Enterococcus avium

Updated : November 11, 2023

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Epidemiology 

The epidemiology of Enterococcus avium is the study of the distribution and determinants of the infection caused by this bacterium in human and animal populations. Enterococcus avium is a gram-positive, facultatively anaerobic coccus mostly found in birds but can also be transmitted through food products such as poultry meat, eggs, cheese, and honey. Enterococcus avium can cause various infections in humans and animals, such as brain abscesses, endocarditis, bacteremia, urinary tract infections, wound infections, and peritonitis. 

Enterococcus avium is a rare and opportunistic pathogen that usually affects immunocompromised or debilitated patients with underlying diseases or conditions, such as diabetes mellitus, malignancy, renal failure, liver cirrhosis, or previous surgery. The incidence and prevalence of Enterococcus avium infection are not well known, but some studies have reported that it accounts for less than 1% of all enterococcal isolates from clinical specimens. The mortality rate of Enterococcus avium infection needs to be better established. Still, it may range from 20% to 50%, depending on the site and severity of the infection and comorbidities. 

Nosocomial enterococcal bacteremia in Taiwan: incidence, features of the disease, and prognosis. The study found that the incidence of enterococcal bacteremia was 3.9 per 10,000 admissions and that Enterococcus faecium was the predominant species (74%), followed by Enterococcus faecalis (20%). Enterococcus avium accounted for only 0.6% of the cases. The mortality rate of enterococcal bacteremia was 28%, and the risk factors for mortality were older age, malignancy, septic shock, polymicrobial infection, and inappropriate empirical therapy. 

Classification and Structure 

  • Kingdom: Bacteria 
  • Phylum: Firmicutes 
  • Class: Bacilli 
  • Order: Lactobacillales 
  • Family: Enterococcaceae 
  • Genus: Enterococcus 
  • Species:Enterococcus avium 

Enterococcus avium is a Gram-positive bacterium that retains the crystal violet stain in the Gram-staining process. It is spherical or oval and typically arranged in pairs or short chains. As a member of the Enterococcus genus, it shares certain characteristic features with other enterococci, such as the ability to grow in the presence of 6.5% NaCl and inactive catalase are present. 

Enterococcus avium, like other enterococci, possesses a cell wall containing peptidoglycan, which provides structural support to the bacterium. The cell wall is a vital target for some antibiotics. It also has a cytoplasmic membrane, cytoplasm, and genetic material (DNA) responsible for its metabolic functions and replication. 

This bacterium is facultatively anaerobic, which can survive in both oxygenated and oxygen-limited environments. Additionally, Enterococcus avium is known for its resistance to multiple antibiotics, making it a concern in clinical settings, as it can be involved in healthcare-associated infections. 

Antigenic Types 

There is no information about the antigenic types of Enterococcus avium. However, Enterococcus avium is a species of Enterococcus mainly found in birds. Rarely is it also a cause of infection in humans, and in such cases, it may be vancomycin-resistant and is referred to as VREA. Linezolid has been used to treat VREA instances in people. 

The genome of Enterococcus avium includes a round chromosome and a plasmid. The chromosome is about 4.8 Mb in size and has a 39% or so of the GC. The plasmid includes 99 protein-coding sequences and is around 88 kb in size. The bile adaptation genes bsh, sbcC, mutS, nifI, galU, & hupB are among those found in the genome. Additionally, it has genes related to virulence, including esp, fss1, fss3, bsh, ecbA,  lap, clpC, clpE, & clpP. 

The type of strain of Enterococcus avium is ATCC 14025. It has been deposited in several culture collections worldwide, including CCUG, CIP, DSM, JCM, BCCM/LMG, NBRC, NCDO, NCIMB, NCTC, VKM, and personal. The strain type was isolated from chicken feces in 1967 by Nowlan and Deibel. 

Pathogenesis 

The pathogenesis of Enterococcus avium is not well understood, but some studies have suggested that it may involve several factors, such as: 

  • possessing the capacity to cling to and penetrate host cells, including macrophages and epithelial cells, through surface proteins such as Esp, Fss1, Fss3, and EcbA. 
  • The ability to resist host defenses, such as bile salts, oxidative stress, and antimicrobial peptides, through genes such as bsh, sbcC, mutS, nifI, galU, and hupB. 
  • The ability to produce biofilms may enhance its persistence and resistance to antibiotics and host immune responses. 
  • The ability to acquire antibiotic resistance genes, such as vanA and vanB, confer resistance to vancomycin and teicoplanin. 
  • The ability to secrete enzymes, such as alpha galactosidase, may degrade host glycoproteins and glycolipids. 
  • Enterococcus avium can cause various infections in humans and animals, such as brain abscesses, endocarditis, bacteremia, urinary tract infections, wound infections, and peritonitis. It can also be transmitted through food products such as poultry meat, eggs, cheese, and honey. 

