Atten-shun! Legionnaires’ Disease

In a previous blog I wrote about bugs that hide out inside our cells to escape attack from our immune systems. I have another, fascinating creepy crawly to add to this list of undercover undesirables: Legionella. While the “ella” part of this particular nasty’s name may have the effect of making it sound all cute and cuddly (or even something akin to a lesser-known but no less delicious member of the family of hazelnut- and cocoa-based spreads) there is nothing warm or huggy about Legionella. She is insidious. And lethal.

She also has a great (albeit tragic) story-behind-the-name story. If you get me.

As described in this report in the New England Journal of Medicine, no such bug as Legionella had been isolated and characterised up until one fateful day in July 1976, when, at a convention of the American Legion at the Bellevue-Stratford Hotel, Philadelphia, 182 attendees contracted a form of pneumonia which ended up killing 29 of them. The outbreak is described as “explosive”, the agent “airborne” and the epicentre of the organism’s spread attributed to the hotel lobby or the area in its immediate vicinity. Perhaps the bug should have been called Lobby-ella!

Although the paper doesn’t engage in speculation as to the exact pinpoint of Legionella‘s debut outbreak’s ground zero, it was most likely the hotel’s air conditioning system or a water feature. Because, as we all know now, over forty years after the name was coined, Legionella is a veritable floozy in the jacuzzi: this femme fatale lurves nothing more than to schmooze (and reproduce) in the toasty waters of cooling towers, hot water pipes, fountains, mist sprayers, hot tubs, shower heads and the like. And it is really only in the last forty years that exposure to these Legionella breeding grounds has become a feature of everyday life. Hence the bacterium’s sudden appearance on the list of medical microbiologists’ most wanted. Like sin, Legionella has always been among us — it is only very recently in Homo sapiens’ history that the lass has gotten the opportunity to become a mass murderer of us. There were no cooling towers in the caves of Lascaux or the hanging gardens of Babylon!

Legionella is spread via aerosols. If breathed into the lungs the bug wiggles its way into our cells and proceeds to make itself very much at home*. It nests, forming structures called “Legionella-containg Vacuoles” (LCVs) which provide the perfect environment for replication, as well as protecting it from cellular components such as peroxisomes which might otherwise obliterate her. They aren’t just any old cells that the bacterium targets, by the way, but those charged with protecting the lungs — cells called alveolar macrophages. As such, a Legionella infection becomes a kind of ever decreasing circle of infection: it knocks out immune cells, which gives it a further chance of infecting even more cells leading to a further reduction of immune cells, which . . . Lethal cases of Legionnaires’ disease result from complications such as respiratory failure, septic shock or acute kidney failure. If caught in time, however, there are a number of effective treatments against the infection. It is important that the antibiotics used have high cellular penetration in order to bunker-bust Legionella in her LCV lairs.

As an aside, as well as seeing off 29 Legionnaires, the outbreak also finished off the Bellevue, at the time one of North America’s most iconic hotels. After its appearance in the news headlines, the hotel’s occupancy rate fell to 4%, forcing it to close for business. The Bellevue was thereafter thoroughly restored and has been back in business for over two decades, offering the city of Philadelphia, among other things, its highest dining experience.

 

*The infectious dose can be as low as one organism, especially if one’s lungs are in a sufficiently receptive state (i.e. damaged) to “welcome” the bug,  — smokers have a far higher chance of contracting Legionnaires’ disease than non-smokers

How Bugs Turn Your Food Waste into Fuel

They are far from appetising, and out-of-date meat and dairy products may even induce the gagging reflex, but the food trimmings, leftovers and beyond-best-befores that go into your garbage are still high in energy. Even though they might be in the process of breaking down, your mouldy oranges, crusts of bread and rancid walnuts are still chock full of calorie-giving molecules such as sugars, starches, fats, proteins and organic acids. In the context of global warming we all want to be carbon neutral (or even good little carbon sinks), so the responsible thing to do is to capture and re-use all that trapped energy.

In the old days when we all lived on farms and when even urban dwellers had pigs and chickens to deal with slops, very little food waste was sent to landfill. At the very least, back in our grandparents’ time potato skins, gristle and the like was put on the compost heap to eventually be recycled back into the soil. At present we are throwing out worrying amounts of food, to the extent that even swivel-eyed Brexit politicians and the Pope are expressing concern. Most of the food waste we dump goes to landfill, meaning that the carbon that cost so much in terms of energy, water and other resources to incorporate into our munchables returns slowly to the atmosphere with nobody benefiting except the dumpsite decomposers (beetles, worms, fungi and bacteria) whose job it is to gobble up macromolecules and spit out water, carbon dioxide and a bit of methane and hydrogen sulphide.

What can be done to recapture the energy we are losing through discarding so much food? One excellent option is to convert it to biogas. And guess who are the stars in the story of the conversion of old soggy spinach and crusty peanut butter to methane? You guessed it, our old friends, bacteria. And not just one bacterium or one group of bacteria, but a whole bunch of them working in co-operative layers (called “trophic” layers). Here’s a helicopter view of the process, which takes place in a huge tank known as an anaerobic digester. Your green waste management company collects you and thousands of others’ food waste and transports it to its site where after some pre-processing it is packed into the temperature-controlled digester. The bugs get to work on it immediately. The first group of bugs, hydrolysers, chop up the big molecules in the waste (e.g. starches) into smaller ones (e.g. sugars). These simpler molecules then become the foodstuff for acidogenic bacteria, who produce acidy compounds like those found in pickles. A third group of bugs work on the acids to form primarily acetic acid (found in vinegar), carbon dioxide and hydrogen. Finally, methanogenic bacteria mop up the waste products of the other three groups and produce — you guessed it — methane. This gas is our biofuel and can be burned to produce heat or drive turbines that generate electricity. It’s not just waste disposal companies who are getting into anaerobic digestion: many factories now have their own on-site anaerobic digestors to convert their own waste into usable energy.

You may be wondering why “anaerobic” digestion? Anaerobic means “in the absence of air. More correctly, we are talking about the absence of oxygen. Aerobic digestion carried out by aerobic bacteria is basically like slow-burning your waste: you oxidise (burn) your macromolecules and generate heat, carbon dioxide and water, but no usable high-energy compounds such as methane are left behind by the process.

Finally, a special form of recycling food waste, is the conversion of cooking oil to biodiesel. Companies such as Olleco collect used cooking oil from chippers, Chineses and caffs and, using a chemical process (no bacteria involved, unfortunately), turn what would be a potent building block for sewer fatbergs into fuel.

Waste not want not!