From Dr M. Cockcroft
SIR,—I would like to try to solve Dr Marshall's problem regarding the apparently deteriorating behaviour of Escherichia coli (PJ, January 22, p131). First, we must revise the Linnaean classification system used to identify organisms.
Escherichia is the genus of the organism being discussed. What type of Escherichia it is is given by the species part of the name - in this case coli. To give an example which may be more familiar, Canis (genus) familiaris (species) is commonly known to us as "dog". Thus, if you were to ask me if the organism Canis familiaris was a potential killer, I would have to tell you it depends on the subspecies: Canis familiaris subspecies Rottweiler presents a definite biohazard, whereas Canis familiaris subspecies guide dog generally lives a mutually rewarding symbiotic relationship with Homo sapiens.
You can therefore find various characteristics within a species: generally, to be members of the same species, you must simply be able to mate and produce viable offspring with other species members. So, within the group of organisms called E coli some representatives will be relatively benign, such as the ones used by Dr Marshall which did him no harm. Others, such as the infamous E coli subspecies 0157 can present a great hazard in suitable circumstances.
Regarding the recent appearance of E coli 0157, there are two possibilities. First, it may have appeared as a result of DNA copying errors during cell replication: these errors may lead to new characteristics in cells (such as toxin production), which are then passed on the next time the cell replicates.
Alternatively, E coli 0157 may have been there all the time, with its relatively recent discovery being attributable either to advances in scientific techniques, changes in husbandry methods allowing the organism to spread rapidly, or changes in social behaviour regarding the foods we eat.
Either way, Dr Marshall should rest assured that, currently, his intestinal microfauna are probably not in a state of revolt, planning toxic attacks on their host. We should just be careful of what we eat!
Martin Cockcroft
Stockton-on-Tees, Cleveland