Abstract
Resistance to β-lactam antibiotics in enteric Gram-negative bacilli may be difficult to detect using standard methods of either Kirby-Bauer disc diffusion (KBDD) or broth dilution for minimal inhibitory concentration (MIC). This difficulty is due to genetic differences in resistance determinants, differences in levels of gene expression, and variation in spectra of enzymatic activity against the substrate β-lactams used for susceptibility testing. We have examined 95 clinical isolates reportedly susceptible to ceftazidime and ceftriaxone, as originally determined by either KBDD or MIC methods. The organisms studied here were isolated in 2002 from two pediatric hospital centers (Seattle, USA and Shanghai, China). They belong to the inducible β-lactamase producing Gram-negative bacilli, such as Enterobacter spp., Citrobacter spp., Serratia spp., Morganella spp., Providencia spp., and Proteus vulgaris. A Kirby-Bauer disc approximation (KBDA) method identified inducible phenotypes of third-generation cephalosporin resistance in 76% of isolates, which would otherwise be considered susceptible by standard KBDD methods.
Highlights
Nosocomial infections due to antibiotic-resistant, enteric Gram-negative bacilli have increased at an alarming rate in intensive care facilities, and are frequently associated with immunocompromised hosts, for whom they may be devastating [1,2,3,4,5]
Standard Kirby-Bauer disc diffusion (KBDD) methods and automated minimal inhibitory concentration (MIC) instruments used in most clinical laboratories do not readily detect ampC-type of inducible resistance
A few instructive studies have reported that the observation of increased MICs to thirdgeneration cephalosporins using high-density inocula
Summary
Nosocomial infections due to antibiotic-resistant, enteric Gram-negative bacilli have increased at an alarming rate in intensive care facilities, and are frequently associated with immunocompromised hosts, for whom they may be devastating [1,2,3,4,5]. (as well as other Enterobacteriaceae) carrying plasmid-borne extended-spectrum β-lactamases (ESBLs) have attracted much interest among clinical microbiologists, infectious disease specialists, and infection control practitioners [6,7,8]. Standard Kirby-Bauer disc diffusion (KBDD) methods and automated minimal inhibitory concentration (MIC) instruments used in most clinical laboratories do not readily detect ampC-type of inducible resistance. Therapy based on such susceptible reports may result in selection of resistance in vivo [9,10,11,12,13]. A few instructive studies have reported that the observation of increased MICs to thirdgeneration cephalosporins using high-density inocula (increasing sensitivity for detection of derepressed mutant (page number not for citation purposes)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: Annals of Clinical Microbiology and Antimicrobials
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
