The American Association of Swine Veterinarians (AASV) held its 49th annual meeting March 3-6 in San Diego, Cal., covering the science and practice of swine veterinary medicine.

In an industrial partners session, Dr. David Nolan with Huvepharma Inc. raised the question of whether an antibiotic (bambermycins) may actually reduce antibiotic resistance. (Note that bambermycins is currently marketed by Huvepharma under the trade name Flavomycin in swine and GAINPRO in cattle. It is not currently labeled by the Food & Drug Administration to reduce antibiotic resistance.)

Nolan explained that bambermycins (flavophospholipol), also known as moenomycin, is a phosphoglycolipid antimicrobial produced by a number of Streptomyces strains. Bambermycins was the first member of the phosphoglycolipid family discovered during routine soil screening by A.G. Hoechst in 1960 in Bamberg, Germany.

In the U.S., bambermycins is sold for increased rate of weight gain and improved feed efficiency in swine, broilers and turkeys and multiple production classes of cattle. Neither Bambermycins nor any of the phosphoglycolipids have therapeutic uses in people, and therefore, their growth promotion (production) label claims were not affected by the voluntary label modifications as a result of FDA’s industry guidance #209 or #213 that expanded the Veterinary Feed Directive program, Nolan said.

He pointed out that bambermycins is not absorbed from the gastrointestinal tract and has been shown to actively suppress certain microorganisms considered detrimental in the gut -- such as Staphylococcus spp. and Enterococcus faecalis -- while promoting the propagation of those considered to be beneficial for overall gut health, e.g., Lactobacillus spp. and Bifidobacterium.

Bambermycins interferes with bacterial wall synthesis, but its activity is distinctly different from the beta-lactam antibiotics, Nolan said. The moenomycins are the only known class of antibiotics to inhibit peptidoglycan glycosytransferase. Because of the different site and mechanism of activity, bambermycins does not lead to beta-lactam resistance, nor is it affected by pre-existing beta-lactam resistance.

Although labeled only for growth and efficiency in swine, bambermycins repeatedly has been shown to reduce the presence, or the spread, of antimicrobial resistance in both in vitro and in vivo studies, Nolan reported, suggesting that this leads to a potentially beneficial mechanism that may have the practical impact of restoring the efficacy of antimicrobial therapy to a site or herd with previous antimicrobial resistance.

Furthermore, Nolan said the molecule has the possibility to reduce resistance in the bacterial population as a whole by reducing the transfer of antimicrobial resistance to other bacterial populations.

Although the discussion continues regarding the exact mechanisms by which bambermycins may reduce resistance, there is much agreement that reduced resistance is a beneficial result, especially if realized in the field under production conditions, Nolan said.

As the public concern over antibiotic resistance continues to grow, Nolan said the swine industry must proactively develop tools and standards for measurement and improvement (reduction) of antimicrobial resistance. Further investigation of bambermycins and other feed ingredients — along with production practices — is warranted for the reduction of antibiotic-resistant bacterial populations in the environments where pigs are raised and processed, he concluded.

Separate ecosystems

In another session, Dr. James Lowe from the University of Illinois discussed his research on how perinatal antibiotic administration in piglets affects the gut microbiota composition and prevalence of antibiotic resistance factors.

Lowe said his research was not about questioning, "Does this antibiotic work or that one, but how do we shift the microbiome" of young pigs?

While many sources refer to "antibiotic resistance genes," this is incorrect terminology, Lowe said, explaining that resistance factors — some are mobile plasmids, and others are chromosomally coded — are the real concern, and these make up a separate ecosystem within the gut.

Lowe's specific research results can be found in the proceedings of the AASV meeting, but the main point of his presentation was that everything (in the gut microbiome) is relative and how an analysis is conducted determines how the results are interpreted, which can have "profound impacts" on how veterinarians practice medicine.