Melissa Kaplan's
Herp Care Collection
Last updated January 1, 2014

Pros and Cons of Long-Term Probiotic Use in Green Iguanas

The following is a summary of discussions that took place on the Iguanas Mailing list in February/March 1999

Compiled by Melissa Kaplan


Melissa Kaplan, in response to an IMLer who promotes the use of Nutribac as a "cure" for iguanid Salmonella, 2/21/99
I read through the literature the developer/seller of Nutribac sent me some time back when he first started pushing it on RPH. At that time I talked to several researchers, vets and biologists who all agreed that his product was highly questionable due to hundreds, if not thousands (now that Arizona spp. is included with Salmonella) of serotypes of Salmonella found naturally in all reptiles, including health ones. (For more information, please see my article on Human Health Concerns as well the Salmonella articles at the Zoonoses page.)

This is aside from the issue of: is it even safe to try to eliminate organisms that are naturally found and probably serve an important function in an animal's gut? Salmonella is now found in so many healthy reptiles - iguanas, other lizards, snakes and chelonians - that biologists and vets now believe them to be saprophytic if not commensal and thus normal, not a sign of illness or abnormal pathophysiology. In other words, trying to eradicate or quash Salmonella in an iguana is similar (and I am quoting Dr. Jon Mirmen of the CDC) like trying to do the same with normal levels of E. coli in healthy humans: not a smart thing to do.


For most people, washing hands and never kissing the iguana will work fine to prevent the caretaker from getting salmonella. In other words, for many people, having an animal *with* salmonella and trying to be as clean as possible when handling is a fine solution.

I couldn't agree more. My objection is to a magazine editor and product manufacturer pushing a product of questionable value and misleading consumers who don't have access to biologists, vets and other researchers to ask about it.


But for other people, like a pregnant woman, or others who have children in the house, or for people like me who travel overseas with their iguana, using probiotics as an extra added measure to pretty much eliminate salmonella is the way to go. I would not say using antibiotics is a good way to go though.

Do the countries that require iguanas to be 'certified' Salmonella-free have the same requirements for all other pet reptiles crossing their borders? If not, then it would appear that they are responding to the media hype about Salmonella and iguanas, ignoring the fact that the majority of reptiles have communicable Salmonella, as well as Giardia and Coccidia.

Did your iguana test positive for Salmonella before being treated with Nutribac? How many retests are done each year to maintain the "free of Salmonella" status?


I encourage people to read the article, see the websites, and make intelligent decisions for themselves.

Agreed. However, the article and Nutribac's website won't tell them what Dr. Mirmen said or the other people I talked to why is there a problem with my saying what I have to say on the subject...? :)


The salmonella issue aside, it can only help an iguana's health to have a good dose of healthy microflora in their intestinal system without using yogurt, i.e. a decent dose of animal protein.

Is there research that documents the need for additional flora in an otherwise healthy iguana's gut? Research that documents that eradicating a normal commensal or saprophytic gut constituent in an otherwise healthy animal is in fact healthy in the long run for that animal?

One nice thing about using lactobacillus, such as is easily obtained in yogurt, or acidophilus in a free-standing product, is that it is required in *very* small amounts for a very short period of time - following a period on antibiotics when healthy gut organisms are destroyed along with the infectious ones, or following a period of starvation. Since neither of these conditions are long term nor do owners seek to prolong them, there is no need for long term or even regular bacillus administration.

This seems to be different than the ongoing administration of the type of probiotic you are using, including Nutribac. Based on the premise of Nutribac and similar probiotic, it has to be constantly re-administered or else the organisms the products are trying to crowd out will multiply to normal levels again. This is very different than the reasons why small, short-term use of acidophilus is recommended. The latter is to re-seed the gut after a major gut constituent die-off, giving the native flora a chance to make a come-back and do their job of digesting food; the former is an ongoing program of suppression, if not an actual attempt at eradication.


Using a microscope, I have seen ***with my own eyes*** that the amount of undigested plant fibers decreases dramatically in an iguana's poop after being fed NutriBAC. The poop looks fine either way to the naked eye, but there is a big difference under the microscope.

