Viridans Streptococci
These streptococci, which cause 30 to 65 per cent of NVE case unrelated to drug abuse, are normal inhabitants of the oropharynx, characteristically produce alpha-hemolysis when grown on sheep blood agar, and are usually nontypable using Lance-field’s system. The species causing streptococcal NVE were distributed as follows: Streptococcus mitior (31 per cent of cases). Streptococcus sanguis (24 per cent). S. bovis (27 per cent), Streptococcus faecalis (now Enterococcus faecalis (7 per cent) and streptococcus salivarius and other species (2 per cent). S bovis NVE is frequently associated with coexistent colonic polyps or malignancy.
Sreptococcus Pneumoniae
Although pneumococcal bacteremia occurs frequently, S. pneumoniae accounts for only 1 to 3 per cent of NVE cases. When causing IE, S. pneumoniae frequently involves a previously normal aortic valve and progresses rapidly with valve destruction, myocardial abscess formation and acute congestive heart failure (CHF).
Enterococci
E. Faecalis and Enterococcus faecium cause 85 per cent and 10 per cent of cases of enterococcal IE, respectively. Enterococci are part of the normal gastrointestinal flora and cause genitourinary tract infection. Enterococci account for 5 to 15 per cent of cases of NVE and a similar percentage of PVE cases. Cases occur in young women as a consequence of genitourinary tract manipulation or infection and in older predominantly male patients, who have the urinary tract as a likely portal of entry. Enterococci infect either normal or previously abnormal valves and present as either acute or subacute IE.
Staphylococci
The coagulase-positive staphylococci are a single species, s. aureus. Of the 13 species of coagulase-negative staphylococci that colonize humans, one s. epidermidis has emerged as an important pathogen in the setting of implanted devices and hospitalized patients.
These streptococci, which cause 30 to 65 per cent of NVE case unrelated to drug abuse, are normal inhabitants of the oropharynx, characteristically produce alpha-hemolysis when grown on sheep blood agar, and are usually nontypable using Lance-field’s system. The species causing streptococcal NVE were distributed as follows: Streptococcus mitior (31 per cent of cases). Streptococcus sanguis (24 per cent). S. bovis (27 per cent), Streptococcus faecalis (now Enterococcus faecalis (7 per cent) and streptococcus salivarius and other species (2 per cent). S bovis NVE is frequently associated with coexistent colonic polyps or malignancy.
Sreptococcus Pneumoniae
Although pneumococcal bacteremia occurs frequently, S. pneumoniae accounts for only 1 to 3 per cent of NVE cases. When causing IE, S. pneumoniae frequently involves a previously normal aortic valve and progresses rapidly with valve destruction, myocardial abscess formation and acute congestive heart failure (CHF).
Enterococci
E. Faecalis and Enterococcus faecium cause 85 per cent and 10 per cent of cases of enterococcal IE, respectively. Enterococci are part of the normal gastrointestinal flora and cause genitourinary tract infection. Enterococci account for 5 to 15 per cent of cases of NVE and a similar percentage of PVE cases. Cases occur in young women as a consequence of genitourinary tract manipulation or infection and in older predominantly male patients, who have the urinary tract as a likely portal of entry. Enterococci infect either normal or previously abnormal valves and present as either acute or subacute IE.
Staphylococci
The coagulase-positive staphylococci are a single species, s. aureus. Of the 13 species of coagulase-negative staphylococci that colonize humans, one s. epidermidis has emerged as an important pathogen in the setting of implanted devices and hospitalized patients.
S. aureus is a major cause of IE in all population groups. S. aureus IE is characterized by a highly toxic febrile illness, frequent focal metastatic infection and a 30 to 50 per cent rate of central nervous system complications. Among addicts, left-sided S. aureus IE resembles that in nonaddicts. In contrast, in patients with IE limited to the tricuspid valve, complications are rare and mortality rates are only 2 to 4 per cent.
