Abstract
Virulent phages have been used for many years to type Brucella isolates, but until recently knowledge about the genetic makeup of these phages remains limited. In this work the host specificity and genomic sequences of the original set (deposited in 1960) of VLA Brucella reference phages Tb, Fi, Wb, Bk2, R/C, and Iz were analyzed and compared with hitherto described brucellaphages. VLA phages turned out to be different from homonymous phages in other laboratories. The host range of the phages was defined by performing plaque assays with a wide selection of Brucella strains. Propagation of the phages on different strains did not alter host specificity. Sequencing of the phages TbV, FiV, WbV, and R/CV revealed nucleotide variations when compared to same-named phages previously described by other laboratories. The phages Bk2V and IzV were sequenced for the first time. While Bk2V exhibited the same deletions as WbV, IzV possesses the largest genome of all Brucella reference phages. The duplication of a 301 bp sequence in this phage and the large deletion in Bk2V, WbV, and R/CV may be a result of recombination caused by repetitive sequences located in this DNA region. To identify new phages as potential candidates for lysotyping, the host range and Single Nucleotide Polymorphisms (SNPs) of 22 non-reference Brucella phages were determined. The phages showed lysis patterns different from those of the reference phages and thus represent novel valuable candidates in the typing set.
Highlights
Brucellae are highly infectious and facultative intracellular bacterial pathogens causing brucellosis, a frequent zoonosis with more than 500,000 human cases reported worldwide every year (de Figueiredo et al, 2015)
“novel” Brucella species were isolated from cetaceans (B. ceti) and pinnipeds (B. pinnipedialis; Foster et al, 2007), voles (B. microti; Scholz et al, 2008b), baboons
A comprehensive study with 10 Brucella species represented by 26 reference and type strains was performed to elucidate in which strains the group I to group VI Brucella reference phages TbV, FiV, WbV, Bk2V, R/CV, and IzV (Corbel, 1987) replicate and which strains are merely lysed by lysis from without at high MOIs
Summary
Brucellae are highly infectious and facultative intracellular bacterial pathogens causing brucellosis, a frequent zoonosis with more than 500,000 human cases reported worldwide every year (de Figueiredo et al, 2015). “novel” Brucella species were isolated from cetaceans (B. ceti) and pinnipeds (B. pinnipedialis; Foster et al, 2007), voles (B. microti; Scholz et al, 2008b), baboons 2014), red foxes (B. vulpis; Scholz et al, 2016) and from a human breast implant infection (B. inopinata; Scholz et al, 2010). All Brucella species are closely related exhibiting genome similarities of >90% at the nucleotide level (Al Dahouk et al, 2010). Because of the close genetic relationship of several genetic loci (e.g., 16S rRNA, 98.7% and recA, 85.5%) and a biochemical profile similar to Ochrobactrum spp., atypical Brucella species like B. microti and B. inopinata are often misidentified using commercially available biochemical test systems (Scholz et al, 2008a,c)
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