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CORRESPONDENCE
Year : 2014  |  Volume : 32  |  Issue : 2  |  Page : 203-204
 

Comparative in vitro activity of polymyxins against carbapenem susceptible and resistant non-fermenters from critically ill-patients


1 Department of Microbiology, Government Medical College Hospital, Chandigarh, India
2 Department of Anesthesia and Intensive Care, Government Medical College Hospital, Chandigarh, India

Date of Submission03-Sep-2013
Date of Acceptance10-Nov-2013
Date of Web Publication2-Apr-2014

Correspondence Address:
V Gupta
Department of Microbiology, Government Medical College Hospital, Chandigarh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0255-0857.129849

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How to cite this article:
Gupta V, Bansal N, Palta S, Gombar S, Chander J. Comparative in vitro activity of polymyxins against carbapenem susceptible and resistant non-fermenters from critically ill-patients. Indian J Med Microbiol 2014;32:203-4

How to cite this URL:
Gupta V, Bansal N, Palta S, Gombar S, Chander J. Comparative in vitro activity of polymyxins against carbapenem susceptible and resistant non-fermenters from critically ill-patients. Indian J Med Microbiol [serial online] 2014 [cited 2019 Dec 12];32:203-4. Available from: http://www.ijmm.org/text.asp?2014/32/2/203/129849


Dear Editor,

The reappraisal of a relatively old group of antibiotics, polymyxins, has been done by clinicians and microbiologists as there is marked decline in the development of novel antibiotics in the past with an alarming increase in resistance to existing ones. Unfortunately, polymyxins also do not escape development of resistance. There are quite a few suggested mechanisms of resistance to colistin/polymyxin B in Gram-negative bacteria, most of which involve changes in the outer membrane related to loss of lipopolysaccharide or/and PmrAB two component system. [1] Thus, taking into an account increase in clinical use of polymyxins, a comparative study was carried out to evaluate the in vitro activity of colistin and polymyxin B against susceptible and multidrug resistant strains of Pseudomonas aeruginosa and Acinetobacter baumannii in tertiary care hospital setting from India. The study was conducted on two groups of isolates. Group I: imipenem susceptible A. baumannii (n = 50) versus imipenem resistant A. baumannii (n = 50); Group II: imipenem susceptible P. aeruginosa (n = 50) versus imipenem resistant P. aeruginosa (n = 50). The isolates collected were consecutive, non-duplicate and were derived from various clinical samples from critically ill-patients in intensive care unit. Organisms were identified as per standard protocols and antibiotic sensitivity for imipenem resistance in P. aeruginosa and A. baumannii was done by disc diffusion methodology as per Clinical Laboratory Standards Institute (CLSI) 2011 guidelines. [2] Minimum inhibitory concentration (MIC) to colistin and polymyxin B (Sigma) was determined using the agar dilution method with a concentration range of 0.12-16 μg/ml on Mueller-Hinton agar (Difco). The MIC 50 and MIC 90 for each of the comparable groups were noted and statistical analysis was performed using unpaired t-test and P < .05 was considered to be statistically significant. The results of the study are depicted in the [Table 1]. Considerable in vitro activity of colistin and polymyxin B was observed against imipenem susceptible as well resistant isolates of both P. aeruginosa and A. baumannii. Although four imipenem resistant strains of P. aeruginosa were found to be intermediate sensitive to colistin as per CLSI interpretative criterion, however, no statistically significant difference (P < 0.05) was observed in the MICs of comparable isolates. In recent years, increasing multi-drug resistant Gram-negative bacterial infections have renewed interest in colistin as a therapeutic option. However, there are regional variations in the susceptibility of polymyxins and trends to greater resistance is found in the areas where these are prescribed heavily like greater resistance in Klebsiella spp. was observed in the Asia-Pacific and Latin American regions. [3] Colistin resistance is most commonly found in A. baumannii, followed by Klebsiella pneumoniae and P. aeruginosa. [4] Furthermore, almost complete cross-resistance exists between colistin and polymyxin B. [1] Increasing reports of heteroresistance to colistin in clinical isolates is an additional pointer indicative of declining therapeutic success of polymyxins in near future. [5] Hence, to conclude although the antimicrobial activity of polymyxins remained high for both cabapenem-susceptible and-resistant strains evaluated at our center probably due to its limited clinical use, still the use should be cautious, surveillance monitored and studies on appropriate combination therapies with colistin are warranted in near future.
Table 1: In vitro activity of colistin and polymyxin B against susceptible and multidrug resistant organisms

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 ~ References Top

1.Cai Y, Chai D, Wang R, Liang B, Bai N. Colistin resistance of Acinetobacter baumannii: Clinical reports, mechanisms and antimicrobial strategies. J Antimicrob Chemother 2012;67:1607-15.  Back to cited text no. 1
    
2.Clinical and Laboratory Standards Institute. Performance Standards for Antimicrobial Susceptibility Testing. Twenty-First Informational Supplement. CLSI Document M100-S21. Wayne, PA: Clinical and Laboratory Standards Institute; 2011.  Back to cited text no. 2
    
3.Gales AC, Jones RN, Sader HS. Contemporary activity of colistin and polymyxin B against a worldwide collection of Gram-negative pathogens: Results from the SENTRY Antimicrobial Surveillance Program (2006-09). J Antimicrob Chemother 2011;66:2070-4.  Back to cited text no. 3
    
4.López-Rojas R, Jiménez-Mejías ME, Lepe JA, Pachón J. Acinetobacter baumannii resistant to colistin alters its antibiotic resistance profile: A case report from Spain. J Infect Dis 2011;204:1147-8.  Back to cited text no. 4
    
5.Li J, Rayner CR, Nation RL, Owen RJ, Spelman D, Tan KE, et al. Heteroresistance to colistin in multidrug-resistant Acinetobacter baumannii. Antimicrob Agents Chemother 2006;50:2946-50.  Back to cited text no. 5
    



 
 
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