Systemic therapy with oxytetracycline is often used for treatment of clinical metritis although data about its penetration into the uterus and uterine secretion are lacking. Uterine secretions and milk from six cows with clinical metritis were collected for microbiological assay. The animals were treated intramuscularly with long-acting oxytetracycline (20 mg/kg) and samples of plasma, milk and uterine secretions were collected for determination of the antibiotic concentrations by HPLC-PDA analysis. Pharmacokinetics of the antibiotic and in silico prediction of its penetration into the uterus were described. Trueperella pyogenes with MIC values of 16–64 µg mL⁻¹ was isolated (n of cows = 4) from uterine secretions. Oxytetracycline showed fast absorption and penetration in the uterine secretions and milk. No change of withdrawal time for milk was necessitated in cows with clinical metritis. Maximum levels in uterine secretions and predicted concentrations of oxytetracycline in the uterus were lower than MIC values. Systemic administration of long-acting oxytetracycline did not guarantee clinical cure and was not a suitable choice for treatment of clinical metritis associated with Trueperella pyogenes. The appropriate approach to antibiotic treatment of uterine infections of cows requires knowledge on penetration of the antibiotics at the site of infection and sensitivity of pathogens.

Puerperal metritis in cows is often treated with antibacterial drugs. The prudent use of antibiotics in farm animals requires state-of-the-art knowledge of their pharmacokinetics and data from sensitivity tests of pathogenic bacteria. Changes in oxytetracycline levels in the uterine secretion over time after intrauterine administration in cows with metritis were evaluated in relation to the sensitivity of pathogenic bacterial isolates. Oxytetracycline levels in plasma, milk and uterine secretion were determined via LC–MS/MS analysis. Pathogenic bacteria were isolated and their sensitivity to oxytetracycline was determined. The concentrations of oxytetracycline in the uterine secretion were 433.79 (39.17–1668.76) µg·mL⁻¹ six hours after the third application at a dose of 8 mg/kg and 84.33 (1.58–467.55) µg·mL⁻¹ 96 h after the last treatment. These levels were higher than the minimum inhibitory concentrations—namely, between 4 and 64 µg·mL⁻¹—against pathogenic isolates Trueperella pyogenes, Streptococcus intermedius, Escherichia coli and Bacillus pumilis. Higher concentrations over time were measured in milk rather than in plasma, indicating the need to monitor the withdrawal time for milk. The intrauterine infusion of oxytetracycline for three consecutive days resulted in the successful treatment of metritis in terms alleviating inflammation and restoring the estrus cycle in cows.

As natural biopolymers, chitosan and lignin are characterized by their good biocompatibility, high biodegradability and satisfactory biosafety. The active polymers’ functional groups are responsible for the potential of these biomaterials for use as carrier matrices in the construction of polymer–drug conjugates with prospective applicability in the fields of medicine, food and agriculture—subjects that have attracted attention in recent years. Hence, the aim of this research was to place substantial emphasis on the antimicrobial potential of flavonoid–biopolymer complex systems by assessment of the probable synergetic, additive or antagonistic effects arising as a function of systemic complexity. The joint implementation of morin, chitosan and lignin in conjugated two- and three-component systems provoked species-dependent antimicrobial synergistic and/or potentiation effects against the activity of the tested bacterial strains Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853 and the clinical isolate Bacillus cereus. The double combinations of morin–chitosan and morin–lignin resulted in a 100% increase in their inhibitory activity against S. aureus as compared to the pure biocompounds. The inhibitory effects of the three-component system, in decreasing order, were: S. aureus (IZ = 15.7 mm) > P. aeruginosa (IZ = 15 mm) > B. cereus and E. coli (IZ = 14 mm). All tested morin-containing two- and three-component systems exhibited clear and significant potentiation effects, especially against S. aureus and B. cereus. The results obtained are a prerequisite for the potential use of the studied conjugated lignin–morin–chitosan combinations in the construction of novel drug-carrier formulations with improved bioactivities.

Biofilm-forming bacteria are associated with difficult-to-cure bacterial infections in veterinary patients. According to previous studies, N-acetyl-L-cysteine (NAC) showed an inhibitory effect on biofilm formation when it was applied in combination with beta-lactam antibiotics and fluoroquinolones. The lack of information about the effect of NAC on doxycycline activity against biofilm-forming strains was the reason for conducting this study. Staphylococcus aureus (S. aureus) ATCC 25923, Staphylococcus aureus O74, Escherichia coli (E. coli) ATCC 25922 and Pseudomonas aeruginosa (P. aeruginosa) ATCC 27853 were used to evaluate the activity of doxycycline with and without addition of NAC on planktonic bacteria and on biofilm formation. The minimum inhibitory concentrations (MICs) of doxycycline were not affected by NAC for Gram-negative strains and were found to be two times higher for the strains of S. aureus. The minimum biofilm inhibitory concentrations (MBICs) for Gram-negative bacteria (2 μg/mL for E. coli ATCC 25922 and 32 μg/mL for P. aeruginosa ATCC 27853), determined using a standard safranin colorimetric assay, were higher than the MICs (0.5 and 4 μg/mL, respectively). The data suggest that the combinations of doxycycline and NAC could stimulate the growth of planktonic cells of S. aureus and biofilm-forming E. coli ATCC 25922. NAC did not affect the strong inhibitory effect of doxycycline on the biofilm formation by the strains of S. aureus.

SARS-CoV-2 emerged in 2019 and found diagnostic laboratories unprepared worldwide. To meet the need for timely and accurate virus detection, laboratories used rapid Ag tests and PCR kits based on costly multi-channel real-time techniques. This study aimed to develop a conventional nested PCR based on the SARS-CoV-2 N gene, validate it against some approved assays, and apply it to samples from six cats with respiratory symptoms obtained in early 2020 during the first COVID-19 wave in humans in Bulgaria. The nested PCR technique showed 100% sensitivity and specificity; it could detect extracted SARS-CoV-2 RNA at concentrations as low as 0.015 ng/μL. The results identified the six tested cat samples as positive. Sequence analysis performed in two of them confirmed this. The presented technique is reliable, easy to implement and inexpensive, and can be successful in strategies for the prevention and control of SARS-CoV-2 in humans, cats and other susceptible species.

The aim of this study was to verify whether the human DR-ELISA for the detection of anti-SARS-CoV-2 antibodies can be applied in cats, and to assess the risk factors that determine the spread of the virus among the cat population in Bulgaria. The study included 92 serum samples collected from 68 domestic and 24 stray cats aged from 3 months to 20 years of age in the period of January–June 2021. The samples originated from three regions in Bulgaria and from three places of inhabitance. DR-ELISA based on peroxidase-labeled SARS-CoV-2 N protein was employed to detect IgA, IgG and IgM antibodies in the samples. Subsequently, the results were compared with a commercially available multi-species ELISA kit. There was high seroprevalence (83.33%) in stray cats and 41.18% in domestic cats, confirmed by the human and veterinary ELISA kit. The positive cases in the regional cities were 42.86%, in small towns 50% and in villages 78.26%. Cats under 7 years had a five times higher risk than those over 7 years (p = 0.001). The risk was seven times higher for stray cats than for domestic cats (p = 0.001). In addition, the results indicate that the risk was the highest for cats in villages (p = 0.006) compared to cats in other places of inhabitance. This study demonstrates that human DR-ELISA may be successfully applied to monitor the circulation of SARS-CoV-2 in cats and other susceptible species. Cats might serve as sentinel animals for tracking the virus in nature and in inhabited areas (strays) and to discover asymptomatic cases in humans/owners.