Microbiology with Diseases by Body System

Microbiology with Diseases by Body System

Introduction

Numerous characteristic descriptions of enterococci have been documented for nearly hundred years, together with their presence in sewage and feces, their ability to bring about UTIs or urinary tract infections and endocarditis and their aptitude to endure harsh environmental circumstances including high temperatures, drying and contact to several antiseptics (Emori & Gaynes, 1993). Enterococci are found in the intestinal tract of most animals and humans. Enterococci, predominantly Enterococcus faecalis, are a widespread source of endocarditis and can be a frequent basis of nosocomial urinary tract infections.

Discussion

Microbiology Classification

Enterococci are gram positive cocci that shape small to average length chains. In the ensuing 45 to 50 years, enterococci continued to be taxonomically classified in the genus Streptococcus (Gross, 1976). However, it was recognized by some authorities that these organisms had a number of distinguishing features, suggesting that the classification might be incorrect. In the mid-1980s, with advances in taxonomic techniques based upon nucleic acid analyses, it was proposed that S. Faecium and S. faecalis be removed from the genus Streptococcus, transferred to a new genus, Enterococcus, and reclassified as E. faecalis and E. faecium, respectively (Coque & Murray, 1995). Subsequently, other enterococcal species were also reclassified from the genus Streptococcus to the genus Enterococcus; a number of new species have also been recognized.

The characteristic features of enterococci as being bile esculin positive, reactive with group D antiserum, and able to grow in 6.5 percent sodium chloride were used by clinical laboratories for decades to distinguish enterococci from other catalase-negative gram-positive cocci. However, some problems arise with the use of these criteria. As an instance, the presence of group D antigen can be difficult to detect in some enterococcal isolates. In addition, other organisms such as lactococci also can grow in high salt and/or be bile esculin positive; however, lactococci do not grow at 45ºC.

Two other genera that share a number of biochemical features with enterococci, including their ability to produce the group D antigen, are Leuconostoc and Pediococcus, which can also grow at 45ºC. These organisms are intrinsically vancomycin resistant, which was a reliable distinguishing trait prior to the emergence of vancomycin resistant enterococci or VRE. These genera are now best distinguished from VRE by the addition of tests for production of pyrrolidonyl arylamidase (PYR) and leucine aminopeptidase (LAP). Expected results are: +/+ with enterococci; -/+ for Pediococcus; and -/- for Leuconostoc; Leuconostoc also produce gas from glucose.

Many laboratories do not identify enterococci to the species level. Prior to the emergence of vancomycin resistance, the majority of clinical enterococcal isolates were E. Faecalis, but the incidence of E. faecium in the United States has increased, coincident with emergence of ampicillin and vancomycin resistance. Although commercial kits for E. faecalis are generally reliable, commercial strips and kits for non-E. faecalis have been less reliable.

With the increase in non-faecalis and the increased attention paid to vancomycin resistant organisms, including E. gallinarum and E. casseliflavus, there is renewed interest in identifying these ...