The use of antimicrobials in livestock production and their effect on the development of antimicrobial resistance (AMR) is a global health problem for humans, animals and the environment. The aim of this study was to determine antimicrobial residue levels in milk and feces samples during the withdrawal period in dairy cattle administrated with a single dose of the drug, as well as to characterize the antimicrobial resistance patterns of Escherichia coli cultured from feces samples. In the study, dairy cows from three different farms in North Macedonia were included. Raw milk and feces samples were collected before drug administration (0 day) and on the 1st, 2nd, 3rd, 7th and 21st day after drug administration. The antimicrobial residues of oxytetracycline, enrofloxacin, amoxicillin, trimethoprim and procaine-benzylpenicillin were determined using a validated liquid chromatography combined with tandem mass spectrometry (LC-MS/MS) method involving stable isotopes. According to results obtained, the highest levels of analyzed antimicrobial residues were determined on the first day after drug administration, which then gradually decreased until their elimination (7th day). The highest AMR of E. coli (100%) was found in β-lactam antimicrobials. Less exposure to broad-spectrum antimicrobials could be an important factor for reduction of AMR on dairy farms.

The dissemination of resistant pathogens through food supply chains poses a significant public health risk, spanning from farm to fork. This study analyzed the distribution of Shiga toxin-producing Escherichia coli (STEC) across various sources within the animal-based food supply chain. A total of 500 samples were collected from livestock, poultry, the environment, fisheries, and dairy. Standard microbiological procedures were employed to isolate and identify E. coli isolates, which were further confirmed using MALDI-TOF and virulence-associated genes (VAGs) such as stx1, stx2, ompT, hylF, iutA, fimH, and iss. The phenotypic resistance patterns of the isolates were determined using the disc diffusion method, followed by molecular identification of antibiotic resistance genes (ARGs) through PCR. STEC were subjected to PCR-based O typing using specific primers for different O types. Overall, 154 (30.5%) samples were confirmed as E. coli, of which 77 (50%) were multidrug-resistant (MDR) E. coli. Among these, 52 (67.53%) isolates exhibited an array of VAGs, and 21 (40.38%) were confirmed as STEC based on the presence of stx1 and stx2. Additionally, 12 out of 52 (23.07%) isolates were identified as non-O157 STEC co-harbouring mcr-1 and bla_NDM-1. O26 STEC was found to be the most prevalent among the non-O157 types. The results suggest that the detection of STEC in food supply chains may lead to serious health consequences, particularly in developing countries with limited healthcare resources.

Background and Aim: The emergence of multidrug-resistant (MDR) Proteus mirabilis in food-producing animals and their associated environments is a growing public health concern. The indiscriminate use of antimicrobials in animal husbandry exacerbates resistance development, posing significant threats to food safety and sustainability. This study investigates the distribution, antibiotic resistance patterns, and virulence-associated genes (VAGs) of P. mirabilis isolated from poultry, livestock, fish, and their environments in Pakistan under a One Health perspective. Materials and Methods: A total of 225 samples were collected from poultry (n = 100), livestock (n = 75), and aquatic sources (n = 50) from March 2023 to September 2024. Standard microbiological methods were employed for the isolation and identification of P. mirabilis. Polymerase chain reaction (PCR)-based detection of antibiotic resistance genes and VAGs was performed using specific primers. Antibiotic susceptibility was assessed through the disk diffusion method following Clinical and Laboratory Standards Institute 2022 guidelines. Statistical analyses, including analysis of variance and correlation models, were applied to assess the relationships between variables. Results: P. mirabilis was detected in 28.44% (64/225) of the total samples, with the highest occurrence observed in poultry (38%), followed by livestock (22.67%) and aquatic sources (18%). Resistance to ampicillin (100%), chloramphenicol (82%), cefepime (75%), and ciprofloxacin (75%) was widespread. PCR analysis revealed a high occurrence of extended-spectrum beta-lactamase-producing P. mirabilis carrying blaCTX-M (49%), blaOXA (54%), and blaTEM (25.67%) genes. In addition, VAGs such as zapA (39.53%), ucaA (34.88%), and hpmA (32.55%) were frequently identified. The presence of MDR P. mirabilis in fish and related environments (18%) is alarming, highlighting potential zoonotic and foodborne transmission risks. Conclusion: The study underscores the widespread distribution of MDR P. mirabilis in animal-based food sources, raising significant concerns regarding food safety and antimicrobial resistance. The findings reinforce the need for stringent monitoring and regulatory policies to mitigate MDR bacterial dissemination across the food supply chain. Future research should employ metagenomic approaches for comprehensive surveillance and risk assessment. Keywords: animal-derived foods, antimicrobial resistance, multidrug-resistant Proteus mirabilis, One Health, virulence genes.

