Background and Aim: Salmonella causes most foodborne bacterial illnesses worldwide. It is found in various hosts, including pets, farm animals, and wild animals, as well as the environment. This study aimed to examine the epidemiological relationship between Salmonella isolates from aquatic environments and those from other avian hosts. Materials and Methods: The study examined 12 water samples, 210 aquatic animals, and 45 migratory aquatic bird samples collected from the protected area of Lake Qarun in El-Fayoum Governorate, Egypt, during migration seasons from different waterfowl migration areas (from October 2018 to January 2019). In addition, 45 fecal samples from domestic chickens were collected from the same geographic location from poultry farms. Bacteriological examination and polymerase chain reaction assay of two virulence genes (i.e., invA and stn) were performed to isolate and identify Salmonella. Results: Salmonella was isolated from 58.3% (7/12) of Lake Qarun water samples, 13.3% (6/45) of migratory waterfowl, 6.6% of (3/45) of chickens (Gallus gallus domesticus), and 4.3% (3/70) of fish and pooled brine shrimp. In migratory aquatic bird species that were sampled, Salmonella were isolated from 23.1% (3/13) of Eurasian coot (Fulica atra), 12.5%, (1/8) of green-winged teal (Anas cardolinesis), 10% (2/20) of northern shoveler (Spatula clypeata), and 0% (0/4) of mallard duck (Anas platyrhynchos). In 35 Tilapia, Salmonella was isolated by (8.6%) 5.7% of external surfaces, 2.85% from the intestine, and 0% from the muscle. No Salmonella was isolated from the 175 brine shrimp samples. Phylogenetic analysis using the stn genes of Salmonella isolated from the aquatic environment, migratory aquatic birds, and chicken showed a strong association between these isolates. In addition, a higher nucleotide identity percentage was observed between the sequences recovered from migratory aquatic birds and Lake Qarun water samples. Conclusion: Salmonella distribution was confirmed through migratory aquatic birds, based on our phylogeny tree analysis, Salmonella considered a likely carrier of zoonotic bacterial pathogens. Furthermore, the close relationship between chicken and fish sequences highlights the scenarios of using chicken manure in fish farms and its public health implications. The presence of Salmonella in different environmental sources spotlights the urgent need to control and break down its epidemiological cycle.

Background: In recent years, anthropogenic activities have released heavy metals and polluted the aquatic environment. This study investigated the ability of the silica-stabilized magnetite (Si-M) nanocomposite materials to dispose of lead nitrate (Pb(NO₃)₂) toxicity in Nile tilapia and African catfish.Results: Preliminary toxicity tests were conducted and determined the median lethal concentration (LC₅₀) of lead nitrate (Pb(NO₃)₂) to Nile tilapia and African catfish to be 5 mg/l. The sublethal concentration, equivalent to 1/20 of the 96-hour LC₅₀Pb(NO₃)₂, was selected for our experiment. Fish of each species were divided into four duplicated groups. The first group served as the control negative group, while the second group (Pb group) was exposed to 0.25 mg/l Pb(NO₃)₂(1/20 of the 96-hour LC₅₀). The third group (Si-MNPs) was exposed to silica-stabilized magnetite nanoparticles at a concentration of 1 mg/l, and the fourth group (Pb + Si-MNPs) was exposed simultaneously to Pb(NO₃)₂and Si-MNPs at the same concentrations as the second and third groups. Throughout the experimental period, no mortalities or abnormal clinical observations were recorded in any of the treated groups, except for melanosis and abnormal nervous behavior observed in some fish in the Pb group. After three weeks of sublethal exposure, we analyzed hepatorenal indices, oxidative stress parameters, and genotoxicity. Values of alkaline phosphatase (ALP), gamma-glutamyl transferase (GGT), urea, and creatinine were significantly higher in the Pb-intoxicated groups compared to the control and Pb + Si-MNPs groups in both fish species. Oxidative stress parameters showed a significant decrease in reduced glutathione (GSH) concentration, along with a significant increase in malondialdehyde (MDA) and protein carbonyl content (PCC) concentrations, as well as DNA fragmentation percentage in the Pb group. However, these values were nearly restored to control levels in the Pb + Si-MNPs groups. High lead accumulation was observed in the liver and gills of the Pb group, with the least accumulation in the muscles of tilapia and catfish in the Pb + Si-MNPs group. Histopathological analysis of tissue samples from Pb-exposed groups of tilapia and catfish revealed brain vacuolation, gill fusion, hyperplasia, and marked hepatocellular and renal necrosis, contrasting with Pb + Si-MNP group, which appeared to have an apparently normal tissue structure.Conclusions: Our results demonstrate that Si-MNPs are safe and effective aqueous additives in reducing the toxic effects of Pb (NO₃)₂on fish tissue through the lead-chelating ability of Si-MNPs in water before being absorbed by fish.

