Hidden Beta-Lactamases in the Enterobacteriaceae – Dropping the Extra Disks for Detection, Part I

Resistance to our beta-lactam and carbapenem antibiotics is becoming daunting for antimicrobial therapy for infections involving the Enterobacteriaceae. Similarly, laboratory testing to detect these resistance mechanisms is becoming more complex and perplexing for microbiology laboratories. Automated testing alone will not detect all of the resistance patterns that occur via beta-lactamases and carbapenemases. Failure to detect organisms with these enzymes can result in erroneous reports that would indicate an isolate is susceptible to beta-lactam and/or carbapenem antibiotics. In addition to the risk of compromised care of the patient, when pathogens with these enzymes go undetected, necessary infection control measures are precluded, thereby allowing the risk that these resistant organisms will become endemic in a hospital environment. Supplemental testing in addition to the routine susceptibility tests of isolates has become necessary in order to detect the deluge of beta-lactamases and carbapenemases that clinical laboratories face today. Part I of this article reviews some of the major mechanisms of bacterial resistance to beta-lactam antibiotics, including extended-spectrum beta-lactamases, and methods for their laboratory detection.