Taxonomy, spoilage, and virulence characteristics of Kaistella species isolated from fish
Loading...
Files
Date
2023
Authors
Gavu, Masabata Lydia
Journal Title
Journal ISSN
Volume Title
Publisher
University of the Free State
Abstract
In previous studies at the University of the Free State, aerobic, Gram-negative bacteria were isolated from Cape hake (Merluccius capensis), intended for human consumption. Although some of these isolates could be identified, six isolates remained unidentified. The purpose of this study was to determine the genomic and phenotypic characteristics of these isolates to assign them to the correct genus, to describe novel species, if present, to determine the significance of these isolates in terms of pathogenicity and/or spoilage, and to isolate bacteriophages against the bacterial strains for possible biocontrol strategies. Based on 16S rRNA gene sequences, phylogenetic analysis confirmed that the six unidentified bacterial strains used in this study represented members of the genus Kaistella. Four of these six isolates were further characterized to determine whether they were novel species. Using genomic and phenotypic techniques, the DNA G+C content of strains SH 11-4(b), SH 19-2(b), SH 20-4 and SH 40-3 supported their affiliation with the genus Kaistella. Digital DNA-DNA hybridization, average nucleotide identity and amino acid identity values, and phenotypic characteristics demonstrated that strains SH 11-4(b), SH 19-2(b) and SH 40-3 represented novel species of the genus Kaistella. Results for strain SH 20-4 confirmed that it was not a novel species but represented another member of Kaistella carnis. The names of the novel species were proposed as Kaistella merluccii SH 11-4(b), Kaistella piscis SH 19-2(b), and Kaistella frigidipiscis SH 40-3. The potential pathogenicity and/or food spoilage capability of the six Kaistella fish isolates and reference strains were then evaluated by determining the production of siderophores, the production of a variety of enzymes that function as virulence factors, evaluating their antimicrobial resistance patterns, their ability to form biofilms, as well as the determination of their resistance to antibiofilm compounds. All the Kaistella isolates produced Siderophores indicating their ability to sequester iron for survival. Gelatinase, whose expression has been linked to enhanced biofilm formation, was produced in the most significant amounts by most organisms in this study. ‘Kaistella merluccii’ SH 11-4(b) could be regarded as a potential pathogen since it produced more than 4/8 virulence enzymes. Kaistella strains SH 11-3(a) and ‘K. frigidipiscis’ SH 40-3 were the most resistant to antimicrobials. The antimicrobial resistance/susceptibility of the Kaistella and Chryseobacterium species in this study was determined using the Kirby-Bauer disc diffusion susceptibility method. The antimicrobial tests concluded that the fluoroquinolone and cephem antimicrobials would be the most effective in treating Kaistella infections. Kaistella carnis SH 20-4 was regarded as a strong biofilm former since it gave positive results for biofilm formation using three different methods, while strains SH 11-3(a) and ‘K. merluccii’ SH 11-4(b) were the least successful at forming biofilms. This study revealed that 100 mM D-glucose was the most effective biofilm inhibition compound against the Kaistella test strains. Organisms whose biofilms showed the most resistance towards the inhibition compounds included K. carnis SH 20-4 and ‘K. frigidipiscis’ SH 40-3 and susceptibility to the inhibition compounds mainly was observed in SH 11-3(a), SH 11-3(b), ‘K. merluccii’ SH 11-4(b) and ‘K. piscis’ SH 19-2(b). Another aim of this study was to isolate lytic bacteriophages against the Kaistella species that may be pathogenic to fish or may cause food spoilage by using a two-fold agar overlay in a plaque experiment. Thirty-four phage isolates were obtained from the sewage and fishpond water samples. Strains SH 11-3(a) and SH 11-3(b) showed sensitivity toward a few phage isolates while ‘K. piscis’ SH 19-2(a) displayed the greatest resistance towards phage infection. Phage strains 11-3(b)-S2 showed a broader host spectrum than other phage isolates because they displayed lytic activity against 5/12 Kaistella isolates. Most of the isolated phages were identified by transmission electron microscopy as members of the Corticoviridae, Plasmaviridae, Microviridae, Siphoviridae and Tectiviridae families. The three new members of the genus Kaistella were accurately classified, described, and named. The role of the six Kaistella species in virulence was determined. Some isolated phages can potentially prevent, eliminate, or reduce Kaistella infections in fish.
Description
Keywords
Thesis (Ph.D. (Microbiology and Biochemistry))--University of the Free State, 2023, Kaistella, chryseobacterium taxonomy, potential pathogenicity, antimicrobial resistance, biocontrol strategies, biofilm formation, bacteriophage isolation