Enterococcus faecium

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A Microbial Biorealm page on the genus Enterococcus faecium

Classification

Higher order taxa

Domain: Bacteria; Phylum Firmicutes; Class: Bacilli; Order: Lactobacillales; Family: Enterococcus (1)

Species

NCBI: Taxonomy

Enterococcus faecium (2)

Description and significance

E. faecium is a human pathogen that causes nosocomial bacteremia, surgical wound infection, endocarditis, and urinary tract infections. Nosocomial infections are those acquired in medical setting during treatment of a prior complaint. The normal habitat includes the gastrointestinal tract of a multitude of animals but it can also be found in the oral cavity and vaginal tract.(3) The microbe can survive for long periods of time in soil, sewage, and inside hospitals on a variety of surfaces.(6) It can grow in temperatures ranging from 10 to 45 degrees Celsius, in basic or acidic environments, and in environments which are isotonic or hypertonic.(3)

E. faecium is a Gram-positive, spherical cell that can occur in pairs or chains. The colonies formed are 1-2 mm in length and appear wet. The cells are non-motile. (8)

E. faecium can be highly drug resistant and acquires its drug resistance by plasmids and conjugative transposons as well as chromosomal genes that encode resistance. Some strains have become resistant to vancomycin, penicillin, gentamicin, tetracycline, erythromycin and teicoplanin. Spread of the disease occurs between patients in hospitals due to transfer of the pathogen by hands or medical instruments. Also antibiotic use can decrease the number of other intestinal bacteria that are susceptible to the antibiotic and decrease competition for the drug resistant E. faecium. (3)

E. faecium was known as Streptococcus faecium until its name changed in 1984 due to a re-categorization. (2)

Genome structure

The Joint Genome Institute in collaboration with Dr. Barbara Murray sequenced the genome of E. faecium in one day. It has an estimated size of 2.8 Mbp. The genome project is still under construction and has not been fully analyzed. (12)

E. faecalis is a close relative of E. faecium and its genome has been sequenced and analyzed. The sequencing of a vacomycin resistant E. faecalis strain, Enterococcus facalis V583, revealed 1 circular chromosome and 3 plasmids. The chromosome consists of 3218031 base pairs and each plasmid, pTEF1, pTEF2, pTEF3, consists of 66320, 57660, and 17963 base pairs respectively.

Two of the plasmids are pheromone-sensing conjugative plasmids. Also found was a mobile conjugative transposon that encodes vacomycin resistance. Over a quarter of E. feacalis’ 3337 open reading frames are mobile and/or exogenously acquired DNA. These mobile and/or exogenously acquired DNA include seven integrated phage regions, 38 insertion elements, conjugative and composite transposons, a patheogenicity island, and integrated plasma genes. Its ability to acquire outside DNA contributes to E. faecalis’ multiple drug resistance. The genes encoding vacomycin resistance in E. faecalis’ are similar to E. faecalis’ vanB vancomycin-resistance conjugative transposon Tn1549 and were probably transferred as a cassette by lateral gene transfer. (5)

Cell structure and metabolism

Cell Structure E. faecium is a gram-positive bacterium. Gram-positive cells have a thick peptidogycan layer along with teichoic and lipoteichoic acids. It has circular DNA as well as several plasmids. It is capable of conjugation through the release of sex pheromones and secretes aggregation substances and also forms biofilms. The cell has pili and flagella(4, 6, 9)

Metabolism E. faecium lacks the Krebs’s cycle and respiratory chain and therefore it gains energy through fermentation. It is a facultative anaerobe which means it can make ATP by aerobic respiration if oxygen is present but will utilize fermentation if no oxygen is present.(3)

Ecology

E. faecium can acquire drug resistance through three types of conjugation: pheromone-responsive plasmids, broad host-range plasmids, and conjugative transposons. Pheromone response plasmid occurs when the cell secretes a sex pheromone for a specific plasmid. When a donor cell comes into contact with the pheromone, transcription of the relevant portion of the plasmid is turned on and it also secretes a sticky substance. The sticky or aggregation substance facilitates the transfer of the plasmid to the recipient cell by helping them to stick together. Transfer of other plasmids can also occur between different genera of bacteria including staphylococci, and streptococci. The consequence of the ability of E. faecium to acquire broad host-range plasmids is that drug resistance can be widely and more easily spread. Conjugative transposons can also transfer antibiotic resistance between genera as well as between gram-positive and gram-negative bacteria because they do not need to cooperate with host machinery in order to insert themselves into a plasmid or chromosome of the bacterium. E. faecium can interact with other bacteria to spread drug resistance through conjugation. (4)

Pathology

E. faecium is considered a super-bug. It can colonize many organs of the body including the gastrointestinal tract and the skin, and can also survive for long periods on inanimate objects. This along with its multi-drug resistant characteristics makes it a particularly nasty pathogen.

