2010-12-英文文章大肠杆菌感染.doc
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1、-glucan and E. coli infectionIntroductionEscherichia coli is commonly found in the avian gastrointestinal tract and other mucosal surfaces. Although most of the strains are commensals, a separate group, designated avian pathogenic E. coli, has the ability to cause extraintestinal disease in poultry,
2、 collectively called colibacillosis (Kariyawasam et al., 2006; Bonnet et al., 2009). Serotypes O1, O2, and O78, and to some extent O15 and O55, are the most common serotypes associated with colibacillosis found in chickens (Gomis et al., 1997; Raji et al., 2007). They commonly cause airsacculitis, p
3、ericarditis, perihepatitis, peritonitis, salpingitis, and subsequently the most acute form, septicemia, resulting in sudden death (Mellata et al., 2003; Ask et al., 2006). The poultry industries worldwide suffer great financial losses every year because of the high morbidity and mortality rates caus
4、ed by colibacillosis. Treatment strategies include the control of environmental factors and the use of antibiotics. However, concerns exist regarding the emergence of antibiotic resistance of normal microflora and pathogenic bacteria, which may in turn threaten human health through transfer f drug r
5、esistance genes to zoonotic bacteria (Food and griculture Organization of the United Nations, World ealth Organization, and World Organization for Animal ealth, 2003).Avian colibacillosis, a disease caused by a group of bacteria called avian pathogenic Escherichia coli (APEC) in chickens, turkeys, a
6、nd other avian species, is an infectious disease that often causes severe mortality and subsequently results in economic losses to the poultry industry ( Gibbs et al., 2004). The disease is associated with a complete set of syndromes including septicemia, airsaculitis, pericarditis, and swollen head
7、 syndrome (Chevilleand Arp, 1978; Rodriguez-Siek et al., 2005). Several E.coli isolates are commonly associated with colibacillosisin poultry, and the serogroups O1, O2, and O78 have been recognized as the predominant sources involved in this disease (Whittam and Wilson, 1988; McPeake et al., 2005).
8、 A high raA high rate of antibiotic resistance was observed while testing these serogroups, which probably originates from the extensive use of antibiotics in the poultry industry (Allan et al., 1993), as well as by acquisition of R plasmids (Johnson et al., 2005b; Skyberg et al., 2006). Numerous co
9、ncerns about the use of antibiotics in the poultry industry have been raised including the further selection of drug-resistant strains (Franklin, 1999; Angulo et al., 2004). There are also human health issues involved due to the potential transfer of E. coli from animals via the food chain (Angulo e
10、t al., 2004; Johnson et al., 2005a). This has attracted considerable attention from researchers who are seeking alternatives for control and treatment of colibacillosis in animals.One promising alternative to antibiotics is the use of virulent bacteriophage against E. coli serogroups O1, O2, and O78
11、, a well-established approach that phages for these serogroups are able to be isolated and used in phage therapy against bacterial cells. Bacteriophages are a class of viruses that live and replicate in bacteria (Ackermann, 2000) and have the ability to attack a single species or subset of a species
12、 of bacterium, making them potential antibacterial agents. -Glucans have been well studied in human and animal subjects, and their immune-enhancing effects have been well noted (Volman et al., 2008). Due to their ability to augment the immune response, -glucans have been termed biological response m
13、odifiers.-Glucans are structural components of the cell wall of many bacteria, fungi, and yeast, as well as cereal grains such as oat and barley. -Glucans from fungal and yeast sources have been widely studied and shown to be most effective in enhancing protective immunity against infectious agents
14、(Soltanian et al., 2009). Though the immune-enhancing capabilities of -glucans have been proven in mammals, limited reported research is available for poultry, with mixed results in terms of performance and immune response. Some studies have shown that -glucan supplementation improves BW (Zhang et a
15、l., 2008), whereas other groups have found no significant effects (Chae et al., 2006). Huff et al. (2006) reported contradictory results in which -glucan supplementation was detrimental to BW in a nonchallenge setting but was found to be beneficial during an Escherichia coli challenge. These varying
16、 results indicate that more research needs to be carried out to determine the optimal dosage and proper usage of -glucans to obtain consistent results. -Glucans have beneficial effects on both the innate and adaptive immune systems. When exposed to -glucans in vitro, chicken macrophages and splenocy
17、tes have been shown to experience enhanced proliferation and improved phagocytic capabilities (Chen et al., 2003; Guo et al., 2003). In terms of the adaptive immune response, -glucans magnify plasma IgG and IgA levels, indicating an upregulation of the humoral immune response (Zhang et al., 2008). T
18、he T-lymphocyte subpopulations are also affected, with higher CD4+, CD8+, and CD4+:CD8+ T-cell populations found in chickens supplemented with -glucan (Chen et al., 2003; Chae et al., 2006). Furthermore, -glucans have demonstrated the ability to augment the secretion of several cytokines to aid in p
19、athogen elimination. Macrophages isolated from birds fed -glucans demonstrated enhanced interleukin (IL)-1 (Guo et al., 2003), IL-2, and interferon (IFN)- levels (Zhang et al., 2008). Dietary -glucan has also been shown to increase the size of the primary and secondary lymphoid organs, providing fur
20、ther evidenceof their immunomodulating capabilities (Guo et al., 2003; Zhang et al., 2008).Materials and methods Experimental Animals and TreatmentsA 3-wk experiment was conducted to determine the efficacy of bacteriophage EC1 in treating respiratory infection in birds caused by E. coli O78:K80. A t
21、otal of 480 one-day-old male broiler chicks (Ross 308) were obtained from a commercial hatchery. The chicks were assigned randomly to 4 treatment groups, each with 4 pens of 30 chicks per pen. Water and broiler feed (antibiotic free) were provided ad libitum throughout the experimental period. The 4
22、 treatment groups were group I (control), in which untreated, unchallenged birds were administered 0.2 mL of PBS only (0.14 M NaCl, 0.0027 M KCl, 0.01 M Na2HPO4, 0.0018 M KH2PO4; pH 7.4); group II (control), in which unchallenged birds were treated with 0.2 mL of bacteriophage EC1 (1011 pfu/ mL); gr
23、oup III, in which birds were challenged with 0.2 mL of a 5-h-old E. coli O78:K80 culture (grown in Luria-Bertani broth at 37C and shaken at 180 rpm) containing 109 cfu of bacterial cells/mL, followed by 0.2 mL of bacteriophage EC1 (1011 pfu/mL) at 2 h postchallenge; and group IV, in which birds were
24、 challenged with 0.2 mL of a 5-h-old E. coli O78:K80 culture containing 109 cfu of bacteria cells/mL only. The time point at which to inoculate the bacteriophage (2 h postchallenge) was selected based on the results of a preliminary trial showing that E. coli O78:K80 had colonized the lungs and that
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