Extended-Spectrum- -Lactamase, AmpC, and Carbapenemase Issues

Optimal use of microbiology laboratories is essential to combat the spread of multiply antibiotic-resistant pathogens. This is vital for patient care, as advocated by Jarvis in stressing the importance of active detection and isolation to control methicillin-resistant Staphylococcus aureus and other resistant hospital-acquired pathogens (17). It is also vital for hospital accreditation in the United States, where the Joint Commission has set requirements for the control of acquisition and transmission of multidrug-resistant organisms (http: //www.jointcommission.org/NR/rdonlyres/31666E86-E7F4-423E -9BE8-F05BD1CB0AA8/0/HAP_NPSG.pdf-NPSG.07.03.01). These requirements cannot be met without excellence in diagnostic microbiology. The absence of new, effective anti-gram-negative antibiotics makes infection control the most important countermeasure against multidrug-resistant gram-negative pathogens. Infection control can prevent additional infections and the spread of resistant pathogens and thereby reduce the need to use antibiotics. Infection control is most effective when directed by rapid, accurate laboratory results. In short, excellence in diagnostic microbiology is critical to quality initiatives in hospitals. Some resistant pathogens may not be recognized because they are falsely susceptible in routine tests. This can lead to patients receiving ineffective antibiotics and contribute to the spread of the pathogens. Because the detection of such “hidden” resistance is so critical, this Commentary focuses on its detection in gram-negative pathogens. Because susceptibility tests may be unreliable, special tests are required to detect the resistance mechanisms involved. The mechanisms include extended-spectrum -lactamases (ESBLs), AmpC -lactamases, and carbapenemases of molecular classes A and B.