Indian Journal of Medical Research

CORRESPONDENCE
Year
: 2012  |  Volume : 136  |  Issue : 5  |  Page : 884-

Pitfalls of interpreting ciprofloxacin minimum inhibitory concentrations in Salmonella enterica serovar Typhi


Sadia Khan, V Anil Kumar 
 Department of Microbiology, Amrita Institute of Medical Sciences, Kochi 682 041, Kerala, India

Correspondence Address:
Sadia Khan
Department of Microbiology, Amrita Institute of Medical Sciences, Kochi 682 041, Kerala
India




How to cite this article:
Khan S, Kumar V A. Pitfalls of interpreting ciprofloxacin minimum inhibitory concentrations in Salmonella enterica serovar Typhi.Indian J Med Res 2012;136:884-884


How to cite this URL:
Khan S, Kumar V A. Pitfalls of interpreting ciprofloxacin minimum inhibitory concentrations in Salmonella enterica serovar Typhi. Indian J Med Res [serial online] 2012 [cited 2020 Nov 28 ];136:884-884
Available from: https://www.ijmr.org.in/text.asp?2012/136/5/884/105421


Full Text

Sir,

We read with interest the article on emergence of fluoroquinolone resistance in Salmonella enterica serovar Typhi in Andaman and Nicobar Islands [1] . As fluoroquinolones are widely used in the empirical therapy of enteric fever, it is important to determine the minimum inhibitory concentrations (MIC) of this group of antimicrobials in an endemic area. However, there were certain points in the article that needed clarification, which we would like to highlight:

(i) CLSI 2007 guidelines have been used though the study was conducted in 2009-2010.

(ii) The Table showed that five out of six isolates had an MIC of 0.25 μg/ml. Based on CLSI guidelines till 2011 [2] , MICs of <1 μg/ml have indicated that the organism is susceptible to ciprofloxacin. The 2012 CLSI guidelines have reduced the MIC indicating ciprofloxacin susceptibility to <0.06 μg/ml, probably making most of our strains resistant to ciprofloxacin [3] .

(iii) The authors have interpreted that five isolates of S. Typhi with MICs of 0.25 and 1 μg/ml showed intermediate level resistance to ciprofloxacin and norfloxacin, respectively. As per CLSI guidelines (2011) MICs of 2 and 8 μg/ml for ciprofloxacin and norfloxacin, respectively, indicate intermediate resistance. The authors probably implied "reduced susceptibility" to ciprofloxacin based on their molecular data. Nalidixic acid resistance in salmonellae indicates reduced susceptibility to fluoroquinolones (MICs 0.125-1 μg/ml) and may be associated with clinical failure or delayed response in fluoroquinolone treated patients [4] . It should not be confused with intermediate level resistance to fluoroquinolones.

References

1Tamizhmani R, Bhattacharya D, Sayi DS, Bhattacharjee H, Muruganandam N, Ghosal SR, et al. Emergence of fluoroquinolone resistance in Salmonella enterica serovar Typhi in Andaman and Nicobar Islands, India. Indian J Med Res 2012; 136 : 98-101.
2Clinical and Laboratory Standards Institute (CLSI). Performance standards for antimicrobial susceptibility testing; twenty-second informational supplement. M100-S21. Wayne, Pa: CLSI; 2012.
3Clinical and Laboratory Standards Institute (CLSI). Performance standards for antimicrobial susceptibility testing; twenty-second informational supplement. M100-S22. Wayne, Pa: CLSI; 2012.
4Gaind R, Paglietti B, Murgia M, Dawar R, Uzzau S, Cappuccinelli P, et al. Molecular characterization of ciprofloxacin- resistant Salmonella enterica serovar Typhi and Paratyphi A causing enteric fever in India. J Antimicrob Chemother 2006; 58 : 1139-44.