Enterococcus

Classification

General Characteristics

Enterococci (formerly classified as group D streptococci) are part of the normal flora of the human GI tract. Fewer than ⅓ of the known species are responsible for clinically significant human disease. 

Genus characteristics

• Oval-shaped gram-positive Gram-Positive Penicillins cocci Cocci Bacteriology 
• Arranged in pairs or short chains
• Facultative anaerobes Facultative anaerobes Yersinia spp./Yersiniosis
• Catalase-negative
• Optochin-resistant
• Pyrrolidonyl arylamidase (PYR)–positive
• Possess Lancefield group D antigen Antigen Substances that are recognized by the immune system and induce an immune reaction. Vaccination (hence, previously classified as group D streptococci)
• Can be cultured in bile Bile An emulsifying agent produced in the liver and secreted into the duodenum. Its composition includes bile acids and salts; cholesterol; and electrolytes. It aids digestion of fats in the duodenum. Gallbladder and Biliary Tract: Anatomy media and 6.5% NaCl
• Clinically significant human pathogens (most common):
  • Enterococcus faecalis 
  • E. faecium

Pathogenesis

Enterococci most commonly appear in nosocomial infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease.

• Reservoir Reservoir Animate or inanimate sources which normally harbor disease-causing organisms and thus serve as potential sources of disease outbreaks. Reservoirs are distinguished from vectors (disease vectors) and carriers, which are agents of disease transmission rather than continuing sources of potential disease outbreaks. Humans may serve both as disease reservoirs and carriers. Escherichia coli: human GI tract
• Transmission:
  • Translocation from colonization Colonization Bacteriology site in the colonized patient (frequently associated with GI and genitourinary procedures)
  • Transmission to health care workers and other patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship through direct contact, fecal–oral transmission, or fomites Fomites Inanimate objects that carry pathogenic microorganisms and thus can serve as the source of infection. Microorganisms typically survive on fomites for minutes or hours. Common fomites include clothing, tissue paper, hairbrushes, and cooking and eating utensils. Adenovirus
• Virulence factors Virulence factors Those components of an organism that determine its capacity to cause disease but are not required for its viability per se. Two classes have been characterized: toxins, biological and surface adhesion molecules that affect the ability of the microorganism to invade and colonize a host. Haemophilus:
  • Antimicrobial resistance Resistance Physiologically, the opposition to flow of air caused by the forces of friction. As a part of pulmonary function testing, it is the ratio of driving pressure to the rate of air flow. Ventilation: Mechanics of Breathing:
    • Intrinsic ( beta-lactam Beta-Lactam Penicillins antibiotics (through penicillin-binding proteins Penicillin-Binding Proteins Bacterial proteins that share the property of binding irreversibly to penicillins and other antibacterial agents derived from lactams. The penicillin-binding proteins are primarily enzymes involved in cell wall biosynthesis including muramoylpentapeptide carboxypeptidase; peptide synthases; transpeptidases; and hexosyltransferases. Penicillins), trimethoprim Trimethoprim The sulfonamides are a class of antimicrobial drugs inhibiting folic acid synthesize in pathogens. The prototypical drug in the class is sulfamethoxazole. Although not technically sulfonamides, trimethoprim, dapsone, and pyrimethamine are also important antimicrobial agents inhibiting folic acid synthesis. The agents are often combined with sulfonamides, resulting in a synergistic effect. Sulfonamides and Trimethoprim– sulfamethoxazole Sulfamethoxazole A bacteriostatic antibacterial agent that interferes with folic acid synthesis