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 abiotrophia defectiva is part of the normal human microbiota , colonizing the oral , genitourinary , and intestinal tracts .
it is a rare , yet important , cause of infective endocarditis , and is estimated to cause approximately 5 - 6% of all cases of infective endocarditis , including being a major cause of blood culture - negative infective endocarditis .
it affects diseased valves in 90% of cases and it is implicated in embolic complications and valvular destruction , despite being sensitive to antibiotics .
previous studies have shown mortality and relapse rates as high as 17% despite antibiotic treatment , and this makes accurate and quick identification important .
herein we report the first case of infective endocarditis caused by a. defectiva in korea .
a 62-year - old female was admitted to the emergency department ( ed ) after two consecutive episodes of syncope .
the patient was diagnosed with severe rheumatic mitral stenosis , and underwent a mitral valve replacement ( mvr ) .
two months previously , the patient had undergone a simple extraction of her # 16 tooth due to secondary dental caries and had taken prophylactic antibiotics ( amoxicillin 2,000 mg ) . upon admission to the ed the patient was alert and had a body temperature of 38.6c , a pulse rate of 66 beats / min , and blood pressure of 149/51 mmhg . upon physical examination , no cardiac murmur was auscultated and no other evidence , such as clubbed fingers ,
laboratory studies showed a white blood cell count of 14,260/mm(neutrophil 79.6% ) , erythrocyte sediment rate of 92 mm / h and c - reactive protein of 111.1 mg / l .
chest x - ray revealed mild cardiomegaly and electrocardiography showed a newly developed complete atrioventricular block .
chest ct and abdominal - pelvic ct was performed to evaluate fever focus , which showed no significant finding . a transthoracic echocardiogram ( tte )
showed that the mechanical prosthetic mitral valve functioned well , and there was no visible vegetation , however , infective endocarditis could not be completely ruled out because of the patient s previous mvr .
thus , empirical antibiotics ( vancomycin 1 g intravenous q12hr , gentamicin 60 mg intravenous q8hr and rifampin 600 mg per oral q24hr ) were administered , and a transesophageal echocardiogram ( tee ) performed the day after admission showed mitral valve vegetation and mild transvalvular mitral regurgitation ( fig
. 1 ) , leading to a conclusive diagnosis of infective endocarditis according to duke criteria ( one major and three minor criteria ) .
( a ) long - axis view ( 135 ) of a transesophageal echocardiography showing two examples of vegetation attached to the prosthetic mitral valve .
the larger one measures 0.7  0.5 cm ( large arrow head ) and the smaller one measures 0.5  0.3 cm ( small arrow head ) .
( b ) two - chamber view ( 59 ) of a transesophageal echocardiography ( zoomed view ) showing vegetation attached to the prosthetic mitral valve ( arrowhead ) .
a color doppler shows the jet flow with mild transvalvular mitral regurgitation in systole ( arrow ) .
three sets of blood cultures taken on admission showed tiny , non - hemolytic colonies on a blood agar plate ( asan pharmaceutical , hwaseong , korea ) , and pleomorphic gram - positive cocci from smear preparation of the blood agar plate ( fig .
a. defectiva was identified by maldi - tof - ms ( matrix - assisted laser desorption / ionization time - of - flight mass spectrometry , bruker daltonics inc .
, ma , usa ) , not identified in vitek 2 ( biomrieux , marcy l'etoile , france ) systems . however , because the amount of bacteria was insufficient , cultures were sub - cultured on a medium containing vitamin b6 to assess antibiotic susceptibility .
tiny , non - hemolytic colonies on a blood agar plate ( asan pharmaceutical , hwaseong , korea ) after 48 hour of incubation at 35c with 5% co2 ( left ) , and pleomorphic gram - positive cocci from smear preparation of the blood agar plate ( gram stain , 1,000 , right ) .
susceptibility to cefotaxime , penicillin g and vancomycin was tested by the e - test method ; the isolate tested cefotaxime - sensitive ( mic 0.75 g / ml ) , penicillin g - intermediate ( mic 1.0 g / ml ) and vancomycin - sensitive ( mic 0.38 g / ml ) .
an adjusted antibiotic regimen of vancomycin 1 g q12hr and gentamicin 60 mg q8hr was initiated , after which the patient s fever subsided .
vancomycin therapeutic drug monitoring was performed , and vancomycin dosage was adjusted to 400 mg q12hr . on day 12 of admission ,
the patient became feverish once more and in the subsequent tee the mitral valve vegetation on the medial side seemed to have resolved , but there was an increase in the size of the vegetation on the lateral annulus ( 0.5  0.3 cm  0.8  0.3 cm ) which indicated a perivalvular infection ( fig .