Host Defenses 

The host defenses of Enterococcus avium are the human or animal immune system’s mechanisms to fight against the infection caused by this bacterium. Some of the host defenses that are involved in this process are: 

  • Creating antibodies capable of binding to and neutralizing enterococcal antigens, such as cell wall components, surface proteins, and toxins. 
  • The activation of a complement system that can opsonize and lyse the enterococcal cells or enhance the phagocytosis by macrophages and neutrophils. 
  • inflammatory cells, like macrophages, are drawn to the area of neutrophils and natural killer cells that can produce reactive oxygen and nitrogen species, cytokines, and chemokines that can kill or inhibit the growth of enterococci. 
  • Antimicrobial peptide expression, including defensins, cathelicidins, and histatins, can disrupt enterococci’s membrane integrity and function. 
  • The maintenance of normal microbiota in the mucosal surfaces that can compete with enterococci for nutrients and attachment sites and produce substances that can inhibit their growth or virulence. 

Clinical manifestations 

Enterococcus avium is a species of bacteria that is mainly found in birds. It is a rare cause of infection in humans, and it may be resistant to vancomycin, a common antibiotic. This type of infection is called VREA, which stands for vancomycin-resistant Enterococcus avium. 

Some of the clinical manifestations of Enterococcus avium infection are: 

  • Brain abscess: This is a collection of pus in the brain that can cause headaches, fever, seizures, and neurological deficits. A case report described a patient with a brain abscess due to Enterococcus avium who was successfully treated with surgery and linezolid, another antibiotic. 
  • Bacteremia is the blood with bacteria that can cause sepsis, a life-threatening condition affecting multiple organs. A study reported nine Enterococcus avium bacteremia patients with underlying conditions such as diabetes, cancer, and HIV. The mortality rate was high (67%), and the role of Enterococcus avium as a pathogen or a marker of severe illness was unclear. 
  • Endocarditis: This infection of the heart valves can cause heart failure, embolism, and stroke. A case report described a patient with endocarditis due to Enterococcus avium who was successfully treated with surgery and linezolid. 

Diagnosis 

These diagnostic approaches play a crucial role in identifying the presence of the bacterium and determining the appropriate treatment. Let’s recap the methods briefly: 

  • Gram stain: This method involves staining a specimen (e.g., blood, urine, cerebrospinal fluid, wound exudate, or peritoneal fluid) and observing it under a microscope. Gram-positive cocci in pairs or short chains suggest the presence of enterococci, including Enterococcus avium. 
  • Culture: Specimens are cultured on specific media like blood agar or selective media to promote the growth of Enterococcus avium colonies. These colonies are typically alpha-hemolytic (partial breakdown of red blood cells) and grey. Further identification of the species can be made through biochemical tests, such as catalase, bile esculin, salt tolerance, and pyrrolidonyl arylamidase (PYR). 
  • Molecular methods: Advanced techniques like polymerase chain reaction (PCR), pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), or whole-genome sequencing (WGS) are used to detect and characterize Enterococcus avium at the genetic level. These methods help identify specific strains, determine antibiotic resistance profiles, and assess clonal relationships among isolates. 
  • Serological tests: Serological tests, like enzyme-linked immunosorbent assay (ELISA) or agglutination, detect antibodies against Enterococcus avium antigens in the patient’s serum. The presence of these antibodies indicates a recent or ongoing infection. 

Control 

Prevention of Enterococcus avium infection: 

  • Avoid contact with sick or dead birds; use protective gloves and masks when handling them. 
  • Wash hands thoroughly after touching animals or animal products. 
  • Cook poultry meat and eggs thoroughly to prevent cross-contamination. 
  • Store cheese and honey properly and discard spoiled products. 
  • Seek prompt medical attention if infection symptoms occur after bird exposure. 
  • Follow prescribed antibiotics and complete the treatment. 
  • Practice good hygiene and disinfect contaminated surfaces. 
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Enterococcus avium

Updated : November 11, 2023

Mail Whatsapp PDF Image



Epidemiology 

The epidemiology of Enterococcus avium is the study of the distribution and determinants of the infection caused by this bacterium in human and animal populations. Enterococcus avium is a gram-positive, facultatively anaerobic coccus mostly found in birds but can also be transmitted through food products such as poultry meat, eggs, cheese, and honey. Enterococcus avium can cause various infections in humans and animals, such as brain abscesses, endocarditis, bacteremia, urinary tract infections, wound infections, and peritonitis. 

