01. Introduction
02. Gram-Positive Cocci
03. Gram-Positive Bacilli
04. Gram-Positive Branched Filaments
05. Gram-Negative Diplococci
06. Gram-Negative Bacilli
07. Gram-Negative Coccobacilli
08. Additional Bacteria
09. RNA Viruses
10. DNA Viruses
11. Fungi
12. Opportunistic Fungi
13. Protozoa (single-celled eukaryotes - small parasites)
14. Helminths (parasitic worms - large macroparasites)
15. Prions

2.05 Enterococcus faecalis and Streptococcus bovis

Enterococcus faecalis and Streptococcus bovis – Audio and Lecture Notes – Click to Expand

Enterococcus faecalis and streptococcus bovis are catalase negative, gram positive cocci.

They have variable haemolysis i.e. they can be alpha, beta or gamma haemolytic.  They are able to grow in a 40% bile environment; and are bile esculin test positive.

Additional note: Bile esculin agar typically inhibits the growth of gram-positive organisms; except for Enterococcus faecalis and group D streptococcus (e.g. Streptococcus bovis). As these bacteria produce an enzyme - esculinase - that hydrolyses esculin to esculetin and glucose. The esculetin then reacts with iron salts to form iron complexes that darken the solution. Therefore a positive esculin test is when the solution within the testing tube turns a dark brown or black colour.

To differentiate the two, sodium chloride (NaCl) may be used:

    • Enterococcus faecalis grows in 6.5% NaCl
    • Strep Bovis does not. 
 

Focusing on Enterococcus faecalis, its natural flora is in the biliary, intestinal and genitourinary tract. Due to its multi-drug resistance, prolonged antibiotic use may favor its growth by killing off competing pathogens, leading to Enterococcus faecalis specific disease. 

Enterococcus can cause local infections such as:

    • Biliary tract infections or UTI (linked to indwelling catheter use); 
    • It can cause systemic disease if it travels in the blood to colonised heart tissue, causing Subacute Bacterial Endocarditis. Heart valves previously damaged by streptococcus pyogenes (i.e. Rheumatic fever), are more at risk of being colonised by Enterococcus. 

Systemic spread of enterococcus has been linked to breakages in the skin barriers e.g. bedsores, intra-abdominal wounds, vascular or peritoneal catheters, intravenous drug use etc.

Treatment involves combining a penicillin (like ampicillin) with an aminoglycoside (like gentamicin); or combining vancomycin with an aminoglycoside. 

The emergence of Enterococcus faecalis strains resistant to vancomycin has been observed. These are termed Vancomycin-Resistant Enterococci (VRE); treatment of these involves combining daptomycin with linezolid.

Enterococcus faecalis and streptococcus bovis are catalase negative, gram positive cocci.

They have variable haemolysis i.e. they can be alpha, beta or gamma haemolytic.  They are able to grow in a 40% bile environment; and are bile esculin test positive.

To differentiate the two, sodium chloride (NaCl) may be used:

    • Enterococcus faecalis grows in 6.5% NaCl
    • Strep Bovis does not
 

Focusing on Streptococcus bovis, it is a Lancefield group D Streptococci and is a normal flora in the GI tract. And mainly invades when there is breakage to the epithelium of the bowel lumen. For this reason, a Strep bovis infection is often linked to:

    • inflammatory bowel disease or bowel cancer.

Haematogenous spread of this bacteria favours heart tissue, resulting in:

    • Subacute Bacterial Endocarditis. 

Treatment is with penicillins.

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