Streptococcus iniae causes high mortality in cultured and wild fish stocks globally. Since the first report in captive Amazon river dolphins Inia geoffrensis in 1976, it has emerged in finfish across ...all continents except Antarctica. In March 2016, an estimated 17000 fish were observed dead and dying along a remote 70 km stretch of the Kimberley coastline north of Broome, Western Australia. Affected species included finfish (lionfish Pterois volitans, angelfish Pomacanthus sp., stripey snapper Lutjanus carponotatus, sand bass Psammoperca waigiensis, yellowtail grunter Amniataba caudavittata, damselfish Pomacentridae sp.), flatback sea turtles Natator depressus, and olive (Aipysurus laevis) and black-ringed (Hydrelaps darwiniensis) sea snakes. Moribund fish collected during the event exhibited exophthalmia and abnormal behaviour, such as spiralling on the surface or within the water column. Subsequent histopathological examination of 2 fish species revealed bacterial septicaemia with chains of Gram-positive cocci seen in multiple organs and within brain tissue. S. iniae was isolated and identified by bacterial culture, species-specific PCR, Matrix-Assisted Laser Desorption Ionisation Time-Of-Flight (MALDI-TOF) and biochemical testing. This is the first report of S. iniae associated with a major multi-species wild marine fish kill in Australia. Extreme weather events in the region including a marked decrease in water temperatures, followed by an extended period of above-average coastal water temperatures, were implicated as stressors potentially contributing to this outbreak.
•A septicaemic outbreak by P. multocida occurred in a resident group of squirrel gliders following importing two squirrel gliders from another zoo.•Whole genome sequencing and phylogenomic analysis ...confirmed that the outbreak strain was introduced through animal movement between the zoos.•A comparison of P. multocida strains from fatal and asymptomatic cases revealed structural differences in their latB, a structural LPS gene.•Isolates collected from fatal cases always had a fully intact latB gene, which is predicted to code for an acyltransferase.
A septicaemic disease outbreak caused by Pasteurella multocida at a zoo in Western Australia (Zoo A) occurred in a resident group of squirrel gliders (Petaurus norfolcensis) following the introduction of two squirrel gliders imported from another zoo (Zoo B). P. multocida isolates obtained from the affected animals and asymptomatic, cohabiting marsupials at both zoos were typed via lipopolysaccharide outer core biosynthesis locus (LPS) typing, repetitive extragenic palindromic PCR (Rep-PCR) typing, and multilocus sequence typing (ST). Investigation of isolate relatedness via whole genome sequencing (WGS) and phylogenomic analysis found that the outbreak isolates shared the same genetic profile as those obtained from the imported gliders and the positive marsupials at Zoo B. Phylogenomic analysis demonstrated that these isolates belonged to the same clone (named complex one), confirming that the outbreak strain originated at Zoo B. As well, the carriage of multiple different strains of this pathogen in a range of marsupials in a zoo setting has been demonstrated. Importantly, the genomic investigation identified a missense mutation in the latB, a structural LPS gene, resulting in introduction of an immediate stop codon in the isolates carried by asymptomatic squirrel gliders in Zoo B. The identified diversity in the latB gene of LPS outer core biosynthesis loci of these isolates is consistent with a novel phase variable mechanism for virulence in P. multocida.
Our study demonstrates the benefit of WGS and bioinformatics analysis in epidemiological investigations of pasteurellosis and its potential to reveal unexpected insights into bacterial virulence.
Ovine footrot is a highly contagious bacterial disease of sheep, costing the Australian sheep industry millions of dollars annually. Dichelobacter nodosus, the causative agent of footrot, is a ...gram-negative anaerobe classed into virulent and benign strains as determined by thermostability of their respective protesases. Current methods for detection of D. nodosus are difficult and time-consuming, however new molecular techniques capable of rapidly detecting and typing D. nodosus have been reported.
A competitive real-time PCR (rtPCR) method, based on the ability to detect a 2 nucleotide difference in the aprV2 (virulent) and aprB2 (benign) extracellular protease gene has been tested on Australian samples for determining detection rates, along with clinically relevant cut-off values and performance in comparison to the traditional culturing methods. The rtPCR assay was found to have a specificity of 98.3% for virulent and 98.7% for benign detection from samples collected. Sheep with clinical signs of footrot showed a detection rate for virulent strains of 81.1% and for benign strains of 18.9%. A cut-off value of a Ct of 35 was found to be the most appropriate for use in Victoria for detection of sheep carrying virulent D. nodosus.
In summary, the rtPCR assay is significantly more capable of detecting D. nodosus than culturing, while there is no significant difference seen in virotyping between the two methods.
The genus
Treponema
contains a number of human and animal pathogenic as well as symbiotic bacteria that are found in vastly different anatomical and environmental habitats. Our understanding of the ...species range, evolution, and biology of these important bacteria is still limited. To explore the diversity of treponemes, we established, validated, and tested a novel metataxonomic approach. As the informative nature of the hypervariable regions of the 16S rRNA gene differ, we first analyzed each variable region independently. Considering the
in silico
results obtained, we established and validated the sequencing of the V4-region of the 16S rRNA gene using known mixtures of
Treponema
species as well as a selected number of clinical samples. The metataxonomic approach was able to identify
Treponema
to a near-species level. We demonstrate that using a spirochete-specific enrichment, our method is applicable to complex microbial communities and large variety of biological samples. The metataxonomic approach described provides a useful method to unravel the full diversity and range of
Treponema
in various ecosystems.