The reason large herbivores have survived to exploit the niche they do is because they have developed digestive systems that can take in huge amounts of relatively low-nutrient, high-fiber material, extract what they need to grow, maintain and reproduce, and efficiently get rid of the unused portions along with their systemic waste products. One EXPECTS to find, and indeed it is desirable to find, undigested plant fibers. Most plant fibers are in fact indigestible - that's why we humans are encouraged to add insoluble as well as soluble fiber to our diets (at least because here in the 'civilized' West (US), we don't get enough in our typically fast food, highly processed, high fat diet. Perhaps the biologists and zoologists on this list can tell us if there have been any comparisons or data on the amount of undigested plant fibers in other large herbivores, such as cows, giraffes, gorillas, horses, tortoises, etc.

Since your igs are healthy, I would expect them to have lots of undigested plant matter in their feces...I would be worried if it was in pieces large enough to indicate that the gut wasn't breaking them down properly, but I know that isn't an issue given the way you care for them...and not because you are giving them the probiotic.


I have used this product for quite some time on my remarkably long-lived 9 year old green anole and also my iguanas with good results.

But is it really doing anything? I guess that's the bottom line question. I could eat (gag) a tablespoon of wheat germ every day for 40 years. Given an otherwise healthy diet and lifestyle, would that wheat germ be doing anything for me? No. Even though it is recommended as a good fiber. In fact, the medical research community recently come out to say that fiber intake does NOT affect one's likelihood of developing colon cancer... So, who knows? Someone with money to burn on a research project, or a vet seeing unusual digestive problems in a variety of reptiles, may someday find that probiotics administered on a routine long-term, rather than on a short-term medically-necessary basis, is causing problems not foreseen by those who saw no adverse effects killing off naturally occurring, harmless (to the host) microorganisms...

Until then, my open mind is asking whether there was indeed harmful levels of Salmonella found when your igs were tested, and will continue to question the long-term use of something designed to kill or crowd out organisms when we aren't sure what long-term beneficial role they may perform for their reptile host. Commensal and saprophytic organisms are nothing to mess around with, not without long-term multigenerational testing being done first. And Midwest Zoological only tested Nutribac for one year...


Alta Brewer, responding to a post, 2/22/99

Poster #1: Panacur (fenbendazole) is effective in the treatment of most nematodes (hepatic worms, lungworms, hookworms, roundworms, strongyloids, and pentastomids), not against bacteria - which is what Salmonella is... So being treated with fenbendazole is unlikely to affect existing Salmonella.

Poster #2: So then I can assume that Dax was salmonella free before the Panacur? Since Dax to the best of my knowledge has not come in contact with any thing that was infected with salmonella he should still be free from salmonella.

No. You cannot assume that. In fact, you should assume that Dax has salmonella.

The test for salmonella produces lots of false negatives, meaning that the test can say the ig does not have salmonella when the ig in fact does have it. That's why testing for salmonella isn't that helpful. You can believe a positive result, but not a negative one.

Igs don't have to "get" salmonella from anywhere. They come with it. All animals have bacterial colonies of some sort. Humans have beneficial bacteria in their bodies too. There are germs all around us and in us. That's just the way life is.

There are something like 2,000 strains of salmonella. The strains of salmonella typically found in igs (mainly the marina serotype if memory serves) are not usually found elsewhere in American homes, so you can assume the salmonella strain came from the ig rather than the environment. IOW, the ig didn't catch the salmonella in the home.

If I were you, I wouldn't let Dax free-roam where your two-year-old niece plays when she's at your home. I would also make sure she washed her hands well after touching the ig. It is much safer to assume the ig has salmonella and act accordingly than to depend on a potentially inaccurate test and take a chance.


Pam Hanratty, 2/22/99
In chickens, at least, eggs are now becoming contaminated with Salmonella *before* the shells are formed. The ovaries of the female can become infected with salmonella, and thus the bacterium is able to enter the egg *before* the shell is formed. Thus the embryo which develops is already infected.

Due to the size of the pores present in reptile eggs, it is also possible that Salmonella might enter through pores in the egg...once again transmitted from the infected mother (or possibly from infected male to uninfected female during mating, then on to the embryo).

Check out the CDC website for more info on this situation in chickens.

Adam Britton, 2/22/99

Poster #2: Well, salmonella, as Melissa Kaplan pointed out *may* be a natural inhabitant of iguana intestines.

