Gram versus Derm

by Elio
 

Fig. 1. Schematic depiction of the structural dif­fer­ences of Gram neg­a­tive and Gram pos­i­tive cell en­vel­opes. Source

As you well know, bacteria are div­ided into two groups, his­tor­ic­ally known as Gram posi­tives and Gram nega­tives (Archaea are all Gram nega­tive as they lack the tel­ling pep­tido­gly­can). By and large, Gram posi­tives have a cell envel­ope con­sis­ting of a single mem­brane and a thick layer of pep­tido­gly­can. In con­trast, Gram nega­tives us­ually sand­wich their thin pep­tido­gly­can bet­ween two mem­branes. How­ever, ex­cep­tions keep aris­ing, punch­ing holes in the clas­sical def­ini­tions. Can we do better? Radhey Gupta of McMaster University thinks so. He prop­oses that all bac­teria be div­ided into two groups, those with a single mem­brane cell en­vel­ope (single skin­ned), the "mono­derms," and the double skin­ned "di­derms." Will this catch on? Well it might, as it is already gain­ing con­sider­able trac­tion. What do I think? Speak­ing for myself, I am ready to adopt the "derm" term­inol­ogy as it is well groun­ded in scien­tific re­ality and sounds quite ac­ces­sible to the tongue.
 

But a prob­lem arises: how can you tell which a newly found bac­ter­ium is? Strictly speak­ing, one would have to det­ermine if the cell en­vel­ope is single or double skin­ned, some­thing that req­uires look­ing at a thin sec­tion under an elec­tron micro­scope. This may be handy in some labs but not in others. But there are bio­chem­ical stand-ins that ap­proach the an­swer, so a good ap­proxi­ma­tion is pos­sible with sim­pler tools. And then again, while you wait for those res­ults, you might as well do a Gram stain!