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Original ArticleOpen Access
Varidans Streptococci in the Oral Flora of the Patients at Risk for Infective Endocarditis : Species and Penicillin Susceptibilities
Chayakul P 
,
Yipintsoi T ,
Hortiwakul R ,
lngviya N
,
Yipintsoi T ,
Hortiwakul R ,
lngviya N TADA YIPINTSOI, M.B.*,
NATNICHA INGVIYA, M.Sc.**
This study examined viridans streptococci (SV) in oral flora of patients at risk of infective
endocarditis (IE) by obtaining 57 isolates from gum-tooth margin swabs of 3 groups of patients. Peni-
cillin minimal inhibitory concentrations (MICs) were determined by E test. Group 1 was from 30
patients with prosthetic heart valves who did not receive antimicrobial agents within 3 months prior
to recruitment. Group 2 consisted of 21 patients with known rheumatic heart diseases who regularly
received penicillin prophylaxis. Group 3 was 2 patients with IE caused by SV in whom dental swabs
were performed before and on the third day of treatment.
Streptococcus mitis
was found most fre-
quently (49% among 51 oral isolates of SV from patients in group 1 and 2) and in both blood cultures
of IE patients. Ninety-four per cent of the isolates were penicillin-susceptible and the rest were
intermediate-resistant (IR) equally distributed in both groups 1 and 2. In 2 patients with IE, oralเธ— SV
obtained after 3 days of penicillin therapy had MICs rising 3 and 5 folds of the baselines. It is sug-
gested that surveillance of susceptibilities of oral SV in patients at risk for IE should be kept up since
this will affect the dose and type of antimicrobial agents in IE prophylaxis.
Key word : Viridans Streptococci, Oral Flora, Infective Endocarditis
NATNICHA INGVIYA, M.Sc.**
This study examined viridans streptococci (SV) in oral flora of patients at risk of infective
endocarditis (IE) by obtaining 57 isolates from gum-tooth margin swabs of 3 groups of patients. Peni-
cillin minimal inhibitory concentrations (MICs) were determined by E test. Group 1 was from 30
patients with prosthetic heart valves who did not receive antimicrobial agents within 3 months prior
to recruitment. Group 2 consisted of 21 patients with known rheumatic heart diseases who regularly
received penicillin prophylaxis. Group 3 was 2 patients with IE caused by SV in whom dental swabs
were performed before and on the third day of treatment.
Streptococcus mitis
was found most fre-
quently (49% among 51 oral isolates of SV from patients in group 1 and 2) and in both blood cultures
of IE patients. Ninety-four per cent of the isolates were penicillin-susceptible and the rest were
intermediate-resistant (IR) equally distributed in both groups 1 and 2. In 2 patients with IE, oralเธ— SV
obtained after 3 days of penicillin therapy had MICs rising 3 and 5 folds of the baselines. It is sug-
gested that surveillance of susceptibilities of oral SV in patients at risk for IE should be kept up since
this will affect the dose and type of antimicrobial agents in IE prophylaxis.
Key word : Viridans Streptococci, Oral Flora, Infective Endocarditis
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