Microbes, Exposed

In this modern world of antimicrobial cleansers and irradiated foods, people have developed this phobia toward microbes. Most don’t even think twice about downing antibiotics either as suggested by the doctor or injected unknowingly into our food supply. But the truth is, we all live in an incredibly bio-dense world where our bodies–our cells–are constantly in flux, communicating, co-mingling, occasionally battling with other microorganisms. Despite what product propaganda might have you think, becoming a voluntary bubbleboy isn’t all what it’s cracked up to be.

Think of taking oral antibiotics as leveling an atomic bomb on the residents of your digestive tract. It’s going to kill off everything–from the nasty bug giving you diarrhea to the other microbes who were just hanging out, maybe making your daily dose of vitamin K on the side. The problem is, we don’t know very much about how microbes are beneficial to us. To say the least, a microbe making vitamin K isn’t going to elicit much of a side effect compared to Salmonella you might get from undercooked meat. So people reason that if we use the antibiotic to kill off everything, we’ll get rid of the bad stuff and if the good stuff is gone too, well that’s too bad but we’ll manage somehow.

But eliminating everything isn’t all right. Like a nuclear blast, that antibiotic you’ve swallowed has unintended consequences. In various studies using the mouse as a model, the gut microflora is responsible for many aspects of our well-being–nutrition, digestion, immunotolerance, defense, prevention of immune system atrophy from lack of challenge. A recent paper from the Proceedings of the National Academy of Sciences gives us another angle to look at host-microbe interaction by using another model besides the mouse, zebrafish.

Specifically, Rawls et al. used young zebrafish which are transparent until adulthood. Normally zebrafish, like any other organism with a gut, acquire microflora soon after birth. In this study, some zebrafish were raised as germ-free (GF). (To prevent any microbes from getting into the fish in the first place, the parents were killed and the eggs were fertilized in a sterile environment. The rest of these fish’s lives were spent in a sterile beaker.) When the morphology of GF zebrafish were compared to conventional zebrafish, there was a striking difference. GF zebrafish, like GF mice in prior studies, had distinct abnormalities in the intestine. The frequency of shedding cells in the intestine which normally is quite often in the conventional zebrafish was reduced in the GF animal.

Using microarray technology, the researchers were also able to monitor the expression levels of many genes in the gut. Although there is the caveat that gene expression changes throughout fish development, some of the genes observed in the GF zebrafish had similar expression patterns as that of GF mice. Also, when GF zebrafish were infected with a single microbial strain, Rawls et al. were able to detect a specific host response in gene expression levels to the bacteria.

What is intriguing here is that the data gathered from zebrafish corroborate previous studies done in mice. Although fish and mammals are evolutionarily divergent, host-microbe interactions appear to be conserved on some level. This is very cool news. Zebrafish may turn out to be a relevant model to study how the microflora interacts with us. It may even be a more easier model in some respects. Not only are they’re cheaper than mice but they are also transparent–providing a window to an aspect of microbe life that’s still very murky.