Genomic Analysis of Natural Rough Brucella melitensis Rev.1 Vaccine Strains: Identification and Characterization of Mutations in Key Genes Associated with Bacterial LPS Biosynthesis and Virulence.

Mali Salmon-Divon,David Kornspan,Shubham Mathur,Adva Yeheskel,Regina Lubkovskaia

doi:10.3390/ijms21249341

Mali Salmon-Divon, David Kornspan + Show 3 more

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https://doi.org/10.3390/ijms21249341

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Abstract

Brucella species are facultative intracellular bacteria that cause brucellosis, a zoonotic world-wide disease. The live attenuated B. melitensis Rev.1 vaccine strain is widely used for the control of brucellosis in the small ruminant population. However, Rev.1 induces antibodies against the O-polysaccharide (O-PS) of the smooth lipopolysaccharide thus, it is difficult to differentiate between infected and vaccinated animals. Hence, rough Brucella strains lacking the O-PS have been introduced. In the current study, we conducted a comprehensive comparative analysis of the genome sequence of two natural Rev.1 rough strains, isolated from sheep, against that of 24 Rev.1 smooth strains and the virulent reference strain B. melitensis 16M. We identified and characterized eight vital mutations within highly important genes associated with Brucella lipopolysaccharide (LPS) biosynthesis and virulence, which may explain the mechanisms underlying the formation of the Rev.1 rough phenotype and may be used to determine the mechanism underlying virulence attenuation. Further complementation studies aimed to estimate the specific role of these mutations in affecting Brucella morphology and virulence will serve as a basis for the design of new attenuated vaccines for animal immunization against brucellosis.

Highlights

Brucella species are Gram-negative, facultative intracellular bacteria that cause brucellosis, a zoonotic world-wide disease [1]
LPS (S-LPS) strains (i.e., Brucella abortus, B. melitensis, B. suis, B. neotomae, B. microti, B. pinnipedialis, and B. ceti), which contain LPS that is modified with an O-antigen, while B. ovis, B. canis, B. abortus RB51, and B. melitensis B115 are typically rough strains (R-LPS) which lack the O-side chain from LPS [3,4]
We evaluated the genetic characteristics of two natural Rev.1 rough strains, isolated from sheep, compared to 24 Rev.1 smooth strains and the virulent smooth reference B. melitensis 16M strain, in order to reveal the specific gene mutations in the genomes of the natural Rev.1 rough strains

Summary

Introduction

Brucella species are Gram-negative, facultative intracellular bacteria that cause brucellosis, a zoonotic world-wide disease [1]. LPS (S-LPS) strains (i.e., Brucella abortus, B. melitensis, B. suis, B. neotomae, B. microti, B. pinnipedialis, and B. ceti), which contain LPS that is modified with an O-antigen, while B. ovis, B. canis, B. abortus RB51, and B. melitensis B115 are typically rough strains (R-LPS) which lack the O-side chain from LPS [3,4]. Mutants of B. melitensis, B. suis, and B. abortus lacking the O-antigen modification were shown to be considerably less virulent than their respective parent strains [6,7,8]. It has been suggested, that the Brucella LPS plays a key role in the invasion, intracellular multiplication and protection against complement-mediated lysis [3]. Brucella is able to evade detection by the host immune system and to form a chronic intracellular infection [9,10]

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