Extended-spectrum and metallo-beta-lactamases among ceftazidime-resistant Pseudomonas aeruginosa in Riyadh, Saudi Arabia.

We investigated the extended-spectrum (ESBLs) and metallo-beta-lactamases (MBLs) among Pseudomonas aeruginosa isolates in Saudi Arabia. Disc susceptibility testing was performed on 200 P. aeruginosa isolates collected during 2010 at the Armed Forces Hospital in Riyadh, with MIC testing and phenotypic screening for ESBLs and MBLs carried out on those found to be ceftazidime resistant. Genes for ESBLs and MBLs were sought by PCR. Thirty-nine (19.5%) P. aeruginosa isolates were ceftazidime resistant, mostly with considerable resistance to other antibiotics except colistin. Twenty-three of these 39 (59%) appeared ESBL positive and 16 (41%) had MBLs. bla(VEB), and bla(GES) genes were found in 20 (86.95%), and 5 (21.74%) of 23 ESBL-positive isolates, respectively whilst bla(VIM) was detected in all 16 MBL-producers. bla(OXA-10-like) often accompanied bla(VEB), bla(VIM) or bla(GES). Several isolates had similar antibiogram and β-lactamase profiles, and may represent outbreaks; nevertheless, the collection was not dominated by any single clone. This dominance of acquired ceftazidime-inactivating beta-lactamases, often in combination is in contrast to the situation in Europe and the USA, where most ceftazidime resistance in P. aeruginosa is attributable to AmpC and efflux.