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Carbapenem Resistant Enterobacteriaceae (CRE) has become an
increasingly recognized cause of infection during the past decade, likely
because of the emergence of carbapenemase-producing strains. The ability
to limit the spread of these pathogens will require effective laboratory
methods to rapidly identify patients infected with these organisms.
The objective of this study was to evaluate the Carbapenem
inactivation assay (Modified Hodge Test) as a confirmatory test for
carbapenemase production among clinical isolates of Enterobacteriaceae.
Seventy samples of urine were collected during a month, from May
٢٠١١ to June ٢٠١١from patients with indwelling urinary catheters for more
than ٤٨ hours of catheterization (to reach a final number of Sixty one Gram
negative rod isolates ). All patients were hospitalized in different ICUS of
Ain Shams University and Kobry El kobba Military Hospitals. All urine
samples were centrifuged, and then the deposit of each sample was
inoculated onto the surface of different culture media; Blood, MacConkey’s
agar and the new chromogenic Uriselect ٤ media. All inoculated media were
incubated aerobically at ٣٧oC for ٢٤ hours. The growing colonies were
identified by standard microbiological techniques.
The sixty one isolates included in this study with Gram negative rod,
morphology and negative oxidase test results were completely identified
down to species level using the overnight ID ٣٢ E strips. Thirty six isolates
of them were E.coli (٥٩٫٠٢٪) while ٢٥ isolates were Klebsiella pneumoniae
(٤٠٫٩٨٪).Twenty eight E.coli isolates (٧٨%) among ٣٦ E.coli isolates were
identified as ESBL producers using the standard disk diffusion method.
while a total number of ١٦ E.coli isolates (٤٤٫٤٤٪) were identified as ESBLs
by disk approximation method.
Eleven Klebsiella pneumoniae isolates (٤٤٪) among ٢٥ Klebsiella
pneumoniae isolates were identified as ESBL producers using the disk
diffusion method. while ١٥ Klebsiella pneumoniae isolates (٦٠٪) were
identified as ESBLs by disk approximation method.
The comparison between the disc diffusion and the disc
approximation methods for detection of ESBLs among the study isolates
showed ٦٢٪ rate of positive agreement.
As regards detection of CRE, disc diffusion method identified ١٨
isolates (١١ E.coli and ٧ K. pneumoniae) as resistant. The Sensitivity,
Specificity, positive predictive value and negative predictive value of Disk
diffusion test in correlation with MIC as a standard test for detection of CRE
isolates were ١٠٠٪, ٨٦%, ٦١% and١٠٠٪ respectively.
All Enterobacteriaceae isolates were tested for carbapenemases
production using The Modified Hodge Test. Eight (٢٢٫٢٢٪) among ٣٦ E.coli
isolates were positive for the Modified Hodge testing. While ٣ out of the ٢٥
Klebsiella pneumoniae isolates (١٢٪) were positive for carbapenemases
production detected by the Modified Hodge testing.
All isolates giving positive MHT were identified as being resistant to
imipenem by tube dilution method (MIC ≥٤ μg/mL).MHT showed high performance quality in comparison to tube dilution
method for detection of CRE (١٠٠٪ for sensitivity, specificity, PPV and