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ORIGINAL ARTICLE
Year : 2005  |  Volume : 23  |  Issue : 2  |  Page : 120-124
 

Evaluation of Methods for AmpC Beta-Lactamase in Gram Negative Clinical Isolates from Tertiary Care Hospitals


1 New Drug Discovery Research, Ranbaxy Research Laboratories, Gurgaon - 122 001, India
2 Department of Zoology and Microbiology, University of Rajasthan, Jaipur - 302 004, India
3 Department of Microbiology, Safdurjung Hospital, New Delhi - 110 029, India

Correspondence Address:
A Rattan
New Drug Discovery Research, Ranbaxy Research Laboratories, Gurgaon - 122 001
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0255-0857.16053

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 ~ Abstract 

The purpose of this study was to simultaneously screen for Extended-spectrum b-lactamases (ESBL) and AmpC b-lactamases in gram negative clinical isolates from four tertiary care hospitals and further to compare two detection methods three-dimensional extraction method and AmpC disk test for AmpC b-lactamases. A total of 272 isolates were screened for ESBL and AmpC β-lactamase by modified double disk approximation method (MDDM). Synergy observed between disks of ceftazidime/cefotaxime and clavulanate were considered as ESBL producer. Isolates showing reduced susceptibility to either of the test drugs (ceftazidime or cefotaxime) and cefoxitin were considered as presumptive AmpC producers and further confirmed by three-dimensional extraction method and AmpC disk test. A total of 173 (64%) of the isolates were found to be ESBL positive and 61 (23%) showed resistant to cefoxitin. ESBL was detected in 80 (62%) isolates of E. coli and 71 (73%) of Klebsiella spp. The occurrence of AmpC b-lactamases was found to be 8% (22) of the total isolates and the two detection methods for AmpC b -lactamase showed concordant results. Screening for ESBL and AmpC can be simultaneously done by MDDM method and confirmation for AmpC β-lactamase should be carried out routinely in tertiary care hospitals by AmpC disk test, as it is a simple and rapid procedure.


Keywords: ESBL, AmpC β -lactamases, Disk test


How to cite this article:
Singhal S, Mathur T, Khan S, Upadhyay D J, Chugh S, Gaind R, Rattan A. Evaluation of Methods for AmpC Beta-Lactamase in Gram Negative Clinical Isolates from Tertiary Care Hospitals. Indian J Med Microbiol 2005;23:120-4

How to cite this URL:
Singhal S, Mathur T, Khan S, Upadhyay D J, Chugh S, Gaind R, Rattan A. Evaluation of Methods for AmpC Beta-Lactamase in Gram Negative Clinical Isolates from Tertiary Care Hospitals. Indian J Med Microbiol [serial online] 2005 [cited 2017 Mar 27];23:120-4. Available from: http://www.ijmm.org/text.asp?2005/23/2/120/16053


Extended-spectrum b-lactamases (ESBLs) and AmpC b-lactamases are of increasing clinical concern. ESBLs are most commonly produced by Klebsiella spp. and  Escherichia More Details coli but may also occur in other gram-negative bacteria. They are typically plasmid mediated, clavulanate susceptible enzymes that hydrolyze penicillins, expanded-spectrum cephalosporins (cefotaxime, ceftriaxone, ceftazidime, cefepime and others) and aztreonam.[1] AmpC class b-lactamases are cephalosporinases that are poorly inhibited by clavulanic acid. They can be differentiated from other ESBLs by their ability to hydrolyze cephamycins as well as other extended-spectrum cephalosporins.[2] AmpC- b-lactamases, demonstrated or presumed to be chromosomally or plasmid mediated, have been described in pathogens e.g., Klebsiella pneumoniae , Escherichia coli ,  Salmonella More Details spp., Proteus mirabilis, Citrobacter freundii , Acinetobacter , Enterobacter spp. and Pseudomonas aeruginosa .[3] Although reported with increasing frequency, the true rate of occurrence of AmpC b-lactamases in different organisms, including members of Enterobacteriaceae , remains unknown. Coudron et al[4] used the standard disk diffusion breakpoint for cefoxitin (zone diameter <18 mm) to screen isolates and used a three- dimensional extract test as a confirmatory test for isolates that harbour AmpC b-lactamases. The current National Committee for Clinical Laboratory Standards (NCCLS) guidelines do not describe any method for detection of isolates producing AmpC b-lactamases.[5] The present study was designed to increase awareness and demonstrate the need to detect the occurrence of ESBLs and AmpC enzymes in clinical strains. We had screened the isolates by modified double disk approximation method (MDDM) and selected the isolates showing reduced susceptibility to ceftazidime/cefotaxime and cefoxitin or showing blunting of ceftazidime or cefotaxime zone of inhibition adjacent to cefoxitin. These isolates were further subjected for AmpC b-lactamases confirmation by modified three-dimensional extract test[2] and AmpC disk test.[6]


