Just a quick post for Taxon of the Week this time around - blame it on the time of year (I am definitely one of those who move into full "Bah, Humbug!" mode around this time of year, though personally I always associate the word "humbug" more with The Phantom Tollbooth than A Christmas Carol*). And in this time of year with its tradition of kissing under the mistletoe (or so we're told - that tradition never made it to the Antipodes), what could be more appropriate than an introduction to an organism most commonly associated in the public mind with throat infections?
*Remember that Phantom Tollbooth allusion - hopefully, I will be having cause to make further reference to it within the year.
Streptococcus is one of the most familiar bacterial genera. There was a time when the name was used to refer to almost any spherical, Gram-positive bacterium that grew in a chain-shaped colony, but the old Streptococcus calved off a few genera in the mid-1980s, most notably Enterococcus and Lactococcus. One of the most significant features distinguishing Streptococcus from the latter two genera is that Streptococcus secretes a protective capsule of slimy polysaccharides. In pathogenic species, this capsule apparently mimics the host's connective tissue, allowing the bacterium to pass unnoticed by the host's immune system.
The best-known members of the genus include Streptococcus pneumoniae and S. pyogenes. Streptococcus pneumoniae causes (unsurprisingly) pneumonia. Streptococcus pyogenes causes... well, almost anything that you'd care to mention, really. It's most commonly associated with "strep throat", but it can also cause such dreadful conditions as scarlet fever, toxic shock syndrome and ye olde puerperal fever that caused the death of so many new mothers before Oliver Wendell Holmes suggested in 1843 that getting doctors to wash their hands before delivering a baby was perhaps not such a bad idea. The most infamous (though thankfully, one of the rarest) condition caused by S. pyogenes is necrotising fasciitis - the dreaded flesh-eating bacterium. Yes, it does exist. No, it is not just something invented by B-grade horror movies.
Not all members of Streptococcus are pathogens. Streptococcus thermophilus, for instance, is used in the production of yoghurt. Unfortunately, though all too typically for bacteria, the non-pathogenic taxa have generally been ignored in favour of their more attention-seeking cousins.
Prescott, L. M., J. P. Harley & D. A. Klein. 1996. Microbiology (3rd ed.) Wm. C. Brown Publishers: Dubuque (Iowa).