Working out with microbes

08 Mar 2019

Working out with microbes

I’m happy to admit to a sports addiction. Each year I cycle over 3000 km, swim over 180 km and purposely hike around 1500 km, excluding any walking I do as part of my daily routine. 

I’ll give any sport a go! Although this is physically beneficial for my body, is there an increased chance of acquiring an infection? 

There are documented horror stories of contamination in health spas and some people seem to avoid swimming, due to fear of ‘germs’ in the water. The term ‘swimming pool’ appears to provoke images of howling children and gushing urine. ‘Ocean swimming’ seems to instil worry about raw sewage and whale sperm. Are any of these fears justified?


Pooling resources


In a swimming pool, one is likely to be exposed to microbes that have entered the water from fellow swimmers. These can include Escherichia coli, Salmonella, and Campylobacter which can all cause diarrhoea [1].


The water could also contain norovirus and parasites such as cryptosporidium which can again cause diarrhoea to an unsuspecting swimmer. However, chlorinated pools will also contain microbes common in water and common on human skin including Comamonas acidovorans, Pseudomonas aeruginosa, Pseudomonas fluorescens and Staphylococcus aureus [2].


Potentially a lot of the human dwelling microbes could be washed off by simply showering before a swim. This is not fool proof, as the pool I use was closed due to Legionella in 2008, with the bacterium detected in its showers [3].


Indoor swimming pool


Enjoying the chemistry

"Many people think that when a pool smells of chlorine, that means that it's clean," says Mary Ostrowski, director of the Chlorine Issues at the American Chemistry Council, a trade organization. "But that smell is actually chloramines, a substance that results from a mix of chlorine and bacteria, urine and sweat."


It’s the chloramines which irritate eyes and airways. A pungent chemical smell actually suggests the pool's water is unclean and should have its chlorine and pH levels tested and adjusted. A properly maintained pool should be odourless.


Chlorine, when added to water, forms hypochlorous acid. This acid is adept at killing bacteria such as salmonella and E. coli, while also taking out quite a few viruses.


Neutral advantage


Hypochlorous acid is a nemesis to microbes, due to the acid's neutral electrical charge. The cell walls around bacteria have a net negative charge, thus repelling other negatively charged particles in the water. As hypochlorous acid is neither positively nor negatively charged, it can bust into bacterial cells.

Diarrhoea-inducing protozoa such as Cryptosporidium and Giardia, which are both transmittable have protective outer shells that chlorine can’t invade. That’s why people should shower before entering the pool.


Swim ring in clear pool


Swimming to victory


This information doesn’t put me off swimming, I’m in the pool 4 times a week and figure my immune system is used to whatever microbes I’m submerged in.


Having earned my title as the fastest female in the pool on a Monday morning, I’m more worried about trying to beat the one man that swims faster, than what might be invading my body!


Come summer and it is time to put on some sun cream and take to the seas for a swim. Currently, I’m an infrequent sea swimmer, but this is likely to change as a friend is about to introduce me to surfing.


Undoubtably, this will lead to exposure to some faecal indicating bacteria. There is research indicating that surfers contain a higher abundance of antibiotic resistant E. coli in their guts than non-surfers, and that a surfer can swallow 11-86 cfu of enterococci per surf [4, 5].


Surfer riding a wave at sunset


Riding the waves

Thankfully as most of my local beaches sport a ‘Blue Flag’ the quantity of faecal indicating bacteria is likely to be low, as sampled water needs less than 2.5 cfu/ ml of E. coli and 1 cfu/ml Streptococci to retain their flag [6]. Probably a good thing as I’m likely to smash my head off a board multiple times, gulping water while trying to get my surfing legs.


If water exposes the user to a wide array of microbes, what about walking, hiking and cycling?

With regard to these activities, one has to focus on specific environments. There’s only two occasions when health concerns have arisen after al fresco exercise.


One was respiratory issues from cycling in March/ June 2010, which I linked to the ash released from the Eyjafjallajökull volcano in Iceland as the issue cleared up when I cycled with a scarf over my mouth and the volcano completed its eruption.


Tick it away


In June 2018, I found a tick embedded in my leg after hiking. Ticks are well known for transmitting diseases including Lyme’s disease [7], but thankfully I didn’t become ill. With this in mind, I don’t need to be concerned with microbes while walking or cycling as the exposure risk is likely to be low and I can reduce the risk of ticks by swapping shorts for trousers.


It appears that outdoor land-based sports have lower microbial exposure than water sports, but what if I decide to exercise indoors at my college's gym? Gyms are notorious for hosting really sweaty machines which have been touched by multiple users.


What if one of the users was at the early infection stage with something nasty? Could these machines transfer the infection to me? My view is unjust as I place the orders and so I know there is a regular supply of antibacterial sprays and blue towels for users to wipe the machines after use. Nevertheless, studies of gym equipment show a high abundance of human derived microbes including Pseudomonas and Acinetobacter [8].


It seems no matter where I exercise, the microbes I meet are unlikely to do me any real harm. If anything, the exercise will keep me healthy and is likely to boost my immune system thus protecting me from infection. My sports addiction can only be advantageous!  


Further Reading:


[1] Wallentine, C. (2017). Most Pools contain dangerous faecal bacteria – here’s how to stay safe

[2] Ibarluzea, J., Moreno, B., Zigorraga, C., Castilla, T., Martinez, M., Santamaria, J. (1997). Determinants of the microbiological water quality of indoor swimming pools in relation to disinfection. Water Research, 32: 865-871.


[3] BBC news (2008). Bug scare shuts leisure centre 


[4] Leonard, A.F.C., Zhang, L., Balfour, A.J., Garside, R., Hawkey, P.M., Murray, A.K., Ukoumunne, O.C., Gaze, W.H. (2018) Exposure to and colonisation by antibiotic-resistant E. coli in UK coastal water users: Environmental surveillance, exposure assessment, and epidemiological study (Beach Bum Survey). Environmental International, 114: 326-333.


[5] Stone, D.L., Harding, A.K., Hope, B.K., Slaughter-Mason, S. (2008) Exposure assessment and risk of gastrointestinal illness among surfers. Journal of Toxicology and Environmental Health, 71: 1603:1615.


[6] Beachawards (2018) Blue flag beach criteria and explanatory notes 2018

[7] NHS (2018) Lyme’s Disease 


[8] Wood, M., Gibbons, S.M., Lax, S., Eshoo-Anton, T.W., Owens, S.M., Kennedy, S., Gilbert, J.A., Hampton-Marcell, J.T. (2015) Athletic equipment microbiota are shaped by interactions with human skin. Microbiome, 3: 2-8.