Circumcision shuffles the penis ecosystem

In adults, the snip alters more than the shape.

by Jeffrey Perkel


“Isaac’s Circumcision”, from the Regensburg Pentateuch, c. 1300 (Wikipedia)

Can we talk about penises for a moment? It’s not what you think — well, maybe it is, actually.

Lately it seems I’ve become the go-to guy on microbiomes here at Double X Science, writing, in just the past few weeks, about both the vaginal ecosystem and the oral microbiome. So I suppose it was only fitting that when the opportunity arose to write about the microbiome of yet another body part, I took it. And it was about penises, which also seemed … appropriate.

In this case, the story’s about circumcision and microbes. Microbes are essential cohabitants of all our bodies. Yes, they can cause infection. But “good bacteria” help us digest food and absorb nutrients. They modulate our metabolism. And they influence genital health. Naturally, researchers want to understand the symbiotic relationship we have with these communities, and they’ve launched some large-scale efforts to work that out.

In the mid-2000s, researchers in Baltimore and Uganda initiated a large prospective clinical trial in that African nation to determine whether adult male circumcision would reduce the risk of HIV transmission. It did, cutting the HIV transmission rate more or less in half, from 1.33 cases per 100 person-years to 0.66.

In the course of conducting that trial, the study physicians collected penile swabs both before and one year after circumcision. Now, as described in a new paper in the journal mBio, a team led by researchers at the Translational Genomics Research Institute in Arizona and at Johns Hopkins University has analyzed the microbial content of some of those swabs to look for any changes in the microbial load.

Why would they want to know that? One reason is that male circumcision is associated with a lower incidence of sexually transmitted disease in both men and women. In part, this distinction could stem from an anatomic difference: “[Male circumcision] removes the prepuce (Ed. note: a.k.a., the foreskin), which decreases the number of available HIV target cells on the penis,” the authors write. But there could also be an inflammatory component, the authors suggest, in which microbial antigens “elicit local immune responses that promote epithelial inflammation and recruitment of HIV target cells.” In that case, it’s a good idea to know what bacteria are normally there, and what they do. And let’s not forget, a man’s sexual partner is exposed to the same microbes: When you put the P in the V, you also get whatever bacteria come along for the ride (condoms, people!).

Long story short, the researchers did indeed find differences in penile microbiomes before and after circumcision, and we’ll get to that in a mo’. But first, I must detail for you how the sample collection was done:

“At each visit, clinicians collected penile swabs from the coronal sulcus as follows. Sterile cotton-tipped applicators … were premoistened with sterile saline and rolled over the coronal sulcus twice in a nontraumatic fashion.”

Two things here. First: nontraumatic. I’m not sure how rolling a Q-tip over one’s penis could be anything else, but I assume that if it were, enrollment would surely have dropped off.

Second: coronal sulcus. Allow me to state here that I, a member of that 50% (or so) of our species currently in possession of a penis, had no idea what this term referenced. My trusty copy of Gray’s Anatomy was no help. Like an idiot, I performed a Google search.

People, learn from my mistake: Never, ever perform a search for the term “coronal sulcus” without activating Google Safe Search first. (My wife, behind me: “Whoa!”)

Let the record show that I still don’t know precisely to what this term refers [Ed. note: It’s the area just under that little ridge at the base of the glans, or “head”; the area under an intact foreskin that demarcates the head and the shaft). But I will punt and allow the American Society for Microbiology press release accompanying this study to help me out. “Researchers studied the effects of adult male circumcision on the types of bacteria that live under the foreskin [emphasis mine] before and after circumcision…” That should clear things up, more or less.

So, back to the paper. The authors catalogued the type and abundance of bacteria in each sample, or the, uh, junk in your junk, as it were. Their methods included sequencing 16S ribosomal RNA genes, which help identify bacterial strains.

The study population consisted of 156 men aged 15–49, split evenly into two groups. Most of the men were married and largely monogamous, and few (30%–40%) used condoms routinely. Both groups were to be circumcised, but one group (the intervention arm) was circumcised immediately; the other (control) arm was circumcised two years later (but tested while still uncircumcised).