 ~ Materials and Methods Top


Bacterial isolates

A total of 272 gram negative consecutive, nonrepetitive clinical isolates from blood and urine from tertiary care hospitals of India were studied over a period of four months (January to April 2004). All the isolates were identified by standard biochemical methods at the referral hospitals. The participating hospitals were Safdarjung Hospital, New Delhi; AMU, Aligarh; BHU, Varanasi and KIMS, Hubli. NCCLS reference strains ESBL positive K. pneumoniae ATCC 700603 and sensitive E. coli ATCC 25922 were also included in the study.

Screening for ESBL and AmpC producing isolates

In order to simultaneously detect ESBL and AmpC, a modified double disk approximation method (MDDM), was devised. A 0.5 McFarland of test isolate was swabbed on Mueller Hinton Agar (Difco) plates and disk of cefotaxime (30 g) and ceftazidime (30 g) were placed adjacent to clavulanic acid (10 g) and Cefoxitin (30 g) disk at a distance of 20 mm from each other. After incubation, an enhanced zone of inhibition between any of the disks (ceftazidime / cefotaxime) and clavulanic acid were interpreted as presumptive evidence for the presence of ESBL [Figure 1a]. All ESBL positive isolates were further confirmed by determining their MICs in presence of clavulanate as per NCCLS micro broth dilution method.[7] Isolates showing blunting of ceftazidime or cefotaxime zone of inhibition adjacent to cefoxitin disk [Figure 1b] or showing reduced susceptibility to either of the above test drugs (ceftazidime or cefotaxime) and cefoxitin were considered as "screen positive" and selected for detection of AmpC b-lactamases.

Detection of AmpC b-lactamases

Modified three dimensional test

The selected isolates were studied for the presence of AmpC enzyme by modified three-dimensional extract test.[2] Briefly, fresh overnight growth from Mueller Hinton agar (MHA) was transferred to a preweighed sterile micro centrifuge tube. The tube was weighed again to determine the weight of bacterial mass to obtain 10-15 mg of bacterial wet weight. The bacterial mass was suspended in peptone water and pelleted by centrifugation at 3000 rpm for 15 minutes. Crude enzyme extract was prepared by repeated freeze thawing of the bacterial pellet (approximately 10 cycles). Lawn culture of E. coli ATCC 25922 was prepared on MHA plates and cefoxitin (30 g) disk were placed on the plates. Linear slits (3 cm) were cut using sterile surgical blade, 3 mm away from cefoxitin disk. At the other end of the slit a small circular well was made and the enzyme extract was loaded. A total of 30 to 40 l of extract was loaded in the well at a 10 l increment. The plates were kept upright for 5 to 10 minutes until the liquid dried and were incubated at 37C for 24h. Enhanced growth of the surface organism at the point where the slit inserted the zone of inhibition of cefoxitin was considered a positive three-dimensional test and was interpretated as evidence for the presence of AmpC b-lactamases. Three different types of results were recorded. Isolates showing clear distortion of the zone of inhibition of cefoxitin were taken as AmpC producers. Isolates with no distortion were recorded as non-AmpC producers where as isolates showing minimal distortion were considered as indeterminate strains

