Opportunistic Enterobacteriaceae

Many Enterobacteriaceae with minimum pathogenicity are classic opportunists. The most frequent opportunistic infections caused by them are: urinary tract infections, respiratory tract infections, wound infections,

Table 4.9 Overview of the Most Important Enterobacteriaceae That Cause Opportunistic Infections

Bacterial species


Escherichia coli

Citrobacter freundii; C. divs.; C. amalonaticus

Klebsiella pneumoniae; K. oxytoca and others

Klebsiella ozaenae

Klebsiella rhinoscleromatis

Enterobacter cloace; E. aerogenes; E. agglomerans; E. sakazakii, and others

Serratia marcescens and others

Proteus mirabilis Proteus vulgaris

Morganella morganii Providencia rettgeri; P. stuartii

Can use citrate as its sole source of C; delayed breakdown of lactose; nonmotile

Lactose-positive; nonmotile; many strains have a polysaccharide capsule. Cause approx. 10% of nosocomial infections. Causative organism in so-called Friedlander's pneumonia in predisposed persons, especially in the presence of chronic pulmonary diseases.

Causative pathogen in ozena; atrophy of nasal mucosa

Causative pathogen in rhinoscleroma; granuloma in the nose and pharynx

Lactose-positive; motile; frequent multiple resistance to antibiotics

Lactose-positive; motile; frequent multiple resistance to antibiotics, some strains produce red pigment at 20 °C

Lactose-negative; highly motile; wanders on surface of nutrient agar (swarming). O antigens OX-2, OX-19, and OX-K from P. vulgaris are identical to rickettsiae antigens. For this reason, antibodies to rickettsiae were formerly identified using these strains (Weil-Felix agglutination test)

Lactose-negative; frequent multiple resistance to antibiotics

Lactose-negative; frequent multiple resistance to antibiotics

dermal and subcutaneous infections, and sepsis. Such infections only occur in predisposed hosts, they are frequently seen in patients with severe primary diseases. Another reason why opportunistic Enterobacteriaceae have become so important in hospital medicine is the frequent development of resistance to anti-infective agents, which ability enables them to persist at locations where use of such agents is particularly intensive, i.e., in hospitals. Occurrence of multiple resistance in Enterobacteriaceae is due to the impressive genetic variability of these organisms (p. 170). Table 4.9 provides an overview of the most important opportunistic Enterobacteriaceae.

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