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Klebsiella , Enterobacter , and Serratia Infections

By Larry M. Bush, MD, Maria T. Perez, MD

Klebsiella, Enterobacter, and Serratia are closely related normal intestinal flora that rarely cause disease in normal hosts.

Infections with Klebsiella, Enterobacter, and Serratia are often hospital-acquired and occur mainly in patients with diminished resistance. Usually, Klebsiella, Enterobacter, and Serratia cause a wide variety of infections, including bacteremia, surgical site infections, intravascular catheter infections, and respiratory or urinary tract infections that manifest as pneumonia, cystitis, or pyelonephritis and that may progress to lung abscess, empyema, bacteremia, and sepsis. Klebsiella pneumonia, a rare and severe disease with dark brown or red currant–jelly sputum, lung abscess formation, and empyema, is most common among diabetics and alcoholics. Serratia, particularly S. marcescens, has greater affinity for the urinary tract. Enterobacter most often cause nosocomial infections but can cause otitis media, cellulitis, and neonatal sepsis.

Treatment is with 3rd-generation cephalosporins, cefepime, carbapenems, fluoroquinolones, piperacillin/tazobactam, or aminoglycosides. However, because some isolates are resistant to multiple antibiotics, susceptibility testing is essential.

Klebsiella strains that produce extended-spectrum β-lactamase (ESBL) may develop resistance to cephalosporins during treatment, particularly with ceftazidime; these ESBL strains are inhibited to a variable extent by β-lactamase inhibitors (eg, sulbactam, tazobactam, clavulanate). Carbapenemase-producing species of K. pneumoniae (KPC) have been isolated internationally as well as in the US, making treatment of some infections very problematic.

Enterobacter strains may become resistant to most β-lactam antibiotics, including 3rd-generation cephalosporins; the β-lactamase enzyme they produce is not inhibited by the usual β-lactamase inhibitors (clavulanate, tazobactam, sulbactam). However, these Enterobacter strains may be susceptible to carbapenems (eg, imipenem, meropenem, ertapenem). Carbapenemase-resistant Enterobacteriaceae have also been detected. In certain cases, tigecycline and perhaps colistin may be the only available active antibiotics.

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