Friday, August 28, 2015

Bacteria can colour our insides!

Included in the vast array of molecules put together by bacteria are pigments, with a blotch of colour often marking the presence of a large bacterial population in nature. In addition to green stains on damp concrete and vibrant rainbows of ooze in hot springs, pigment-making bacteria will very occasionally announce their presence by infecting us and changing the colour of our body parts and fluids.

The king of turning people a different colour is Serratia marcescens. This bacterium, being opportunistic yet moisture-dependent, is found in soil, bathrooms, and people. It produces a reddish-pink pigment called prodigiosin, which has resulted in its growth being mistaken for blood many times throughout the centuries. It also led to piles of it being secretly wafted onto San Francisco, producing a mysterious outbreak of sometimes-deadly infections. Nothing like testing a biological weapon on an unsuspecting populace!

An autopsy of a patient who died after S. marcescens got into their bloodstream and caused widespread damage revealed the presence of several pink abscesses in the wall separating the two ventricles of their heart. If it gets into the lungs, the bacterium can cause people to cough up red sputum (sputum = mixture of saliva and respiratory tract gunk). Prodigiosin has also been observed in tooth abscesses and can stain teeth. Infection of the urinary tract with S. marcescens or its close relative S. rubidae can give your pee a reddish tinge.

Pink abscesses caused by Serratia marcescens infecting a heart (Source)

S. marcescens can also cause the front chamber of an eyeball to fill slightly with pink pus, if it manages to get inside there. It's sort of like watching a front loading washer slowly fill with water, only it's the iris of your eye and a delightful mixture of bacteria and white blood cells. The accumulated pus is known as hypopyon and is typically associated with inflammation of the inside lining of an eye (endophthalmitis). Cases of pink hypopyon due to S. marcescens in the scientific literature include a senior who left a contact lens in her eye and developed a large corneal ulcer, and an infant who was infected with the bacterium via an umbilical artery catheter.

Try to ignore the intentionally green-stained pupil, for a pink hypopyon is just below it (Source)

I found a report from 1936 in which the author casually mentioned once seeing a patient with lung cancer who was coughing up thick sputum with yellow granules due to an unknown species of Actinobacteria growing inside them. Yellow sputum can also be caused by an infection with Staphylococcus aureus, some strains of which produce the golden pigment staphyloxanthin.

Orange sputum is sometimes observed in people with pneumonia caused by Legionella pneumophila, the principal pathogen responsible for Legionnaires' disease. This bacterium can break down the amino acids phenylalanine and tyrosine into homogentisic acid, which can then be linked together to form a brown-orange pigment. The pigment and its progenitor are used by the bacterium to acquire iron, an essential yet sometimes scarce nutrient, from either insoluble iron minerals (e.g. rust present in a cooling tower) or iron-binding proteins found in mammals.

Orange stuff horked up by someone with Legionella pneumophila in their lungs (Source)

Green sputum can result from a lung infection with Pseudomonas aeruginosa. This bacterium resides in lakes and soils, yet can also munch on people if given the opportunity. Some strains produce blue-green pigments called pyoverdin and pyocyanin, which they use to do useful things like acquire nutrients and kill nearby cells. P. aeruginosa tends to hang out in the lungs of people with cystic fibrosis, in whom it can cause lifelong and eventually fatal infections. It can also cause urinary tract infections featuring searing pain and green-coloured urine. Wounds infected with P. aeruginosa can take on a turquoise colour, as can the pus they leak.

If you tear a little hole in the hyponychium, the thickened skin holding the end of a nail to the finger beneath (it’s basically a wall protecting the nail bed), or have a hole made for you there by a skin-eating fungus, P. aeruginosa can get in under the nail and start growing. If it happens to be a pigment-making strain, your nail can turn a vivid emerald green. Green nail syndrome, as it’s perhaps unsurprisingly called, tends to occur under the warm and moist conditions. Scenarios known to foster green nails include spending a vacation mostly in ski boots, doing a lot of gardening in a wet climate, or working as a dishwasher.

Green nail caused by Pseudomonas aeruginosa (Source)


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