C. Dominique Gibson

The Truth About Flesh-Eating Bacteria: It’s All Relative

When it comes to bacterial infections -Necrotizing fasciitis is the Big Kahuna of them all.  It’s so scary that people began calling it flesh eating disease, or flesh eating bacteria.  Don’t let my choice of words fool you.  Necrotizing fasciitis is a deadly disease and though such a severe infection is rare, death due to the condition is not.  This is why early detection is paramount to lessening the chance of mortality [1].

I know the thought of host of bacteria systematically degrading subcutaneous tissue is quite daunting but I think there are a few truths about this disease everyone should know.

• Necrotizing fasciitis can be caused by several microbes and is not isolated to one species or strain.
• The microbes which cause this disease enter the body through abrasions of the skin or through the blood from a remote area when there is blunt trauma. While patients with immune-suppressed or compromised systems have a higher risk for infection, the disease also affects presumably young and healthy patients.
• “Flesh eating” is a misnomer.  The bacteria do not eat flesh.  Instead, the microbes involved release toxins which cause the destruction of tissue from the superficial fascia to the deep fascia of the skin.  This mechanism leads me to the next truth.
• Streptococcus pyogenes is usually responsible for infections by which the entry point is not discernable.  These infections are limited to humans but the mechanism of infection is similar to that of other pathogens.  My favorite microbe, Pectobacterium carotovorum, comes to mind. 

Streptoccocus pyogenes releases an exotoxin which is also a superantigen.  Superantigens cause the activation of a large numbers of T-cells which trigger the release of loads of cytokines specifically, TNF-alpha which is a major player in the body’s inflammatory response.

I know you’re probably thinking, “Isn’t this supposed to happen?” Under normal circumstances, in a localized area and in small amounts, this is absolutely fine.  However, in large amounts it can lead to toxic shock. In the case of S. pyogenes as the causal agent of necrotizing fasciitis, toxic shock is one of the leading causes of death.

So how does this relate to Pectobacterium carotovorum?  Let’s recap.  P. Carotovorum which causes soft-rot enters its host through surface abrasions during post harvest or in the field.  It releases enzymes which lead to the degradation of pectin which cements cells together.   However, like necrotizing bacteria, this is not the only mode of virulence.   The enzymes which Pectobacterium carotovorum release also trigger the plant to release a host of its own enzymes which aid in pectin hydrolysis [2].

Both pathogens attack their hosts at a point of weakness. Sound familiar?  If you’ve watched The Lord of the Ring’s The Two Towers, you’ll remember the part when the armies of Sauron discovered a weak point in the wall bordering Helm’s Deep.  Once they attacked this point, they were able to gain access to the inside and do some major damage to the Rohirrim and Elven army[3].

Apparently, all’s fair in infection and war…

My Favorite Microbe

When most people hear the word “microbe”, they automatically associate it with disease causing agents commonly referred to as pathogens.  But the term “microbe”  is a vast category including all micro-organisms not just pathogens.

After completing my masters, I became obsessed with the beneficial properties of these tiny, often misjudged and neglected creatures.  So I’d like to begin with the microbe of interest during my thesis research: Pectobacterium carotovorum.

Have you ever left a bag of potatoes in the cupboard for too long?  Ever notice the odor and the new mushy texture of it? If you have observed these symptoms in your potatoes then chances are they are infected with P. carotovorum or soft rot.

This highly virulent pathogen releases enzymes which lead to the degradation of pectin in the middle lamella which cements the cell wall of one cell to another.  Imagine building a house and having all the cement wash away.  The structural integrity of your house is now compromised and will most likely lead to the collapse of the building.  Similar effects can be observed in plant tissue infected with soft rot.

Like late Blight (Phytophthora infestans),  soft-rot leads to major losses in potato crop output _[1]. Although P. carotovorum is a major pathogen of the Solanum genus, it also has some surprising alternate uses.  One that really caught my attention is its role in forensic science.

Post mortem tissue and fluids are tested for volatile chemicals to rule out or confirm the cause of death. In cases where alcohol (ethanol, 1 butanol etc.) is thought to be related to the cause of death, contamination by microbes must be considered.  Several microbes in the human body produce ethanol and 2,3 butanediol via fermentation post mortem.  P. carotovorum formerly Erwinia is one of them.  The presence of this microbe also reveals something about the postmortem subject_[2].  That said… I’d like to introduce you to my favorite microbe - Pectobacterium carotovorum.  Unfortunately, P. carotovorum  has a very busy schedule so please be understanding if you are not able to ask a question or get an autograph.

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