title: Comparison of four phenotypic methods for detection of metallo-β-lactamase-producing Gram-negative bacteria in rural teaching hospital.
abstract: BACKGROUND
  Metallo-β-lactamase (MBL)-producing bacteria lead to resistance to carbapenem an antibiotic that used as the last resort for treatment of multidrug-resistant bacteria, extended spectrum beta-lactamases, and AmpC β-lactamase-producing Gram-negative bacteria (GNB). The emergence of MBL-producing GNB is challenge to microbiology laboratories because there are no standardized guidelines available to detect them. The aim of this study was to compare four phenotypic methods to detect MBL production in GNB and to determine antibiotic sensitivity of MBL-producing isolates.
  
  
  METHODS
  A total of 107 clinical isolates of GNB were tested for MBL production. Imipenem (IPM)-resistant GNB were taken as positive for MBL screening. MBL detection was done using ethylene diamine tetra acetic acid (EDTA) as MBL inhibitor. Four phenotypic methods were evaluated: (1) Combined disk synergy test (CDST) with 0.5M EDTA (CDST-0.5 M EDTA), (2) CDST with 0.1 M EDTA (CDST-0.1 M EDTA), (3) double-disk synergy test (DDST) with 0.5M EDTA (DDST-0.5 M EDTA), and (4) DDST with 0.1 M EDTA (DDST-0.1 M EDTA).
  
  
  RESULTS
  Out of 107 GNB, 30 were resistant to IPM considered as screening positive. Out of 30, 21 (70%) isolates were MBL positive by CDST-0.1 M EDTA, 19 (63.33%) by CDST-0.5M EDTA, 17 (56.67%) by DDST-0.1 M EDTA, and 16 (53.33%) by DDST-0.5M EDTA. All MBL-producing Gram-negativeBacilliwere resistant to ampicillin/sulbactam. Polymyxin B was found to be the most sensitive drug.
  
  
  CONCLUSIONS
  CDST-0.1 M EDTA is the most sensitive method MBL detection. The detection of MBL-producing GNB is very important to control spread of the resistance.
authors.affiliation: Department of Microbiology, GMERS Medical College, Gotri, Gujarat, India.
authors.forename: Chinjal A
authors.initials: CA
authors.lastname: Panchal
authors.affiliation: Department of Microbiology, CU Shah Medical College and Hospital, Surendranagar, Gujarat, India.
authors.forename: Sweta Sunil
authors.initials: SS
authors.lastname: Oza
authors.affiliation: Department of Microbiology, CU Shah Medical College and Hospital, Surendranagar, Gujarat, India.
authors.forename: Sanjay J
authors.initials: SJ
authors.lastname: Mehta
keywords: Carbapenem; Gram-negative bacteria; combined disk test; double-disk test; ethylene diamine tetra acetic acid; imipenem; metallo-β-lactamase