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	What is the standard zone of inhibition of meropenem against pseudomonas? If a Pseudomonas isolate is sensitive to imipenem but resistant to meropenem, do I still go ahead and test for metallobetalactamase production?
	In CLSI disk diffusion tests Pseudomonas aeruginosa is susceptible to meropenem if the zone diameter is 16 mm or greater. Isolates that are resistant to meropenem but susceptible to imipenem are probably overexpressing an efflux pump. This does not exclude the possibility that a metallo-beta-lactamase is produced. There are many types of metallo-beta-lactamases and P. aeruginosa possesses multiple resistance mechanisms. This makes it a complex pathogen for which it is very difficult to elucidate the resistance mechanisms from susceptibility results.

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