A convenient microbiological assay employing cell-free extracts for the rapid characterization of Gram-negative carbapenemase producers.
OBJECTIVE
The dissemination of metallo and serine carbapenem-hydrolysing beta-lactamases among Gram-negative nosocomial bacteria represents an acute problem worldwide. Here, we present a rapid and sensitive assay for the characterization of carbapenemase producers to aid in infection control and prevention.


METHODS
The assay involves a rapid disruption of bacterial isolates with silicon dioxide microbeads, followed by the testing in cell-free extracts of hydrolytic activity towards various beta-lactams including two carbapenems (imipenem and meropenem) and a cephalosporin (ceftazidime). A parallel testing of the effects of selective beta-lactamase inhibitors such as EDTA and clavulanic acid allows differentiation of metallo carbapenemases from serine carbapenemases, and also clavulanic-acid-sensitive from -resistant enzymes among the latter.


RESULTS
The efficiency of bacterial disruption using silicon dioxide microbeads was identical to that of ultrasonic treatment. The subsequent microbiological assay aimed to evaluate both substrate specificity and inhibitor profile of carbapenem-hydrolysing enzymes present in the extracts and allowed an accurate differentiation of A, B and D types, as judged by the analysis of 24 well-characterized clinical strains that included metallo-beta-lactamase producers (i.e. VIM-, IMP- and SPM-type Pseudomonas producers; an L1 Stenotrophomonas maltophilia producer; and a GOB-18 Elizabethkingia meningoseptica producer) as well as serine carbapenemase producers (i.e. an SME-type Serratia marcescens producer, a GES-2 Pseudomonas aeruginosa producer, Klebsiella pneumoniae and Citrobacter freundii KPC-2 producers and OXA-type Acinetobacter baumannii producers).


CONCLUSIONS
We have developed a convenient microbiological assay aimed to more accurately and in a short time characterize carbapenem-hydrolysing enzymes produced by Gram-negative bacteria. The assay possesses broad applicability in the clinical setting.
Marchiaro
Patricia
P
Departamento de Microbiología, Instituto de Biología Molecular y Celular de Rosario (IBR), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Argentina.
Ballerini
Viviana
V
Spalding
Tamara
T
Cera
Gabriela
G
Mussi
María A
MA
Morán-Barrio
Jorgelina
J
Vila
Alejandro J
AJ
Viale
Alejandro M
AM
Limansky
Adriana S
AS
D001426:Bacterial Proteins / Q000032:analysis*; D001431:Bacteriological Techniques / Q000379:methods*; D001433:Bacteriolysis; D019818:Clavulanic Acid / Q000494:pharmacology; D045424:Complex Mixtures / Q000378:metabolism; D004492:Edetic Acid / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006090:Gram-Negative Bacteria / Q000201:enzymology* / Q000302:isolation & purification; D008863:Microspheres; D012822:Silicon Dioxide; D013379:Substrate Specificity; D001618:beta-Lactamases / Q000032:analysis*; D047090:beta-Lactams / Q000037:antagonists & inhibitors* / Q000378:metabolism
D001426:Bacterial Proteins; D045424:Complex Mixtures; D004791:Enzyme Inhibitors; D047090:beta-Lactams; D019818:Clavulanic Acid; D012822:Silicon Dioxide; D004492:Edetic Acid; D001618:beta-Lactamases; C063912:carbapenemase