The Good Virus
There are 10-100x more phages on Earth than bacteria themselves
First named in 1917 by Félix d’ Herelle
Phage therapy was first demonstrated to cure Salmonella in poultry in 1919, and had been used as a medical treatment for humans
Modern phage therapy in crop agriculture has already been approved in some countries
Why use phages?
Unlike antibiotics, phages are highly specific. They quickly co-evolve to overcome any resistance in the bacteria they infect
Antibiotics are toxic and disrupt an animal’s microbiome. Phages are naturally found in animals and are better tolerated
Phages self-replicate, so treatment could involve just a single dose
Using a cocktail of phages would make it less likely that bacteria would develop resistance to all
Some phages can even reduce AMR in bacteria, and could be used in synergy with antibiotics
An alternative therapy to antibiotics The future?
Africa could develop its own ‘phage banks’-places to store and provide phages for tailored treatment
lytic cycle. To accomplish a successful cycle, the phage uses its tail fibres to attach to specific receptor(s) on the host cell surface, after which they inject their DNA and commandeer the host’s metabolic processes. Eventually, as the phages replicate, they kill the bacterial host and release more virions. The killing capacity of a phage is determined by screening it against multiple strains of the target pathogen. To control bacterial infections both narrow and broad host range phages can be used. Highly specific, narrow host range phage can be applied with minimal disturbance to other microbial populations, while a broad host-range phage provides a better scope of lysis on a wider number of bacterial pathogens. Multiple phages can also be combined as a cocktail to improve phage coverage of distinct bacterial species. Phage therapy has been explored extensively in poultry in different parts of
Figure 1 - Percentage of samples containing Salmonella phages against various Salmonella strains.
10 20 30 40 50 60 70
0 Salmonella Typhimurium 86
Salmonella Pullorum
Salmonella Kentucky
Urban areas Peri-urban area
the world to treat Escherichia coli, Campylobacter spp., Salmonella spp and Clostridium perfringens. In the fight to control Salmonellosis in poultry, samples from numerous poultry farms in Kenya were analysed for phages that target multiple strains of interest (Figure 1).
Hurdles of phage therapy in Kenya Four different kinds of challenge face the use of phages against bacterial infections in farming, either pre- or post-slaughter: initial phage selection, phage delivery, resist- ance development and regulatory approval. Encouraging farmers to understand the value of a phage product and the impact it will have for them is undeniably challenging, con- sidering the dynamics of poultry farming in most of the low- and middle-income countries. In addition, consideration must be given to the needs of the farmer, such as the need for storage without a cold chain, ease of mass delivery to the flock, the use for combination therapy targeting multiple viral and bacterial pathogens simultaneously, and whether the price per head may be affordable to most poultry farmers.
The future of bacteriophages Though the dynamics of farming may be different in developing countries, there are multiple intervention points that could be targeted with different phage therapeutic strategies. Factoring this in, phages can play a potentially vital role in contributing to the arsenal against antibiotic resistance.
Salmonella Brandenburg
Salmonella Enteritidis
Salmonella Braenderup
Salmonella Choleraesuis
Salmonella Heildelberg
References are available on request. ▶ ANTIBIOTIC REDUCTION | DECEMBER 2021
% of crude lysates
INFOGRAPHIC BY ANNABEL SLATER- ILRI
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96