Background and Aim: Multidrug-resistant (MDR) Pseudomonas aeruginosa is a global threat to public health. This study aimed to determine biofilms and efflux pump regulatory gene (mexR) in MDR P. aeruginosa isolates. Materials and Methods: A total of 42 fecal samples of aquatic migratory birds collected during hunting season in Egypt were evaluated for the detection of P. aeruginosa according to standard culture-based methods. The antibiotic susceptibility of P. aeruginosa strains was evaluated using disk diffusion methods. The biofilm formation ability of the isolates was phenotypically determined using a colorimetric microtitration plate assay. Polymerase chain reaction amplification was performed to detect biofilm genes (PelA and PslA) and mexR. Results: In total, 19 isolates (45.2%) were recovered from the 42 fecal samples of migratory birds. All isolates were identified as MDR P. aeruginosa, and 78.9% of the strains produced biofilms at different degrees. Molecular detection of biofilm extracellular polymeric substances revealed that PelA was the most predominant gene in the biofilm-producing isolates, followed by PslA. mexR was detected in 63.2% of MDR P. aeruginosa isolates, and its prevalence was higher in non–biofilm-producing strains (75%) than in biofilm-producing strains (60%). Conclusion: Antibiotic resistance in P. aeruginosa isolates recovered from migratory birds through various mechanisms is a major public and animal health problem. It is important to consider the significance of migratory birds in disease transmission.

The escalating prevalence of antibiotic resistance poses a significant challenge to controlling aquatic diseases, underscoring the need for innovative antimicrobial approaches. Therefore, the current study aimed to investigate the effects of thyme-synthesized silver nanoparticles (thyme-AgNPs) on modulating the immunosuppressive, oxidative stress, and histopathological changes induced by multidrug-resistant Enterococcus faecalis (MDR E. faecalis) infection in Oreochromis niloticus (Nile tilapia). The antibiotic susceptibility profiling of the isolated E. faecalis (PQ084785) revealed resistance to multiple antibiotic classes. The in vitro bactericidal efficacy of thyme-AgNPs was confirmed, with minimum bactericidal concentrations (MBC) and minimum inhibitory concentrations (MIC) of 62.5 µg/mL and 31.5 µg/mL, respectively. In vivo, the 96-h median lethal concentration (LC₅₀) of thyme-AgNPs was determined to be 1 mg/L. Meanwhile, eighty O. niloticus (30.00 ± 5.00 g) were categorized into four groups in duplicate: group I was the negative control group, group II was intraperitoneally injected with MDR E. faecalis (0.2 mL of 0.79 × 10⁸ CFU/mL), group III was exposed to the sublethal dose of thyme-AgNPs in water (0.1 mg/L), and group IV was challenged with the E. faecalis and exposed to thyme-AgNPs simultaneously for 15 days. Results outlined that E. faecalis induced clinical abnormalities, reduced immunoglobulin M levels, elevated oxidant indicators (malondialdehyde), decreased antioxidant capacity (reduced glutathione content, catalase, and superoxide dismutase), and significantly upregulated immune gene expression (tumor necrosis factor-α and interleukin-1β) with marked histopathological and histochemical alterations in gill and liver tissues. Interestingly, the thyme-AgNPs intervention resulted in a noticeable improvement in all measured biomarkers as well as histopathological regeneration. Overall, thyme-AgNPs are a recent antibacterial tool against immune-oxidant/antioxidant and histopathological changes triggered by MDR E. faecalis infection.

