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Year : 2015  |  Volume : 33  |  Issue : 5  |  Page : 160--161

Report of carbapenem resistant Ps. aeruginosa, isolates carrying ESBLs, AmpC and MBL enzymes based on phenotypic methodology and susceptibility to Fosfomycin

R Garg, V Gupta, J Chander, M Kaur 
 Department of Microbiology, Government Medical College Hospital, Chandigarh, India

Correspondence Address:
V Gupta
Department of Microbiology, Government Medical College Hospital, Chandigarh

How to cite this article:
Garg R, Gupta V, Chander J, Kaur M. Report of carbapenem resistant Ps. aeruginosa, isolates carrying ESBLs, AmpC and MBL enzymes based on phenotypic methodology and susceptibility to Fosfomycin.Indian J Med Microbiol 2015;33:160-161

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Garg R, Gupta V, Chander J, Kaur M. Report of carbapenem resistant Ps. aeruginosa, isolates carrying ESBLs, AmpC and MBL enzymes based on phenotypic methodology and susceptibility to Fosfomycin. Indian J Med Microbiol [serial online] 2015 [cited 2020 Jan 23 ];33:160-161
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Dear Editor,

Pseudomonas aeruginosa can harbour several mechanisms of resistance, which generates multi-drug resistant (MDR) or pan-resistant (PDR) isolates. [1] For treating infections with MDR, P. aeruginosa limited drug options are there like polymyxins alone or in various combinations. Recently, efficacy of fosfomycin has been seen in severe infections, including those due to MDR bacteria, especially in P. aeruginosa that Escherichia coli even in critical situations. [2]

Based on this, a study was planned on MDR P. aeruginosa from pus samples of indoor patients with the following objectives: To evaluate various phenotypic assays for enzyme production amongst the P. aeruginosa isolates and to determine fosfomycin susceptibility for the isolates by E-test methods (Biomerieux).

One hundred non-duplicate isolates of P. aeruginosa that were MDR were obtained from pus samples received in the Microbiology department of the Government Medical College Hospital, Chandigarh, over a period of one year were included in this study. The identification of the isolates was done by standard biochemical methods. An antibiotic susceptibility method using 10 antibiotics covering most Gram-negative organisms was followed and helped in screening for  extended spectrum beta-lactamase (ESBL) and AmpC ß-lactamases together with carbapenem susceptibility. The antibiotics used were ceftazidime, cefotaxime, cefepime, cefoxitin, amikacin, gentamicin, ciprofloxacin, imipenem, amoxicillin-clavulanic acid, and piperacillin-tazobactam. The sensitivity pattern of these isolates to various antibiotics was studied by Kirby-Bauer disk diffusion method according to Clinical Laboratory Standards Institute (CLSI) guidelines. The detection of different classes of ß-lactamases enzymes that is ESBL, AmpC, and metallo-β-lactamase (MBL) in clinical isolates of P. aeruginosa was done by standard protocols. Minimum inhibitory concentration (MIC) of fosfomycin was tested by E-test method with fosfomycin gradient concentrations ranging from 0.04 μg/ml to 1,024 μg/ml added along with 50 μg/ml glucose-6-phosphate. [3]

Out of 100 imipenem/meropenem non-susceptible P. aeruginosa isolates, those producing various enzymes alone and in combination is depicted in [Table 1]. Out of 100 isolates, one isolate of P. aeruginosa showed all the three β-lactamase resistance mechanisms [Table 1]. Falagas et al., in their study have also reported similar results. [4] All the isolates were MDR. The MIC of fosfomycin for different MDR isolates of P. aeruginosa having different enzymes is also shown in [Table 1].{Table 1}

The limited therapeutic options against P. aeruginosa stresses upon the usefulness of testing for fosfomycin susceptibility, particularly to support the combination therapy when MIC values are ≤128 μg/ml. [5] In P.aeruginosa isolates that are resistant to other antimicrobial agents and having MIC of <32 μg/ml for fosfomycin, combination of fosfomycin with other agents has good activity. It is speculated that fosfomycin induces new permeability routes for antimicrobial agents into the outer membrane by destroying the outer membrane of bacteria and thus increase the permeability of antimicrobials. [6]

In soft-tissue infection treatment, there is high inter individual variability in the  pharmacokinetic (PK) of fosfomycin in pus due to highly variable abscess permeability. Antimicrobial effective levels of fosfomycin in pus may be reached with a significant or critical delay in some abscesses. However, prolonged half-life and sustained high concentration have been achieved with multiple doses in some patients. Although overall tissue distribution is good, the clinical response depends on the location of pus/abscess cavities as well. Fosfomycin has excellent tissue penetration properties, which may be attributed to its low molecular weight, low plasma protein binding, high hydrophilicity, and a good volume of distribution. Despite favourable tissue penetration of fosfomycin, monotherapy with fosfomycin has limited use because of the rapid development of resistance and so it is advised to use fosfomycin with other antimicrobials. [7] However, fosfomycin single time oral therapy has been recommended in uncomplicated urinary tract infection. [8]

Thus the present study emphasizes the high prevalence of MDR P. aeruginosa producing β-lactamase enzymes of diverse mechanisms. Fosfomycin MICs as shown are still less in India and so for treating abscesses combination of fosfomycin with other antimicrobials represents good option as it shows high-tissue penetration in soft- tissue infections.


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