Plasmid mediated Metallo-Beta Lactamase (MBL)

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Plasmid mediated Hydrolyses all beta-lactam (except aztreonam)

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Inhibited by EDTA Binds zinc (Zn 2+ )

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Pseudomonas aeruginosa or Enterobacteriaceae

MBL producing Pseudomonas aeruginosa. The isolate is resistant to imipenem (IPM 10) ceftazidime (CAZ 10), tazocin (TZP 55), cefepime (FEP 10), Timentin (TIM 85), and susceptible to aztreonam (ATM 30).

MBL producing Pseudomonas aeruginosa. The blank disc contains 750 μg EDTA.

The zone of inhibition of imipenem (IPM 10) and meropenem (MEM 5) is increased with the addition of EDTA indicating the presence of a Metallo-Beta Lactamase.

MBL producing Escherichia coli resistant to cefotaxime (CTX 5), cefotetan (CTT 30), Augmentin (AMC 60), and susceptible to aztreonam (ATM 30). The blank disc contains 750 μg EDTA. Note the borderline resistance to imipenem (IPM 10) and the large zone around the IPM disc loaded with 750 μg EDTA.

MBL producing Klebsiella pneumoniae with multiple resistance: R/ imipenem (IPM 10), cefotaxime (CTX 5), cefotetan (CTT 30), and Augmentin (AMC 60).

The resistance to aztreonam (ATM 30) is due to the presence of an ESBL (key hole). Note the borderline resistance to IPM and the large zone around the IPM disc loaded with 750 μg EDTA.

Beta-Lactamases vs Beta-Lactams

P/C FEP CTT ATM MBL ESBL P P AmpC P/C R R S R S R S R S/R

P = Plasmid, C = Chromosomal