Burkholderia pseudomallei
is predominantly a tropical pathogen uncommonly found in the environment of temperate climatic regions. It is unclear if introduction into temperate regions is sporadic and ...temporary or if
B. pseudomallei
can persist in such environments.
B. pseudomallei
was identified in the environment of southwest Western Australia with melioidosis cases between 1966 and 1991. We report a new cluster with 23 animal fatalities in the same region from 2017, with
B. pseudomallei
again being recovered from the environment. Comparison of the isolates from the first and second clusters using genomics revealed a single sequence type, high clonality, and limited recombination, even though the time of recovery of the isolates spanned 51 years. This is a major contrast to the extensive genomic diversity seen in the tropics. Our data support the suggestion that
B. pseudomallei
has the ability to persist in nontropical environments, potentially in a latent state, and has the ability to activate following favorable conditions (rainfall) and then infect animals and humans.
ABSTRACT
Burkholderia pseudomallei
is the causative agent of the high-mortality disease melioidosis. Although melioidosis is classified as a tropical disease, rare autochthonous cases have been reported from temperate climatic regions, with uncertainty as to whether
B. pseudomallei
is persistent in the local environment and whether specific genetic mechanisms facilitate the survival of
B. pseudomallei
outside the tropics. Sporadic cases of melioidosis occurred in a valley region (latitude 31.6°S) in southwest Western Australia, Australia, between 1966 and 1992. We report a new melioidosis cluster in the same region following high rainfall in January 2017. More than 20 animals died, and
B. pseudomallei
was isolated from four alpacas, a parrot, and three environmental samples taken from the farm where the alpacas resided. Epidemiological data and genomics revealed that two locations on the farm were the probable sources of the alpaca infections. We determined that
B. pseudomallei
isolates from the 2017 cluster belonged to sequence type 284 (ST-284), as did all isolates recovered from 1966 to 1992. Genomic analysis confirmed that the ST-284 isolates were clonal and contained conserved genomic islands and limited evidence of recombination. We identified protein-coding regions unique to these isolates that might influence the persistence of
B. pseudomallei
in this temperate region. We demonstrate the environmental persistence of
B. pseudomallei
in a temperate region for over 50 years, with limited genetic changes suggesting a latent state and with activation, potential aerosolization, and local dispersal following unusually high rainfall.
IMPORTANCE
Burkholderia pseudomallei
is predominantly a tropical pathogen uncommonly found in the environment of temperate climatic regions. It is unclear if introduction into temperate regions is sporadic and temporary or if
B. pseudomallei
can persist in such environments.
B. pseudomallei
was identified in the environment of southwest Western Australia with melioidosis cases between 1966 and 1991. We report a new cluster with 23 animal fatalities in the same region from 2017, with
B. pseudomallei
again being recovered from the environment. Comparison of the isolates from the first and second clusters using genomics revealed a single sequence type, high clonality, and limited recombination, even though the time of recovery of the isolates spanned 51 years. This is a major contrast to the extensive genomic diversity seen in the tropics. Our data support the suggestion that
B. pseudomallei
has the ability to persist in nontropical environments, potentially in a latent state, and has the ability to activate following favorable conditions (rainfall) and then infect animals and humans.
The growth inhibition ability of nine probiotic strains were investigated against 15 Vibrio spp. isolated from western king prawns, Penaeus latisulcatus (Kishinouye), and eight pathogenic Vibrio ...strains from other aquatic animals. Five different inhibition test methods such as bacteriocin-like inhibitory substance (BLIS), modified BLIS, disc-diffusion, well-diffusion and co-culture method were compared in order to select the most suitable probiotics for use in the culture of western king prawns. The results showed that the modified BLIS method was the most effective one for the selection of probiotics. Pseudomonas synxantha and P. aeruginosa were promising probiotics as they caused a significantly higher (P<0.05) growth inhibition of all the Vibrio spp. tested, with Pseudomonas aeruginosa being more effective than P. synxantha. The growth inhibition zones were significantly greater (P<0.05) when probiotics were grown on Marine Salt Agar (MSA) for three days before inoculating the plate with the Vibrio spp., but were not significantly different (P>0.05) when the probiotics and the Vibrio spp. were inoculated onto the plate at the same time. In the co-culture method, probiotics at a concentration of 103 CFU/mL allowed the Vibrio spp. (103 CFU/mL) to grow, but the Vibrio spp. cell densities never reached beyond their initial inoculum levels during the culture. At higher concentrations (105–107 CFU/mL), the probiotics dominated the growth of the Vibrio spp. Therefore, administering a suitable concentration of probiotics and allowing growth and production of antimicrobial compounds before the addition of Vibrio spp. produced the best inhibition results.
Bacterial pathogens causing diseases in fishes have broad host ranges, and may cause high mortality or ongoing chronic infections. Pathogen treatments using antibiotics are becoming limited due to ...increasing concerns for the development of resistance and environmental dissemination of bacteria harboring resistance genes. This study aimed to determine whether nano‐emulsions of selected plant‐derived essential oils (Origanum vulgare, Eucalyptus globulus, Melaleuca alternifolia and Lavendula angustifolia) were bacteriostatic or bactericidal to Aeromonas hydrophila, Streptococcus iniae and Photobacteriumdamselae subspecies damselae. All treatments showed antibacterial activity, and in almost all cases the activity of the nano‐emulsions was superior to their essential oil counterparts. Origanum vulgare (oregano) nano‐emulsion had the most effective antibacterial activity, with a minimal inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of 3.12 µg/ml against all three species; substantially better than tetracycline. The present study highlights the potential of new formulations of essential oils to enhance bacterial disease control in cultured fish.
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