|Year : 2015 | Volume
| Issue : 2 | Page : 320-321
Comparison of selective and enrichment media for isolation of vancomycin-resistant enterococci from rectal swab specimens
G Ongut1, OK Ozyurt1, BO Baysan1, D Daglar2, D Ogunc1, D Inan3, D Colak1, YY Senol4, F Gunseren3
1 Department of Medical Microbiology, University School of Medicine, Antalya, Turkey
2 Microbiology Laboratory, Antalya Education and Research Hospital, Antalya, Turkey
3 Department of Infectious Diseases and Clinical Microbiology, University School of Medicine, Antalya, Turkey
4 Department of Medical Education, Akdeniz University School of Medicine, Antalya, Turkey
|Date of Submission||09-Jan-2014|
|Date of Acceptance||05-Jun-2014|
|Date of Web Publication||10-Apr-2015|
Department of Medical Microbiology, University School of Medicine, Antalya
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Ongut G, Ozyurt O K, Baysan B O, Daglar D, Ogunc D, Inan D, Colak D, Senol Y Y, Gunseren F. Comparison of selective and enrichment media for isolation of vancomycin-resistant enterococci from rectal swab specimens. Indian J Med Microbiol 2015;33:320-1
|How to cite this URL:|
Ongut G, Ozyurt O K, Baysan B O, Daglar D, Ogunc D, Inan D, Colak D, Senol Y Y, Gunseren F. Comparison of selective and enrichment media for isolation of vancomycin-resistant enterococci from rectal swab specimens. Indian J Med Microbiol [serial online] 2015 [cited 2020 May 25];33:320-1. Available from: http://www.ijmm.org/text.asp?2015/33/2/320/154897
The prevalence of vancomycin resistant enterococci (VRE) infections has increased dramatically throughout the world. 
A proven effective strategy for the control of VRE in health-care facilities is detection of colonised patients and implementation of contact isolation precautions. Stool or rectal swab specimens should be cultured on selective and differential media for the identification of intestinal colonisation. 
In this study, we compared direct plating and VRE broth enrichment culture from rectal swabs for the detection of intestinal colonization by VRE among hospitalised patients.
One thousand four hundred and twelve rectal swab specimens from 987 patients hospitalised at Akdeniz University Hospital between May 2011 and September 2011 were included in the study. Rectal swab specimens were suspended in 0.5 ml brain heart infusion based VRE broth (Thermo Fisher Scientific, UK). From these, 100 μl of suspension was inoculated onto Enterococcosel agar containing 6 μg/ml of vancomycin (BBL, Becton Dickinson, USA) and 100 μl of suspension was inoculated into VRE broth with meropenem for enrichment. Inoculated VRE broth tubes and Enterococcosel agar plates were incubated at 35°C for 24 h and 48 h, respectively. Following incubation, broths were subcultured to enterococcosel agar and incubated at 35°C for 48 h. Gram positive, catalase negative black colonies formed on Enterococcosel agar were subcultured to blood-agar plates containing 5% sheep's blood and incubated at 35°C for 24 h. All isolates were identified by colony morphology, Gram stain and biochemical tests. Species identification and antimicrobial susceptibility testing was performed using BD Phoenix System (BD Diagnostic Systems, USA). The minimal inhibitory concentrations (MICs) of vancomycin and teicoplanin were also determined by Etest method (BioMérieux, France). Carriage of vanA or vanB gene was confirmed using BD GeneOhm VanR assay (BD Diagnostic Systems, USA), a rapid real-time polymerase chain reaction (PCR) test, according to the manufacturer's instructions.
A total of 94 vancomycin resistant Enterococcus faecium were isolated from1,412 rectal swab specimens. Vancomycin and teicoplanin MICs for the isolates were ≥64 μg/ml and ≥32 μg/ml, respectively. All VRE carried vanA gene which was detected by PCR method. From 94 rectal swabs, 76 cultures were positive for VRE by both methods while 18 cultures were detected by the broth method but not the direct plating. A significant difference was found between direct plating and enrichment broth for VRE isolation (P < 0.001; [Table 1]) False positivity rates were higher by the enrichment method and the difference was statistically significant (P < 0.001). The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were 81.9%, 81.3%, 23.5% and 98.4% for direct plating, and 100%, 75.6%, 22.6% and 100% for enrichment method, respectively.
|Table 1: Performance of direct plating and VRE broth enrichment culture from rectal swabs for the detection of VRE |
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Traditionally, screening of intestinal colonisation of VRE is performed by stool or rectal swab culture on bile-esculin-azide agar containing 6 µg/ml of vancomycin In this study, we found that broth enrichment was more sensitive than direct plating to Enterococcosel agar for detection of VRE colonisation. The VRE recovery rate increased by 23.7% with broth enrichment compared to direct plating on Enterococcosel agar. Marner et al., reported that the sensitivity of the direct culture method was too low and the false-negative rate was too high for active surveillance of VRE, based on agar culture alone.  Brown et al., evaluated two different agars and two broth media for detection of VRE colonisation, however, no advantage was found with enrichment compared to direct plating.  Novicki et al., reported in their study that addition of broth enrichment led to the detection of significantly more VRE isolates than direct plating alone.  Although direct inoculation of rectal swabs on vancomycin-containing solid media offers the advantage of earlier detection of VRE, our study suggests that the rate of detection of VRE from rectal swabs increased significantly with broth enrichment.
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