Jessica Snyder Sachs, Science Writer

Health magazine recently asked me to take an in-depth look at the increasing number of products being sold with a "probiotic" claim. As readers of Good Germs, Bad Germs know, the benefits of probiotics, or beneficial bacteria, are highly strain specific. That is, the so-called "good" bacteria in cultured foods and supplements vary widely in their effects--even between two strains, or "subspecies," of a given bug such as the familiar Lactobacillus acidophilus.

Research into several dozen products and probiotic strains produced a "best bets" list of those backed by bona fide science including clinical trials showing tangible benefits in people (not just lab animals). 

The story and a chart of products and their known benefits are in this month's issue. 

You may have seen or heard the recent headlines, along the lines of "Women's Hands 'Germier' than Men's." The report behind the rather misleading news flash is more interesting.

University of Colorado professor Noah Fierer studies the ecology of bacteria, fungi, and related microbes in natural systems such as soil, water, and the atmosphere. Turning his survey techniques to the human body, he looked at the diversity of bacteria on the hands of 51 students--all healthy except for the interesting twist that they'd all just finished their final exams. (Sweatier palms than usual, perhaps?)

Fierer and his colleagues used a gene-sequencing technique to count the number of different types of bacteria on each subject's hands. They tallied an impressive 4,742 types.

The quirky news headlines jumped out of the unexpected finding that the hands of female students harbored a greater diversity (but not necessarily more germs, per se) than did the guys'. 

Just as interesting, perhaps, was the finding that while everyone seemed to share a core group of common skin bacteria, these common species made up just 13 percent of the total diversity. In fact, over 80 percent of the microbial species found on a person's left hand were different from those found on the right.

All this seems to suggest that most of the bacteria on our hands are fleeting transients. We pick them up as we touch objects, surfaces, and other body parts.

That said, the researchers found that hand washing--while a good idea when you're around others who might be ill--did little to change the diversity of the a palm's rainforest-rich ecosystem.

Hre's the study, in the Proceedings of the National Academy of Sciences, with more interesting stuff at Fierer's website at the University of Colorado.

The care of the critically ill is full of Catch-22s. Mechanical ventilators deliver life-saving oxygen to failing lungs. But the same intubation introduces bacteria to cause ventilator-associate pneumonia. Worse, in a hospital setting, those bacteria often include some of the world's nastiest, drug-resistant pathogens. In an effort to beat back this threat, nurses wash out patients' mouths with the potent antiseptic chlorhexidine. But that, in turn, tends to ipe out all the patient's mouth bacteria--both good and bad--opening up territory for more drug-resistant hospital bugs to move in. Even scarier hospital, strains of methicillin resistant Staphylococcus aureus (MRSA) are proving increasing resistant to this disinfectant

Now, in the spirit of "if you can't beat 'em ...," doctors at Sweden's Lund University Hospital are deliberately inoculating their patients with "good germs." Specifically, anesthesiologist Bengt Klarin and colleagues are swabbing the mouths of critically ill, intubated patients with a well-studied strain of Lactobacillus plantarum--a normal resident of healthy mouths and the active ingredient in sauerkraut and many other fermented foods.

The probiotic bacteria prevented infection as well as did standard disinfection with chlorhexidine. Using L. plantarum also avoided such common chlorhexidine side effects as mouth irritation and potentially deadly allergic reactions the researchers report.

Here's the full report, in last month's issue of Critical Care. 

Dubbed AAD, for antibiotic-associated diarrhea, the problem results when antibiotics raze the normal complement of digestive bacteria that live in our intestines. These bacteria not only help us digest our food, they actively protect us from would-be invaders such as the bugs that cause food-poisoning (salmonella, shigella, campylobacter, et al) and colitis (Clostridium difficile, Klebsiella oxytoca, and kin). They also play less-understood roles in regulating immunity and other aspects of our physiology (including fat storage).

(Salmonella on otherwise-barren gut epithelial cells, courtesy the NIH.)

To get an ecological picture of the disruption, researchers at California's Stanford University and Cape Cod's Marine Biological Laboratory used a bacterial-DNA tagging technique to take a before- and after-antibiotic gut census, with the help of three volunteers on a five-day course of Cipro (ciprofloxacin). One of today's most widely used antibiotics, Cipro is considered relatively benign in its gut effects.

Still, by the end of the five days, the Cipro had produced wholesale changes in the abundance of about a third of the approximately 4,000 types of bacteria that had established a stable ecosystem in these three human guts.

None of the three volunteers reported any digestive problems through the brief trial--a finding the researchers took as confirmation of the general redundancy in our gut microflora. i.e. When some species get razed, others can generally pick up the slack. Moreover, the volunteers' gut "ecosystems" had more or less returned to normal by the four-week mark, though a few obscure species never reappeared or remained at abnormally low levels.

These exceptions may suggest that we need to know more about the lasting effects of antibiotics on our intestinal milieu. For example, the researchers note that increased risk of kidney stones results when the gut loses its complement of oxalate-degrading bacteria. The best known of these is Oxalobacter formigenes--a bug that's abundant in children, but which tends to disappear by adulthood (at least in the developed world). The disappearance has generally been attributed to O. formigenes' susceptibility to many commonly used antibiotics.