Guidance on the identification of Enterococci and Streptococci

Public Health England have revised their guidance on the identification of Enterococci and Streptococci.

 

The genus name Enterococcus, previously called Streptococcus faecalis and Streptococcus faecium, was revived in 1984 when other bacteria were transferred to the genus. There are now more than 50 recognised species of the genus Enterococcus. Enterococcus faecalis and Enterococcus faecium are the most common enterococci isolated from human infections.

 

 

The genus Streptococcus comprises a large number of commensal and pathogenic species. With the help of recent rapid development of methods for microbial phenotyping and molecular identification, the genus Streptococcus has undergone a significant expansion and revision. There are now over 100 recognised species of Streptococcus, many of which are pathogens or commensals in humans and animals.

Streptococci are Gram-positive and catalase-negative bacteria that are facultatively anaerobic but some requiring CO₂ for growth. Cells are usually coccus-shaped (spherical or ovoid) and arranged in chains and/or pairs. Cells are nonmotile, endospores are not formed and are 2 μm in diameter. Carbohydrates are metabolised fermentatively; lactic acid is the major metabolite. Streptococci produce the enzyme leucine aminopeptidase (LAP), which has also been called leucine arylamidase. Temperature vary among species, but optimum temperature usually is about 37°C.

Streptococci growth on solid media can be enhanced by the addition of blood, serum or glucose. On blood agar, the species exhibit various degrees of haemolysis, which can be used as an early step in identifying clinical isolates. Haemolysis produced by colonies on blood agar and Lancefield serological grouping are important factors in presumptive identification, however there are many overlapping characteristics therefore genetic analysis is a more definitive method for identification.

To access the document, see: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/987272/ID_4_dh+.pdf

Posted by Dr. Tim Sandle, Pharmaceutical Microbiology Resources (http://www.pharmamicroresources.com/)