biofilm, monocytes 22 Copyright © 2014, Yu Pan 23 An Investigation of Histophilus somni Virulence Factors in Pathogenesis and 24 Diagnosis 25 26 Yu Pan 27 28 ABSTRACT 29 30 H. somni is capable of forming a prominent biofilm, and luxS is known to play an important 31 role in biofilm formation through quorum sensing, but has also been postulated to function in gene 32 regulation. In order to further study the function of H. somni LuxS, mutants 2336::TnluxS and 33 2336::TnuspE were identified from a bank of mutants generated with EZ-Tn5 <KAN-2>Tnp 34 transposome (EpiCentre). The 2336::TnluxS and 2336::TnuspE mutants were highly attenuated in 35 mice, but only 2336::TnuspE was deficient in biofilm formation. However, the electrophoretic 36 profiles of the LOS and serum sensitivity of both mutants were substantially altered compared to the 37 parent strain, but exopolysaccharide production during biofilm formation also only decreased in 38 2336::TnuspE. The altered phenotypes were partially restored in complemented recombinant clones 39 obtained using shuttle vector pHS649S. To clarify whether luxS regulates the expression of various 40 virulence genes, mRNA from both the parent strain and 2336::TnluxS was sequenced. It was 41 determined that the transcription level of 53 genes in 2336::TnluxS and 42 genes in 2336::TnuspE in 42 planktonic form were changed. In biofilm, 320 genes in 2336::TnluxS and 230 genes in 43 2336::TnuspE were differentially regulated compared to biofilm formed by strain 2336. 44 The immunogloblin binding protein A (IbpA) of H. somni is known to be cytotoxic to 45 phagocytic cells. In this study, we found that strains with a mutation in ibpA were less capable of 46 early replication in monocytes. The IbpA protein concentrated from the culture supernatant of 47 strain 2336 facilitated the intracellular survival of strain 129Pt, which lacks IbpA. However, the 48 ability of several ibpA mutants to resist intracellular killing was not significantly impaired by 48 49 h post-infection. Two transposon mutants 2336::TnluxS and 2336::TnuspE replicated in 50 monocytes in a similar manner as the ibpA mutants. Confocal microscopy revealed that the 51 intracellular-replicable strains (2336, 64Vc, 2336::TnluxS, 2336::TnuspE and the ibpA mutants) 52 prevented the acidification of the bacterial-containing phagosome and the expression of 53 lysosome marker LAMP-2, which may facilitate survival of H. somni in monocytes. 54 An enzyme-linked immunosorbent assay was developed to detect bovine antibodies to 55 the H. somni exopolysaccharide that is formed during biofilm formation. When an index value of 56 0.268 was used the sensitivity of the assay for experimentally- and naturally-infected calves was 57 90.5% at 3 weeks post-infection, and the specificity of the assay for healthy calves was 92.5%. 58 The EPS ELISA may aid in identifying calves with diseases due to H. somni. 59 60 61 iii Dedication 62 For my family, who are the sources of unconditional support. 63 For my friends, who gave me a second family. May our future be bright! 64 iv Acknowledgement 65 66 I first wish to express my great appreciation and sincere gratitude to my advisor, Dr. 67 Thomas J. Inzana. Dr. Inzana’s instruction was indispensable for me to finish this work. His 68 kindness and thoughtfulness inspired me throughout my doctoral study. It has been a great honor 69 and a pleasure for me to be his student. 70 I would also like to thank the members of my committee, Dr. Stephen Boyle, Dr. Stephen 71 Melville, and Dr. Sharon Witonsky. Dr. Boyle has been patient and detailed in his instruction, 72 yet he always helped me look at the bigger picture of my project. Dr. Melville offered me more 73 insightful ideas on the molecular aspects of my study. As the only immunologist on my 74 committee, Dr. Witonsky offered great suggestions for the phagocytosis study. 75 My doctoral research has also greatly benefited from other Virginia Tech researchers. 76 Abey, Anna and Indra were always a great help for technical issues. Dr. Lindsay provided me 77 with the M-617 cell line, on which a large portion of my work depended. The support and help 78 from Kathy, Kristi, and other university technicians, who helped me to carry out some 79 experiments are also greatly appreciated. 80 Finally, and most importantly, I would like to thank my family and friends, without their 81 support, both physical and mental, I could never possibly accomplish my work. 82 This research was supported by USDA-NIFA grants 2013-67015-21314 and 2007- 83 35204-18338 from the United States Department of Agriculture-National Institute of Food and 84 Agriculture, and the Virginia-Maryland Regional College of Veterinary Medicine. 85 86 v Table of Contents 87 Chapter 1: Introduction ................................................................................................................... 1! 88 1.1.! General description and significance of Histophilus somni ............................... 1! 89 1.2.! Classification ...................................................................................................... 2! 90 1.3.! Characteristics .................................................................................................... 2! 91 1.4.! Virulence factors ................................................................................................ 3! 92 1.4.1! Modification of lipooligosaccharide (LOS) .............................................. 3! 93 1.4.2! Host-parasite interaction ............................................................................ 4! 94 1.4.3! Production of exopolysaccharide (EPS) and biofilm formation ............... 6! 95 1.4.4! Surface Proteins ......................................................................................... 7! 96 References ....................................................................................................................................... 9! 97 Chapter 2 Functional and phenotypic characterization of Histophilus somni luxS ...................... 17! 98 Abstract ..................................................................................................................... 18! 99 2.1! Introduction ...................................................................................................... 20! 100 2.2! Materials and Methods ..................................................................................... 23! 101 2.2.1! Bacteria and culture conditions ............................................................... 23! 102 2.2.2! Construction of luxS and uspE knockout mutants ................................... 23! 103 2.2.3! Complementation of mutant 2336::TnluxS ............................................. 23! 104 2.2.4! mRNA isolation and sequencing ............................................................. 24! 105 2.2.5! Purification of LOS and electrophoretic analysis .................................... 25! 106 2.2.6! Serum sensitivity ..................................................................................... 25! 107 2.2.7! Biofilm formation, staining, and visualization ........................................ 26! 108 2.2.8! Purification of exopolysaccharide (EPS) from biofilm ........................... 26! 109 vi 2.2.9! Extraction of outer membrane proteins (OMP) and electrophoresis 110 analysis .................................................................................................... 27! 111 2.2.10!Animal challenge ..................................................................................... 27! 112 2.3! Results .............................................................................................................. 28! 113 2.3.1! The impact of luxS on growth ................................................................. 28! 114 2.3.2! Effect of luxS and uspE mutations on the electrophoretic profile of OMPs 115 28! 116 2.3.3! Impact of the luxS and uspE genes on biofilm formation and EPS 117 production ................................................................................................ 28! 118 2.3.4! Effect of luxS and uspE on LOS electrophoretic profile and serum 119 sensitivity ................................................................................................. 29! 120 2.3.5! Virulence of strains 2336::TnupsE and 2336::TnluxS in a mouse model 29! 121 2.3.6! Gene expression analysis ......................................................................... 30! 122 2.4! Discussion ........................................................................................................ 52! 123 References ................................................................................................................. 58! 124 Chapter 3 Histophilus somni survives in macrophages by interfering with phagosome-lysosome 125 fusion ............................................................................................................................................
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