9.1 How to confirm the presence of an ESBL

9.1.1 Screening

It is important that the correct antimicrobials are used to screen for ESBLs in routine AST as only some cephalosporins are useful. If the wrong antimicrobial is used the ESBL may be missed. A combination of cefotaxime and ceftriaxone, or cefpodoxime alone will allow all types of ESBL to be detected.

  • What is the rationale behind this screening strategy?

  • Neither cefotaxime nor ceftazidime alone will pick up all the ESBLs. For example, CTX-M may look falsely susceptible to ceftazidime on disk testing but would be detected by using a cefotaxime disk. Cefpodoxime is useful because it detects all the common ones (mentioned above in section 3.1.1).

9 Confirming resistance mechanisms in practice

9.1.2 Synergy testing