We share our bodies with 100 trillion bacteria. Not only are these bacteria not harmful to us but they are absolutely essential to our continued health and wellbeing. Our intestines alone contain buckets of these “good” bacteria that help us digest our food, provide additional nutrients and keep out the “bad” bacteria. When things get out of whack because of poor diet, stress, or the improper use of antibiotics the “bad” bacteria gain a foothold and vomiting and diarrhoea result (and possibly wailing and gnashing of teeth). It makes some sense to try and restore the balance by tipping a few zillion “good” bacteria back into the system. This is where probiotics come in, as they are supposed to contain these “good” bacteria. Probiotics have become big business and, as usual where money is involved, the hype outweighs the science.

The theory that “good” bacteria should be used to replace the “bad” bacteria and make us well again is sound. However, this is not what is put into practice. As can be imagined different species have different bacteria in their guts, because they have different diets, consume different food stuffs and, therefore, have different needs. Even within the human species different people have different bacteria as some of us are vegetarian (Prevotella spp. dominate), while others are more carnivorous (Bacteroides spp. dominate) ( Different bugs are needed to deal with these varied diets. What, then, is the logic behind a probiotic such as Protexin Concentrate, which claims to assist digestive function in poultry, pigs, sheep, goats and cattle ( Presumably each group of animals contains a whole range of different gut bugs, while this product only contains one specific bacterium: Enterococcus faecium. Human intestines are estimated to contain between 300 and 1000 different bacterial species. Is adding one more bacterium to this broth really going to make a difference?

NutriBAC ( is a probiotic sold for use in reptiles and amphibians. How one probiotic can satisfy the demands of such a diverse group of animals as frogs, snakes, iguanas and bearded dragons is beyond me. Salmonella is one of the “bad” bacteria reptile keepers worry about. One of the claims made by probiotic manufacturers is that they will stop reptiles shedding Salmonella. A recent study failed to corroborate this assertion (Holz and Middleton 2002).

Probiotics need to be species specific to have any positive effect. One study demonstrated increased resistance to Salmonella colonisation in chickens fed probiotics, but results were better when they were fed actual caecal contents from healthy chickens (Fuller 1999).

Young animals are inoculated with “good” bacteria from their mothers. Orphans that are hand raised may lack these bacteria and often develop diarrhoea. One common method used to counteract this is the shit shake. Faeces are taken from a healthy animal of the same species and mixed in with the animal’s milk. It doesn’t sound particularly attractive but hopefully provides the animal with the bacteria it needs to survive. In fact koalas produce a special type of faeces called pap that is excreted directly from the caecum. Without this pap koala joeys cannot digest the eucalyptus leaves they need to live. Research has shown that koala faeces can be fed if pap is unavailable but the numbers of bacteria are much lower (Osawa et al 1993). These bacteria do not survive freezing, so it must be fed fresh. It seems ludicrous to suggest that a specialised feeder like the koala could benefit from some type of generic probiotic.

Bacteria are like everything else. Once they have settled down and made their home somewhere they are very difficult to shift. Research has shown that the bacteria provided in probiotics do not establish themselves in the intestine but are rapidly washed out (Tannock 1999), necessitating a continual input of bacteria. Very handy for the manufacturers. To have any kind of lasting effect they need to be fed to juvenile animals that haven’t had their guts colonised by bacteria. Or to an adult that has had its bacteria nuked with a big dose of antibiotics. Like me. This was attempted some years ago to cure my intestinal complaint; lots of antibiotics followed by lots of probiotics followed by no improvement whatsoever. N = 1, however.

The other problem with probiotics is that they are not very well regulated. An interesting study published some years ago examined eight veterinary and five human probiotics.  Only two of these were accurately labelled. Five of the veterinary products did not specifically list their contents. Most products contained low concentrations of viable organisms (dead bacteria are no good to anyone). Five products did not contain one or more of the stated organisms, and three products contained additional species. Some products contained organisms with no reported probiotic effects; some of which could be pathogens (Weese 2002).

To sum up, there is no doubt that the bacteria in all our guts are vital for our survival. There appears to be some evidence that probiotics can have mild beneficial effects but the important thing is that the bacteria are species specific. So, unless you’re prepared to drink a faecal shake from a healthy friend of yours you are better off saving your money.

Dr. F. Bunny


Fuller, R. 1999. Probiotics for farm animals. In: Tannock, G.W. (ed.). Probiotics: A Critical Review. Horizon Scientific Press, Wymondham, Norfolk, U.K. Pp. 15-22.

Holz, P.H., and D.R. Middleton. 2002. The effect of probiotic feeding on Salmonella excretion in carpet pythons (Morelia spilota). Journal of Herpetological Medicine and Surgery 12: (3) 5-7.

Osawa, R., W. H. Blanshard, and P.G. O’Callaghan. 1993. Microbiological studies of the intestinal microflora of the koala, Phascolarctos cinereus. II. Pap, a special maternal faeces consumed by juvenile koalas. Australian Journal of Zoology 41: (6) 611-620.

Tannock, G.W. 1999. A fresh look at the intestinal microflora. In: Tannock, G.W. (ed.). Probiotics: A Critical Review. Horizon Scientific Press, Wymondham, Norfolk, U.K. Pp. 5-14.

Weese, J.S. 2002. Microbiologic evaluation of commercial probiotics. Journal of the American Veterinary Medical Association 220: (6) 794-797.


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