Various salmonella serotypes are found in the great majority of reptile guts. Crocodiles also have them - wild or captive - and they exist naturally at low levels much like E. coli in human guts. Attempts at eliminating them entirely seem highly inadvisable, and without any real research (published, that is) to suggest the benefits / detriments of doing this I wouldn't start throwing the stuff at every iguana I saw. It is possible that iguanas where salmonella bacteria become more prevalent - e.g. immunocompromised individuals - then Nutribac may be useful in reducing their numbers back to normal levels and re-establishing correct levels of gut flora, and the right environment for that flora. (I don't know why we call them "flora" as bacteria are not in the plant kingdom!). If Nutribac is aimed at such a goal, it might have merit. If it's aimed at eliminating salmonella in your iguana, treat with long pointy stick.


Anne Marsden, 2/23/99
Salmonella is just a bacterium. It lives with a lot of its hosts as a commensal. It can't be said to be 'infecting' the host, any more than the 1,000,000,000,000,000 bacteria humans have in their feces per milliliter (a couple of fingernails full) can be said to be infecting humans. They are just there, and they live their lives, we live ours, and nobody gets hurt. The problems occur when the harmless organism in our pet is pathogenic (disease causing) to us. This has happened dozens of times in human history. For instance, it's very likely that no human would ever have suffered influenza if they had not domesticated pigs, who don't really get bad 'flu but certainly amp it up and pass it on to creatures who sleep in the same room. Iguanas are new pets, and their salmonella types are new scares.


Melissa Kaplan, 2/23/99

Poster #2: Now a question for the rest of the list, if I was to use a yogurt, is there a specific type that is better to use than another? What should I look for on label? Is there a supplement that should be provided with it? Should I only be using it after administering antibiotic?

There are many people who cannot tolerate many of the additives found in the most popular grocery store brands - aspartame and other artificial sweeteners, thickeners such as corn starch, etc. I can't tolerate any artificial sweeteners (which are found in both the sugar free AND fat free yogurts, for some reason!) nor anything with corn or wheat or corn or wheat byproducts. So I look for brands, and flavors within brands, that don't have these in them. Generally, these are found in the health food stores and are plain, as the corn starch is used to thicken the fruit juices used.

The presence of pectin (used for thickening) or beet juice (used for coloring) isn't a problem as both are derived from fruits and vegetables.

As for the bacillus content, those brands that meet the National Yogurt Association's criteria for live and active cultures are permitted to display a logo stating "LAC - live and active cultures." I have a couple of news items from the Univ. of Iowa archives that I can email anyone who's interested or you can find it online at FSNet June 1/98. You might want to use your browser's Edit>Find (or CTRL+F) function and search on the words National Yogurt Association so that you can skip all the other articles on this page.


Adam Britton, 2/26/99
The issue of probiotics is an important one, so we must be sure we're considering all the factors here. It is not a simple issue, which is why this discussion is not producing simple answers. Salmonella has, for example, many different strains or serotypes. Some can be considered to be "naturally occurring" in an iguana's gut, and others cannot. All will kill an iguana if their presence becomes too high, but the same can be said of the "naturally occurring" E. coli bacteria in human guts.

The fact is, we do not fully understand the issues surrounding Salmonella organisms. Why do iguanas have them in their guts and remain apparently healthy? What triggers these organisms to grow wildly out of control and kill the iguana? How resistant are iguanas to the different serotypes? What is the effect of completely eliminating these bacteria on the gut flora and on the iguana's health? Will it be beneficial, detrimental, or make no difference in the short or long term?

If you attend a conference of reptile vets and ask such questions of them, for example, you'll get a wide array of different answers and opinions. Some strong arguments one way or another are put forward, but nobody can provide a definitive answer at this point in time. Just because Nutribac claim a thing about their product does not mean we should all accept that claim either. That doesn't mean Nutribac is worthless. For all I know, it is brilliant and we should all be using it with our iguanas, but there is not enough conclusive evidence - as far as I'm concerned at least - to draw such a conclusion. If people believe it can work, then please try it - as long as you tell us the results in both the short and long term. Whenever we use any product, we must be aware of potential flaws in it. Some of the greatest drugs have later been found to have side-effects. If we think intelligently about these things, perhaps we can become better at predicting its pros and cons.

Poster #2: I really think that if there is even the slightest chance that Nutribac or any other vegan acidophilus preparation might reduce the salmonella load in an iguana, and thereby *keep that iguana his home,* then I say DO IT.

