Let Them Eat Dirt. B. Brett Finlay

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СКАЧАТЬ needed to fully understand all of this, it’s becoming evident that complex interactions between microbes, the immune system, and other aspects of human metabolism, occurring as early as in utero (before birth), influence the risk of disease later in life.

Getting Smart About Antibiotics

      In light of all these findings it is crucial to understand that using antibiotics should not be discouraged when they’re really needed, but the overuse or abuse of antibiotics should be prevented. So, when are antibiotics necessary during pregnancy? The answer is simple: antibiotics should be taken for serious bacterial infections, and only bacterial infections. However, this can be hard to put into practice, especially during pregnancy, when doctors want to prevent any possible complications that may arise from an infection. Because of this, many health providers are too quick to prescribe antibiotics, as a safety precaution, to expectant mothers for ailments that don’t require antibiotics, like the flu. The flu is a viral disease that causes symptoms that many people confuse for a bacterial respiratory infection. Its onset is very sudden and people feel awful for about a week, until they start getting better. It’s not hard to imagine a pregnant woman showing up at a doctor’s office almost begging to get a prescription that will make her feel a little bit better. However, antibiotics should not be used for the flu, regardless of how bad a patient feels.

      There are exceptions to this, though; the flu can lead to secondary bacterial infections that do require antibiotic treatment. This usually manifests a little bit differently: you feel truly awful, and after a week or so, you start to get better, but then you start feeling worse, with coughing and chest congestion, which can lead to pneumonia. This is the classic example of a secondary bacterial infection following the flu, which should be treated with antibiotics.

      However, the key concept here is to prevent infections from occurring in the first place if possible. As such, it is currently recommended that pregnant women get a flu shot. Fortunately we have an effective vaccine that is completely safe to use during pregnancy, which significantly decreases the chances of getting the flu and a secondary respiratory bacterial infection during flu season.

      Despite the precautions you can take, infections do happen during pregnancy and antibiotics are prescribed. So what then? Based on the current research, it seems that the period at which antibiotics are taken is important, with microbial changes in the later stages of pregnancy being the most influential. If antibiotics must be used in the second and especially the third trimester, one should start or continue microbial supplementation with probiotics and a diet rich in fiber and vegetables. It’s important to choose a probiotic that contains several species of Lactobacillus and Bifidobacterium, both known to be important early members of an infant’s microbiota. As with any supplement or medication taken during pregnancy, we recommend discussing this with your health care provider.

Heading Off Group B Strep

      During the births of her first two children, Neve had been given antibiotics, an increasingly common occurrence nowadays, with 1 in 3 women receiving antibiotics during labor. Neve knew how frequent antibiotic use is during delivery because she had tested positive for a type of bacteria known as Group B streptococcus, or GBS for her first two births. (Other very common circumstances that require antibiotics during labor are scheduled C-sections, which will be discussed extensively in chapter 4.) In many countries, all women between 35–37 weeks of gestation get tested for GBS. These bacteria commonly reside in 15–40 percent of all pregnant women, yet they rarely cause any symptoms. However, between 40–70 percent of GBS-positive women will pass it on to their babies during natural birth, and a small but very significant number of babies (1–2 percent) will develop a GBS infection (for further discussion of GBS infections, see chapter 4). Fortunately, if a pregnant woman who tests positive for GBS is treated with antibiotics during labor, the risk of her baby developing a GBS infection is reduced by 80 percent, making GBS prevention a pertinent use of antibiotics.

      However, recent studies have shown that receiving antibiotics during labor alters the microbiota of the newborn, even if they are administered only an hour before birth. Reading about these studies made Neve, pregnant with her third child, feel uneasy. She knew that GBS could potentially be very serious and she understood the need for antibiotics during labor, but she wondered if anything could be done to prevent testing positive for GBS. Her second child has asthma and although it’s impossible to know whether his exposure to antibiotics during birth is to blame, she’s left wondering if it contributed. More importantly, Neve wanted to do whatever she could to decrease the risk of her new baby developing asthma, too. She hoped to help by testing negative for GBS, but how could she do something about that?

      It turned out that she might actually have some say in the matter. GBS are bacteria that will expand in numbers only if they’re given the chance. Normally other members of the microbiota keep them in check, usually our bacteria superstars, the Lactobacilli in the gut and the vagina. In fact, if you grow Lactobacilli and GBS together in the lab, the Lactobacilli make it very hard for GBS to multiply; they beat them easily. Furthermore, a small number of studies suggest that applying probiotics directly to the vagina increases Lactobacilli and decreases the number of GBS. This finding was shown in healthy nonpregnant women and remains to be supported in bigger studies, but given how safe it is to administer probiotics to pregnant women, Neve was open to trying this approach and her midwife supported this prophylactic treatment.

      Neve ended up testing negative for GBS at her 36-week visit, and she is expecting to have an antibiotic-free birth very soon. However, it’s important to mention that it remains to be proven in a randomized clinical trial that the prophylactic use of vaginal probiotics prevents or reduces the chance of a GBS-positive test during pregnancy. The use of vaginal probiotic suppositories, as with any treatments during pregnancy, should always be discussed with a health practitioner.

Can Bacteria Influence Us Before Birth?

      So far we have discussed different ways to take care of the maternal microbiota during pregnancy in order to prepare the best kind of microbes that a mother can give to her baby at birth. This is when babies get soaked in microbes, during their trip down the vaginal canal. But very recent research shows that microbes may pay a visit to babies even before birth. For many years it has been widely accepted that humans are germ-free immediately before birth and that the presence of bacteria in utero is considered infectious and dangerous. Often this is true—bacteria growing in the placenta or the amniotic fluid can be a sign of infection and a cause of premature birth or even stillbirth. But what we’re just now beginning to learn is that there may be very low numbers of bacteria that commonly reach the baby in the uterus without causing any harm. We still don’t know how they get there and, more importantly, what they do, but in two separate studies bacteria were detected in the amniotic fluid and placentas of healthy babies. Although some scientists (including us) remain skeptical about these findings, the authors of these studies speculate that these bacteria are involved in immune stimulation of the fetus. Additional studies are needed before we can explain why this occurs, or if it even does.

      Another more likely exposure to microbes before birth may occur in the form of bacterial metabolites, which are very small substances produced by the enormous amount of bacteria in our guts. Bacterial metabolites are known to travel in the bloodstream at all times, and are involved in biochemical reactions in just about every human organ, influencing many aspects of our metabolism. Thus, even if very few bacteria actually reach the fetus during pregnancy, the metabolites may reach the growing baby through the bloodstream and potentially affect fetal growth and development. Much-awaited studies are under way to explore the impact these microbes might have in human development before birth.

      Dos and Don’ts

      ♦Do— eat for your microbes, not just your cravings. Make vegetables, fruits, and fiber staples of your diet, along with the СКАЧАТЬ