Medical Fun Facts Podcast

MFF0027: Lactobacillus

Before I get to my chosen L-word, I’d like to wish everyone happy new year. Today’s show is dropping on Monday 2 January 2017.

One of the most relaxing things I can do is sit down behind a microscope and look at a rack or two of Gram’s stains. I find reading Gram’s stains from female genital swab specimens really satisfying. As much as I love to see pathogenic bacteria and parasites, I really like looking at the normal flora in such specimens. My favourite non-pathogenic genital bacteria are lactobacilli. I find lactobacilli such pretty bacteria to look at. They are so neat and uniform in appearance. They take up the crystal violet really well and resist decolourisation almost completely.

Species in the genus Lactobacillus are Gram-positive bacilli and prefer an environment relatively low in oxygen like the vagina or deep protected crevices in the mouth. Lactobacilli don’t form spores and they convert sugars to lactic acid.

Clinically, lactobacilli are important because the hydrogen peroxide they elaborate inhibit the growth of Candida species. Candidiasis which is also known as thrush, produces a nasty thick cheesy discharge which in severe cases can look like cottage cheese. I remember the very first vaginal examination I did. I was a medical student and doing some time at the Brisbane Sexual Health Clinic. The patient I was assigned to was a sex worker who quite graciously and generously volunteered to let me examine her. The most vivid memory I have of that examination was the volume of thrush in her vagina. In 1995, in my final year of pathology training, I spent every Monday afternoon at the Brisbane Sexual Health Clinic. Most of the patients I saw on those afternoons were couples wanting sexual health checks and patients with penile warts that needed to be removed.

Lactobacilli can also be found in the oral cavity and have been associated with dental caries. Brush your teeth people.

The other important thing about lactobacilli is that they have been used as starters for fermentation in the making of cheeses, yoghurt, and other fermented foods. Sourdough bread depends on a symbiotic relationship between lactobacilli and yeasts.

On the subject of bread and fermented foods, the other interest I have is food blogging. Please feel free to check out my blog at

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