AmpC Disk Test

All isolates subjected to three-dimensional test were also simultaneously checked by AmpC disk test.[6] Here, a lawn culture of E. coli ATCC 25922 was prepared on MHA plate. Sterile disks (6 mm) were moistened with sterile saline (20 l) and inoculated with several colonies of test organism. The inoculated disk was than placed beside a cefoxitin disk (almost touching) on the inoculated plate. The plates were incubated overnight at 35C. A positive test appeared as a flattening or indentation of the cefoxitin inhibition zone in the vicinity of the test disk. A negative test had an undistorted zone.


 ~ Results Top


Screening for ESBLs and AmpC b-lactamases

Two hundred and seventy two isolates were screened for both ESBL and AmpC b-Lactamase production by modified double disk approximation method (MDDM). Of this 173 (64%) isolates were found to be ESBL positive whereas 38 were ESBL negative. Out of the total isolates 73% of Klebsiella spp. (n=71) and 62% of E. coli (n=80) were found to be ESBL positive [Table - 1], [Figure 1a].

Of the 272 isolates, 61 showed reduced susceptibility to either of the test drugs (ceftazidime or cefotaxime) and cefoxitin [Table - 1]. Three of these isolates also showed blunting of the inhibition zone of either ceftazidime or cefotaxime adjacent to cefoxitin disk [Figure 1b] were considered as presumptive AmpC producers and further confirmed by three-dimensional extraction method and AmpC disk test.

Our results also demonstrated the co-existence phenotype of both ESBL and AmpC in two isolates. (One each of Klebsiella spp. and E. coli) .

Detection of AmpC b-lactamases

Modified three dimensional test

AmpC b-lactamase production was confirmed in 22 isolates (8%) of the 272 isolates or 36% of the 61 screen positive isolates by the three-dimensional test. A clear distortion of the zone of inhibition of cefoxitin was observed in 18 isolates whereas three isolates showed minimal distortion and were considered as indeterminate strains [Figure - 2].

AmpC Disk Test

Of the 61 isolates 22 isolates, which were positive by extraction procedure, also showed positive results by AmpC disk test. Indentation indicating strong AmpC producer was observed in 15 isolates whereas flattening (weak AmpC) was observed in seven isolates. Three indeterminate isolates (three dimensional test) also showed flattening in AmpC disk test indicating for weak AmpC enzyme. [Figure - 3], [Table - 2].


 ~ Discussion Top


Despite the discovery of ESBLs and AmpC b-lactamases at least a decade ago, there remains a low level of awareness of their importance and many clinical laboratories have problems in detecting ESBLs and AmpC b-lactamases. Confusion exists about the importance of these resistance mechanisms, optimal test methods, and appropriate reporting conventions. Failure to detect these enzymes has contributed to their uncontrolled spread and sometimes to therapeutic failures.[8]

The objective of this work was to obtain some experimentally based prediction on the possible emergence of 'extended spectrum' AmpC b-lactamases in tertiary care hospitals and further to compare two phenotypic AmpC detecting methods. Detection and reporting isolates producing AmpC b-lactamases are more difficult issues than those associated with ESBLs. E. coli , Klebsiella pneumoniae and  Proteus mirabilis Scientific Name Search  are the species in family Enterobacteriaceae most commonly isolated in the clinical laboratory.[9] However, few studies have assessed the occurrence of AmpC b-lactamases among these species. The NCCLS documents[5] do not indicate the screening and confirmatory test that should be used for the detection of AmpC b-lactamases in Klebsiella pneumoniae and E. coli.

With the modified double disk diffusion screen test we identified 173 ESBLs and 61 isolates as possible AmpC producers resistant to cefoxitin. Further investigation of this phenotypic screening method for identifying possible AmpC producers seems warranted, as it offers the potential to significantly reduce the number of isolates that would require a confirmatory test for AmpC production, such as the three-dimensional test or AmpC disk test with cefoxitin.

