Enterococcus faecalis Case File

Enterococcus faecalis Case File

Eugene C.Toy, MD, Cynthia Debord, PHD, Audrey Wanger, PHD, Gilbert Castro, PHD, James D. Kettering, PHD, Donald Briscoe, MD

CASE 8

A 72-year-old female nursing home resident is transferred to the hospital because of fever and altered mental status. She has advanced Alzheimer disease, is bed bound, and has an indwelling Foley catheter as a consequence of urinary incontinence. Her baseline mental status is awake and talkative, but oriented only to person. In the hospital now, she has a temperature of 38.3°C (101°F) and tachycardia (a rapid heart rate). She mumbles incoherently and is otherwise nonverbal. Her skin is cool, dry, and without ulceration. Her mucous membranes are dry. Her abdomen is soft, has normoactive bowel sounds, and is apparently tender in the suprapubic region. Her urinary catheter is draining cloudy urine. A urinalysis reveals too numerous to count white blood cells and bacteria. Gram stain of the urinary sediment reveals gram-positive cocci. Blood and urine cultures also grow gram-positive cocci.

◆ What is the most likely cause of this infection?

◆ How does this organism acquire antibiotic resistance?

ANSWERS TO CASE 8: Enterococcus faecalis

Summary: A 72-year-old woman with an indwelling urinary catheter has a urinary tract infection and bacteremia. Gram-positive cocci are isolated from the urine and blood cultures.

◆ Most likely etiology of infection: Enterococcus faecalis

◆ Mechanism of development of antibiotic resistance: DNA mutation, or plasmid or transposon transfer

CLINICAL CORRELATION

Enterococci are normal flora of the gastrointestinal (GI) tract and are therefore more likely to cause infections in patients with a history of preceding abdominal or genital tract procedures. Although a common cause of community acquired urinary tract infections (UTIs), enterococci are most often associated with nosocomial UTI, particularly in patients with urinary catheters. Bacteremia and rarely endocarditis can result as complications of enterococcal urinary tract or wound infections, with the GI tract the most likely source. Patients at higher risk for enterococcal endocarditis are elderly patients and those with underlying heart disease, particularly the presence of artificial heart valves. Enterococci usually are a cause of subacute left-sided or mitral valve endocarditis.

APPROACH TO SUSPECTED ENTEROCOCCAL UTI

Objectives

1. Know the characteristics of E. faecalis.
2. Know the nature of the intrinsic and acquired antibiotic resistances of E. faecalis.

Definitions

Tachycardia: Increased heart rate above 100 beats per minute.

Transposons: Small pieces of DNA that can replicate and insert randomly in the chromosome.

Leukocyte esterase: An enzyme present in leukocytes, therefore used as an indirect marker of their presence.

DISCUSSION

Characteristics of Enterococcus Species

Enterococcus faecalis is an aerobic gram-positive coccus commonly found as normal fecal flora of healthy humans and other animals. It is capable of growing in extreme conditions, including a wide range of temperatures, high pH, the presence of high concentrations of bile salts, and saline concentrations of up to 6.5 percent. Enterococci have also been isolated from soil, food, and water. Enterococci are difficult to distinguish morphologically from streptococci, and for years were considered a member of the Streptococcus family. They possess the group D streptococcal carbohydrate antigen on their cell surface. Like streptococci, enterococci are often seen singly, in pairs, or short chains on microscopy. Little is known about the virulence factors associated with E. faecalis. Some strains of Enterococcus produce factors, not totally elucidated, which allow their adherence to both heart valves and urinary epithelial cells. One of its other major virulence factors is an intrinsic resistance to multiple antibiotics, including ampicillin, penicillin, and aminoglycosides, which are effective against other gram-positive bacteria. There is also evidence for acquired antibiotic resistance, either by mutation of native DNA or acquisition of new DNA from plasmid or transposon transfer. It is capable of acquiring resistance both from other enterococci and from other bacterial species and has recently been shown to transfer the gene for vancomycin resistance to Staphylococcus aureus.

