Klebsiella and enterobacter: antibiotic resistance and treatment implications

KLEBSIELLA: spp. and Enterobacter spp. are widespread throughout the environment and also carried by humans. Both genera are well-recognized community and nosocomial pathogens and cause significant infections. They are a common cause of respiratory and nonrespiratory infections. Klebsiella spp. is responsible for 1% to 5% of all cases of community-acquired pneumonia and between 0% to 23% of those acquired in the hospital, and its frequency is greater in alcoholic patients. The majority of cases are unilateral in the posterior segment of the right upper lobe. Lung abscess can occur after a pneumonic process or secondarily to Klebsiella spp. infections and have high rates of morbidity and mortality. K. pneumoniae is one of the most common microorganisms responsible for empyema. Klebsiella spp. and Enterobacter spp. rank fourth and third, respectively, as causes of hospital-acquired pneumonia mainly in patients during the early period of mechanical ventilation. Klebsiella spp. are intrinsically resistant to penicillins and can acquire resistance to third- and fourth-generation cephalosporins owing to the production of plasmid-mediated extended-spectrum beta-lactamases (ESBLs). These plasmids frequently carry aminoglycoside-modifying enzymes. Enterobacter spp. are intrinsically resistant to ampicillin, amoxicillin, amoxicillin-clavulanate, first-generation cephalosporins, and cefoxitin owing to the production of constitutive AmpC beta-lactamase. The derepression of this enzyme is increasingly frequent among clinical isolates and confers resistance to third-generation cephalosporins, and ureido- and carboxypenicillins; fourth-generation cephalosporins retain reasonable activity against depressed strains. Most isolates of Klebsiella spp. and Enterobacter spp. are susceptible to fluoroquinolones, trimethoprimsulfamethoxazole, aminoglycosides, and carbapenems. In some instances, treatment of severe infections caused by these microorganisms may benefit from the combination of beta-lactams (or fluoroquinolones) with aminoglycosides. Because of the high risk for developing resistance during treatment, all severe infections should be carefully watched during therapy.