Our initial screening also demonstrated the co-existence phenotype of both ESBL and AmpC in two isolates (one each of Klebsiella spp. and E. coli ). This could be because plasmid-mediated AmpC enzymes have also been shown to disseminate among Enterobacteriaceae , sometimes in combination with ESBLs. It might be highly desirable to develop an ESBL detection test that includes a substrate displaying a higher degree of resistance to such AmpC enzymes.[9],[10] We used cefoxitin resistance to screen isolates for detecting possible AmpC b-lactamases and three dimensional extract test and AmpC disk test for confirmation. The three dimensional and AmpC disk test are sensitive and 22 isolates were identified by both the methods as AmpC producers.

In the present study, ESBL producing isolates of Klebsiella spp. (73%) and E. coli (62%) were isolated from inpatient units as well as from clinical samples from patients attending outpatient clinics. In contrast, all the AmpC harbouring organisms (8%) were found only in clinical specimens from admitted patients. It has been reported that at present in India AmpC harbouring isolates are largely restricted to the hospitalized patients only.[2],[11] In our study AmpC b-lactamases was seen mainly in Acinetobacter spp. (28.57%) followed by E. coli (6.97%) and Klebsiella spp. (6.18%). The AmpC disk test was an easier, reliable and rapid method of detection of isolates that harbour AmpC b-lactamases. This suggests that AmpC disk test can be used for routine screening of the AmpC enzyme in the clinical laboratory.


 ~ Acknowledgement Top


We appreciate the help of Dr. M. Shahid (AMU) Aligarh, Dr. Ravi (KIMS) Hubli and Dr. Arpita (BHU) Varanasi for providing the clinical isolates for this study.

 
 ~ References Top

1.Moland SE, Black JA, Ourada J, Reisbig MD, Hanson ND, Thomson KS. Occurrence of newer b-lactamases in Klebsiella pneumoniae isolates from 24 U.S. hospitals. Antimicrob Agents Chemother 2002;46 :3837-42.  Back to cited text no. 1    
2.Manchanda V, Singh NP. Occurrence and detection of AmpC b-lactamases among Gram-negative clinical isolates using a modified three- dimensional test at Guru Tegh Bhadur Hospital, Delhi, India. J Antimicrob Chemother 2003;51 :415-8.  Back to cited text no. 2  [PUBMED]  [FULLTEXT]
3.Bauernfeind A, Chong Y, Lee K. Plasmid- encoded AmpC beta-lactamases: How far have we gone 10 years after the discovery? Yonsei Medical Journal 1998;39 :520-5.  Back to cited text no. 3  [PUBMED]  [FULLTEXT]
4.Coudran PE, Moland ES, Thomson KS. Occurrence and detection of AmpC beta- lactamases among Escherichia coli , Klebsiella pneumoniae and Proteus mirabilis isolates at a Vetrans Medical Center. J Clin Microbial 2000;38 :1791-6.  Back to cited text no. 4    
5.National Committee for Clinical Laboratory Standardards. Performance Standards for Antimicrobial Susceptibility Testing-twelfth informational supplement: Wayne, PA, USA: NCCLS; 2002;M 100-S12.  Back to cited text no. 5    
6.Black JA, Moland ES, HossainA, Lockhart TJ, Olson LB, Thomson KS, et al . Prevalence of Plasmid-mediated AmpC b-lactamases in Klebsiella pneumoniae (KP), Klebsiella oxytoca (KO), Proteus mirabilis (PM) , and Salmonella (S) isolates from 42 ICU and 21 non-ICU sites in the United States. Poster (C2-2034) in 43rd Interscience Conference on Antimicrobial Agents and Chemotherapy (ICCAC) 2003.   Back to cited text no. 6    
7.National Committee for Clinical Laboratory Standardards Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically. Wayne, PA, USA: NCCLS; 2000 Standard M7-A5.  Back to cited text no. 7    
8.Thomson KS. Controversies about extended-spectrum and AmpC beta-lactamases. Emerging Infect Dis 2001;7 :333-6.   Back to cited text no. 8  [PUBMED]  [FULLTEXT]
9.Gheldre YD, Avesani V, Berhin C, Delmee M, Glupczynski Y. Evaluation of oxoid combination disks for detection of extended spectrum b-lactamases J Antimicrob Chemother 2003;52 :591-7.  Back to cited text no. 9    
10.Philippon A, Arlet G, Jacoby GA. Plasmid-determined AmpC-type b-lactamases. Antimicrob Agents Chemother 2002;46 :1-11.   Back to cited text no. 10  [PUBMED]  [FULLTEXT]
11.Shahid M, Malik A, Sheeba. Multi drug resistant Pseudomonas aeruginosa strains harboring R-plasmids and AmpC b-lactamases isolated from hospitalized burn patients in a tertiary care hospital of North India. FEMS Microbiology Letters 2003;228 :181-6.  Back to cited text no. 11  [PUBMED]  [FULLTEXT]