in susceptible bacteria. Its broad spectrum of activity has been limited by the development of resistance. Sulfonamides and Trimethoprim, low levels of clindamycin Clindamycin An antibacterial agent that is a semisynthetic analog of lincomycin. Lincosamides and aminoglycosides Aminoglycosides Aminoglycosides are a class of antibiotics including gentamicin, tobramycin, amikacin, neomycin, plazomicin, and streptomycin. The class binds the 30S ribosomal subunit to inhibit bacterial protein synthesis. Unlike other medications with a similar mechanism of action, aminoglycosides are bactericidal. Aminoglycosides)
    • Acquired ( beta-lactam Beta-Lactam Penicillins antibiotics (through beta-lactamases), high-level aminoglycosides Aminoglycosides Aminoglycosides are a class of antibiotics including gentamicin, tobramycin, amikacin, neomycin, plazomicin, and streptomycin. The class binds the 30S ribosomal subunit to inhibit bacterial protein synthesis. Unlike other medications with a similar mechanism of action, aminoglycosides are bactericidal. Aminoglycosides, tetracycline Tetracycline A naphthacene antibiotic that inhibits amino Acyl tRNA binding during protein synthesis. Drug-Induced Liver Injury, fluoroquinolones Fluoroquinolones Fluoroquinolones are a group of broad-spectrum, bactericidal antibiotics inhibiting bacterial DNA replication. Fluoroquinolones cover gram-negative, anaerobic, and atypical organisms, as well as some gram-positive and multidrug-resistant (MDR) organisms. Fluoroquinolones, rifampin Rifampin A semisynthetic antibiotic produced from streptomyces mediterranei. It has a broad antibacterial spectrum, including activity against several forms of Mycobacterium. In susceptible organisms it inhibits dna-dependent RNA polymerase activity by forming a stable complex with the enzyme. It thus suppresses the initiation of RNA synthesis. Rifampin is bactericidal, and acts on both intracellular and extracellular organisms. Epiglottitis, chloramphenicol Chloramphenicol Chloramphenicol, the only clinically relevant drug in the amphenicol class, is a potent inhibitor of bacterial protein synthesis by binding to the 50S ribosomal subunit and preventing peptide bond formation. Chloramphenicol is a broad-spectrum antibiotic with wide distribution; however, due to its toxicity, its use is limited to severe infections. Chloramphenicol, and vancomycin Vancomycin Antibacterial obtained from streptomyces orientalis. It is a glycopeptide related to ristocetin that inhibits bacterial cell wall assembly and is toxic to kidneys and the inner ear. Glycopeptides)
  • Biofilm Biofilm Encrustations formed from microbes (bacteria, algae, fungi, plankton, or protozoa) embedded in an extracellular polymeric substance matrix that is secreted by the microbes. They occur on body surfaces such as teeth (dental deposits); inanimate objects, and bodies of water. Biofilms are prevented from forming by treating surfaces with dentifrices; disinfectants; anti-infective agents; and anti-fouling agents. Staphylococcus formation:
    • Protects against host defenses
    • Allows gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics exchange (further promoting antibiotic resistance Resistance Physiologically, the opposition to flow of air caused by the forces of friction. As a part of pulmonary function testing, it is the ratio of driving pressure to the rate of air flow. Ventilation: Mechanics of Breathing) 
• Host factors that increase susceptibility:
  • Critical illness
  • Receiving lengthy courses of antibiotics
  • Hematologic malignancies
  • Solid organ transplantation Organ Transplantation Transplantation is a procedure that involves the removal of an organ or living tissue and placing it into a different part of the body or into a different person. Organ transplantations have become the therapeutic option of choice for many individuals with end-stage organ failure. Organ Transplantation

