A Modified Breakpopint Improves Detection of ESBL in Proteus mirabilis by disk diffusion.

RADICE M; QUINTEROS M; MATTEO M; MOLLERACH M; POWER P; GUTKIND G

Buenos Aires

Congreso; 9th International Congress on Infectious Diseases; 2000

International Society for Infectious Diseases

In previous communications (ICAAC 1999, Abstract # 893; VIII Cong. Arg. Microbiol., 1998, Abstract # A-44; Int. Cong. on Beta-lactamases, L’Aquila, 1999, Abstract # A27), we compared the  detection abilities of the NCCLS’ recently recommended methods for screening and confirmation of extended spectrum beta lactamases (ESBL) in E. coli and Klebsiella spp., and the use of the single disk of ceftazidime (CAZ) 5 mg in a collection of  almost one hundred different ESBL producing enterobacteria (including ampC producers, proteus, salmonella and shigella) from several regions of our country. At that time, we concluded, that dilution or diffusion methods using cefotaxime (CTX) were efficient for ESBL detection and confirmation, in all the tested microorganisms. NCCLS CAZ based assays were not acceptable, but CAZ 5 mg disks proved an appropriate alternative when 22 mm was chosen as the susceptibility breakpoint, except for a single (out of 6) Proteus mirabilis tested. To confirm the significance of this finding, we analyzed twenty P. mirabilis, nineteen of them were producers of a broad spectrum beta-lactamase (BSBL) and an ESBL compatible with TEM-1 and CTX-M enzymes, observed after analytical isoelectrofocusing as two bands with apparent pIs of 5,4 and 8,2 active on ampicillin (500mg/l), the last one also active on ceftriaxone (1g/l). The other strain was a TEM-1 and SHV-2 producer. The codifying genes for TEM, CTX-M, and SHV enzymes were confirmed by PCR using specific primers. Those methods using CTX were able to detect both resistance and presence of ESBLs in all cases. Disk diffusion methods using CAZ (30 mg) were able to detect ESBL in only two cases, while dilution methods using this antibiotic slightly improve resistance detection (4/20). The SHV-2 producer was detected by any method. A susceptibility breakpoint of 22 mm using CAZ 5 mg disks allowed us to detect 15/20 resistant strains, highly improving this drug detection-abilities. As stated previously, these results clearly show that the current NCCLS recommendations for resistance detection and confirmation of ESBL production in E. coli and Klebsiella sp. may also be appropriate for ESBL producing P. mirabilis (among other enterobacteria), at least for a region with similar beta-lactamases prevalence. CAZ 5 mg disks, although improving resistance detection as compared with the NCCLS recommended CAZ 30 mg, may not solve resistance detection in this species, probably due a low level production of CTX-M.