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Polymicrobial biofilms adhere to surfaces and enhance pathogen resistance to conventional treatments, significantly contributing to chronic infections in the respiratory tract, oral cavity, chronic wounds, and on medical devices. This review examines antimicrobial peptides (AMPs) as a promising alternative to traditional antibiotics for treating biofilm‐associated infections. AMPs, which can be produced as part of the innate immune response or synthesized therapeutically, have broad‐spectrum antimicrobial activity, often disrupting microbial cell membranes and causing cell death. Many specifically target negatively charged bacterial membranes, unlike host cell membranes. Research shows AMPs effectively inhibit and disrupt polymicrobial biofilms and can enhance conventional antibiotics' efficacy. Preclinical and clinical research is advancing, with animal studies and clinical trials showing promise against multidrug‐resistant bacteria and fungi. Numerous patents indicate increasing interest in AMPs. However, challenges such as peptide stability, potential cytotoxicity, and high production costs must be addressed. Ongoing research focuses on optimizing AMP structures, enhancing stability, and developing cost‐effective production methods. In summary, AMPs offer a novel approach to combating biofilm‐associated infections, with their unique mechanisms and synergistic potential with existing antibiotics positioning them as promising candidates for future treatments. Antimicrobial peptides (AMPs) are promising alternatives to conventional treatments for polymicrobial biofilms, which increase pathogen resistance. AMPs disrupt biofilm extracellular matrices and microbial membranes, inhibiting biofilm formation and enhancing antibiotic efficacy. Current research addresses challenges like stability and production costs to optimize clinical applications, highlighting AMPs' innovative potential in treating biofilm‐associated infections.

Salmonella spp. is one of the major foodborne pathogens responsible for causing economic losses to the poultry industry and bringing consequences for public health as well. Both the pathogen survival ability in the intestinal environment during inflammation as well as their relationship with the host immune system, play a key role during infections in poultry. The objective of this study was to quantify the presence of the macrophages and CD4 + /CD8 + cells populations using the immunohistochemistry technique, in commercial lineages of chickens experimentally infected by wild-type and mutant strains of Salmonella Enteritidis and Salmonella Typhimurium lacking ttr A and pdu A genes. Salmonella Enteritidis ∆ ttr A∆ pdu A triggered a higher percentage of the stained area than the wild-type, with exception of light laying hens. Salmonella Typhimurium wild-type strain and Salmonella Typhimurium ∆ ttr A∆ pdu A infections lead to a similar pattern in which, at 1 and 14 dpi, the caecal tonsils and ileum of birds showed a more expressive stained area compared to 3 and 7 dpi. In all lineages studied, prominent infiltration of macrophages in comparison with CD4 + and CD8 + cells was observed. Overall, animals infected by the mutant strain displayed a positively stained area higher than the wild-type. Deletions in both ttr A and pdu A genes resulted in a more intense infiltration of macrophages and CD4 + and CD8 + cells in the host birds, suggesting no pathogen attenuation, even in different strains of Salmonella .

This trial was designed to evaluate the off-label use of ceftiofur with Marek's vaccine in one-day-old broiler chicks, a prophylactic treatment that has been done in some commercial hatcheries, on the emergence of extended-spectrum beta-lactamase producing Escherichia coli (ESBL-E. coli). A total of 168 chicks (Cobb500®) were used in a completely randomized design. Birds were assigned to two treatments (Marek's vaccine plus saline vs Marek's vaccine plus ceftiofur) and six repetitions, with 14 animals each. Cloacal swabs were collected from 1 to 14 days post-hatch. The majority (86%; p<0.0001) of the ESBL-producing isolates harboring blaCTX-M and blaSHV genes originated from animals receiving the antimicrobial. None of the isolates were positive for plasmid-mediated AmpC betalactamase genes (blaACC, blaCMY-2, blaDHA, blaFOX, blaMOX and blaMIR). These findings indicate that the off-label use of ceftiofur with Marek's vaccine is associated with the short-term increase in ESBL-producing Escherichia coli in the gut of chicks.