Enterococcus avium is a rare and opportunistic pathogen that usually affects immunocompromised or debilitated patients with underlying diseases or conditions, such as diabetes mellitus, malignancy, renal failure, liver cirrhosis, or previous surgery. The incidence and prevalence of Enterococcus avium infection are not well known, but some studies have reported that it accounts for less than 1% of all enterococcal isolates from clinical specimens. The mortality rate of Enterococcus avium infection needs to be better established. Still, it may range from 20% to 50%, depending on the site and severity of the infection and comorbidities. 

Nosocomial enterococcal bacteremia in Taiwan: incidence, features of the disease, and prognosis. The study found that the incidence of enterococcal bacteremia was 3.9 per 10,000 admissions and that Enterococcus faecium was the predominant species (74%), followed by Enterococcus faecalis (20%). Enterococcus avium accounted for only 0.6% of the cases. The mortality rate of enterococcal bacteremia was 28%, and the risk factors for mortality were older age, malignancy, septic shock, polymicrobial infection, and inappropriate empirical therapy. 

Classification and Structure 

  • Kingdom: Bacteria 
  • Phylum: Firmicutes 
  • Class: Bacilli 
  • Order: Lactobacillales 
  • Family: Enterococcaceae 
  • Genus: Enterococcus 
  • Species:Enterococcus avium 

Enterococcus avium is a Gram-positive bacterium that retains the crystal violet stain in the Gram-staining process. It is spherical or oval and typically arranged in pairs or short chains. As a member of the Enterococcus genus, it shares certain characteristic features with other enterococci, such as the ability to grow in the presence of 6.5% NaCl and inactive catalase are present. 

Enterococcus avium, like other enterococci, possesses a cell wall containing peptidoglycan, which provides structural support to the bacterium. The cell wall is a vital target for some antibiotics. It also has a cytoplasmic membrane, cytoplasm, and genetic material (DNA) responsible for its metabolic functions and replication. 

This bacterium is facultatively anaerobic, which can survive in both oxygenated and oxygen-limited environments. Additionally, Enterococcus avium is known for its resistance to multiple antibiotics, making it a concern in clinical settings, as it can be involved in healthcare-associated infections. 

Antigenic Types 

There is no information about the antigenic types of Enterococcus avium. However, Enterococcus avium is a species of Enterococcus mainly found in birds. Rarely is it also a cause of infection in humans, and in such cases, it may be vancomycin-resistant and is referred to as VREA. Linezolid has been used to treat VREA instances in people. 

The genome of Enterococcus avium includes a round chromosome and a plasmid. The chromosome is about 4.8 Mb in size and has a 39% or so of the GC. The plasmid includes 99 protein-coding sequences and is around 88 kb in size. The bile adaptation genes bsh, sbcC, mutS, nifI, galU, & hupB are among those found in the genome. Additionally, it has genes related to virulence, including esp, fss1, fss3, bsh, ecbA,  lap, clpC, clpE, & clpP. 

The type of strain of Enterococcus avium is ATCC 14025. It has been deposited in several culture collections worldwide, including CCUG, CIP, DSM, JCM, BCCM/LMG, NBRC, NCDO, NCIMB, NCTC, VKM, and personal. The strain type was isolated from chicken feces in 1967 by Nowlan and Deibel. 

Pathogenesis 

The pathogenesis of Enterococcus avium is not well understood, but some studies have suggested that it may involve several factors, such as: 

  • possessing the capacity to cling to and penetrate host cells, including macrophages and epithelial cells, through surface proteins such as Esp, Fss1, Fss3, and EcbA. 
  • The ability to resist host defenses, such as bile salts, oxidative stress, and antimicrobial peptides, through genes such as bsh, sbcC, mutS, nifI, galU, and hupB. 
  • The ability to produce biofilms may enhance its persistence and resistance to antibiotics and host immune responses. 
  • The ability to acquire antibiotic resistance genes, such as vanA and vanB, confer resistance to vancomycin and teicoplanin. 
  • The ability to secrete enzymes, such as alpha galactosidase, may degrade host glycoproteins and glycolipids. 
  • Enterococcus avium can cause various infections in humans and animals, such as brain abscesses, endocarditis, bacteremia, urinary tract infections, wound infections, and peritonitis. It can also be transmitted through food products such as poultry meat, eggs, cheese, and honey. 