Clinical Relevance

Epidemiology

• Enterococci are 1 of the top 3 species causing nosocomial infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease.
• 4th most common cause of nosocomial bloodstream infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease in the United States
• 35%–40% of enterococcal bloodstream infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease involve vancomycin-resistant E. faecium (VRE)

Diseases caused by enterococci

• Often associated with:
  • Indwelling catheters Indwelling catheters Catheters designed to be left within an organ or passage for an extended period of time. Pseudomonas
  • Surgical instrumentation
  • Underlying structural abnormalities
• Common infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease associated with Enterococcus include:
  • Urinary tract Urinary tract The urinary tract is located in the abdomen and pelvis and consists of the kidneys, ureters, urinary bladder, and urethra. The structures permit the excretion of urine from the body. Urine flows from the kidneys through the ureters to the urinary bladder and out through the urethra. Urinary Tract: Anatomy infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease (most common)
  • Endocarditis Endocarditis Endocarditis is an inflammatory disease involving the inner lining (endometrium) of the heart, most commonly affecting the cardiac valves. Both infectious and noninfectious etiologies lead to vegetations on the valve leaflets. Patients may present with nonspecific symptoms such as fever and fatigue. Endocarditis
  • Bacteremia Bacteremia The presence of viable bacteria circulating in the blood. Fever, chills, tachycardia, and tachypnea are common acute manifestations of bacteremia. The majority of cases are seen in already hospitalized patients, most of whom have underlying diseases or procedures which render their bloodstreams susceptible to invasion. Glycopeptides
  • Intra-abdominal and pelvic infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease (often cholecystitis Cholecystitis Cholecystitis is the inflammation of the gallbladder (GB) usually caused by the obstruction of the cystic duct (acute cholecystitis). Mechanical irritation by gallstones can also produce chronic GB inflammation. Cholecystitis is one of the most common complications of cholelithiasis but inflammation without gallstones can occur in a minority of patients. Cholecystitis)
  • Wound infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease
• Other less common infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease:
  • Meningitis Meningitis Meningitis is inflammation of the meninges, the protective membranes of the brain, and spinal cord. The causes of meningitis are varied, with the most common being bacterial or viral infection. The classic presentation of meningitis is a triad of fever, altered mental status, and nuchal rigidity. Meningitis
  • Pleural space Pleural space The thin serous membrane enveloping the lungs (lung) and lining the thoracic cavity. Pleura consist of two layers, the inner visceral pleura lying next to the pulmonary parenchyma and the outer parietal pleura. Between the two layers is the pleural cavity which contains a thin film of liquid. Pleuritis infection
  • Skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions/ soft tissue Soft Tissue Soft Tissue Abscess infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease

Organism isolation

• Blood cultures: susceptibility testing should be included to choose appropriate therapy
• Stool and perirectal cultures: to evaluate for VRE colonization Colonization Bacteriology

Antibiotic selection Selection Lymphocyte activation by a specific antigen thus triggering clonal expansion of lymphocytes already capable of mounting an immune response to the antigen. B cells: Types and Functions

• Monotherapy:
  • May be appropriate in noncritically ill patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship without endocarditis Endocarditis Endocarditis is an inflammatory disease involving the inner lining (endometrium) of the heart, most commonly affecting the cardiac valves. Both infectious and noninfectious etiologies lead to vegetations on the valve leaflets. Patients may present with nonspecific symptoms such as fever and fatigue. Endocarditis
  • Ampicillin Ampicillin Semi-synthetic derivative of penicillin that functions as an orally active broad-spectrum antibiotic. Penicillins is the drug of choice for susceptible species.
• Combination therapy:
  • Most commonly used in practice
  • For endocarditis Endocarditis Endocarditis is an inflammatory disease involving the inner lining (endometrium) of the heart, most commonly affecting the cardiac valves. Both infectious and noninfectious etiologies lead to vegetations on the valve leaflets. Patients may present with nonspecific symptoms such as fever and fatigue. Endocarditis and all critically ill patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship
  • Cell-wall inhibitor ( ampicillin Ampicillin Semi-synthetic derivative of penicillin that functions as an orally active broad-spectrum antibiotic. Penicillins, ceftriaxone Ceftriaxone A broad-spectrum cephalosporin antibiotic and cefotaxime derivative with a very long half-life and high penetrability to meninges, eyes and inner ears. Cephalosporins, vancomycin Vancomycin Antibacterial obtained from streptomyces orientalis. It is a glycopeptide related to ristocetin that inhibits bacterial cell wall assembly and is toxic to kidneys and the inner ear. Glycopeptides) + aminoglycoside 
  • Often ampicillin Ampicillin Semi-synthetic derivative of penicillin that functions as an orally active broad-spectrum antibiotic. Penicillins and gentamicin Gentamicin Aminoglycosides
• VRE infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease:
  • Linezolid Linezolid An oxazolidinone and acetamide derived anti-bacterial agent and protein synthesis inhibitor that is used in the treatment of gram-positive bacterial infections of the skin and respiratory tract. Oxazolidinones
  • Daptomycin Daptomycin A cyclic lipopeptide antibiotic that inhibits gram-positive bacteria. Lipopeptides and Lipoglycopeptides
  • Tigecycline Tigecycline A tetracycline derivative that acts as a protein synthesis inhibitor. It is used as an antibacterial agent for the systemic treatment of complicated skin and intra-abdominal infections. It is also used for the treatment of community-acquired pneumonia. Tetracyclines
• In addition to antibiotic therapy:
  • All indwelling line and catheters should be removed.
  • Abscesses should be drained.