Miscellaneous Catalase-Negative, Gram-Positive Cocci: Emerging Opportunists

In a whimsical mood and quite extemporaneously, Justice Oliver Wendell Holmes once remarked: 'Facts in isolation amount to mere gossip; facts in relation become philosophy.' And this, perhaps, gives the key to one of the chief ailments of bacterial taxonomy.There are too many 'facts in isolation' and too few 'facts in relation'"From James M. Sherman's classic 1937 treatise on the genus Streptococcus (20) Clinical microbiologists who contemplate the current bewildering assortment of catalase-negative gram-positive cocci that grow aerobically are likely to feel bombarded by what appear to be facts in isolation.They may find themselves longing for the days when laboratory identification of this group of bacteria was simple and straightforward.They no doubt abhor, in Sherman's (20) words, ". ..the hair-splitting divisions which have been set up by some taxonomically-minded bacteriologists."Until the mid-1980s clinical microbiologists viewed catalasenegative gram-positive coccal isolates in essentially the same way Sherman and his colleagues did.All such isolates were streptococci, unless, of course, their cells were arranged in clusters, indicating a probable Aerococcus viridans strain (usually considered a contaminant).The streptococcal isolates could be divided into beta-hemolytic strains, enterococcal strains, pneumococci, and the puzzling "Streptococcus viridans" group, an unruly collection that defied classification by Lancefield's serological methods.This simplistic view of catalasenegative gram-positive cocci fell by the wayside as molecular taxonomic studies of these bacteria gave rise to an ever-expanding list of new genera and species.Taxonomic hair-splitting was, however, not the only factor contributing to the increasing number of recognized catalase-negative gram-positive cocci.Concomitant medical progress in the treatment of serious diseases created a growing population of patients with compromised defenses against infection and altered normal flora.We began to see more frequent opportunistic infections in this patient group, and catalase-negative, gram-positive cocci, some familiar and some not previously described in human clinical specimens, emerged as new agents of infection.Today we recognize at least 15 genera (in addition to Streptococcus and Enterococcus) and numerous new species of catalase-negative