A total of 1145 samples were collected from chicken breeder farms, hatcheries, broiler farms, a slaughterhouse and retail refrigerated chicken stores in an integrated broiler supply chain in Guangdong Province, China, in 2013. One-hundred and two Salmonella enterica strains were isolated and subjected to serotyping, antimicrobial susceptibility testing, virulence profile determination and molecular subtyping by pulsed field gel electrophoresis (PFGE). The contamination rates in samples from breeder farms, hatcheries, broiler farms, the slaughterhouse and retail stores were 1·46%, 4·31%, 7·00%, 62·86% and 54·67%, respectively. The isolated strains of S. enterica belonged to 10 serotypes; most of them were S. Weltevreden (46·08%, 47/102) and S. Agona (18·63%, 19/102). Isolates were frequently resistant to streptomycin (38·2%), tetracycline (36·3%), sulfisoxazole (35·3%) and gentamicin (34·3%); 31·4% of isolates were multidrug resistant. The isolates were screened for 10 virulence factors. The Salmonella pathogenicity island genes avrA, ssaQ, mgtC, siiD, and sopB and the fimbrial gene bcfC were present in 100% of the strains. PFGE genotyping of the 102 S. enterica isolates yielded 24 PFGE types at an 85% similarity threshold. The PFGE patterns show that the genotypes of S. enterica in the production chain are very diverse, but some strains have 100% similarity in different parts of the production chain, which indicates that some S. enterica persist throughout the broiler supply chain.

Pullorum disease caused by Salmonella Pullorum remains an important disease for the poultry industry due to high morbidity and mortality in many countries. Phage therapy is becoming an alternative strategy to control multidrug-resistant Salmonella infections in young chicks. However, how bacteriophages affect the growth performance of chicks infected with S. Pullorum remains poorly understood. Herein, we assessed the therapeutic efficacy of Salmonella phage CKT1 against hypervirulent arthritis - causing S. Pullorum. The results showed that single phage treatment after hypervirulent S. Pullorum infection significantly improved body weight loss of chicks. Compared with enlarged liver and spleen in only Salmonella challenged group, phage administration substantially reduced the liver/body and spleen/body weight ratios, bacterial loads in organs and the degree of hepatic sinusoidal dilatation and congestion. Moreover, phage CKT1 can enter the organs of chicks and stay for at least 3 d in liver and spleen, and promote higher serum levels of IL-6 production within 6 d postinfection, indicating phage-induced bacterial lysis may be involved in inflammatory immune response to S. Pullorum infection. Analysis of the microbiome of gastrointestinal tract of chicks demonstrated that Salmonella challenge significantly reduced the relative abundances of Lachnoclostridium and Blautia, resulting in remarkably increased Escherichia-Shigella and Klebsiella becoming the predominant bacterial taxa. In contrast, the use of phage CKT1 significantly reduced Escherichia-Shigella and Klebsiella populations in intestine, permitting the proliferation of beneficial microbiota in Firmicutes including Lachnoclostridium, Ruminococcus, Lactobacillus , and Pseudoflavonifractor . In addition, phage alone treatments did not affect the normal gut microbiota structure of chicks, and phage therapy on Salmonella infected chicks increased bacteria species richness in the cecum. These results suggest that Salmonella phage CKT1 could improve growth performance of chicks challenged with S. Pullorum by normalizing the abnormal intestinal microbiome.

Effective phage cocktails consisting of multiple virus types are essential for successful phage therapy against pandrug-resistant pathogens, including Salmonella enterica serovar (S.) Typhimurium. Here we show that a Salmonella phage, F118P13, with non-productive infection and a lytic phage, PLL1, combined to inhibit pandrug-resistant S. Typhimurium growth and significantly limited resistance to phages in vitro. Further, intraperitoneal injection with this unique phage combination completely protected mice from Salmonella-induced death and inhibited bacterial proliferation rapidly in various organs. Furthermore, the phage combination treatment significantly attenuated the inflammatory response, restored the generation of CD4+ T cells repressed by Salmonella, and allowed macrophages and granulocytes to participate in immunophage synergy to promote bacterial clearance. Crucially, the non-productive phage F118P13 is less likely to be cleared by the immune system in vivo, thus providing an alternative to phage cocktail against bacterial infections.

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Phage therapy is widely being reconsidered as an alternative to antibiotics for the treatment of multidrug-resistant bacterial infections, including salmonellosis caused by Salmonella. As facultative intracellular parasites, Salmonella could spread by vertical transmission and pose a great threat to both human and animal health; however, whether phage treatment might provide an optional strategy for controlling bacterial vertical infection remains unknown. Herein, we explored the effect of phage therapy on controlling the vertical transmission of Salmonella enterica serovar Gallinarum biovar Pullorum (S. Pullorum), a poultry pathogen that causes economic losses worldwide due to high mortality and morbidity. A Salmonella phage CKT1 with lysis ability against several S. enterica serovars was isolated and showed that it could inhibit the proliferation of S. Pullorum in vitro efficiently. We then evaluated the effect of phage CKT1 on controlling the vertical transmission of S. Pullorum in an adult broiler breeder model. The results demonstrated that phage CKT1 significantly alleviated hepatic injury and decreased bacterial load in the liver, spleen, heart, ovary, and oviduct of hens, implying that phage CKT1 played an active role in the elimination of Salmonella colonization in adult chickens. Additionally, phage CKT1 enabled a reduction in the Salmonella-specific IgG level in the serum of infected chickens. More importantly, the decrease in the S. Pullorum load on eggshells and in liquid whole eggs revealed that phage CKT1 effectively controlled the vertical transmission of S. Pullorum from hens to laid eggs, indicating the potential ability of phages to control bacterial vertical transmission.