Figures

[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4]

Tables

[Table - 1], [Table - 2]

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41 Detection of extended spectrum beta-lactamase production and multidrug resistance in clinical isolates of E.Coli and K.Pneumoniae in Mangalore
Shiju, M.P. and Yashavanth, R. and Narendra, N.
Journal of Clinical and Diagnostic Research. 2010; 4(3): 2442-2445
[Pubmed]
42 ACC-1 β-lactamase-producing Salmonella enterica serovar Typhi, India
Gokul, B.N. and Menezes, G.A. and Harish, B.N.
Emerging Infectious Diseases. 2010; 16(7): 1170-1171
[Pubmed]
43 Ventilator-associated pneumonia in a tertiary care hospital in India: Role of multi-drug resistant pathogens
Joseph, N.M. and Sistla, S. and Dutta, T.K. and Badhe, A.S. and Rasitha, D. and Parija, S.C.
Journal of Infection in Developing Countries. 2010; 4(4): 218-225
[Pubmed]
44 Molecular characterization of antimicrobial resistance in non-typhoidal salmonellae associated with systemic manifestations from India
G. A. Menezes, M. A. Khan, B. N. Harish, S. C. Parija, W. Goessens, K. Vidyalakshmi, S. Baliga, J. P. Hays
Journal of Medical Microbiology. 2010; 59(12): 1477
[VIEW] | [DOI]
45 Ventilator-associated pneumonia: A review
Noyal Mariya Joseph, Sujatha Sistla, Tarun Kumar Dutta, Ashok Shankar Badhe, Subhash Chandra Parija
European Journal of Internal Medicine. 2010; 21(5): 360
[VIEW] | [DOI]
46 Detection of extended spectrum beta-lactamase production and multidrug resistance in clinical isolates of E.Coli and K.Pneumoniae in Mangalore
Shiju, M.P., Yashavanth, R., Narendra, N.
Journal of Clinical and Diagnostic Research. 2010; 4(3): 2442-2445
[Pubmed]
47 Ventilator-associated pneumonia: A review
Joseph, N.M., Sistla, S., Dutta, T.K., Badhe, A.S., Parija, S.C.
European Journal of Internal Medicine. 2010; 21(5): 360-368
[Pubmed]
48 Ventilator-associated pneumonia in a tertiary care hospital in India: Role of multi-drug resistant pathogens
Joseph, N.M., Sistla, S., Dutta, T.K., Badhe, A.S., Rasitha, D., Parija, S.C.
Journal of Infection in Developing Countries. 2010; 4(4): 218-225
[Pubmed]
49 ACC-1 β-lactamase-producing Salmonella enterica serovar Typhi, India
Gokul, B.N., Menezes, G.A., Harish, B.N.
Emerging Infectious Diseases. 2010; 16(7): 1170-1171
[Pubmed]
50 ACC-1 -LactamaseproducingSalmonella entericaSerovar Typhi, India
Bindiganavile N. Gokul,Godfred A. Menezes,Belgode N. Harish
Emerging Infectious Diseases. 2010; 16(7): 1170
[Pubmed] | [DOI]
51 Extended spectrum AmpC and metallo-beta-lactamases in Serratia and Citrobacter spp. in a disc approximation assay
Rizvi, M., Fatima, N., Rashid, M., Shukla, I., Malik, A., Usman, A., Siddiqui, S.
Journal of Infection in Developing Countries. 2009; 3(3): 177-186
[Pubmed]
52 In vitro evaluation of a new cefixime-clavulanic acid combination for gram-negative bacteria
Rawat, D., Hasan, A.S., Capoor, M.R., Sarma, S., Nair, D., Deb, M., Pillai, P., Aggarwal, P.
