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Extended spectrum beta-lactamases

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  • ▀-lactamases capable of hydrolysing extended spectrum cephalosporins and penicillins and aztreonam
  • plasmid mediated
  • aminoglycoside and trimethoprim-sulfamethoxazole resistance often transferred on same plasmid
  • often associated with fluoroquinolone resistance
  • some ESBL-producing organisms have also acquired an AmpC-type ▀-lactamase - this is distinct from from ESBL
  • most often associated with E. coli or Klebsiella pneumoniae but can be transferred to Proteus mirabilis, Citrobacter, Serratia and other enteric bacilli
  • >170 different ESBLs


  • difficult
  • organisms appear sensitive to certain antibiotics (eg 3rd and 4th generation cephalosporins) at standard innoculum but have significantly elevated MIC at higher innoculums. As a result it is necessary to screen all E. coli and Klebsiella pneumoniae with reduced susceptibility to these drugs or aztreonam
  • no current recommendations for screening for ESBL in other organisms which may lead to more widespread dissemination of the problem in other species before microbiological detection
  • all ESBL producing organisms should be considered resistant to all penicillins, cephalosporins and aztreonam. If the organism is sensitive to ▀-lactam/▀-lactamase inhibitor combinations it is suggested that the organism is reported as being susceptible although use of these combinations to treat patients is not ideal



  • probably underestimated. Significant proportion of laboratories do not perform tests specifically designed to detect ESBLs
  • increasing
  • considerable geographical variation.

Risk factors

  • central venous or arterial catheter, gastrostomy or jejunostomy tube, urinary catheter
  • emergency intra-abdominal surgery
  • GI colonization
  • prolonged ICU or hospital stay
  • prior antibiotics (including 3rd generation cephalosporins)
    • number and duration of antibiotics probably most important factors
  • prior nursing home stay
  • severity of illness
  • mechanical ventilation


  • difficulty exacerbated by associated resistance to aminoglycosides and trimethoprim-sulfamethoxazole as well as high frequency of co-existence of fluoroquinolone resistance
  • decreased susceptibility to 3rd and 4th generation cephalosporins seen in vitro at higher innoculums associated with clinically significant reductions in efficacy in vivo
    • although cefamycins (cefoxitin and cefotetan) not hydrolyzed by majority of ESBLs but are hydrolyzed by associated AmpC-type ▀-lactamase
  • similarly ▀-lactam/▀-lactamase inhibitor combinations may not be effective against organisms that produce AmpC-type ▀-lactamase. In vivo studies have yielded mixed results against ESBL-producing K. pneumoniae
  • carbapenems are agents of choice
    • highly stable against ▀-lactamase hydrolysis
    • emergence of carbapenemase-producing organisms is a potential problem

Infection control

  • antibiotic selection pressure for resistance plasmid dissemination and genetic mutation important in spread of resistance
  • clonal strain transmission reported as primary mechanism for ESBL outbreaks indicating that patient-to-patient spread is a significant problem
    • contact precautions (gloves, gowns) important
    • notification by institutions when transferring patients may help limit spread (inter-hospital transfer of ESBL-producing organisms has been described)
  • restrict use of antibiotics, especially cephalosporins

Further reading

Patterson JE. Extended-spectrum beta-lactamases. Sem Respir Crit Care Med, 2003;24(1):79-87

Rupp ME and Fey PD. Extended spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae. Considerations for diagnosis, prevention and drug treatment. Drugs, 2003;63(4):353-65

Potential conflict of interest

The Dept of Anaesthesia & Intensive Care, The Chinese University of Hong Kong received sponsorship for educational activities from Merck Sharp & Dohme and AstraZeneca in 2002 and 2003


ęCharles Gomersall, April, 2014 unless otherwise stated. The author, editor and The Chinese University of Hong Kong take no responsibility for any adverse event resulting from the use of this webpage.
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