The authors aimed to investigate eight strains of Escherichia coli (E. coli) strains from Hungarian layer flocks for antimicrobial resistance genes (ARG), using metagenomic methods. The strains were isolated from cloacal swabs of healthy adult layers. This study employed shotgun sequencing-based genetic and bioinformatic analysis along with determining phenotypic minimum inhibitory concentrations. A total of 59 ARGs were identified in the eight E. coli isolates, carrying ARGs against 15 groups of antibiotics. Among these, 28 ARGs were identified as transferable. Specifically, four ARGs were plasmid-derived, 18 ARGs were phage-derived and an additional six ARGs were predicted to be mobile, contributing to their mobility and potential spread between bacteria.

Antimicrobial resistance threatens humans and animals worldwide and is recognized as one of the leading global public health issues. Escherichia coli (E. coli) has an unquestionable role in carrying and transmitting antibiotic resistance genes (ARGs), which in many cases are encoded on plasmids or phage, thus creating the potential for horizontal gene transfer. In this literature review, the authors summarize the major antibiotic resistance genes occurring in E. coli bacteria, through the major antibiotic classes. The aim was not only listing the resistance genes against the clinically relevant antibiotics, used in the treatment of E. coli infections, but also to cover the entire resistance gene carriage in E. coli, providing a more complete picture. We started with the long-standing antibiotic groups (beta-lactams, aminoglycosides, tetracyclines, sulfonamides and diaminopyrimidines), then moved toward the newer groups (phenicols, peptides, fluoroquinolones, nitrofurans and nitroimidazoles), and in every group we summarized the resistance genes grouped by the mechanism of their action (enzymatic inactivation, antibiotic efflux, reduced permeability, etc.). We observed that the frequency of antibiotic resistance mechanisms changes in the different groups.

Restrictions on the use of antimicrobial compounds have led to a surge of interest in alternative solutions, such as natural, plant-based compounds. In our study, we investigated the efficacy of three feed supplements containing different additives, namely, probiotics (Lactobacillus spp., “Test substance A”), turmeric (Curcuma longa L., “Test substance B”), and fenugreek (Trigonella foenum graecum, “Test substance C”). In the experiment, we tested 180 birds of the Bábolna Tetra-SL laying hybrid breed that were infected with Salmonella enteritidis strains. The birds were randomly divided into six groups: three groups treated with the different additives, a negative control group, a positive control group, and an antibiotic-treated group using enrofloxacin. We examined the maturation and the time course of shedding of Salmonella; at the end of rearing, pathological and histopathological examinations were performed. When Salmonella was isolated from the cloacal swab samples, the enrofloxacin-treated group had a high number of animals shedding Salmonella by day 9, which was like the group treated with test material C. The greatest reduction in Salmonella shedding was observed in the groups treated with test materials A and B. In terms of pathological parameters, villus length and crypt depth were significantly better in the group treated with test material C compared to the positive and negative controls, and when comparing the body weight of the tested animals, the group treated with test material B had a significantly larger absorption surface area compared to the positive control group. Overall, the supplement with test material C proved to be the most effective. In the future, it is worthwhile to investigate the combination of the tested active substances for their possible synergistic effects and to perform a dose-response study to select the optimal dosage.

Florfenicol is a member of the phenicol group, a broad-spectrum antibacterial agent. It has been used for a long time in veterinary medicine, but there are some factors regarding its pharmacokinetic characteristics that have yet to be elucidated. The aim of our study was to describe the pharmacokinetic profile of florfenicol in synovial fluid and plasma of swine after intramuscular (i.m.) administration. In addition, the dosage regimen of treatment of arthritis caused by S. suis was computed for florfenicol using pharmacokinetic/pharmacodynamic (PK/PD) indices. As the first part of our investigation, the pharmacokinetic (PK) parameters of florfenicol were determined in the plasma and synovial fluid of six pigs. Following drug administration (15 mg/kg_bw, intramuscularly), blood was drawn at the following times: 10, 20, 30, 40, 50 and 60 min, 2, 3, 4, 5, 6, 7, 8, 12, 24, 48 and 72 h; synovial fluid samples were taken after 1, 2, 3, 4, 6, 8, 12, 24, 48 and 72 h. The concentration of florfenicol was determined by a validated liquid chromatography-mass spectrometry (LC-MS/MS) method via multiple reaction monitoring (MRM) modes. As the second part of our research, minimum inhibitory concentration (MIC) values of florfenicol were determined in 45 S. suis strains isolated from clinical samples collected in Hungary. Furthermore, a strain of S. suis serotype 2 (SS3) was selected, and killing-time curves of different florfenicol concentrations (0.5 µg/mL, 1 µg/mL and 2 µg/mL) were determined against this strain. Peak concentration of the florfenicol was 3.58 ± 1.51 µg/mL in plasma after 1.64 ± 1.74 h, while it was 2.73 ± 1.2 µg/mL in synovial fluid 3.4 ± 1.67 h after administration. The half-life in plasma was found to be 17.24 ± 9.35 h, while in synovial fluid it was 21.01 ± 13.19 h. The area under the curve (AUC_24h) value was 54.66 ± 23.34 μg/mL·h for 24 h in plasma and 31.24 ± 6.82 μg/mL·h for 24 h in synovial fluid. The drug clearance scaled by bioavailability (Cl/F) in plasma and synovial fluid was 0.19 ± 0.08 L/h/kg and 0.29 ± 0.08 L/h/kg, respectively. The mean residence time (MRT) in plasma and synovial fluid was 24.0 ± 13.59 h and 27.39 ± 17.16 h, respectively. The steady-state volume of distribution (V_ss) in plasma was calculated from Cl/F of 0.19 ± 0.08 L/h/kg, multiplied by MRT of 24.0 ± 13.59 h. For the PK/PD integration, average plasma and synovial fluid concentration of florfenicol was used in a steady-state condition. The obtained MIC₅₀ value of the strains was 2.0 µg/mL, and MIC₉₀ proved to be 16.0 µg/mL. PK/PD integration was performed considering AUC_24h/MIC breakpoints that have already been described. This study is the first presentation of the pharmacokinetic behavior of florfenicol in swine synovia as well as a recommendation of extrapolated critical MICs of S. suis for therapeutic success in the treatment of S. suis arthritis in swine, but it should be noted that this requires a different dosage regimen to that used in authorized florfenicol formulations.

