Tetracyclines have a high resistance percentage in Salmonella spp. of both human and animal origin. Essential oils, such as cinnamon (Cinnamomum zeylanicum), clove (Eugenia caryophyllata), oregano (Origanum vulgare), and red thyme (Thymus zygis), have shown bactericidal activity against this bacterium. However, in many cases, the minimum inhibitory concentration (MIC) exceeds the cytotoxicity limits. The objective of this study was to assess the in vitro efficacy of combining oxytetracycline with essential these oils against field multidrug-resistant (MDR) Salmonella enterica strains. The MIC of each product was determined using the broth microdilution method. The interaction was evaluated using the checkerboard method, by means of the fractional inhibitory concentration index (FIC_index) determination. The results showed a positive interaction (synergy and additivity) between oxytetracycline and the four oils tested, resulting in a reduction in both products’ MICs by 2 to 4 times their initial value, in the case of oils, and by 2 to 1024 times in the case of the antibiotic. The combination of oxytetracycline and cinnamon achieved the best results (FIC_index 0.5), with a decrease in the antibiotic effective concentration to below the sensitivity threshold (MIC of the combined oxytetracycline 0.5 µg/mL). There was no antagonistic effect in any case, although differences in response were observed depending on the bacterial strain. The results of this study suggest that combining oxytetracycline with cinnamon oil could be an effective alternative for controlling tetracycline-resistant strains of Salmonella. However, its individual use should be further evaluated through in vitro susceptibility tests.

Carvacrol is a compound present in essential oils with proven antimicrobial activity against numerous pathogens. We firstly determine the post-antibiotic effect (PAE) of carvacrol (1×, 2×, 4× MIC) and post-antibiotic sub-minimum inhibitory concentration (MIC) effect (1× + 0.25× MIC and 2× + 0.25× MIC) for two concentrations of Salmonella Typhimurium ATCC14028 (10⁶ and 10⁸ CFU/mL). Prior to testing, the minimum concentration and exposure time to achieve the bacterial inhibition (MIC 0.6 mg/mL and 10 min) were determined by broth microdilution and time–kill curve methods, respectively. At the MIC, carvacrol did not generate any PAE. At twice the MIC, the PAE was 2 h with the standard inoculum (10⁶ CFU/mL) and 1 h with the high-density inoculum (10⁸ CFU/mL). At 4× MIC concentrations, the PAE was higher in both cases > 43.5 h. Continuous exposure of post-antibiotic phase bacteria (1× and 2× MIC) to carvacrol at 0.25× MIC (0.15 mg/mL) resulted in an increase in PAE (PA-SME) above 43.5 h with both inocula. These results suggest that the PA-SME of carvacrol for S. Typhimurium can be significantly prolonged by increasing the sub-MICs, which would allow dose spacing, reduce adverse effects and improve its efficacy in the treatment of infected animals and as a disinfectant in agri-food facilities.

Exudative epidermitis (EE) is an occasional infectious disease affecting suckling and weaned piglets, with severe presentation in outbreaks. We described the diagnosis and control measurements conducted after an outbreak of EE caused by Staphylococcus hyicus producing an exfoliative toxin type C (ExhC) in a commercial 4000-head sow farm. Clinical disease was observed in suckling piglets, with a 70 % of morbidity, and a significant increase of mortality rate of 5 % during this period (p < 0.0001) was detected. The bacteria could be recovered from skin and internal organs of affected animals, and the pulsed-field gel electrophoresis (PFGE) analysis showed that all the isolates were genetically indistinguishable, suggesting a common origin. Certain deficiencies in the cleaning and disinfection protocols carried out in the farrowing unit could be responsible for the severity of the outbreak. The efficacy of autogenous vaccination in sows with an inactivated vaccine based on complete ExhC-positive S. hyicus isolates at five and two weeks before farrowing in combination with the improvement of managements measures and selection of healthy animals for replacement allowed the resolution of the outbreak, completely reducing the morbidity and mortality rates after three months. The importance of an adequate diagnosis, biosecurity evaluation and the use of appropriate immune prophylaxis based on autogenous vaccines, are essential tools for the rapid and effective resolution of disease outbreaks of EE.

Pasteurella multocida is an opportunistic pathogen related to the ovine respiratory complex, although its relevance has not yet been fully defined. The objective of the present study is to clarify the role of P. multocida through an integrated approach. A comparative cross-sectional study was conducted in southern Spain analyzing 201 lung samples collected from apparently healthy fattening lambs (50-60 days old) during winter and summer. This study aimed to molecularly characterize pulmonary lesions in fattening lambs and assess their association with the capsular type, lipopolysaccharide (LPS) serovar, virulence-associated genes (VAGs), and sequence types (STs) of P. multocida isolates.Bronchopneumonic lesions of different grades (II–III) were identified in 49.25 % of the animals. Bronchiolitis obliterans, an underrecognized chronic lesion in fattening lambs, was detected in 27.36% of the lungs, most of them associated with diffuse bronchopneumonia (81.8 %). Seasonal variation had a significant effect on lesion severity, with severe pulmonary lesions and bronchiolitis obliterans being more frequently observed during the summer season. P. multocida was isolated in 17.41 % of the 201 samples analyzed, and its presence was associated with increased odds of type III bronchopneumonia (OR = 2.46, 95% CI: 1.10–5.51, p = 0.029). Three capsular types and two LPS serovars were identified, with D:L3 and A:L3 serogroups detected more frequently in diffuse bronchopneumonia and bronchiolitis obliterans. 7 VAGs profiles were identified, although no association with the lesion severity could be demonstrated. A high genetic heterogeneity (20 STs; GD 0.93) was observed among the P. multocida isolates. The results highlight the decisive role of P. multocida in the development of severe cases of bronchopneumonia, underscoring how external factors, such as seasonality, influence the severity of respiratory diseases.

Bacterial contamination of donkey semen samples is a major concern due to its deleterious effects on sperm quality; this issue is exacerbated during semen storage. Therefore, evaluating the effect of antimicrobials on sperm is of utmost importance. This study identified microorganisms present in donkey semen and evaluated the antimicrobial activity of cinnamaldehyde, determined by the Minimum Inhibitory Concentration (MIC), and its effects on sperm quality. Fourteen semen samples from seven donkeys were analysed, identifying 31 bacterial isolates representing 21 different species. Cinnamaldehyde showed antimicrobial activity (MIC ₅₀ = 0.06 mg/mL; MIC ₉₀ = 4 mg/mL). Reactive oxygen species levels in sperm were decreased, suggesting an antioxidant effect. However, high concentrations of cinnamaldehyde reduced sperm motility. In conclusion, cinnamaldehyde is a promising antimicrobial for semen preservation; however, further studies are needed to ensure antimicrobial efficacy and sperm functionality.