Background/Objectives: Salmonella enterica subsp. enterica serovar Enteritidis (S. Enteritidis) is a major pathogen associated with poultry products, and the rise of antimicrobial-resistant strains has intensified the need for effective natural control strategies. Essential oils (EOs) are recognized for their antimicrobial potential, but their volatility, instability, and risk of toxicity at high concentrations limit their practical application. Therefore, the objective of this study was to evaluate the antimicrobial efficacy of EOs in broilers infected with S. Enteritidis and to characterize potential synergistic or antagonistic interactions between the oils. Methods: To achieve this, the oils were first assessed through Minimum Inhibitory Concentration (MIC), Minimum Bactericidal Concentration (MBC), and Fractional Inhibitory Concentration (FIC) assays, and the most effective ones against S. Enteritidis were selected. These selected oils were then microencapsulated and incorporated into the broiler feed for the in vivo assay. Results: The encapsulated formulation retained key bioactive compounds and significantly reduced bacterial shedding and intestinal colonization when administered to broilers experimentally infected with S. Enteritidis. Broilers receiving the optimized half-dose supplementation exhibited a 36% reduction in fecal shedding and a 4 log10 decrease in cecal bacterial counts compared to untreated controls. A transient reduction in liver colonization was also observed, while feed intake remained unaffected. Conclusions: These findings demonstrate that microencapsulated EOs can serve as an effective natural strategy to control S. Enteritidis in poultry. The results support the broader application of lipid-based encapsulation technologies for improving the functional performance of phytobiotics in animal production.

Staphylococcus aureus (S. aureus) is a major cause of opportunistic infections in humans and animals, leading to severe systemic diseases. The rise of MDR strains associated with animal carriage poses significant health challenges, underscoring the need to investigate animal-derived S. aureus. Objectives: This study examined the genotypic relatedness and phenotypic profiles of antimicrobial resistance in S. aureus, previously sampled from nostril swabs of healthy horses from two geographically distant Brazilian states (Northeast and South), separated by over 3700 km. The study also sought to confirm the presence of methicillin-resistant (MRSA) and borderline oxacillin-resistant (BORSA) strains and to characterize the isolates through molecular typing using PCR. Methods: Among 123 screened staphylococci, 21 isolates were confirmed as S. aureus via biochemical tests and PCR targeting species-specific genes (femA, nuc, coa). Results: REP-PCR analysis generated genotypic profiles, revealing four antimicrobial resistance patterns, with MDR observed in ten isolates. Six isolates exhibited cefoxitin resistance, suggesting methicillin resistance, despite the absence of the mecA gene. REP-PCR demonstrated high discriminatory power, grouping the isolates into five major clusters. Conclusions: The genotyping indicated no clustering by geographical origin, highlighting significant genetic diversity among S. aureus strains colonizing horses’ nostrils in Brazil. These findings highlight the widespread and varied nature of S. aureus among horses, contributing to a deeper understanding of its epidemiology and resistance profiles in animals across diverse regions. Ultimately, this genetic diversity can pose a public health risk that the epidemiological surveillance services must investigate.

Salmonella Heidelberg is commonly reported in foodborne outbreaks around the world, and chickens and poultry products are known as important source of these pathogen. Multidrug-resistant S. Heidelberg strains are disseminated into poultry production chair, which can lead to severe clinical infections in humans and of difficult to treat. This study aimed at evaluating the β-lactam susceptibility and genotypic relatedness of Salmonella Heidelberg at Brazilian poultry production chain. Sixty-two S. Heidelberg strains from poultry production chain (poultry, poultry meat and poultry farm) were used. All strains were evaluated to antimicrobial susceptibility by diffusion disk test, as well as β-lactam resistance genes. Genotypic relatedness was assessed by Pulsed-Field Gel Eletrophoresis, using Xba1 restriction enzyme. Forty-one strains were characterized as multidrug-resistant according to phenotype characterization. The resistance susceptibility revealed 31 distinct profiles, with higher prevalence of streptomycin (61/62), nalidixic acid (50/62), tetracycline (43/62) and β-lactam drugs (37/62). blaCMY-2 was the more frequent β-lactamase gene found (38/62); other resistance genes found were blaCTX-M (2/62), blaSHV (3/62) and blaTEM-1 (38/62). No carbapenemase genes was found. The Pulsed-Field Gel Electrophoresis showed 58 different profiles. Strains with a larger number of antimicrobial resistance were grouped into ten major clusters apart from others. The spread of resistance by ampC continues to rise, thereby turning concern to public health, since the β-lactam antimicrobials are used as a therapeutic treatment in humans.