One must still be fully aware of the risks of salmonella in an iguana, even one in which Nutribac is administered. The reduction or even claimed elimination of salmonella in an iguana is not a 100% guarantee that salmonella contraction is not possible. Using Nutribac with the impression that it makes your iguana completely "safe" is, at best, unwise... as it would be with any medical product. Product claims are very rarely bombproof, even when reviewed by purely objective means, and products must be used within their functional limits - whether it's Nutribac, Baytril, the latest iguana salad or Belgian chocolate (ok, maybe not Belgian chocolate). 


Melissa Kaplan, 2/26/99
There are many important questions and ideas that have been raised in the Salmonella/Nutribac threads. There has also been a lot of mixing apples and oranges and zebras, and over-simplification, and avoidance of facts. Some of which that come immediately to mind are:

  • How were the pet iguanas tested, and how often, to determine that they were or were not Salmonella-free?
  • Were they diagnosed with Salmonella before being started on probiotics?
  • Why are people comfortable with the idea that because a probiotic product may reduce, but not eliminate, they are safe from Salmonella contamination?

Salmonella will live and reproduce at temperatures at and above 60F [1]. So, a single Salmonella cell, shed in feces or tracked across an enclosure or floor or missed when scrubbing the tub, can multiply into millions of cells within a day or so. Thus, even if you have suppressed the number of Salmonella cells in the digestive tract, it only takes one passing through to cause potentially serious problems. The Nutribac website says that tests were negative, but doesn't state what type of testing was done or the frequency of re-testing of the individuals. They tout the number of their organisms found lining the gut walls of some of their iguanas, but did they also analyze those same intestinal walls for any Salmonella? We don't know, because they do not say. They just say that, "Iguanas not fed the supplement still showed Salmonella residing in the intestine, colon, and cecum." Pardon my close-minded reaction, but du-uh.

We already know that repeated use of antibiotics will ultimately lead to antibiotic-resistant strains of bacteria. [2] We don't know if Salmonella or any other microbes affected by the routine administration of another (or several) species of bacteria will result in resistance to those species, nor whether the animal in whom all these microbes are battling for supremacy will fare while this is going on. To assume implanting an apparently benign organism is a benign act may be faulty logic.

Finally, the following is probably the most telling argument in this whole discussion. From the Nutribac website: "Midwest Zoological Research, Inc. makes no claims that the NutriBAC products can eliminate, control, or prevent Salmonella contamination, infection, or zoonosis." [3]

It is tragic when a zoonotic disease causes an incapacitating illness or death. But deluding ourselves that we are protecting ourselves when we are not just gives a false sense of security.

1. Outbreaks of Salmonella enteritidis Gastroenteritis -- California, 1993 MMWR October 22, 1993, 42(41);793-797

2. Reptile-Associated Salmonellosis -- Selected States, 1994-1995 CDC MMWR May 05, 1995 / 44(17);347-350 (Update: 1996-1998.)

3. "What research has proved the value of probiotics?" Midwest Zoological Research Inc.


From Steve Grenard (author of Medical Herpetology), 3/8/99:

A group of bactericidal factors conserved by vertebrates for more than 300 million years. M Kawakami et al. Journal of Immunology May, 1984. Vol 132, issue 5, pp 2578-2581

Abstract: A complement-dependent bactericidal factor (RaRF) specific for the Ra chemotype strains of Salmonella and for the Ra-like strains of other enterobacteria has been found in sera of mice. We show here that the anti-Ra bactericidal factors are present in sera of all species, so far tested, of mammals, birds, reptiles, amphibians, and bony and cartilaginous fish. Certain properties, such as binding specificity, requirement of divalent cations for binding, and sensitivities to heat and reducing agents, of the factor in the representative animals were the same as or similar to those of the mouse RaRF. These results indicate that these factors have been conserved by vertebrates for more than 300 million years as a result of the necessity for the resistance to rough mutants of Gram-negative bacteria.

These researchers discovered a bacteriocidal factor specific for Salmonella in mice, and then proceeded to find an genetically identical factor in birds, reptiles, amphibians and fish. Their conclusion: "These results indicate that these factors have been conserved by vertebrates for more than 300 million years as a result of the necessity for resistance to rough mutants of Gram-negative bacteria (e.g. Salmonella)."