At the start of the trial, that is, before half of the participants were circumcised, the microbial content of both populations was more or less the same. A bunch of Prevotella, a smattering of Clostridiales and Corynebacteria, all bacterial species.

After circumcision of participants in the intervention arm, the bacterial load decreased. But here’s where things get weird: Bacterial abundance dropped in both study groups — that is, in both men who were circumcised and men who were not (or at least, not yet). At the start of the trial, the authors measured 150,000 bacteria (16S ribosomal RNA copies) per swab in the control arm and 200,000 bacteria in the interventional arm. A year later, they found 57,000 copies on the uncircumcised men, compared to 38,000 on the circumcised ones. That difference, they say, is significant (albeit with a value of 0.048 — right on the line, statistically speaking).

The authors don’t address the fact that both the interventional and control arms saw drops in microbial counts, except to say there were no significant behavioral changes noted over the course of the study.

“Changes in penile microbiota and STI [sexually transmitted infection] incidence after MC [male circumcision] may be attributable not only to the anatomic alteration itself but also to behavioral changes in circumcised men or men enrolled in a clinical trial in general,” the authors note. “However, analysis of the Rakai data showed that MC did not significantly alter behavior during the trial.”

In any event, not only did the absolute number of bacteria drop in circumcised men, so too did the kinds of bacteria – a reduction in microbial biodiversity. In particular, circumcised penises had fewer so-called anaerobic bacteria, or bacteria that grow in the absence of oxygen. Of 15 species that decreased in abundance, 12 were anaerobic.

Seven species increased in abundance, including Staphylococcus, though five of these also increased in uncircumcised controls. The two species that increased only in circumcised males (Kocuria and Facklamia) are both aerobic, that is, bacteria that live in oxygenated environments.

“From an ecological perspective, it’s like rolling back a rock and seeing the ecosystem change,” says corresponding author Lance Price in a press release. “You remove the foreskin and you’re increasing the amount of oxygen, decreasing the moisture – we’re changing the ecosystem.”

That change, the authors note, includes some bacterial species associated in women with bacterial vaginosis (other associated species were unchanged), and could potentially include species associated with inflammation, and thus, with viral sexually transmitted infection (STI) transfer. As Price is quoted as saying in the ASM press release:

“From a public health perspective the findings are really interesting because some of these organisms that are decreasing could cause inflammation. We’re used to thinking about how disrupting the gut microbiome can make someone more susceptible to an infection. Now we think maybe this disturbance [in the penile microbiome] could be a good thing – could have a positive effect.”

That’s all good news, seemingly. But before you click on that circumcision Groupon for Father’s Day, remember that more work is needed. Yes, circumcision reduces transmission of STIs. But there are a lot of microbes on the penis, and their normal roles in human health are not yet understood.

“Currently, we know little about the role of these fastidious anaerobes in the male urogenital tract or the broader context of human health,” the authors conclude. “Future studies are required to determine if a decreased anaerobic bacterial load modifies foreskin inflammation and HIV target cell recruitment/susceptibility, which may play a role in HIV risk reduction conferred by [male circumcision].”

Also, this study dealt only with men circumcised as adults. What, if anything, it says about circumcising children is … not much.

Take home? Don’t use this paper as justification for or against circumcising yourself, your partner, or your child. If you have questions about circumcision, by all means consult your physician. In the meantime, use a condom.

PS: At least one other study has looked into the penile microbiome. A team led by researchers in Indiana studied the microbiomes of 18 men aged 14-17 over a period of three months. You can read their results here.

This entry was posted in Biology, Everything else and tagged , , , , by Jeffrey Perkel. Bookmark the permalink.
Jeffrey Perkel

About Jeffrey Perkel

Jeff is the DXS tech editor and a recovering scientist who has always had a passion for the technology and the gadgetry of science. He has been a scientific writer and editor since 2000, when he left academia to join the staff of The Scientist magazine as a Senior Editor for Technology. Before that, he studied transcription factor biology at the University of Pennsylvania and Harvard Medical School -- training that, surprisingly, has little application in the real world. In 2006, he and his family headed west to Pocatello, Idaho, and has been a freelance writer ever since. You can see why Double X Science is thrilled to have him on the team!