Southeast Asian Journal of Tropical Medicine and Public Health. 2009; 40(1): 131-139
[Pubmed]
53 Simple screening tests for detection of carbapenemases in clinical isolates of nonfermentative Gram-negative bacteria
Noyal, M.J.C., Menezes, G.A., Harish, B.N., Sujatha, S., Parija, S.C.
Indian Journal of Medical Research. 2009; 129(6): 707-712
[Pubmed]
54 Occurrence of extended-spectrum β-lactamases in Escherichia coli isolated from piggery farms in Imo State, Nigeria
Akujobi, C.O., Ogbulie, J.N., Alisi, C.S.
World Journal of Microbiology and Biotechnology. 2008; 24(10): 2167-2170
[Pubmed]
55 Evaluation of CIVA agar for rapid detection of extended spectrum β-lactamases (ESBL) among isolates of Enterobacteriaceae
Padmini, S.B., Raju, B.A.
Indian Journal of Medical Research. 2008; 127(2): 195-197
[Pubmed]
56 Evaluation of a modified double-disc synergy test for detection of extended spectrum β-lactamases in AmpC β-lactamase-producing Proteus mirabilis
Khan, M.K.R., Thukral, S., Gaind, R.
Indian Journal of Medical Microbiology. 2008; 26(1): 58-61
[Pubmed]
57 Prevalence of extended spectrum beta lactamase and AmpC beta lactamase producers among Escherichia coli isolates in a tertiary care hospital in Jaipur
Sinha, P., Sharma, R., Rishi, S., Sharma, R., Sood, S., Pathak, D.
Indian Journal of Pathology and Microbiology. 2008; 51(3): 367-369
[Pubmed]
58 Occurrence and detection of AmpC β lactamases among clinical isolates of E.coli and K pneumoniae causing UTI
Ekadashi, R., Rawat, U., Malhotra, V.L., Mehta, G.
Journal of Communicable Diseases. 2008; 40(1): 21-25
[Pubmed]
59 Occurrence of extended-spectrum β-lactamases in Escherichia coli isolated from piggery farms in Imo State, Nigeria
Akujobi, C.O. and Ogbulie, J.N. and Alisi, C.S.
World Journal of Microbiology and Biotechnology. 2008; 24(10): 2167-2170
[Pubmed]
60 Occurrence and detection of AmpC β lactamases among clinical isolates of E.coli and K pneumoniae causing UTI
Ekadashi, R. and Rawat, U. and Malhotra, V.L. and Mehta, G.
Journal of Communicable Diseases. 2008; 40(1): 21-25
[Pubmed]
61 Evaluation of CIVA agar for rapid detection of extended spectrum β-lactamases (ESBL) among isolates of Enterobacteriaceae
Padmini, S.B. and Raju, B.A.
Indian Journal of Medical Research. 2008; 127(2): 195-197
[Pubmed]
62 Evaluation of a modified double-disc synergy test for detection of extended spectrum β-lactamases in AmpC β-lactamase-producing Proteus mirabilis
Khan, M.K.R. and Thukral, S. and Gaind, R.
Indian Journal of Medical Microbiology. 2008; 26(1): 58-61
[Pubmed]
63 An update on newer β-lactamases
Gupta, V.
Indian Journal of Medical Research. 2007; 126(5): 417-427
[Pubmed]
64 Extended-spectrum and AmpC β-lactamases in Escherichia coli and Klebsiella pneumoniae from a rural South Indian tertiary care hospital
Navaneeth, B.V.
International Journal of Antimicrobial Agents. 2007; 29(5): 602-603
[Pubmed]
65 Detection of plasmid-mediated class C β-lactamases
Doi, Y. and Paterson, D.L.