Sulfadimethoxine (SDM) and ormetoprim (OMP) are antimicrobials used in combination to treat bacterial infections in fish farming. The use of this drug combination is not yet regulated in some countries, such as Brazil. Due to the lack of regulated drugs for aquaculture in Brazil, this study investigated the residue depletion profile of SDM and OMP in Nile tilapia (Oreochromis sp.) after oral administration. Fish were treated with medicated feed containing a 5:1 ratio of SDM:OMP at the dose of 50 mg kg BW⁻¹ for five consecutive days with an average water temperature of 28 °C. The drugs were incorporated into the feed by using a gelatin coating process which promoted homogeneity in drug concentration and prevented the drug leaching into the water during medication. The SDM and OMP determination in fish fillets (muscle plus skin in natural proportions) was performed using the QuEChERS approach followed by LC-MS/MS quantification. The analytical method was validated according to Brazilian and selected international guidelines. A withdrawal period of 9 days (or 252 °C days) was estimated for the sum of SDM and OMP residues at concentration levels below the maximum residue level of 100 µg kg⁻¹.

The indiscriminate use of antibiotics in food-producing animals serves as a major catalyst for the emergence of antibiotic-resistant infections. This study aimed to assess the genetic diversity and antibiotic resistance of Enterobacterales in animal-derived foods. A total of 905 animal-derived food samples, including meat, dairy, poultry, fish, and environmental sources, were collected from various locations in Pakistan. Isolates were confirmed through selective subculturing, morphological, biochemical, and MALDI-TOF analysis, followed by antibiotic susceptibility testing. Subsequently, PCR-based detection of antibiotic resistance genes and virulence-associated genes. Overall, a total of 263 (29.06%) Enterobacterales were identified, as follows: 58.55% (154/263) E. coli, 6.84% (18/263) K. pneumoniae, 21.29% (56/263) P. mirabilis, and 13.30% (35/263) Salmonella spp. Isolates showed a varying resistance pattern against different studied antibiotics, e.g., beta-lactams and inhibitors, ciprofloxacin, and tetracycline, while colistin and tigecycline remained most effective. All the isolates displayed an array of antibiotic resistance and virulence-associated genes. Particularly significant (<0.05) co-existence of bla_NDM and mcr-1 was observed among the Enterobacterales isolated from various animal-derived foods. This study underscores the need to monitor Enterobacterales in animal-derived foods, especially in developing countries, to curb the spread of resistant pathogens and ensure effective food safety measures.

Dissemination of resistant pathogens via food supply chains is a notable public health danger from farm to fork. The proposed work analysed the distribution of E. coli among various sources of animal-based food supply chain. Overall, 500 samples were heaped up from livestock, poultry sectors, environment, fisheries, and dairy. Standard microbiological procedures were used to isolate and identify E. coli. Further, isolates were confirmed by using MALDI-TOF and virulence associated genes (VAGs). The phenotypic resistance pattern of the isolates was determined by molecular identification of antibiotic resistance genes (ARGs) through PCR using specific primers. Shiga toxin producing E. coli (STEC) were subjected to PCR based O typing using specific primers against different O types. Overall results revealed that 154 (30.5%) samples were confirmed as E. coli, in which77 (50%) isolates were MDR E. coli. Among these, total 52 (67.53%) isolates showed array of VAGs in which 21 (40.38%) were confirmed as STEC based on stx1 and stx2. Furthermore, 12/52 (23.07%) isolates were detected as Non-O157 STEC co-harboring mcr-1 and blaNMD-1. Overall, O26 STEC was found to be the most prevalent among different non-O157 types. Herein, results proposed that detection of such STEC MDR E. coli causing serious public health consequences in developing countries.