The spread of antimicrobial resistance is one of the most serious human and animal health problems of our time. Propolis is a natural substance with antibacterial, antifungal, and antiparasitic activity, the most active components of which are polyphenols and terpenoids. In the present study, the authors investigated the efficacy of propolis against Staphylococcus spp., Enterococcus spp., Escherichia coli and Salmonella enterica, Candida albicans fungi, and Trichomonas gallinae isolated from pigeons. For each pathogen, the minimum inhibitory concentration (MIC) and minimum eradication concentration (MEC) of eight isolates were determined for 96%, 90%, 80%, 70%, and 60% ethanolic extracts of propolis from the region of Észak-Alföld. Propolis was shown to be effective in inhibiting the growth of Gram-positive bacteria, Candida albicans, and Trichomonas gallinae strains. Propolis showed a much better efficacy against Gram-positive bacteria (1.56–400 µg/mL) than against Gram-negative bacteria (>13,000 µg/mL). For Staphylococcus spp., MIC values ranged within 1.56–400 µg/mL and MEC values within 12.5–3260 µg/mL, while for Enterococcus spp. MIC values ranged within 1.56–400 µg/mL and MEC values within 12.5–800 µg/mL. MIC values > 13,000 µg/mL were found for Escherichia coli and Salmonella enterica species. For Candida albicans, MIC values ranging from 1.56 to 400 µg/mL and MEC values ranging from 3.125 to 800 µg/mL were effective. MEC values between 2.5 and 5 mg/mL were observed for three Trichomonas gallinae strains. The effectiveness against Gram-positive bacteria has, in some cases, approached that of antibiotics, making propolis a potential alternative in the treatment of wound infections. Its outstanding efficacy against Trichomonas gallinae holds promise as a potential alternative for treating this widespread infection in pigeons.

Background: The global spread of antimicrobial resistance (AMR) represents one of the most significant challenges of our generation. It is crucial to continuously monitor AMR, not only by investigating clinical, pathogenic strains but also by monitoring commensal bacterial strains, as they can serve as natural reservoirs of resistance. Infections caused by Enterococcus species are increasingly recognized as emerging threats to both animal and public health. Among economically important livestock, poultry as a major source of animal protein for humans is a frequent carrier of enterococci, and also of sporadically detected clinical disease. Methods: This study aimed to determine the antimicrobial susceptibility profile of Enterococcus strains (n = 499) isolated from chicken farms in Hungary. The minimum inhibitory concentration (MIC) was determined for 15 antibiotics, including 10 with established clinical breakpoints. Results: The strains exhibited good sensitivity to amoxicillin, one of the first-line treatments for Enterococcus infections in veterinary medicine, with only 20.8% showing resistance. However, we observed an alarming 27.9% resistance rate to vancomycin, which is reserved to treat infections caused by multidrug-resistant strains in humans. A comparison of our findings with Hungarian hospital records revealed that the resistance patterns of poultry-derived Enterococcus faecalis strains were very similar to those of human isolates, particularly regarding penicillins and aminoglycosides. Conclusions: Overall, the increasing rates of AMR reinforce the importance of conducting periodic studies to establish long-term trends. For multidrug-resistant strains, next-generation sequencing is recommended to elucidate the genetic basis of resistance.