Coagulase-Negative Staphylococci
These are a major cause of PVE, particularly during the initial year after valve surgery, an important cause of nosocomial IE, and the cause of 3 to 8 per cent of NVE cases, usually in the setting of prior valve abnormalities.
Gram-Negative Bacteria
Organisms of the so-called HACEK group, (Haemophilus, Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella species, Kingella kingae) which are part of the upper respiratory tract and oropharyngeal flora, infect abnormal cardiac valves, causing subacute NVE and cause PVE that occurs a year or more after valve surgery. In NVE, the HACEK organisms have been associated with large vegetations and a high incidence of systemic emboli. These organisms are fastidious and slow growing; when they are suspected,blood cultures should be incubated for 3 weeks.
P. Aeruginosa is the gram-negative bacillus that most commonly causes endocarditis.Pseudomonal IE involves normal and abnormal valves on both sides of the heart and often causes valve destruction and heart failure.The rickettsia C. burnetii infects humans after inhalation of desiccated materials from infected animals or contact with infected parturient animals. At variable intervals after acute infection by C. burnetii (Q. fever), persons with abnormal mitral or aortic valves who have not been able to eradicate the organism develop subacute IE with typical manifestations and often with valve dysfunction causing heart failure. The diagnosis is typically based on high IgG and IgA antibody titers to phase I C. burnetii antigens.
Fungi
Candida albicans, and Aspergillus species are the most common of the many fungal organisms identified as causing IE. Fungal endocarditis arises in specific settings. Valve replacement cardiac surgery and IV drug abuse are major predispositions. The most frequent fungi causing PVE are C. albicans, Aspergillus species, and nonalbicans Candida species, whereas addiction-associated fungal IE is most commonly caused by nonalbicans, Candida species,particularly C. parapsilosis. Bulky vegetations, which embolize frequently, are common in fungal IE. Removal and careful microbiological evaluation of an embolic vegetation may provide an etiological diagnosis in fungal IE.
Coagulase-Negative Staphylococci
These are a major cause of PVE, particularly during the initial year after valve surgery, an important cause of nosocomial IE, and the cause of 3 to 8 per cent of NVE cases, usually in the setting of prior valve abnormalities.
Gram-Negative Bacteria
Organisms of the so-called HACEK group, (Haemophilus, Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella species, Kingella kingae) which are part of the upper respiratory tract and oropharyngeal flora, infect abnormal cardiac valves, causing subacute NVE and cause PVE that occurs a year or more after valve surgery. In NVE, the HACEK organisms have been associated with large vegetations and a high incidence of systemic emboli. These organisms are fastidious and slow growing; when they are suspected,blood cultures should be incubated for 3 weeks.
P. Aeruginosa is the gram-negative bacillus that most commonly causes endocarditis.Pseudomonal IE involves normal and abnormal valves on both sides of the heart and often causes valve destruction and heart failure.The rickettsia C. burnetii infects humans after inhalation of desiccated materials from infected animals or contact with infected parturient animals. At variable intervals after acute infection by C. burnetii (Q. fever), persons with abnormal mitral or aortic valves who have not been able to eradicate the organism develop subacute IE with typical manifestations and often with valve dysfunction causing heart failure. The diagnosis is typically based on high IgG and IgA antibody titers to phase I C. burnetii antigens.
Fungi
Candida albicans, and Aspergillus species are the most common of the many fungal organisms identified as causing IE. Fungal endocarditis arises in specific settings. Valve replacement cardiac surgery and IV drug abuse are major predispositions. The most frequent fungi causing PVE are C. albicans, Aspergillus species, and nonalbicans Candida species, whereas addiction-associated fungal IE is most commonly caused by nonalbicans, Candida species,particularly C. parapsilosis. Bulky vegetations, which embolize frequently, are common in fungal IE. Removal and careful microbiological evaluation of an embolic vegetation may provide an etiological diagnosis in fungal IE.
No comments:
Post a Comment
Note: Only a member of this blog may post a comment.