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Year : 2015  |  Volume : 33  |  Issue : 3  |  Page : 461--462

Tigecycline-resistant staphylococcal isolates in a tertiary care centre

S Basireddy, M Singh, S Ali, V Kabra 
 Department of Microbiology, Sri Venkata Sai Medical College, Mahabubnagar - 509 001, Andhra Pradesh, India

Correspondence Address:
M Singh
Department of Microbiology, Sri Venkata Sai Medical College, Mahabubnagar - 509 001, Andhra Pradesh
India

How to cite this article:
Basireddy S, Singh M, Ali S, Kabra V. Tigecycline-resistant staphylococcal isolates in a tertiary care centre.Indian J Med Microbiol 2015;33:461-462

How to cite this URL:
Basireddy S, Singh M, Ali S, Kabra V. Tigecycline-resistant staphylococcal isolates in a tertiary care centre. Indian J Med Microbiol [serial online] 2015 [cited 2019 Dec 9 ];33:461-462
Available from: http://www.ijmm.org/text.asp?2015/33/3/461/158608

Full Text

Dear Editor,

Tigecycline, the first glycylcycline compound derived from minocycline, is highly active against many multidrug resistant organisms including methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus spp., extended spectrum-lactamase (ESBL)-producing Enterobacteriaceae and carbapenem-resistant Acinetobacter spp. It acts by blocking binding of the tRNA aminoacyl site to the 30 S ribosomal subunit and thus inhibits the protein synthesis. It is also active against tetracycline and minocycline-resistant microorganisms and does not present cross-resistance with other antibiotics. [1]

Tigecycline has a very good gram-positive spectrum for which the resistance seems very rare. [2],[3] Only few published reports available from India, and all of them showed absolute sensitivity of this antibiotic against S. aureus. [4] Here, we report a rare S. aureus isolate, which was resistant to tigecycline.

A total of 365 S. aureus were isolated from various clinical specimens during the period of April 2013 to March 2014. Among these, 365 isolates 176 (48.2%) were found to be methicillin resistant (MRSA). Methicillin resistance was detected by disc diffusion method on Muller-Hinton agar using the cefoxitin 30 μg disc.

All these methicillin resistance isolates were tested with the tigecycline 15 μg disc, by disc diffusion methodology. As there were no CLSI guidelines for tigecycline, EUCAST breakpoints for disc diffusion testing against Staphylococcus were adopted. [5] (sensitive ≥ 18 mm and resistant <18 mm zone diameter). ATCC S. aureus 25923 was used as control strain.

All the isolates but one was uniformly sensitive to tigecycline by disc diffusion method with the mean zone size of 20 mm. The one isolate that was resistant to tigecycline had shown a zone diameter of 8 mm and was isolated from pus sample [Figure 1]. The isolate was also resistant to multiple antibiotics, including levofloxacin, gentamicin, erythromycin, cotrimoxazole and doxycycline but was sensitive to linezolid, vancomycin, and clindamycin.{Figure 1}

The minimum inhibitory concentration (MIC) for the isolate was determined by performing the E test method on Muller-Hinton agar plates by applying the E strip (Hi-media). S. aureus ATCC 29213 was used as control strain. EUCAST MIC breakpoints for S. aureus were adopted. [5] (sensitive ≤0.5 mcg/ml and resistant >0.5 mcg/ml). The MIC of the isolate was determined as 1.5mcg/ml which is well above the cut-off breakpoint breakpoint [Figure 2]. As per the EUCAST guidelines such a rare resistance patterns should be tested repeatedly for confirmation. So the resistance was further confirmed by adopting the Stokes methodology for MIC detection using both the control strain and test strain on the same plate and applying the E strip [Figure 3]. Broth micro dilution testing was also done for further confirmation by using the pure powder of tigecycline (united biotech) and microdilution plate with freshly prepared cation adjusted Mueller-Hinton broth and using S. aureus ATCC 29213 as control strain.{Figure 2}{Figure 3}

Tigecycline resistance in gram-positive organisms especially S. aureus is very rare with only a few published reports in the world till date. [6],[7] In India, resistance to this antibiotic has never been detected. Observing the resistance in the absence of any prior exposure to this antibiotic is of concern, as is seen in our case.

References

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2Brandon M, Dowzicky MJ. Antimicrobial susceptibility among Gram-positive organisms collected from pediatric patients globally between 2004 and 2011: Results from the tigecycline evaluation and surveillance trial. J Clin Microbiol 2013;51:2371-8.
3Verkade EJ, Verhulst CJ, Huijsdens XW, Kluytmans JA. In vitro activity of tigecycline against methicillin-resistant Staphylococcus aureus, including livestock-associated strains. Eur J Clin Microbiol Infect Dis 2010;29:503-7.
4Behera B, Das A, Mathur P, Kapil A, Gadepalli R, Dhawan B. Tigecycline susceptibility report from an Indian tertiary care hospital. Indian J Med Res 2009;129:446-50.
5The European Committee on Antimicrobial Susceptibility testing (2013) Breakpoint tables for interpretation of MICs and zone diameters. Version 3.1, EUCAST. Available from: http://www.eucast.org/antimicrobial_susceptibility_testing/previous_versions_of_tables [Last accessed on 2013 Aug 16].
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7Chen YH, Lu PL, Huang CH, Liao CH, Lu CT, Chuang YC, et al. Trends in the susceptibility of clinically important resistant bacteria to tigecycline: Results from the Tigecycline in vitro Surveillance in Taiwan study, 2006 to 2010. Antimicrob Agents Chemother 2012;56:1452-7