In mammals, enteric salmonellas can use tetrathionate ( ttr ), formed as a by-product from the inflammatory process in the intestine, as electron acceptor in anaerobic respiration, and it can fuel its energy metabolism by degrading the microbial fermentation product 1,2-propanediol. However, recent studies have shown that this mechanism is not important for Salmonella infection in the intestine of poultry, while it prolongs the persistence of Salmonella at systemic sites in this species. In the current study, we show that Δ ttr A pdu A strains of Salmonella enterica have lower net survival within chicken-derived HD-11 macrophages, as CFU was only 2.3% ( S. Enteritidis Δ ttr A pdu A), 2.3% ( S. Heidelberg Δ ttr A pdu A), and 3.0% ( S . Typhimurium Δ ttr A pdu A) compared to wild-type strains after 24 h inside HD-11 macrophage cells. The difference was not related to increased lysis of macrophages, and deletion of ttr A and pdu A did not impair the ability of the strains to grow anaerobically. Further studies are indicated to determine the reason why Salmonella Δ ttr A pdu A strains survive less well inside macrophage cell lines. Graphical abstract

Conjugation plays an important role in the dissemination of antimicrobial resistance genes. Besides, this process is influenced by many biotic and abiotic factors, especially temperature. This study aimed to investigate the effect of different conditions of temperature and storage (time and recipient) of poultry meat, intended for the final consumer, affect the plasmid transfer between pathogenic (harboring the IncB/O-plasmid) and non-pathogenic Escherichia coli organisms. The determination of minimal inhibitory concentrations (MIC) of ampicillin, cephalexin, cefotaxime, and ceftazidime was performed before and after the conjugation assay. It was possible to recover transconjugants in the poultry meat at all the treatments, also these bacteria showed a significant increase of the MIC for all antimicrobials tested. Our results show that a non-pathogenic E. coli can acquire an IncB/O-plasmid through a conjugation process in poultry meat, even stored at low temperatures. Once acquired, the resistance genes endanger public health especially when it is about critically and highly important antimicrobials to human medicine.Graphical Abstract

The mechanism of colonisation of the chicken intestine by Salmonella remains poorly understood, while the severity of infections vary enormously depending on the serovar and the age of the bird. Several metabolism and virulence genes have been identified in Salmonella Heidelberg; however, information on their roles in infection, particularly in the chicken infection model, remains scarce. In the present publication, we investigated three Salmonella Heidelberg mutants containing deletions in misL, ssa, and pta-ackA genes by using signature-tagged mutagenesis. We found that mutations in these genes of S. Heidelberg result in an increase in fitness in the chicken model. The exception was perhaps the pta-ackA mutant where colonisation was slightly reduced (2, 7, 14, and 21 days post-infection) although some birds were still excreting at the end of the experiment. Our results suggest that for intestinal colonisation of the chicken caecum, substrate-level phosphorylation is likely to be more important than the MisL outer membrane protein or even the secretion system apparatus. These findings validate previous work that demonstrated the contribution of ackA and pta mutants to virulence in chickens, suggesting that the anaerobic metabolism genes such as pta-ackA could be a promising mitigation strategy to reduce S. Heidelberg virulence.

Despite numerous studies on Salmonella enterica subsp. enterica serovar Typhimurium, the underlying mechanisms of several aspects of its virulence are still under investigation, including the role of the pdu and ttrA genes, associated with the metabolism of 1,2-propanediol using tetrathionate as an electron acceptor respectively. Our objective was to contribute to an understanding of the role of these genes inbacterial virulence for mice (Mus musculus) using an S. Typhumirum ΔttrApduA mutant. The experiment was conducted with a group infected by the S. Typhimurium mutant and a control group infected with a wild-type strain. The mutant was not attenuated compared with the parent strain. There were no differences in the bacterial numbers recovered from the mesenteric lymph nodes and Peyer’s patches but at 8-day after oral infection higher numbers were recovered from the spleen, liver, and cecum. Unlike the single pduA and ttrA mutants, the double ΔttrApduA mutation did not affect invasion and survival in mice, which highlights the need for further studies to clarify the role of these important metabolism genes under reduced redox conditions linked to Salmonella virulence.