Civil War ghost soldiers
An interesting story via io9.com, which presents a neat example of mutualism, microbial antagonism, and the effects of temperature on growth rates. It’s actually a story that’s been around for about 10 years, but recently showed up in the news. Two high school students, Bill Martin and Jon Curtis from Bowie, MD won the Intel International Science Fair competition in 2001 with their research into the curious story of soldiers who survived being wounded at the Battle of Shiloh during the Civil War in the spring of 1862.
Bill and Jon were interested in an anecdote about how some of the wounded soldiers who had to remain at the battleground in the rain and mud for up to two days before medics could reach them noticed that their wounds were glowing in the dark. Furthermore, these soldiers appeared to have a better survival rate than other soldiers, and their wounds healed more quickly. The glowing wounds were nicknamed the “Angel’s Glow,” and nothing more was known about them for over 140 years. The two high school students deduced that the glow might be due to the action of a bioluminescent bacterium called Photorhabdus luminescens, which shares an interesting life cycle with a soil dwelling roundworm called a nematode.
P. luminescens lives in the digestive tract of the worm as part of the worm’s normal microbial flora. The nematodes in turn hunt for insect larvae in the soil. When a nematode burrows into an insect, it regurgitates the bacteria, which then begin to kill the insect and inhibit the growth of other bacteria in a demonstration of microbial antagonism. The nematode and the bacteria digest the inside of the insect until it is completely hollowed out. The nematode then re-ingests the bacteria and moves onto another insect to repeat the process. The nematode and the bacterium therefore share a mutualistic relationship with one another, as the bacterium benefits from being transported from food site to food site (the hapless insect larvae), and the worm benefits as the bacterium help to break down the insect into a usable source of food.
Ordinarily, P. luminescens is not a significant pathogen of humans, as its maximal tolerated growth temperature is below human body temperature. However, as the soldiers waited for medics to arrive at the battlefield, they became hypothermic in the early spring nights. This allowed their wounds to become infected by the nematodes and the bacteria, and the growth of these bacteria in turn inhibited the growth of other pathogens. When the wounded soldiers were removed from the field and warmed up, their temperature was then too high to permit growth of P. luminescens. Because P. luminescens grew in the wounds for several days, the growth of wound-infecting pathogenic bacteria such as Staphylococcus and Streptococcus was limited. In soldiers who did not have the glowing wounds, growth of pathogens prior to treatment led to their much lower survival rates.
So would deliberate infection with Photorhabdus be a reasonable approach to antisepsis? Here is a BONUS opportunity: in the comment thread, suggest a reason why this might not be a tenable proposal for therapy over at York Hospital.