Introduction: Fastidious Gram-negative organisms classified as the HAC
EK group (Haemophilus spp., Actinobacillus actinomycetemecomitans, Car
diobacterium hominis, Eikenella corrodens and Kingella spp.) are rare
causes of infective endocarditis. Case report: In this series, we repo
rt six cases of endocarditis in Saudi patients occurring between 1990
and 1994 in our hospital, caused by two of the organisms in the HACEK
group, i.e. Cardiobacterium hominis and Actinobacillus actinomycetemco
mitans. The clinical features, predisposing factors and treatment of t
he patients are briefly described. The microscopic and cultural charac
teristics of the organisms are described together with the laboratory
methods of diagnosis. Major findings: HACEK endocarditis was frequentl
y associated with prosthetic heart valves or structural heart abnormal
ities. Dental caries or periodontal disease seems to be a predisposing
factor. The prognosis of HACEK endocarditis is very good as clinical
and bacteriological cure were achieved with antibiotic therapy in all
our cases except one who required mitral valve replacement. Contrary t
o previous reports we did not find all the organisms sensitive to peni
cillin and aminoglycosides. However, all our isolates were sensitive t
o amoxycillin, cefuroxime, ceftriaxone and ciprofloxacin. Conclusions:
Laboratory diagnosis of HACEK group of organisms requires a high inde
x of suspicion and should be suspected in cases of endocarditis in whi
ch fastidious Gram-negative coccobacilli are isolated which fail to gr
ow on MacConkey agar. Empiric therapy should be started in suspected c
ases with second generation cephalosporins or wit ciprofloxacin, until
antibiotic sensitivity results become available. Antibiotic therapy s
hould be continued for 4-6 weeks. Progress and outcome was very good i
n the series.