الفهرس 
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Abstract
Salmonellosis represents a critical problem not only to the poultry producers owing to it is economic impact, but also for poultry consumers due to it is zoonotic potential.
In the present study avian Salmonellae were isolated from local hatcheries, diseased broiler as well as native breed chickens in 2 Egyptian governorates, Beni-Suef and Fayoum, during the period from May, 2018 until November, 2019. Samples were collected from 16 local chicken hatcheries in Beni-Suef (N=12) and Fayoum (N=4) governorates. Specimens were collected from liver of dead in shell embryos. Salmonella isolation was successful in 31.25% of the samples. Serotyping revealed detection of S.Kentucky, S.Sinchew, S.Infantis S.Larochelle, and S.Colindale. Salmonelle examination for antimicrobial susceptibility by disc diffusion method showed resistance to several antimicrobial drugs including [penicillin, amoxicillin, cefradine and streptomycine (no sensitivity at all) followed by apramycin and tetracyclines (25% sensitivity for each)]. On the other hand, Salmonellae were sensitive to enrofloxacin (100%) fosfomycin (75%) and sulphamethoxazole-trimethoprime (75%). Molecular screening of both virulence and drug resistance genes revealed the harboring of invA, stn, avrA virulence genes by all isolates. Phenotypic and genotypic variation in drug resistance was observed for different serovars and different classes of antimicrobial agents; S. infantis and S. larochelle were positive for PCR targeting qnrA gene although phenotypically they were sensitive to enrofloxacin. All of the tested serovars (except S. colindale) showed sensitivity to sulphamethoxazole-trimethoprime although they harbored sul1 gene. At the same time S. colindale harbored tetA gene and it was sensitive to oxytetracycline by disc diffusion. Similar discrepancy was observed for florfenicol and some aminoglycosides.
In the second part of the study commercial broiler (N=13) and native breed (N=18) farms in Beni-Suef from March, 2018 through October, 2019 were investigated for salmonellosis. Specimens were collected from liver and caecum (5 chicks per flock) of clinically suspect cases aging 1-15 days old. Bacteriological examination revealed that 6 isolates (19.35% isolation rate) were successfully cultivated including 2/13 (15.38%) and 4/18 (22.22%) isolates for broilers and native breed farms, respectively. Serotyping of different isolates revealed the following serovars; S.Kentucky 8,20:i:z 6 in 4 farms (1 broiler and 3 native breed), S.Bonariensis 6,8:i:e,n,x in one broiler farm and S.Rechovot 8,20:e,h:z6 in one native breed flock. Antimicrobial sensitivity testing of all Salmonella serovars showed 100% sensitivity to fosfomycin, 66.6% to amoxicillin/clavulinic acid, 66.6% to florfenicol, 66.6% to polymyxin- B, 33.3% to gentamycin and 16.66% sensitivity to each of kanamycin, neomycin, apramycin and enrofloxacin. S.Bonarensis was found resistant to amoxicillin/clavulinic acid and of intermediate sensitivity to ciprofloxacin. Molecular screening of different serovars to virulence and drug resistance genes indicated 100% positivity to invA, stn, avrA virulence genes and also the tested antimicrobial genes except qnrA that was detected in only one of the tested Salmonellae.
The antibacterial effect of 4 EOs in camparisron with amoxicillin/clavulanic acid was applied in S.Kentucky and S.Infantis. The selection of the 2 bacteria was determined after pathogenicity testing of 5 Salmonella isolates in broiler one-day-old chicks (10 chicks per group) beside the negative control group. The chicks were floor reared and fed commercial balanced ration without feed additives. A dose of 1.5x108 CFU/ml per bird of each isolate was given orally. The cumulative mortality was 40% [S.Kentucky (B) and S.Infantis infected groups], 10% (S.Colindale infected group), while S.Rechovot and S.Kentucky (H) caused no mortalities.
