Principles and Practice of Clinical Bacteriology Second Edition - Free

28 ORAL AND OTHER NON-β-HAEMOLYTIC STREPTOCOCCI
Under certain conditions (Table 2.5) a 2-week course of treatment
with penicillin and gentamycin is adequate for endocarditis caused by
fully sensitive organisms.
Infective endocarditis occurs less frequently in children than in
adults, although the frequency of disease in children appears to be
increasing since the 1980s despite a decline in the incidence of rheumatic
fever, a major predisposing factor in the past. This is due, at least in
part, to improved survival of children who are at risk, such as those
with congenital heart disease. In children over 1 year old with
endocarditis, the oral streptococci are the most frequently isolated
organisms (32–43% of patients; reviewed by Ferrieri et al., 2002). In
general, the principles of antibiotic treatment of paediatric endocarditis
are similar to those for the treatment of adults.
Prevention and Control
When patients are known to have predisposing cardiac abnormalities,
great care should be taken to protect them from the risk of endocarditis
when undergoing any dental, surgical or investigational procedures
which might induce a transient bacteraemia. However, even if carried
out perfectly, this approach is not likely to prevent all episodes of
endocarditis since up to 50% of cases occur in individuals without
previously diagnosed cardiac abnormalities (Hoen et al., 2002). For
the identified at-risk group, the appropriate antibiotic prophylaxis is
summarized in Table 2.6.
The main principle governing these prophylactic regimens is that a
high circulating blood level of a suitable bactericidal agent should be
achieved at a time when the bacteraemia would occur. For bacteraemia
arising during dental surgery, additional protection may be
achieved by supplementing the use of systemic antibiotics with locally
applied chlorhexidine gluconate gel (1%) or chlorhexidine gluconate
mouthwash (0.2%) 5 min before the procedure. Dental procedures that
require antibiotic prophylaxis include extractions, scaling and surgery
involving gingival tissues. A most important consideration for
patients who are at risk of endocarditis is that their dental treatment be
planned in such a way that the need for frequent antibiotic prophylaxis
and the consequent selection for resistant bacteria among the resident
flora is avoided. For multistage dental procedures, a maximum of two
single doses of penicillin may be given in a month and alternative
drugs should be used for further treatment, and penicillin should not
be used again for 3–4 months.
Abscesses Caused by Non-b-Haemolytic Streptococci
Streptococci are frequently isolated from purulent infections in
various parts of the body, including dental, central nervous system
(CNS), liver and lung abscesses. Commonly, there is a mixture of
several organisms in the pus, which may contain obligate anaerobes as
well as streptococci and other facultative anaerobes. Consequently, it
may be difficult to determine the contribution that any single strain or
species is making to the infectious process. The source of these
bacteria is usually the patient’s own commensal microflora and may
be derived from the mouth, upper respiratory tract, gastrointestinal
tract or genitourinary tract.
Members of the anginosus group of streptococci (previously known
as S. milleri group, or SMG, streptococci) have a particular propensity
to cause abscesses. The development of reliable identification and
speciation methods for this group of streptococci has allowed
epidemiological analysis to determine whether there is a correlation
between species and anatomical site of infection (reviewed by Belko
et al., 2002). Studies indicate that S. intermedius was more frequently
isolated from infections of the CNS and liver, S. constellatus was
more frequently isolated from lung infections, whereas S. anginosus
was more frequently associated with infections of the gastrointestinal
and genitourinary tracts and with soft-tissue infections. Although
studies have identified several virulence determinants of anginosus
Table 2.6
group streptococci (see Pathogenesis), we have little understanding of
the bacterial–host interactions that define the body-site specificity
identified by these epidemiological studies.
Pathogenesis
Recommended antibiotic prophylaxis for endocarditis
Dental procedures under local or no anaesthesia
Patients who have not received more than a single dose of a penicillin in the
previous month, including those with a prosthetic valve (but not those who
have had endocarditis)
• Oral amoxicillin 3 g 1 h before procedure (children under 5 years, quarter
adult dose; 5–10 years, half adult dose)
Patients who are penicillin-allergic or have received more than a single dose of
a penicillin in the previous month
• Oral clindamycin 600 mg 1 h before procedure (children under 5 years,
clindamycin quarter adult dose or azithromycin 200 mg; 5–10 years,
clindamycin half adult dose or azithromycin 300 mg)
Patients who have had endocarditis
• Amoxicillin plus gentamycin, as under general anaesthesia
Dental procedures under general anaesthesia
No special risk (including patients who have not received more than a single
dose of a penicillin in the previous month)
Either
• Intravenous amoxicillin 1 g at induction, then oral amoxicillin 500 mg 6 hours
later (children under 5 years, quarter adult dose; 5–10 years, half adult dose)
Or
• Oral amoxicillin 3 g 4 h before induction, then oral amoxicillin 3 g as soon
as possible after procedure (children under 5 years, quarter adult dose; 5–10
years, half adult dose)
Special risk (patients with a prosthetic valve or who have had endocarditis)
• Intravenous amoxicillin 1 g plus intravenous gentamicin 120 mg at
induction, then oral amoxicillin 500 mg 6 h later (children under 5 years,
amoxicillin quarter adult dose, gentamicin 2 mg/kg; 5–10 years, amoxicillin
half adult dose, gentamicin 2 mg/kg)
Patients who are penicillin-allergic or who have received more than a single
dose of a penicillin in the previous month
• Intravenous vancomycin 1 g over at least 100 min, then intravenous
gentamycin 120 mg at induction or 15 min before procedure (children under
10 years, vancomycin 20 mg/kg, gentamicin 2 mg/kg)
Or
• Intravenous teicoplanin 400 mg plus gentamicin 120 mg at induction or
15 min before procedure (children under 14 years, teicoplanin 6 mg/kg,
gentamicin 2 mg/kg)
Or
• Intravenous clindamycin 300 mg over at least 10 min at induction or 15 min
before procedure, then oral or intravenous clindamycin 150 mg 6 h later
(children under 5 years, quarter adult dose; 5–10 years, half adult dose)
Table adapted from the British National Formulary (2003), based on Recommendations of
the Endocarditis Working Party of the British Society for Antimicrobial Chemotherapy.
Members of the anginosus group of streptococci possess multiple
pathogenic properties that may contribute to disease. These include
adhesion to host tissue components such as fibronectin, fibrinogen
and fibrin–platelet clots (Willcox, 1995; Willcox et al., 1995) and the
aggregation of platelets (Willcox et al., 1994; Kitada, Inoue and
Kitano, 1997) (Table 2.7).
Abscesses are frequently polymicrobial in nature, and studies
suggest that coinfection of streptococci with strict anaerobes such as
Fusobacterium nucleatum and Prevotella intermedia, both common
oral isolates, enhanced pathology. Thus, coinfection of anginosus
group streptococci with F. nucleatum in a mouse subcutaneous
abscess model resulted in increased bacterial survival and increased
abscess size compared with abscesses formed following monoculture
inoculation of streptococcus or F. nucleatum alone (Nagashima,