Contributing to the virulence of E. faecium is the enterococcal surface protein (Esp). This protein allows the bacteria to aggregate and form bioflims. Strains with the Esp gene are normally found in clinical isolates and not found in strains that colonize the gut. Bioflim formation allows colonization of tubing used in hospitals and can lead to infections of the blood as well as urinary tract infections. Esp gene expression increased under increased temperature as well as a change to anaerobic condition. The regulation of the Esp gene in this way allows E. faecium to change its response when it enters a host. (6)

Additional virulence factors include aggregation substance (AS), cytosolin, and gelantinase. AS allows the microbe to bind to target cells and it facilitates the transfer of genetic material between cells. Cytosolin is a protein found in the cytosol and lyses erythrocytes. GeIE can hydrolyze peptides. The presence of virulence factors differ among strains and usually are specific for the host the strain colonizes. (9)

Application to Biotechnology

E. faecium produces antibacterial peptides called bacteriocins. This microbe can be used in fermenting foods such as cheese and vegetables. It is introduced to the starting cultures to inhibit growth of unwanted microbes. E. faecium can also be used as a probiotic to out-compete deleterious bacteria in the gastrointestinal tract.(10)

Current Research

A study showed that the metabolism of E. faecium can cause eukaryotic cell DNA damage through its metabolism. Through the autoxidation of membrane bound demethylmenaquinone E. faecium produces superoxide, hydrogen peroxide, and hydroxyl radicals. These oxidants can produce chromosomal instability that can cause polyps and colon cancer. Hydrogen peroxide derived from E. faecium was shown to damage luminal cells in the colon of rats, demonstrating E. faecium’s potential carcinogenic property. (7)

As vacomycin resistance increases in E. faecium, health care providers must find novel strategies for treating patients affected by the microbe. Often doctors must venture into uncharted territories to save a patient. In one example a premature infant in a neonatal unit was diagnosed with a vacomycin resistant strain that had infected her central nervous system through a ventriculoperitoneal (VP) shunt. Through laboratory testing it was found that the germ was susceptible to linezolid. As published data of treatment of central nervous system infections with linezolid in infants was unavailable the hospital dosed the infant using the resources at hand. As E. faecium continues to acquire drug resistance novel strategies are needed to combat it. (11)

The use of antibiotics in animal feed has caused an increase in resistance to antibiotics. The van A gene began presenting itself outside of hospitals as a result of selective pressure due to antibiotic use. The van A gene was spread through conjugation. Studies have shown that the use of virginiamycin in stock animals produced drug resistant enterococci. (13)

References

1. Skerman, V.B.D., McGowan, V., and Sneath, P.H.A. (editors): "Approved lists of bacterial names." Int. J. Syst. Bacteriol. (1980) 30:225-420. Schleifer KH & Kilpper-Balz R (1984)

2. Schleifer, K.H., and Kilpper-Balz, R. "Transfer of Streptococcus faecalis and Streptococcus faecium to the genus Enterococcus nom. rev. as Enterococcus faecalis comb. nov. and Enterococcus faecium comb. nov." Int. J. Syst. Bacteriol. (1984) 34:31-34.

3. Mark M. Huycke, Daniel F. Sahm, and Michael S. Gilmore. “Multiple-Drug Resistant Enterococci: The Nature of the Problem and an Agenda for the Future” EID (1998) 4:2 http://www.cdc.gov/ncidod/eid/vol4no2/huycke.htm

4. Barbara E. Murray. “Diversity among Multidrug-Resistant Enterococci” EID (1998) 4:1 http://www.cdc.gov/ncidod/eid/vol4no1/murray.htm

5. T. Paulsen, L. Banerjei, G. S. A. Myers. “Role of Mobile DNA in the Evolution of Vancomycin-Resistant Enterococcus faecalis” Science (2003) 299:5615:2071-2074 http://www.sciencemag.org/cgi/content/full/299/5615/2071#R18

6.Willem J. B. Van Wamel, Antoni P. A. Hendrickx, Marc J. M. Bonten. “Growth Condition-Dependent Esp Expression by Enterococcus faecium Affects Initial Adherence and Biofilm Formation” (2007) 75:2:924-932 http://iai.asm.org/cgi/content/full/75/2/924

7. Mark M. Huycke, Victoria Abrams, Danny R. Moore. “Enterococcus faecalis produces extracellular superoxide and hydrogen peroxide that damages colonic epithelial cell DNA.” Carcinogenesis (2002) 23:3:529-536 http://carcin.oxfordjournals.org/cgi/content/full/23/3/529?ijkey=80a120e6d7e4ec480948c0a02f43c42d712ded52

8. Health Protection Agency (2007). Identification of Streptococcus species, Enterococcus species and morphologically similar organisms. National Standard Method BSOP ID 4Issue 2. http://www.hpastandardmethods.org.uk/pdf_sops.asp.

9. Timur G.LHAN, Abdulbaki AKSAKAL, Üsmail HakkÝ EKÜN. “Virulence Factors of Enterococcus faecium and Enterococcus faecalis Strains Isolated from Humans and Pets” Turk. J. Vet. Anim. Sci.30 (2006) 477-482

10. J.H. Kang and M.S. Lee. “Characterization of a bacteriocin produced by Enterococcus faecium GM-1 isolated from an infant” Journal of Applied Microbiology 2005, 98, 1169–1176

11. Swati Kumar, Stephan Kohlhoff, Gloria Valencia. “Treatment of vancomycin-resistant Enterococcus faecium ventriculitis in a neonate” International Journal of Antimicrobial Agents (2007) 29:6:740-741

12. http://www.hgsc.bcm.tmc.edu/projects/microbial/Efaecium/

13. Wolfgang Witte. “Selective pressure by antibiotic use in livestock” International Journal of Antimicrobial Agents (2001)16:1;19-24

Edited by Morgan Feori, UCSD, a student of Racheal Larsen and Kit Pogliano