On this planet, bacteria outnumber every other type of living organism. Researchers estimate the total number of bacteria at any moment in time ranges in the millions of trillions of trillions. (That’s 30 zeros.) Most bacteria never encounter animals of any kind, but many find themselves in close proximity and have adapted to live on, in and with us and the animals in our care. Although potentially pathogenic bacteria certainly exist, most bacteria pose no threat – and some actually provide remarkable benefits.
The challenge is finding those unique strains of bacteria that, when consumed in adequate amounts, confer a demonstrable benefit to their host – that is to say, are probiotic in nature. Finding these unique strains of bacteria from the trillions of bacteria around us isn’t an easy task. Once found, explaining the various modes of action by which bacteria exert their benefits is the essential “proof of the pudding,” so to speak.
Thankfully, with the evolution of advanced microbiological and molecular techniques over the last couple of decades – rapid, robotic genetic testing and advanced laboratory modeling – the task of finding the remarkable bacteria has transitioned from impossible to possible to practical.
Bacteria are similar to humans in terms of our genetic diversity. Not every person is destined to be an Olympic athlete, and not every bacterium is destined to reduce pathogens or to produce enzymes that enhance digestibility.
Within a species of bacteria, there can be thousands of different strains. Bacteria strains are subtypes of a species that have unique genetic identities and distinctive morphological, biochemical and behavioral features. So when reading a label on the back of a package of probiotic product, assuming the species listed has a certain function because of its name is similar to assuming every person with the last name of Bolt is a world-class Olympic sprinter.
Selection of the best strains within species remains one of the highest hurdles in the development of science-based, research-proven probiotic products. For example, the bacterial species Bacillus subtilis has more than 1,000 strains recorded within an international strain bank. To put this in perspective, there are only 250 recognized breeds of cattle, and if a producer wanted to improve the weaning weights of his purebred Angus herd, he would probably want much more information on his next bull purchase than simply that it was a Bos taurus.
The ultimate goal is to develop microbial solutions to address the microbial challenges that face us today. The challenges include, but are not limited to, the sustainable production of meat, milk and eggs; preservation of nutrients; and food safety. To bring those solutions to the world, we must be able to identify those strains that have the best set of genetic gifts, to deduce how those gifts are manifested into physiological benefits in an ever-increasing battery of lab tests, to combine strains with different sets of gifts into a potential product and to test those combinations in various animal production systems.
Full genomic sequencing lets us select strains based solely on genetics. However, not all good genes get translated into effective capabilities. Not all of the bacterial strains that do well in lab tests can survive the rigors of being mass-produced and packaged. Not all of the strains that can be successfully packaged can withstand the acids and bile salts they might encounter once consumed. Not all of the bacterial strains that confer a benefit to their host tolerate other potentially beneficial strains of bacteria. In short, suffice it to say that development of truly effective and safe probiotic products just isn’t easy.
Bacteria for food
To hedge our bets a bit, the human and animal probiotics industries rely on only two basic types of bacteria: lactic acid bacteria (LAB) and spore-forming bacteria (SFB). The well-documented modes of action and life cycles of these two types of bacteria make them great candidates for additional consideration. This is exactly the same logic as saying the food-producing industries rely on only three basic types of animals: those that produce meat, those that produce milk and those that produce eggs.
The well-documented characteristics of cattle, sheep, goats, pigs, fish, chickens and turkeys make them great candidates for consideration. To continue with the former example, LAB are typically non-motile and populate areas of the gastrointestinal tract (GIT) by forming colonies. Their host keeps them warm, in a low- or no-oxygen environment, and provides nutrients for them. In return, they provide some benefits to their host.
As they reach higher numbers and colonize larger areas of the GIT, their cumulative production of lactic acid changes the environment in their favor and, in a relatively passive manner, creates a hostile environment for potentially pathogenic organisms.
Additionally, LAB interact with the cellular lining of the GIT and improve the barrier and immune functions found there. The barrier functions have evolved to limit the escape of pathogenic organisms from the GIT and their entry into the hepatic-portal circulatory system. Immune functions complement the aforementioned barrier functions and involve the cellular mechanisms of the adaptive immune system found in the GIT. Both of these essential functions can be positively impacted by the daily feeding of an effective, probiotic strain of LAB.
In contrast to LAB, SFB are typically motile hunter-killers that have evolved to actively compete for nutrient sources around them and to use several tactics to eliminate their competitors, including the secretion of antimicrobial peptides. Luckily, probiotic SFB appear to work well with LAB but actively kill potentially pathogenic organisms. While moving through the GIT, SFB secrete an array of digestive enzymes to take advantage of the nutrient sources around them.
In fact, the most successful SFB are able to secrete remarkably high concentrations of those enzymes and to alter the type of enzyme produced based on the nature of the nutrient source they’ve encountered. A cow on pasture grazing summer grass will cause the bacteria to produce more fiber-digesting enzymes while a feedlot steer on a finishing diet will see more starch-digesting enzymes produced by bacteria.
The most commonly used genus of probiotic SFB is Bacillus. The fact that SFB form spores which can withstand high temperatures and dry conditions make them ideal candidates for inclusion in pelleted feeds. And please always remember that strain absolutely matters when it comes to finding effective probiotic organisms.
Given the differences in the major modes of action of LAB and SFB, it should come as no surprise that feeding combinations of them may provide the broadest range of probiotic coverage. Furthermore, at minimum, the effects of daily feeding of a combination of probiotic bacteria should be additive, where 1 + 1 = 2, but in many instances, various modes of action can interact to the benefit of the host, so that 1 + 1 is greater than 2. The ultimate goal is to combine the most effective number of strains with unique yet complementary attributes to maximize their probiotic benefit.
