Avian pathogenic Escherichia coli (APEC), the causative agent of colibacillosis belong to the family enterobacteriaceae. The disease is manifested as localised or systemic infections which include peritonitis, airsacculitis, omphalitis, swollen head syndrome and colisepticaemia in poultry. Colibacillosis results in increased mortality, condemnations of carcasses at slaughter, reduced feed conversion and production due to morbidity and increased cost of treatment. The standard method for the control of colibacillosis has been the use of antibiotics either as a treatment or as prophylaxis through the addition of antibiotics into the animal feed at sub-minimal levels. The efficacy of antibiotics has drastically reduced over the years due to the emergence and increased prevalence of antibiotic resistance. The use of some antibiotics and antibiotic growth promoters such as fluoroquinolones has been banned and further bans are still impending. Therefore, colibacillosis can potentially cripple the poultry industry nationally and worldwide, if traditional treatment options are ineffective. There is a great demand for potential alternatives to the use of antibiotics and lytic bacteriophages offer attractive advantages over antibiotics in this regard.
This study focused on the isolation and characterisation of lytic bacteriophages with the aim of determining their potential to control E. coli infections, in poultry. Nine bacteriophages were successfully isolated from sewage samples and five from chicken faecal matter. The lytic patterns of the phages against E. coli K12 and E. coli strains isolated from diseased poultry (presumed to be pathogenic) were determined. Among the phages isolated from sewage samples, 31-5, E13/2, E13/5 and BS4 lysed four or more of the E. coli strains. The widest host strain range was exhibited by E13/2 which infected 8 of the 11 strains. Thus, this isolate may hold the greatest potential for therapy. In contrast, isolates from chicken faecal matter had a very narrow host strain range, lysing a maximum of two E. coli strains including the original host. An interesting observation was made in that the laboratory strain; E. coli K12 was resistant to lysis by four out of the five isolates (from chicken faecal matter). This is an important factor to consider in any potential form of treatment where only the pathogenic strains are targeted while the normal microbiota should remain unaffected. The varied lytic patterns observed for most of the isolates further demonstrate the importance of employing phage cocktails rather than single preparations to treat or prevent colibacillosis. Additionally, some of the isolates may prove useful in phage typing due to their high discriminatory nature in lysis. Although much has been reported on APEC-specific coliphages isolated from sewage, this is one of a few studies where they have been successfully isolated from chicken faecal matter.
Examination of morphological characteristics by transmission electron microscopy revealed the presence of a majority of tailed phages which are members of the Myoviridae and Siphoviridae families. For some viruses definite conclusions could not be made concerning their identity and they were therefore only tentatively placed into certain families.
Molecular analyses included polymerase chain reaction (PCR) using primers specific for the g23 sequence of T4-type phages and the DNA polymerase of T7-like podophages. Although the identity of every phage isolate could not be inferred, the relatedness between isolates SK4 and SK5 was established using the PCR technique of random amplified polymorphic DNA (RAPD). Phylogenetic investigations revealed that 31-5 and SK5 were closely related followed by E13/5 and SK4.
In conclusion, this study demonstrated that some of the isolated phages have the potential to prevent, eliminate or reduce APEC in poultry. Further research is however, necessary to fully characterise the phage isolates and perform efficacy tests in vivo.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-12152010-140446 |
| Date | 15 December 2010 |
| Creators | Kakoma, Kasweka |
| Contributors | Prof RR Bragg |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.uovs.ac.za//theses/available/etd-12152010-140446/restricted/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University Free State or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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