The MIC of four EOs and amoxicillin/clavulanic acid on S.Kentucky and S.Infantis was estimated. The MIC for Carvacrol, Cinnamon, Eugenol, Thymol and amoxicillin/clavulanic acid against S.Kentucky was 0.05 mg/ml, 0.05 mg/ml, 0.1 mg/ml, 0.1 mg/ml and 0.21/0.03 mg/L, respectively. Against S.Infantis, the MIC was 0.025 mg/ml, 0.05 mg/ml, 0.1 mg/ml, 0.1 mg/ml and 109.4/15.6 mg/L, respectively. The motility of S.Kentucky was inhibited by the tested sub-inhibitory concentrations of the EOs; Carvacrol (0.025 mg/ml), Cinnamon (0.025 mg/ml), Eugenol (0.05 mg/ml) and Thymol (0.05 mg/ml) and On the other hand only 2 EOs; Cinnamon (0.025 mg/ml) and Thymol (0.05 mg/ml) inhibited the motility of S.Infantis while neither Carvacrol (0.125 mg/ml) nor Eugenol (0.05 mg/ml) inhibited the motility of S.Infantis. The level of Sul1 and Stn genes expression showed down regulation in S.Kentucky and S.Infantis in comparison to an internal control gene (16s rRNA). For both bacteria a more prominent effect was seen in Carvacrol treated bacteria followed by Eugenol treated one then Cinnamon followed by Thymol treated bacteria. One exception was found for Sul1 gene expression where Thymol showed more suppressive effect in S.Kentucky than Cinnamon.
During evaluation of the antibacterial effect of EOs in broiler chicks, the prominent clinical manifestations in experimentally infected broiler chicks with S.Kentucky were diarrhoea and pasty vent as well as suboptimal growth in the non treated infected group (G7). Diarrhoea was observed in S.Kentucky infected groups treated with Carvacrol, Cinnamon, Eugenol and Thymol with variable degree and to a varied period of time. The signs were prominent early and decreased gradually. Cumulative mortalities were 4% in G2 (Carvacrol/S.Kentucky), G3 (Cinnamon/S.Kentucky), G4 (Eugenol/S.Kentucky) and G6 (Amox./S.Kentucky), 8% in G5 (Thymol/S. Kentucky) and 24% in G7 (non treated S.Kentucky infected). The post-mortem lesions were enteritis, typhlitis and excess ureate salts in the two ureters. Non infected groups (G1, G8, G9, G10, G11) showed neither clinical signs nor mortalities.
Significant variations between non infected and infected non treated groups at 7, 14 and 21 days of age (the end of the experiment). Infected treated groups showed improvement in the performance all over the experiment compared to the non treated group (G7). Body weight and FCR were bad in infected non treated group (G7) all over the experiment followed by G1 (non treated non infected) and G6 (amoxicillin treated infected). At the end of the experiment, the best FCR was achieved in G8 (Carvacrol alone) and G9 (Cinnamon alone) followed by G2 (Carvacrol/ infected), G10 (Eugenol alone) and G11 (Thymol alone). The remaining groups (G3, G4, G5) had intermediate FCR values compared to other groups. S.kentucky was successfully re-isolated from groups G3, G6 and G7 (CN treated infected group, amoxicillin treated infected group and positive control, respectively). Salmonella was not detected in samples collected from other groups.
Specimens from liver, heart and caecal tonsil in chicks at zero day of infection and in the non infected group (G1) showed normal histological structure. At 3dpi and 5 dpi; in the infected non treated group (G7) severe lesions were evident in the examined organs. At 3dpi; Carvacrol and Cinnamon treated groups (G2, G3) had minimal lesions while Eugenol treated group (G4) was moderately affected followed by Thymol (G5) and amoxicillin (G6) treated groups. At 5dpi; Carvacrol (G2), Cinnamon and Eugenol treated groups (G3, G4) had more or less normal histological picture in the examined organs. Amoxicillin treated group (G6) had minimal lesions while, Thymol treated group (G5) was moderately affected.