Diagnosis

Clinical diagnosis of UTI is made by typical clinical symptoms of urgency and/or dysuria followed by a urinalysis and bacterial culture. The presence of white blood cells (positive leukocyte esterase) and bacteria in the urine are indicative of cystitis. The specific etiologic agent can only be determined by culturing the urine in a quantitative manner. The presence of greater than 105 colony-forming units (CFUs) per milliliter of clean catch urine or 104 CFU/mL of catheterized urine is considered significant for a UTI. Colonies of Enterococcus appear nonhemolytic or, in rare cases, α-hemolytic on blood agar and can be specifically identified using a rapid PYR (L-pyrrolidonyl-β-naphthylamide) test. Conventional, overnight identification includes growth in 6.5 percent sodium chloride and esculin hydrolysis in the presence of bile. Further identification of enterococci to the species level is not commonly done in routine clinical laboratories. Although most commercially available identification methods can speciate enterococci difficulties in accurate speciation occurs without the use of DNA sequence analysis. Most clinically significant enterococci are either E. faecalis or E. faecium. Enterococcus faecium tends to be more resistant to antibiotics particularly ampicillin and vancomycin.

Treatment and Prevention

Although enterococci are intrinsically resistant to low concentrations of β-lactam antibiotics, such as ampicillin, these agents are still the first choice for uncomplicated enterococcal urinary tract infections in cases in which the affecting strain is not highly resistant. For complicated UTI or endocarditis, bactericidal therapy is necessary and includes ampicillin or vancomycin plus an aminoglycoside, assuming that the infecting strain is susceptible to ampicillin or vancomycin and high levels of aminoglycosides. An alternative would be vancomycin if it is susceptible; or if resistant, alternative agents such as linezolid or quinupristin/dalfopristin might be appropriate.

Although there is no specific prevention for enterococci because they are able to survive for extended periods of time on inanimate objects, nosocomial outbreaks have been associated with antibiotic-resistant strains of enterococci and proper disinfection and infection control measures are necessary to prevent further spread.

COMPREHENSION QUESTIONS

[8.1] Testing of blood culture isolates from a hospitalized patient revealed grampositive cocci, β-lactamase positive, vancomycin-resistant, PYR-positive, and the presence of Lancefield group D antigen. Which of the following is the most likely isolate identification?

A. Enterococcus faecalis

B. Streptococcus agalactiae

C. Streptococcus bovis

D. Streptococcus pneumoniae

[8.2] Which of the following is the most serious condition that can result as complications of enterococcal urinary tract or wound infections?

A. Cellulitis

B. Gastroenteritis

C. Scarlet fever

D. Subacute endocarditis

E. Toxic shock syndrome

[8.3] After an abdominal surgery for removal of ovarian cysts, this 56-year-old woman has had low-grade fever for the past 2 weeks. She has a history of rheumatic fever as a child. Three of the blood cultures grew gram-positive cocci. Which of the following is the most likely etiologic agent?

A. Group A streptococci

B. Group B streptococci

C. Group C streptococci

D. Group D streptococci

E. Viridans streptococci

Answers

[8.1] A. All bacteria listed are gram-positive cocci. Streptococcus pneumoniae does not have a Lancefield grouping, whereas S. agalactiae has a group B classification. Streptococcus bovis is PYR-negative. Thus, only E. faecalis fulfills all laboratory test results in the above question.

[8.2] D. In patients, the most common sites of enterococci infection are the urinary tract, wounds, biliary tract, and blood. In neonates, enterococci can cause bacteremia and meningitis. In adults, enterococci may cause endocarditis. Thus, bacteremia and/or endocarditis are rare and very serious complications that can result from enterococcal UTI. Cellulitis and toxic shock syndrome are typically associated with both staphylococci and streptococci, whereas scarlet fever is associated only with streptococci. Finally, gastroenteritis can be associated with a number of organisms such as Clostridium difficile.

[8.3] D. Streptococcus bovis is among the nonenterococcal group D streptococci. They are part of the enteric flora and have the ability to cause endocarditis.

MICROBIOLOGY PEARLS ❖ Enterococci, gram-positive cocci, are normal flora of the human and animal GI tract. ❖ Enterococci are a common cause of wound infections following procedures involving the GI or genitourinary (GU) tracts. ❖ Bacteremia and/or endocarditis are rare complications of enterococcal UTIs. ❖ Enterococcal UTIs are often nosocomial infections, especially in elderly patients with urinary catheters. ❖ Ampicillin and vancomycin are the principal antibiotics used to treat enterococcal infections.

REFERENCES

Moellering, RC. Enterococcus species, streptococcus bovis, and leuconostoc species. In: Mandell GL, Bennett JE, Dolin R, eds. Principles and Practice of Infectious Diseases, 5th ed. Philadelphia, PA: Churchill Livingstone, 2000:2147–56. 

Murray PR, Rosenthal KS, Pfaller MA. Enterococcus and other gram-positive cocci. In: Murray PR, Rosenthal KS, Pfaller MA. Medical Microbiology, 5th ed. St. Louis, MO: Mosby, 2005:259–63.

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