265. Cephalosporin Susceptibility Levels of Extended-Spectrum β-Lactamase Genotypes in Latin America
Session: Poster Abstract Session: Antimicrobial Susceptibility and Resistance
Friday, October 21, 2011
Room: Poster Hall B1

Background: Extended-spectrum β-lactamases (ESBLs) typically confer resistance to many β-lactam antimicrobics. The Clinical and Laboratory Standards Institute (CLSI) recently lowered susceptibility (S) breakpoints for many 3rd generation cephalosporins to reflect PK/PD parameters of these drugs, but also to make it easier for clinical labs to differentiate between ESBL+ and ESBL- Enterobacteriaceae without having to do additional testing. Ceftazidime and cefepime now have higher S breakpoints (4 and 8 mcg/ml, respectively) than those of cefotaxime and ceftriaxone (both ≤1 mcg/ml).  This analysis of Latin America data from the SMART program shows the impact of SHV, TEM, or CTX-M ESBLs on reported cephalosporin %S values using CLSI breakpoints.

Methods: 251 Enterobacteriaceae isolates collected in Latin America in 2008-2009 were tested for susceptibility using CLSI broth microdilution; %S was determined using M100-S21 breakpoints. SHV, TEM, and CTX-M ESBLs were screened using the Check-Points assay (Check-Points, The Netherlands), then sequenced and analyzed using SeqScape software. The Check-Points microarray process utilizes a ligation detection reaction using specific probes, a PCR reaction, and then a hybridization-detection step using Check-Points software.

Results:   Distribution of ESBL genotypes was: 211 CTX-M, 26 SHV, 8 SHV+CTX-M, 4 TEM+CTX-M, 2 TEM. The following figure shows %S for each cephalosporin by ESBL type present in isolates.

Conclusion: As expected, cefoxitin was least affected by presence of these 3 ESBLs. Since only 2 isolates were TEM+ and 4 were TEM+CTX-M, limited conclusions can be drawn about this enzyme; however, the relatively high %S values seen with SHV producers vs. ceftazidime (19%) and cefepime (58%), and CTX-M producers vs. ceftazidime (18%) will be problematic for those who deem that ESBL+ isolates should not be treated with cephalosporins.

Subject Category: A. Antimicrobial agents and Resistance

Robert Badal, BS, Meredith Hackel, PhD, Christine Lascols, MS, Samuel Bouchillon, MD and Daryl Hoban, PhD, IHMA, Inc., Schaumburg, IL


R. Badal, Merck & Co, Inc.: Consultant, Consulting fee

M. Hackel, Merck & Co, Inc.: Consultant, Consulting fee

C. Lascols, Merck & Co, Inc.: Consultant, Consulting fee

S. Bouchillon, Merck & Co, Inc.: Consultant, Consulting fee

D. Hoban, Merck & Co, Inc.: Consultant, Consulting fee

Findings in the abstracts are embargoed until 12:01 a.m. EST Thursday, Oct. 20 with the exception of research findings presented at IDSA press conferences.