Aeromonas Diversity and Antimicrobial Susceptibility in Freshwater—An Attempt to Set Generic Epidemiological Cut-Off Values

Abstract

The importance of the role of environment in the dissemination of antimicrobial resistant bacteria is now well recognized. Thus, bacterial indicators to monitor the phenomena are required. The Aeromonas genus is autochthonous in the aquatic environment and easy to detect in any water type, such as freshwater, or wastewater. These microorganisms are also causing infections in humans and animals (including fish). Furthermore, as Aeromonas spp. is able to acquire antimicrobial resistance mechanisms, it is candidate for indicator bacteria to follow antimicrobial resistance dissemination in aquatic environments. Unfortunately, to date, interpretation criteria for Aeromonas spp. for antimicrobial susceptibility tests are scarce in the literature. No epidemiological cut-off values for Aeromonas are currently available at EUCAST to interpret Minimum Inhibitory Concentrations (MIC). The only interpretation criteria available are clinical breakpoints from CLSI that are adapted from Enterobacteriaceae. Based on the results of MIC distributions obtained for a collection of environmental isolates of Aeromonas, this study aimed at proposing tentative epidemiological cut-off values (COWT) for Aeromonas spp. assessing whether the genus is an acceptable level of definition. Thus, 233 isolates collected from 16 rivers were identified at species level using Maldi-Tof (Bruker). Eleven different species were identified, the most abundant were A. bestiarum (n = 54), A. salmonicida (n = 45), A. sobria (n = 41), and A. eucrenophila (n = 37). 96-well micro-plates containing different concentrations of 15 antimicrobials, namely cefotaxime, ceftazidime, chloramphenicol, colistin, enrofloxacin, erythromycin, florfenicol, flumequine, gentamicin, nalidixic acid, oxolinic acid, streptomycin, temocillin, tetracycline, and trimethoprim-sulfamethoxazole, were prepared. The broth micro-dilution method was used to determine the antimicrobial susceptibility of each isolate. The estimation of COWT values was satisfactory obtained at genus level for all antimicrobials except cefotaxime and erythromycin. This first step is an invitation for other research teams to increase the amount of antimicrobial resistance data collected. Then, robustness of our proposed provisional generic epidemiological cut-off values could be assessed by testing antimicrobial susceptibility of various Aeromonas collections.

Occurrence and antibiotic susceptibility of fish bacteria isolated from Oreochromis niloticus (Nile tilapia) and Clarias gariepinus (African catfish) in Uganda

“…The bacteria were isolated from common environments and are therefore likely to be exposed to similar antibiotic resistance selection pressure. Besides, this finding may be in support of previous reports that genus Aeromonas is an indicator bacterium for antimicrobial resistance in the aquatic ecosystem (Baron et al 2017;Penders and Stobberingh 2008;Usui et al 2016).…”

“…Two genera were tested: genus Aeromonas, due to its high pathogenicity in fish and high prevalence in the study area. It has also been used as an indicator bacterium for antibiotic susceptibility in aquatic environments (Baron et al 2017;Penders and Stobberingh 2008;Usui et al 2016); and Genus Plesiomonas due to its high prevalence in the study area, it was considered to represent family Enterobacteriaceae, a group to which many fish bacteria belongs. A total of 155 isolates (Aeromonas spp.…”

NaCl promotes antibiotic resistance by reducing redox states in Vibrio alginolyticus

“…The extensive use and misuse of antimicrobial agents in hospitals and in fish farming and the consequent selective pressure lead to the development of antibiotic resistance; which has become a serious global problem (Akova, 2016;Dubert et al, 2016;Baron et al, 2017). It is well documented that both clinical and environmental bacterial pathogens may harbour severe antibiotic resistance traits that lead to challenges in treating patients with existing antibiotics.…”

Single‐strain regression analysis evaluating disc potencies of flumequine and enrofloxacin for testing Aeromonas sobria and Vibrio anguillarum

“…For the two antimicrobials, in the present studies very little information of that kind is available. Among environmental A. sobria the wild‐type cut‐off was 0.016/0.031 . The enrofloxacin MIC values of the strains tested were 0.03, 0.015, 0.008, 0.03 and 0.015 mg/L for A. sobria , and 0.004, 0.06, 0.008, 0.004 and 0.004 mg/L for V. anguillarum .…”

“…In studies of environmental Aeromonas spp. , Baron et al found a provisional cut‐off value (CO WT ) for A. sobria of 0.06/0.03 mg/L . Transforming the 0.03 mg/L CO WT level to inhibition zone diameter values and comparing it with an MIC level of 0.5 mg/L the resulting curves are shown in Fig.…”