Enterococcus

Introduction

For a long time, enterococci were labeled as streptococcal microorganisms belonging - due to their peculiar antigenic characteristics - to Lancefield's D group.

However, starting in the late 1980s, the researchers decided to review the aforementioned division and to insert the enterococci in a group of their own. In this way, a new genus of bacteria was created, known as Enterococcus .

The decision to design a new genus of bacteria was taken following some considerations:

1. Enterococci show several differences from other streptococci (eg S. pneumoniae, S. pyogenes, S. agalactiae, etc.)
2. They are bacteria that are particularly resistant to the environment
3. They also grow on soils with a NaCl concentration of 6.5% and in the presence of 40% bile salts
4. They replicate at pHs ranging from 4.5 to 10.0
5. They withstand temperatures ranging from 10 ° C to 45 ° C
6. They are able to survive for 30 minutes at a temperature of 60 ° C
7. They develop a high resistance to antibiotics and antibacterials
8. Enterococci are less virulent than staphylococci and streptococci

Microbiological description

Enterococci are gram-positive, catalase-negative, round or oval-shaped bacteria, often arranged in chains. Again, enterococci are generally immobile, aerobic / optional anaerobic microorganisms having a lactic-type fermentative metabolism. These cocci, although they excellently withstand external environmental conditions, are not sporogenous.

Enterococci are rarely beta-hemolytic; in fact, they often do not generate any hemolysis in blood agar soil. Enterococci are widely distributed in nature and are often found in the fecal material of vertebrate animals (including humans).

Some enterococci usually populate the human intestine: these include E. faecalis (90-95%) and E. faecium, isolated in 90-95% and 5-10% of human faecal samples, respectively. In addition to these species of enterococci, there are approximately ten others, almost impossible to find in the human organism.

Occasionally, these commensal enterococci can cause damage, to the point of causing endocarditis, mastoiditis, abscesses and urinary tract infections.

In general, enterococci are practically ubiquitous in the environment. The wide spread of these bacteria may probably depend on their excellent ability to survive and adapt to temperatures, pH, oxygenation and concentration of different metal ions compared to the other cocci.

When enterococci are found in water, we are faced with a clear sign of faecal pollution or reduced efficiency of the water purification system. Fortunately, at the present time it is observed that the presence of enterococci in water intended for consumption is very rarely reported.

Enterococci and infections

Although they tend to develop a balanced cohabitation with the host, habitually populating the intestine, enterococci can become pathogenic and cause damage. However, it is important to note that enterococci are decidedly less virulent when compared to streptococci and staphylococci.

The main problem of enterococci is the extraordinary ability to develop resistance to antibiotics (the topic will be discussed later).

Enterococci-mediated diseases include:

• bacteremia
• bacterial endocarditis
• diverticulitis
• abdominal infections
• urinary tract infections (the most frequent pathologies)
• meningitis (a rare condition)

From recent studies it seems that enterococci contribute, in some way, to the appearance of chronic bacterial prostatitis.

Still, it seems that enterococci demonstrate a certain ability to adhere to renal epithelial cells and heart valves, developing pyelonephritis and enterococcal endocarditis.

Although the modest virulence of enterococci is ascertained with respect to staphylococci and streptococci, the infections sustained by them are not of simple resolution, nor are they without complications. In fact it seems that enterococcal septicemia is burdened by a high mortality, with an average incidence estimated around 30-40%.

Transmission mode

We analyzed that the major reservoir of enterococci consists of the intestinal tract of man and other vertebrates; more rarely, the bacteria also populate the oropharynx, vagina, skin and perianal area.

But how are enterococci transmitted?

It is believed that most of the infections carried by these bacteria are of nocosomal origin, therefore acquired within health and hospital facilities. Probably a similar infection has its roots on an endogenous basis: they are the same enterococci that populate the digestive tract to trigger the infection. It appears that the gastrointestinal tract and the hands of nurses, doctors and all health personnel are often contaminated with enterococci. The transmission can also take place through the use of infected instruments.

• Risk factors: many enterococcal infections are acquired in the hospital setting because they are probably favored by the co-presence of other diseases, bladder catheter, neutropenia and prolonged hospital admission.

Antibiotic resistance

While on the one hand the enterococci create damage to humans only sporadically, on the other the infection transmitted by them is particularly difficult to eradicate. In fact, many enterococci show a high level of intrinsic resistance to penicillins, cephalosporins, aminoglycosides and carbapenems. But that's not all: in the last two years, another strain of enterococci capable of developing resistance against vancomycin has been isolated. These bacteria are known by the acronym "VRE" ( vancomycin-resistant Enterococcus ) precisely to emphasize the resistance of these bacteria to vancomycin. VRE enterococci seem to be implicated in the appearance of so-called nosocomial infections in hospitalized patients, especially in the United States. E. faecium- supported infections can be eradicated with quinupristin / dalfopristin: 70% of patients undergoing this therapy respond positively. Rifampicin and TIGECICLINA can also be used to remove pathogenic enterococcus.