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.
We investigated the impact of the hatchery practice of administering third-generation cephalosporin (3GC) on the selection and persistence of 3GC-resistant Escherichia coli in poultry. We studied 15 3GC-treated (TB) and 15 non-3GC-treated (NTB) broiler flocks and 12 3GC-treated (TL) and 10 non-3GC-treated (NTL) future layer flocks. Fecal samples from each flock were sampled before arrival on the farm (day 0), on day 2, on day 7, and then twice more. E. coli isolates were isolated on MacConkey agar without antibiotics and screened for 3GC resistance, and any 3GC-resistant E. coli isolates were further analyzed. 3GC-resistant E. coli isolates were found in all 3GC-treated flocks on at least one sampling date. The percentages of 3GC-resistant E. coli isolates were significantly higher in TB (41.5%) than in NTB (19.5%) flocks and in TL (49.5%) than in NTL (24.5%) flocks. In the day 2 samples, more than 80% of the E. coli strains isolated were 3GC resistant. 3GC-resistant E. coli strains were still detected at the end of the follow-up period in 6 out of 27 3GC-treated and 5 out of 25 non-3GC-treated flocks. Many 3GC-resistant E. coli strains were resistant to tetracycline, and there were significant differences in the percentages of resistance to sulfamethoxazoletrimethoprim, streptomycin, or gentamicin between treated and nontreated flocks. bla CTX-M and bla CMY-2 were the most frequently detected genes. These results clearly demonstrated that 3GC-resistant strains are introduced early in flocks and that the use of 3GC in hatcheries promotes the selection of 3GC-resistant E. coli. Measures must be implemented to avoid the spread and selection of 3GC-resistant strains.T hird-generation cephalosporins (3GC) have been classified as "critically important antimicrobials" in human medicine by the World Health Organization. In many European countries, there has been a dramatic increase in the prevalence of 3GC-resistant Escherichia coli in broilers and broiler meat (1-3), and these isolates are considered of public health concern.Several studies have suggested a possible link between use of 3GC in hatcheries and the increase in 3GC resistance in E. coli. The presence of these resistant isolates in the broiler production pyramid has been recently demonstrated (2, 4). 3GC antimicrobials are sometimes used to control the early mortality rate associated with E. coli. It is automatically administered in ovo to broilers (5) or by subcutaneous injection to 1-day-old future layers (6), together with Marek's disease vaccination. It is strongly suspected that use at hatcheries is responsible for the increase in 3GC resistance in poultry production (3,7,8). However, to our knowledge, no direct evidence of this potential cause-effect relationship has been published.The purpose of this study was to investigate the impact of hatchery use of 3GC on the selection and persistence of 3GC-resistant E. coli in poultry intestinal flora throughout the lifetime of the birds, by comparing flocks of broilers and future laying hens (layers) that ha...
The early 2000s marked the end of the Golden age of the antibiotics and the beginning of the awareness on the potential threat to human health due to the dissemination of antimicrobial resistance. As a base-line study, we investigated the antimicrobial susceptibility of 99 strains of non-O1/non-O139 Vibrio cholerae isolated from wastewater and shellfish in 2000/2001 within La Rance estuary (Brittany, France). All isolates were susceptible to amoxicillin-clavulanic acid, cefotaxime, imipenem, chloramphenicol, nalidixic acid, ciprofloxacin, norfloxacin, amikacin, gentamicin, tetracycline, doxycycline, trimethoprim-sulfamethoxazole, and erythromycin. The only resistances were to streptomycin, sulfonamides and ampicillin: 54.6% of the isolates had acquired resistance to at least one antimicrobial agent among them and only six isolates from cockles were multidrug resistant. On the basis of the distribution of a limited selection of resistance associated genes, our study shows that V. cholerae can constitute an environmental reservoir for these genes. However, none of our isolates harbored integron. This result casts doubt on the capacity of non-O1/non-O139 V. cholerae to acquire resistance-associated genes in such context, and on its potential role of indicator of the dissemination of antimicrobial resistance in the aquatic environment.
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