operation finding showed small vegetation in prosthetic mv and annulus , which was removed , and mvr was conducted using 23 mm ats medical open pivot heart valve ( ats medical , inc . ,
pathology finding showed myxoid degeneration , acute and chronic inflammation , fibrosis and calcification , and tissue culture showed no growth of organism ( it was on the 19 day on antibiotics , and blood culture was negatively converted at this time ) . on day 23 of admission ,
the patient was treated with antibiotics for 5 weeks and was discharged on day 36 .
the patient was followed - up at an out - patient clinic for 3 months after discharge with no significant complications .
organisms of the genus abiotrophia were first classified as nutritionally variant streptococci ( nvs ) in 1961 .
bouvet et al . identified two species of nvs ; streptococcus defectivus and streptococcus adjacens . in 1995 , kawamura et al .
nvs are part of the normal flora of the mouth and urogenital and intestinal tracts .
recently , an increasing number of cases have been described of a. defectiva isolates recovered from invasive and non - invasive infections following dental procedures .
has fastidious culturing and the unspecific colony morphology that they presents on primary detection , such strains have caused major diagnostic difficulties .
thus , it has been supposed that many culture - negative endocarditis could have been caused by these species , which could have lead to an underestimation as pathogens of infective endocarditis . in this case report
maldi - tof - ms is a new technology for routine identification of bacteria in clinical microbiology laboratories .
much of the work using maldi - tof - ms for microbial identification has focused on demonstrating that reproducible mass spectra can be obtained using intact cells and developing algorithms for interpretation and comparison of these spectra . by testing colonies
, it takes only a few minutes to have a correct identification which makes not only possible to identify the microorganisms at the species levels but sometimes at the sub - species and strains levels , allowing the detection of epidemic lineages .
a. defectiva can cause serious infections such as bacteremia , osteomyelitis , brain abscess , pancreatic abscess , septic arthritis , crystalline keratopathy and in rare cases , infective endocarditis .
endocarditis caused by nvs is implicated in 56% of all streptococcal endocarditis cases , and < 1% of all endocarditis cases are caused by a. defective . however , a. defectiva has a higher affinity for the endocardium because of its ability secrete exopolysaccharide , enabling it to adhere to fibronectin in the extracellular matrix .
of all the nvs - induced endocarditis patients , 90% suffered from heart disease , and in most cases , bacteremia associated with the pre - existing valvular heart disease led to the development of endocarditis with subacute prognoses .
infective endocarditis caused by a. defectiva and other nvs had higher mortality , morbidity and complication rates than those caused by other viridans streptococci .
most deaths were due to refractory congestive cardiac failure or major systemic emboli . a mortality rate of up to 17% has been reported , which is higher compared to endocarditis caused by viridians streptococci ( 012% ) .
previous studies have shown a treatment failure rate as high as 41% , despite the use of appropriate antibiotics .
the antibiotic regimen to combat a. defectiva endocarditis includes penicillin or ampicillin , plus an aminoglycoside or vancomycin for cases of antimicrobial resistance , taken for 46 weeks .
infective endocarditis due to a. defectiva progresses slowly , but despite its sensitivity to antimicrobials ~50% of cases need surgical management . surgical treatment combined with concurrent antimicrobial therapy result in better prognoses , and
the main indications for surgery are persistent sepsis and vegetation , severe congestive heart failure and recurrent embolism . in korea ,
2 cases of infective endocarditis caused by s. adjacens were first reported in 1996 . since then , a case of infective endocarditis by grnulicatella adjacens was reported in 2010 .
after classified as a. defectiva , this is the first report as the pathogen of infective endocarditis in korea .
the case presented here is an example of the successful treatment of infective endocarditis caused by a. defectiva following a tooth extraction in a post - mvr patient , and represents the first reported case of infective endocarditis caused by a. defectiva in korea .
this case shows that a. defectiva could be considered as a causative organism of infective endocarditis in korea .
abiotrophia defectiva , a nutritionally variant streptococci can cause bacteremia , brain abscess , septic arthritis and in rare cases , infective endocarditis , which accounts for 5 - 6% of all cases . 
 a. defectiva is characteristically difficult to diagnose and the mortality , morbidity and complication rates are high . here 
 , we discuss a case of infective endocarditis caused by a. defectiva . 
 a 62-year - old female had previously undergone prosthetic valve replacement 6 years prior to admission . 
 she developed infective endocarditis after tooth extraction . 
 her endocarditis was successfully treated with antimicrobial therapy and mitral valve replacement surgery . 
 this is the first case of infective endocarditis caused by a. defectiva reported in korea . 
 this case shows that a. defectiva could be considered as a causative organism of infective endocarditis in korea .