Essentially also what this proves is that the Salmonella in an iguana born yesterday is, like the iguana itself, descended from Salmonella in an early reptile a few hundred million years ago. There is only one way this could've happened so totally and that is transmission to offspring by the mother. This occurs transovarially (through the egg) and has been proven time and again in chickens who have a much less porous egg than reptiles or by direct contact in live born offspring as they pass through the cloaca (now a birth canal in addition to a passage for excretion of feces, urine and, of course, for sexual intercourse. If anyone doubts this, ask them how Salmonella got in the shelled egg of the chicken which we are now all cautioned to cook well to prevent infecting ourselves. Can't get a genuine Caesar salad or steak tartar anywhere in New York for the past 20 years!

Baby iguanas and other herps also pick up Salmonella by eating fecal material or, in the case of some species, by bathing in fecal material to make them less palatable to predators including adults of their own species. This has been well documented in Komodo Dragons and is probably true of other species. Others slither around in their poop or soil their food. And of course some acquire the disease anew with the food that they eat as Salmonella is ubiquitous in nature and mice and insects are important carriers. But even if captive born and prevented from engaging in such habits, baby herps continue to test + for Salmonella and there is only one way left which could cause this, transmission from mom to offspring.

Reptile nutrition researcher Susan Donoghue VMD wrote, in her November 2000 HerpNutrition newsletter:

To do a rigorous review requires examination of each specific probiotic (there are many different types), dosages, host species, etc. A question was raised about over-the-counter probiotics marketed specifically for reptiles. These have been marketed as a preventives or adjunctive therapies against salmonella. The genesis for this idea is found in research in chickens. To my knowledge, supporting data have never been published for reptiles.

The thinking has been that probiotics in reptiles, especially hatchling green iguanas coming into the country, could eliminate salmonella from their GI tracts. I don't know of data showing that this has been tried in reptiles.

I'd like to see a study on salmonella and green iguanas that first looked at a variety of potential therapies (rather than marketing a blend of probiotics with no corroborating data and no assurances about quality control of the products). Here's an example of a well-designed study: Letellier A et al. Assessment of various treatments to reduce carriage of Salmonella in swine. Canadian J Veterinary Research, 2000; 64:27-31. These investigators (Universite de Montreal, Quebec) looked at probiotics, prebiotics, vaccination and acidification of drinking water. Prebiotics looked to be most promising.

In 2001, Mark Mitchell DVM, in conjunction with several other vets, reported the findings of two studies that they did in the use of enrofloxacin to eradicate Salmonella in green iguanas under controlled conditions, and on the use of a commercial poultry antivirus vaccine used in poultry/Salmonella research on the preventing the recolonization of Salmonella in the same iguanas.

The vaccine was found to be ineffective in preventing the types of Salmonella serotypes found in iguanas but not in poultry.

While the antibiotic enrofoxacin (Baytril) was effective in eliminating the Salmonella in the iguanas kept under controlled Salmonella-free conditons and fed a Salmonella-free food, having once been treated with the antibiotic was no protection against further colonization once the iguanas are again exposed to Salmonella.

Mitchell, M.A.. et al. Effect of an avirulent Salmonella vaccine on Salmonella colonization of hatchling green iguanas, Iguana iguana. Proceedings of the Association of Reptilian and Amphibian Veterinarians (September 19-23, 2001. Orlando FL), pp 187-188.

Mitchell, M.A., et al. Establishing a Salmonella-free iguana, Iguana iguana, model using enrofloxacin. Proceedings of the Association of Reptilian and Amphibian Veterinarians (September 19-23, 2001. Orlando FL), pp 189-190.

Related Articles

Live, Active and Probiotic: Yogurt Culture

Probiotics abstracts

Need to update a veterinary or herp society/rescue listing?

Can't find a vet on my site? Check out these other sites.

Amphibians Conservation Health Lizards Resources
Behavior Crocodilians Herpetology Parent/Teacher Snakes
Captivity Education Humor Pet Trade Societies/Rescues
Chelonians Food/Feeding Invertebrates Plants Using Internet
Clean/Disinfect Green Iguanas & Cyclura Kids Prey Veterinarians
Home About Melissa Kaplan CND Lyme Disease Zoonoses
Help Support This Site   Emergency Preparedness

Brought to you thanks to the good folks at Veterinary Information Network, Inc.

© 1994-2014 Melissa Kaplan or as otherwise noted by other authors of articles on this site