The Effect of Antimicrobial Treatment upon the Gill Bacteriome of Atlantic Salmon (Salmo salar L.) and Progression of Amoebic Gill Disease (AGD) In Vivo.

Branchial surfaces of finfish species contain a microbial layer rich in commensal bacteria which can provide protection through competitive colonization and production of antimicrobial products. Upon disturbance or compromise, pathogenic microbiota may opportunistically infiltrate this protective barrier and initiate disease. Amoebic gill disease (AGD) is a globally significant health condition affecting salmonid mariculture. The current study examined whether altering the diversity and/or abundance of branchial bacteria could influence the development of experimentally induced AGD. Here, we challenged Atlantic salmon (Salmo salar) with Neoparamoeba perurans in a number of scenarios where the bacterial community on the gill was altered or in a state of instability. Administration of oxytetracycline (in-feed) and chloramine-T (immersion bath) significantly altered the bacterial load and diversity of bacterial taxa upon the gill surface, and shifted the community profile appreciably. AGD severity was marginally higher in fish previously subjected to chloramine-T treatment following 21 days post-challenge. This research suggests that AGD progression and severity was not clearly linked to specific bacterial taxa present in these systems. However, we identified AGD associated taxa including known pathogenic genus (Aliivibrio, Tenacibaculum and Pseudomonas) which increased in abundance as AGD progressed. Elucidation of a potential role for these bacterial taxa in AGD development is warranted.

Evaluation of the Infectious Potential of Neoparamoeba perurans Following Freshwater Bathing Treatments.

Freshwater bathing for 2-3 h is the main treatment to control amoebic gill disease of marine-farmed Atlantic salmon. Recent in vitro studies have demonstrated that amoebae (Neoparamoeba perurans) detach when exposed to freshwater and that some eventually reattach to culture plates when returned to seawater. Here, we evaluated the potential for gill-detached N. perurans to survive a commercially relevant treatment and infect AGD-naïve fish and whether holding used bathwater for up to 6 h post treatment would lower infectivity. AGD-affected fish were bathed in freshwater for 2 h. Naïve salmon were exposed to aliquots of the used bathwater after 2, 4, 6 and 8 h. The inoculation was performed at 30 ppt for 2 h, followed by gradual dilution with seawater. Sampling at 20 days post inoculation (dpi) and 40 dpi confirmed rapid AGD development in fish inoculated in 2 h used bathwater, but a slower AGD development following exposure to 4 h bathwater. AGD signs were variable and reduced following longer bathwater holding times. These results suggest that viable amoebae are likely returned to seawater following commercial freshwater treatments, but that the risk of infection can be reduced by retention of bathwater before release.

The interaction between temperature and dose on the efficacy and biochemical response of Atlantic salmon to hydrogen peroxide treatment for amoebic gill disease.

Hydrogen peroxide (H2 O2 ) is a commonly used treatment for a range of parasitic diseases of marine finfish, including amoebic gill disease (AGD). While this treatment is partially effective at reducing parasite load, H2 O2 can have detrimental effects on the host under certain conditions. Treatment temperature and dose concentration are two factors that are known to influence the toxicity of H2 O2 ; however, their impact on the outcome of AGD treatment remains unclear. Here, we investigated the effects of treatment temperature (8, 12 or 16°C) and dose concentration (750, 1,000, 1,250 mg/L) on the efficacy of H2 O2 to treat AGD. We demonstrated that a 20-min bath treatment of H2 O2 at all doses reduced both parasite load and gross gill score significantly. Parasite load and gross gill score were lowest in the 1,000 mg/L treatment performed at 12°C. At the high dose and temperature combinations, H2 O2 caused moderate gill damage and a significant increase in the plasma concentration of electrolytes (sodium, chloride and potassium). Taken together, our study demonstrates that higher H2 O2 treatment temperatures can adversely affect the host and do not improve the effectiveness of the treatment.

Mechanical chest compression devices are associated with poor neurological survival in a statewide registry: A propensity score analysis.

OBJECTIVE: To compare functional survival (discharge cerebral performance category 1 or 2) among victims of out-of-hospital cardiac arrest (OHCA) who had resuscitations performed using mechanical chest compression (mech-CC) devices vs. those using manual chest compressions (man-CC). METHODS: Observational cohort of 2600 cases of OHCA from a statewide, prospectively-collected cardiac arrest registry (Utah Cardiac Arrest Registry to Enhance Survival). Comparison of functional survival among those receiving mech-CC vs man-CC was performed using a mixed-effects Poisson model with inverse probability weighted propensity scores to control for selection bias. RESULTS: Overall, mech-CC was utilized in 405/2600 (16%) of the total arrests in Utah during this period. 371/405 (92%) were of the load-distributing band type (AutoPulse(®)) and 22/405 (5%) were mechanical piston devices (LUCAS™), while 12/405 (3%) employed other devices. The relative risk (RR) for functional survival comparing mech-CC to man-CC after propensity score adjustment was 0.41 (95% CI 0.24-0.70, p=0.001). CONCLUSIONS: Mechanical chest compression device use was associated with lower rates of functional survival in this propensity score analysis, controlling for Utstein variables and early return of spontaneous circulation.