Egg Industry - December 2017 - 22
22 ❙ EggIndustry
WILL NO-ANTIBIOTICS-EVER POULTRY IMPROVE HUMAN HEALTH?
tested for antibiotic resistance according to the
NARMS protocol. Birds raised in conventional and
no-antibiotics-ever growing programs are included
in the study, but the study commenced when no-antibiotics-ever growing programs were a small niche
part of the industry. Results for the study have not
been published yet.
The problem of coselection
Plasmids are small DNA circles outside the
bacterial chromosome. Some bacteria can have
plasmids that contain genes that provide resistance
to more than one class of antibiotics or metals.
Bacteria-carrying plasmids like this are called coresistant. Coselection is the process where exposure to
one antibiotic or metal selects for resistance to one
gene in the plasmid and then also selects for all the
other resistance genes that are in the plasmid.
Singer, speaking at the National Meeting on
Poultry Health, Processing and Live Production,
gave an example of how coselection complicates
efforts to halt the increase in antimicrobial resistance. He said that one plasmid pulled out of E. coli
found in a cow conveyed resistance to a number of
antibiotics as well as some metals like copper and
zinc. Copper and zinc are sometimes used in noantibiotics-ever growing programs to help regulate
gut microflora, but if a plasmid containing genes for
resistance to the metals and antibiotics were present
on the farm, then we might not be improving resistance like we think we are.
Hofacre said resistance genes to quaternary ammonia disinfectants has been found in plasmids containing antibiotic-resistant genes, so how the farm or
hatchery is cleaned could theoretically affect resistance to antibiotics.
Antibiotic resistance is a natural process
Just as the original antibiotics used in medicine
were first found in nature, antibiotic resistance has
evolved over millions of years in just about every environment on earth. We will never get to a zero level
of antibiotic resistance. It evolved naturally long
before humans harnessed antibiotics.
Joerger said the question is whether we can get
back to what would be considered the natural or basal level of antimicrobial resistance in the bacteria in
the bird's environment. He said no one really knows
what the basal level of resistance really would be,
but he said that it definitely wouldn't be as high as
what we see on poultry farms today.
Competitive exclusion and probiotics
Many successful no-antibiotics-ever husbandry
programs for broilers, turkeys and laying hens utilize probiotics added to the feed to maintain healthy
flocks with good performance. Hofacre said that a
microorganism selected for inclusion as a probiotic
because it helps keep Clostridia from colonizing
the gut may not help prevent Salmonella colonization. In the future, Hofacre said probiotic cultures
containing more than one serovar of microorganism
could be used to accomplish multiple objectives, like
preventing colonization with Salmonella and improving bird health.
Probiotics could contribute to food safety by
aiding the production of poultry products with
reduced need for antibiotics, which could reduce selection pressure for antibiotic resistance
in the poultry house. Probiotics could also help
prevent colonization of the digestive system with
Salmonella and Campylobacter, which should
means less of a pathogen load on ready-to-cook
poultry products. ■
This is the 12th article In WATT Global Media's 100-year anniversary series, which looks at
key drivers that will shape the future of the worldwide poultry industry.
www.WATTAgNet.com ❙ December 2017