Belonging to the tribe Klebsielleae found in the family Enterobacteriaceae, the genus Klebsiella is the second most populous enteric genus found in the gastrointestinal tract of man. The genus Klebsiella is named after the late nineteenth century German microbiologist, Edwin Klebs, but the Klebsiella bacillus was for many years referred to as the Friedlander bacillus after being described by Carl Friedlander. The genus consists of four species, recognized by the Centers for Disease Control (CDC), and Bergey's Manual of Determinative Bacteriology, namely, K. pneumoniae (the type species), K. ozaenae, K. rhinoscleromatis, and K. oxytoca. K. pneumoniae is one of a few gram-negative rods that can cause a primary pneumonia.

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During a 3-month period 252 blood cultures were obtained on adult patients seen in our emergency room with fever and chills suggesting bacteremia. 62/252 blood cultures were positive by standard aerobic/anaerobic blood culture techniques. Buffy coat smears were positive in 76% of patients (47/62) when stained with the acridine orange technique and in 52% (32/62) when stained by the Gram method. Acridine orange was thus superior to the Gram stain for the detection of bacteremia (p less than 0.05). Gram-negative organisms were present in 70% of the buffy coat preparation stain by the acridine orange method. Escherichia coli was the most common organism in buffy coat smears and subsequently identified by blood culture. We conclude that acridine orange stained buffy coat smears provide rapid detection of clinically suspected bacteremia in preselected acutely ill adult patients.

The genus Enterobacter belongs to the tribe Klebsielleae found in the family Enterobacteriaceae. Members of this genus had previously been referred to as Aerobacter. The clinical importance of this genus as a separate entity was not fully appreciated until the 1960s. Until that time, the differentiation of Enterobacter from Klebsiella was not routinely performed, which resulted in many infections reported as being caused by the Klebsiella-Aerobacter group. Added confusion occurred at this time with the taxonomy change of Aerobacter to Enterobacter.