Infections with Klebsiella, Enterobacter, and Serratia are often hospital-acquired and occur mainly in patients with diminished resistance. These three bacteria can 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, as in the following:
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.
Diagnosis is by culture of blood and/or other infected tissue. Susceptibility testing is also done.
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 beta-lactamase (ESBL) may develop resistance to cephalosporins during treatment, particularly with ceftazidime; these ESBL strains are inhibited to a variable extent by beta-lactamase inhibitors (eg, sulbactam, tazobactam, clavulanate, vaborbactam, avibactam). Carbapenemase-producing species of K. pneumoniae (KPC) have been isolated internationally as well as in the US, making treatment of some infections very problematic. Ceftazidime/avibactam and meropenem/vaborbactam (which include new beta-lactamase inhibitors that also inhibit KPC carbapenemases) as well as eravacycline have activity against KPC isolates.
Enterobacter strains may become resistant to most beta-lactam antibiotics, including 3rd-generation cephalosporins; the beta-lactamase enzyme they produce (AmpC beta-lactamase) is not inhibited by the usual beta-lactamase inhibitors (clavulanate, tazobactam, sulbactam). However, these Enterobacter strains may be susceptible to carbapenems (eg, imipenem, meropenem, doripenem, ertapenem). Carbapenemase-resistant Enterobacteriaceae have also been detected. In certain cases, ceftazidime/avibactam, meropenem/vaborbactam, imipenem/relebactam, tigecycline, eravacycline, and perhaps colistin may be the only available active antibiotics (1).
1. Thaden JT, Pogue JM, Kaye KS: Role of newer and re-emerging older agents in the treatment of infections caused by carbapenem-resistant Enterobacteriaceae. Virulence 8(4):403–416, 2017. doi: 10.1080/21505594.2016.1207834.