Enterobacter and Pantoea
The genus Enterobacter is composed of 12 species, one of which consists of two biotypes. Clinically significant
Enterobacter spp. that have been isolated from clinical samples include E. cloacae, E. aerogenes, E. gergoviae, E. sakazakii, and E. hormaechei. Members of this genus are motile. The colony morphology of many of the species resembles that of Klebsiella when growing on MacConkey agar. Enterobacter spp. Grow on Simmons citrate medium and in potassium cyanide broth; the methyl red test is negative and the Voges- Proskauer test is positive. Unlike Klebsiella, however, Enterobacter spp. usually produce ornithine decarboxylase;
lysine decarboxylase is produced by most species but not by E. gergoviae or E. cloacae. E. cloacae and E. aerogenes are the two most common isolates from this genus. These two species have been isolated from wounds, urine, blood, and CSF.
Distinguishing characteristics between E. cloacae, E. aerogenes, and K pneumoniae are shown in Table 20-6.
E. agglomerans gained notoriety with a nationwide outbreak of septicemia resulting from contaminated intravenous fluids. Later designated as E. agglomerans complex, it includes species that are lysine, ornithine,
and arginine negative or “triple decarboxylases negative.”
More than 13 hybridization groups (HG) have been described in this complex. E. agglomerans HG XIII, which may produce a yellow pigment, is primarily a plant pathogen. E. agglomerans has been renamed Pan toea agglomerans. Figure 20-4 depicts a yellowpigmented P. agglomerans. E. gergoviae is found in respiratory samples but is rarely isolated from blood cultures. E. sakazakii, a yellow-pigmented Enterobacter sp., has been docu-mented as a pathogen in neonates, causing meningitis and bacteremia. It has also been isolated from cultures taken from brain abscesses and respiratory and wound infections. Figure 20-5 illustrates the colonial
morphology of E. sakazakii. E. hormaechei has been isolated from human sources such as blood, wounds, and sputum. E. asburiae is similar biochemically to E. cloacae and has been isolated from blood, urine, feces, sputum, and wounds. E. dissolvens and E. nimipressuralis are newly recognized species with unknown
clinical significance .