enterobactericiae

• enterobactericiae

  • ubiquitous organisms found worldwide in soil, water, and vegetation and are part of the normal intestinal flora of humans
  • opportunistic pathogens
  • gram negative rods
  • examples of virulence factors
  • endotoxin --> lipid A component of LPS, which is released at cell lysis
  • antibiotic resistance
• escherichia coli

  • lactose fermenting GNR
  • colonizes colon
  • either opportunistic pathogen (most common) or toxin producing (GI outbreaks)
  • laboratory diagnosis: culture
  • outbreak (GI infections) vs. community infections (UTIs) vs. hospital infections (pyelo, blood, wounds, etc.)
• other enterobactericiae

  • lactose fermenters
  • Klebsiella pneumoniae
  • Klebsiella oxytoca
  • Enterobacter clocae
  • Enterobacter aerogenes
  • Citrobacter koseri
  • Citrobacter freundii
  • non-lactose fermenters
  • Serratia macrescens
  • Morganella morganii
  • Proteus mirabilis
  • mostly hospital-related infections:
  • complicated urinary tract infections
  • hospital-acquired or ventilator-associated pnuemonia
  • bacteremia
  • wound/surgical infections
  • note that all are opportunistic pathogens
• beta-lactamases

  • enzyme that bind and hydrolyze beta-lactams
  • over > 1500 types of beta lactamases have been described
  • focus on
  • extended-spectrum beta-lactamases (ESBL)
  • carbapenemases
  • AmpC beta-lactamases
• extended spectrum beta lactamases

  • hydrolyzes penicillin, cephalosporins and aztreonam
  • do NOT hydrolyze carbapenems
  • acquired resistance --> generally located on plasmids, which may be transmitted btwn Enterobacteriaceae
  • note: plasmids often contain resistance genes to other antibiotics
  • drug of choice: carbapenem
• carbapenemases

  • hydrolyze all classes of beta-lactam antimicrobials including PCNs, cephalosporins, aztreonam and carbapenems
  • most common example is Klebsiella pneumoniae carbapenemase (KPC)
  • acquired resistance --> plasmid mediated and can spread to other Enterobacteriaeae
  • often carry other resistance genes making them multidrug resistance and limiting therapeutic options
  • drug of choice depends on type of infection
  • one option is ceftazidime / avibactam
• AmpC (chromosomal) beta-lactamases

  • inducible antibiotic resistance via the AmpC gene
  • genes such as the AmpC gene which the bacteria naturally harbor in their chromosomes is typically not being expressed --> exposure to cephalosporins can cause the AmpC gene to become expressed --> resistance to the 1 - 3rd gen cephalosporins
  • most commonly associated w/ Enterobacter spp
  • also reported in Serratia, Citrobacter spp.
  • lab detection not routinely done so MICs will still show susceptibility to 3rd generation cephalosporins
  • drug(s) of choice: cefepime or carbapenem for serious infections