Antimicrobial Susceptibility of Flavobacterium psychrophilum Isolates from Ontario

Abstract

Flavobacterium psychrophilum is the etiological agent of bacterial coldwater disease (BCWD), an important disease in the Ontario fish farming industry and in finfish aquaculture in temperate waters worldwide. The development of antimicrobial resistance by F. psychrophilum is a concern because management of outbreaks of BCWD often requires the use of antibiotics. Seventy-two isolates of F. psychrophilum collected over a 16-year period from farmed salmonids with clinical signs of BCWD were tested for susceptibility to 10 antimicrobial agents using cation-adjusted Mueller-Hinton broth in custom Trek Sensititre susceptibility plates for aquaculture. The minimum inhibitory concentrations (MICs) for the isolates were determined by means of a broth microdilution antimicrobial susceptibility testing method established by the Clinical and Laboratory Standards Institute. Most of the F. psychrophilum isolates had decreased susceptibility to two of the four antibiotics licensed for use in Ontario (i.e., ormetoprim-sulfadimethoxine [> or =0.5/9.5 .tg/mL for 93% of isolates] and trimethoprim-sulfamethoxazole [> or = 0.25/4.8 microg/mL for 89% of isolates]). High MIC values (> or =2 microg/mL) were obtained for florfenicol and oxytetracycline in 53% and 61% of the isolates, respectively, and 83% of the isolates were relatively susceptible (< or =16 microg/mL) to erythromycin. The MIC values were also high for ampicillin, oxolinic acid, and gentamicin.

Antimicrobial Susceptibility of Flavobacterium psychrophilum from Chilean Salmon Farms and Their Epidemiological Cut-Off Values Using Agar Dilution and Disk Diffusion Methods

“…There are a number of studies (Kum et al, 2008; Del Cerro et al, 2010; Durmaz et al, 2012) where the number of isolates investigated was too small for valid estimates of CO WT to be made. In addition the distribution of MIC values in some studies (Rangdale et al, 1997; Hesami et al, 2010) was too diverse to allow the calculation of a valid CO WT . The study carried out under conditions most similar to those used in this work and, therefore, providing the most suitable data for comparison, was that of 387 Danish isolates by Bruun et al (2000).…”

“…Some studies have employed disk diffusion (Dalsgaard and Madsen, 2000; Kum et al, 2008; Durmaz et al, 2012; Henríquez-Núñez et al, 2012) whilst others determined MIC values. The MIC studies have variously employed agar dilution (Hawke and Thune, 1992; Bruun et al, 2000; Schmidt et al, 2000; Michel et al, 2003; Izumi and Aranishi, 2004; Kum et al, 2008), broth macro-dilution (Del Cerro et al, 2010), or broth micro-dilution (Rangdale et al, 1997; Hesami et al, 2010; Henríquez-Núñez et al, 2012: Smith et al, 2016). Although most studies used diluted Mueller-Hinton (MH) media there has been variation in the extent of the dilution and the use of additives.…”

Assessment of cross‐protection to heterologous strains of Flavobacterium psychrophilum following vaccination with a live‐attenuated coldwater disease immersion vaccine

“…Currently, there is not a commercial BCWD vaccine that is available for use in the USA, leaving treatment with antibiotics as a primary means of controlling mortality due to this disease. However, there are increasing reports of antibiotic resistance in F. psychrophilum (Cipriano & Holt, ; Henríquez‐Núñez, Evrard, Kronvall, & Avendaño‐Herrera, ; Hesami et al., ; Van Vliet, Loch, Smith, & Faisal, ) and the number of antibiotics available for treatment of BCWD is limited. As such, there have been significant efforts to develop an effective vaccine against BCWD (Gomez, Mendez, Cascales, & Guijarro, ).…”

Penicillin-G: Efficacy against &lt;i&gt;Flavobacterium psychrophilum&lt;/i&gt; and evaluation of lethal dose limits for rainbow trout

“…Injection of brood stock with antibiotics prior to spawning is also possible. A number of different studies with F. psychrophilum have reported on the efficacy of various antibiotics including oxytetracycline, amoxicillin, erythromycin, ormetoprim-sulfadimethoxine, ampicillin, doxycycline, enrofloxacin, florfenicol, flumequine, gentamicin, oxolinic acid, sarafloxacin, and sulfamethoxazole-trimethoprim [8][9][10][11][12][13]. These studies were primarily standard laboratory tests to determine minimum inhibi-tory concentrations (MIC; [14]) for each antibiotic in Petri dishes and to document increasing resistance of the bacteria to the antibiotics.…”