This study aimed to assess the in vitro and in vivo disinfectant potential of peracetic acid (PAA) (1 mg/L) and hydrogen peroxide (H₂O₂) (20 mg/L) on the physicochemical and microbiological water quality parameters of fish aquaria, the microbial density of Nile tilapia muscular tissue, fish hepatic cortisol levels, and antioxidant biomarkers. In vitro, PAA and H₂O₂ reduced A. hydrophila colony viability by 5 log units after 30 and 5 min of contact time, respectively. PAA and H₂O₂ were added to aquaria water twice a week for the three-week experiment. Increased fish escape reflexes were observed only in the PAA group, which returned to normal within 10 min. No mortalities were reported in either the PAA or H₂O₂ groups. An in vivo experimental challenge with a pathogenic strain of A. hydrophila revealed a 20% reduction in mortality in the PAA group, with no mortalities in the H₂O₂ group. Cortisol levels and antioxidant markers were measured to assess the impact of PAA and H₂O₂ on fish health. Cortisol levels in the PAA and H₂O₂ groups were significantly higher than in the control group after disinfectant exposure, but they progressively returned to normal. A significant reduction in superoxide dismutase (SOD) and catalase (CAT) activity, along with considerably higher glutathione peroxidase (GPx) and malondialdehyde (MDA) enzymatic activity, was observed in the PAA and H₂O₂ groups compared to the control group. A substantial increase in total antioxidant capacity (TAC) was recorded in the PAA group. Physicochemical analyses revealed reduced pH and increased dissolved oxygen levels in the PAA and H₂O₂ groups. Microbiological analyses showed a significant reduction in bacterial density in water by 64% and 76% after 30 min of exposure to PAA and H₂O₂, respectively, with a non-significant increase in microbial count after bacterial challenge. Additionally, aerobic bacterial count, Aeromonas spp., and psychotropic bacterial count in fish muscle showed a significant reduction in the H₂O₂ group compared to the PAA and control groups before and after infection. The study concludes that regular application of PAA and H₂O₂ can temporarily reduce bacterial load in aquaria and fish muscle, regulate stress responses, and improve fish health by reducing A. hydrophila-induced infections and improving survival.

This study demonstrated that some bacteria could form biofilms and detect microbial residues. Two broiler housing facilities at Giza Governorate were investigated for microbiological status during production cycle days 7, 21, and 31, and after disinfection. 27 water samples were taken: 18 using the sponge stick method from water lines, 3 from major water sources, and 6 from the cooling pad water. Additionally, 25 dust samples were collected from fans and house floors. The samples were analyzed for aerobic bacteria, coliforms, pseudomonas, fungi, and yeast. After disinfection, 18 swab samples were taken from water lines, floors, and fans to assess residual microbial counts and biofilm. Generally, the counts of microorganisms were higher at the entrance of water lines compared to the end. Total colony counts (TCC) were 342 and 23.99 CFU per 106/20 cm2, total coliform counts (TCFC) were 36 and 0.97 CFU per 106/20 cm2, pseudomonas counts were 257.50 and 12.61 CFU per 106/20 cm2, and fungal counts (TFC) were 10.65 and 1.97 CFU per 105/20 cm2, respectively. Additionally, the highest number of colonies was discovered at 31 days (3,375 and 2,145 CFU per 106 g from the floors and fans, respectively). After disinfection, a variety of bacteria were found; the predominant bacteria were identified using VITEK 2, and they included Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Proteus mirabilis. Forty-five percent of the isolates that created a moderate biofilm were P. aeruginosa and K. pneumoniae, which could pose a risk to animal health in subsequent production cycles.