International Journal of Infectious Diseases. 2007; 11(3): 191-197
[Pubmed]
66 An update on newer β-lactamases
Gupta, V.
Indian Journal of Medical Research. 2007; 126(5): 417-427
[Pubmed]
67 Prevalence of multi and pan drug resistant Pseudomonas aeruginosa with respect to ESBL and MBL in a tertiary care hospital
Jayakumar, S., Appalaraju, B.
Indian Journal of Pathology and Microbiology. 2007; 50(4): 922-925
[Pubmed]
68 Detection of Amp C beta lactamases production in Escherichia coli & Klebsiella by an inhibitor based method
Hemalatha, V., Padma, M., Sekar, U., Vinodh, T.M., Arunkumar, A.S.
Indian Journal of Medical Research. 2007; 126(3): 220-223
[Pubmed]
69 Detection of plasmid-mediated class C -lactamases
Yohei Doi,David L. Paterson
International Journal of Infectious Diseases. 2007; 11(3): 191
[Pubmed] | [DOI]
70 Extended-spectrum and AmpC β-lactamases in Escherichia coli and Klebsiella pneumoniae from a rural South Indian tertiary care hospital
B.V. Navaneeth
International Journal of Antimicrobial Agents. 2007; 29(5): 602
[VIEW] | [DOI]
71 Incidence of multidrug-resistant organisms causing ventilator-associated pneumonia in a tertiary care hospital: A nine months prospective study
Dey, A., Bairy, I.
Ann Thorac Med. 2007; 2(2): 52-57
[Pubmed]
72 Detection of plasmid-mediated class C β-lactamases
Doi, Y., Paterson, D.L.
International Journal of Infectious Diseases. 2007; 11(3): 191-197
[Pubmed]
73 Extended spectrum beta lactamase producing Gram negative bacilli in a tertiary referral hospital of Assam - Experience with two methods
Nath, R., Saikia, L., Mahanta, J.
Indian Journal of Pathology and Microbiology. 2006; 49(4): 623-625
[Pubmed]
74 Modified double-disc test for detection of extended-spectrum β-lactamases in Escherichia coli and Klebsiella pneumoniae
Kader, A.A., Angamuthu, K.K., Kamath, K.A., Zaman, M.N.
British Journal of Biomedical Science. 2006; 63(2): 51-54
[Pubmed]
75 Modified double-disc test for detection of extended-spectrum β-lactamases in Escherichia coli and Klebsiella pneumoniae
Kader, A.A. and Angamuthu, K.K. and Kamath, K.A. and Zaman, M.N.
British Journal of Biomedical Science. 2006; 63(2): 51-54
[Pubmed]
76 Sensitive EDTA-based microbiological assays for detection of metallo-β-lactamases in nonfermentative gram-negative bacteria
Marchiaro, P. and Mussi, M.A. and Ballerini, V. and Pasteran, F. and Viale, A.M. and Vila, A.J. and Limansky, A.S.
Journal of Clinical Microbiology. 2005; 43(11): 5648-5652
[Pubmed]
77 Sensitive EDTA-based microbiological assays for detection of metallo-β-lactamases in nonfermentative gram-negative bacteria
Marchiaro, P., Mussi, M.A., Ballerini, V., Pasteran, F., Viale, A.M., Vila, A.J., Limansky, A.S.
Journal of Clinical Microbiology. 2005; 43(11): 5648-5652
[Pubmed]



 

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2004 - Indian Journal of Medical Microbiology
Published by Wolters Kluwer - Medknow

Online since April 2001, new site since 1st August '04