Colistin Resistance among Gram Negative Organisms; an Evolving Problem from Tertiary Care Hospital, Pakistan 2014

Corresponding Author: Tuba Bashir Department of Microbiology, The Indus Hospital, Korangi Crossing, Karachi, Pakistan Off: +92-21-35112709-17; Fax: +92-21-35112718 Email: tuba_bashir@yahoo.com; tuba.bashir@tih.org.pk Abstract: This Study was design to report the evolving Colistin Resistant Gram Negative Organisms from Pakistan in 2014. From 885 isolates of hospitalized patients, 03 Colistin resistant isolates were reported, 02 were Escherichia coli and 01 was Acinetobacter specie. Colistin of all three isolates was tested by Disk diffusion method, MIC by Phoenix 100 (BD) and E-strip. This report contributes a useful addition in literature of Gram Negative Organisms Susceptibility pattern reported from Pakistan, as Colistin is extensively used for the treatment of Multi drug resistant Gram Negative’s in hospital settings.


Introduction
Colistin is bactericidal antibiotic; it binds to lipo polysaccharides and phospholipids of Gram Negative Bacterial Cell membrane. This binding results the intracellular leakage of Cell components and finally cell death (Alfahad and Omrani, 2014). It was introduced in 1952 in clinical practice to treat infections caused by Gram Negative Bacteria (Biswas et al., 2012). In 1970's better antimicrobials was available to treat Gram Negative Infections, as Colistin has poor safety profile (Alfahad and Omrani, 2014 The Colistin MIC of all three isolates was reported as > 4 mg L −1 by Automated Phoenix 100. The Tigecycline MIC was ≤1 mg L −1 for both Escherichia coli and 2 mg L −1 for Acinetobacter specie by Phoenix 100.
The E-strip MIC results of Colistin were 8 mg L for both Escherichia coli and 16 mg L −1 for Acinetobacter specie.
We did not find any in vitro Colistin resistance in Klebsiella specie and Pseudomonas aeroginosa.
The best of our knowledge, this is the 1st report of Colistin resistance among Gram Negative Organisms from Pakistan (Pubmed). Reports of in vitro Colistin resistance has been published from Saudi Arabia and India in recent years (Musa et al., 2013;Abeer et al., 2013) From Greece in vitro colistin resistance was also reported (George et al., 2010). Colistin has been extensively used to treat Multi drug resistant Gram Negative infections (Alfahad and Omrani, 2014).
It has been reported that the growing threat of Colistin resistance might be due to its extensive use as a result of increased Carbapenem resistance among Gram Negative Organisms (Musa et al., 2013).
For clinical laboratories, colistin reporting by disk diffusion method is not recommended, as for Enterobacteriaceae and Acinetobacter spp. no interpretation criteria is available by CLSI. Despite the guidelines criteria MIC testing should also encourage in MDR isolates to improve treatment strategies, leads to better outcomes.
In our study, Table 1 showed that 03 patients were reported as colistin resistant isolates, 02 were Escherichia coli and 01 was Acinetobacter specie. 02 were male patients and 01 was female. All Colistin resistant isolates were sensitive to Tigecycline. 02 were Sensitive only to Tigecycline and Tetracycline whereas, 01 Colistin Resistant Isolate was Sensitive to many other antibiotics including carbapenems. This finding wass also reported in other publications (George et al., 2010). Colistin MIC of all three isolates was very high done by E-strip (Fig. 1).
The limitation of this study was that; we did not perform molecular testing; therefore we are not able to report that which genes are responsible for the Colistin resistance.
On the other hand, there is a great need of MIC reporting of Colistin due to extremely high resistance among Gram Negative's and extensive use of Colistin in hospitalized patients.

Conclusion
This report is unique, as it is the 1st in vitro Colistin resistance report from Pakistan. Colistin resistance is an alarming concern because it is used as last resort of treatment in healthcare facilities. Therefore, Strict infection Control guidelines and Antimicrobial Stewardship should implement to overcome the new resistance spread and MIC reporting of MDR isolates should encourage.