Host Defenses 

The host defenses of Enterococcus avium are the human or animal immune system’s mechanisms to fight against the infection caused by this bacterium. Some of the host defenses that are involved in this process are: 

  • Creating antibodies capable of binding to and neutralizing enterococcal antigens, such as cell wall components, surface proteins, and toxins. 
  • The activation of a complement system that can opsonize and lyse the enterococcal cells or enhance the phagocytosis by macrophages and neutrophils. 
  • inflammatory cells, like macrophages, are drawn to the area of neutrophils and natural killer cells that can produce reactive oxygen and nitrogen species, cytokines, and chemokines that can kill or inhibit the growth of enterococci. 
  • Antimicrobial peptide expression, including defensins, cathelicidins, and histatins, can disrupt enterococci’s membrane integrity and function. 
  • The maintenance of normal microbiota in the mucosal surfaces that can compete with enterococci for nutrients and attachment sites and produce substances that can inhibit their growth or virulence. 

Clinical manifestations 

Enterococcus avium is a species of bacteria that is mainly found in birds. It is a rare cause of infection in humans, and it may be resistant to vancomycin, a common antibiotic. This type of infection is called VREA, which stands for vancomycin-resistant Enterococcus avium. 

Some of the clinical manifestations of Enterococcus avium infection are: 

  • Brain abscess: This is a collection of pus in the brain that can cause headaches, fever, seizures, and neurological deficits. A case report described a patient with a brain abscess due to Enterococcus avium who was successfully treated with surgery and linezolid, another antibiotic. 
  • Bacteremia is the blood with bacteria that can cause sepsis, a life-threatening condition affecting multiple organs. A study reported nine Enterococcus avium bacteremia patients with underlying conditions such as diabetes, cancer, and HIV. The mortality rate was high (67%), and the role of Enterococcus avium as a pathogen or a marker of severe illness was unclear. 
  • Endocarditis: This infection of the heart valves can cause heart failure, embolism, and stroke. A case report described a patient with endocarditis due to Enterococcus avium who was successfully treated with surgery and linezolid. 

Diagnosis 

These diagnostic approaches play a crucial role in identifying the presence of the bacterium and determining the appropriate treatment. Let’s recap the methods briefly: 

  • Gram stain: This method involves staining a specimen (e.g., blood, urine, cerebrospinal fluid, wound exudate, or peritoneal fluid) and observing it under a microscope. Gram-positive cocci in pairs or short chains suggest the presence of enterococci, including Enterococcus avium. 
  • Culture: Specimens are cultured on specific media like blood agar or selective media to promote the growth of Enterococcus avium colonies. These colonies are typically alpha-hemolytic (partial breakdown of red blood cells) and grey. Further identification of the species can be made through biochemical tests, such as catalase, bile esculin, salt tolerance, and pyrrolidonyl arylamidase (PYR). 
  • Molecular methods: Advanced techniques like polymerase chain reaction (PCR), pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), or whole-genome sequencing (WGS) are used to detect and characterize Enterococcus avium at the genetic level. These methods help identify specific strains, determine antibiotic resistance profiles, and assess clonal relationships among isolates. 
  • Serological tests: Serological tests, like enzyme-linked immunosorbent assay (ELISA) or agglutination, detect antibodies against Enterococcus avium antigens in the patient’s serum. The presence of these antibodies indicates a recent or ongoing infection. 

Control 

Prevention of Enterococcus avium infection: 

  • Avoid contact with sick or dead birds; use protective gloves and masks when handling them. 
  • Wash hands thoroughly after touching animals or animal products. 
  • Cook poultry meat and eggs thoroughly to prevent cross-contamination. 
  • Store cheese and honey properly and discard spoiled products. 
  • Seek prompt medical attention if infection symptoms occur after bird exposure. 
  • Follow prescribed antibiotics and complete the treatment. 
  • Practice good hygiene and disinfect contaminated surfaces. 

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