|Year : 2011 | Volume
| Issue : 3 | Page : 280-282
Assessment of trends of ofloxacin resistance in Mycobacterium tuberculosis
JS Verma1, D Nair1, D Rawat1, N Manzoor2
1 Department of Microbiology, VMMC and Safdarjung Hospital, New Delhi, India
2 Department of Bio-Sciences, Jamia Millia Islamia University, New Delhi, India
|Date of Submission||06-Dec-2010|
|Date of Acceptance||06-Mar-2011|
|Date of Web Publication||17-Aug-2011|
Department of Microbiology, VMMC and Safdarjung Hospital, New Delhi
Source of Support: Indian Council of Medical Research, Conflict of Interest: None
Purpose: Ofloxacin (OFX) is one of the potent fluoroquinolone (FQ) recommended to treat MDR-TB. Over a decade, the preexposure of this drug for the treatment of other bacterial infections has resulted in acquisition of FQ resistance among Mycobacterium tuberculosis strains. Considering this possibility, a study was undertaken in a tertiary care center in the capital city (India) to assess the drug resistance trends of OFX among susceptible and multidrug resistant (MDR) strains of M. tuberculosis. Materials and Methods: A total of 102 M. tuberculosis isolates (47 susceptible to first-line drugs and 55 MDR isolates) were screened for susceptibility testing of OFX with a critical concentration of 2 μg/ml by Lowenstein Jensen (LJ) proportion method. Results: The results showed 40 (85.1%) isolates among 47 susceptible isolates and 34 (61.8%) isolates among 55 MDR isolates, were found to be susceptible to OFX. Fisher's exact test showed significant P-value (0.0136) demonstrating 1.377 fold (95% confidence interval) increased risk to become resistant to OFX than susceptible isolates. These finding shows decreased OFX susceptibility is not only limited to MDR isolates but also increasingly seen in susceptible strains as a result of drug abuse. Conclusions: Our finding were not alarming, but highlights the general risk of acquiring resistance to OFX, jeopardizing the potential for these drugs to be used as second-line anti-TB agents in the management of drug-resistant TB and creating incurable TB strains .
Keywords: Fluoroquinolone, MDR-TB, ofloxacin
|How to cite this article:|
Verma J S, Nair D, Rawat D, Manzoor N. Assessment of trends of ofloxacin resistance in Mycobacterium tuberculosis. Indian J Med Microbiol 2011;29:280-2
|How to cite this URL:|
Verma J S, Nair D, Rawat D, Manzoor N. Assessment of trends of ofloxacin resistance in Mycobacterium tuberculosis. Indian J Med Microbiol [serial online] 2011 [cited 2020 Sep 25];29:280-2. Available from: http://www.ijmm.org/text.asp?2011/29/3/280/83913
| ~ Introduction|| |
Despite all the advances made in tuberculosis (TB) treatment and management, India accounts for one-fifth of the global incidence ad two-thirrd of the cases in South-East Asia.  The increasing global burden of this disease and the escalating problem of multidrug resistant (MDR) and extensive drug-resistant tuberculosis (XDR-TB) have led to increase pressure on using second-line drugs (SLDs).  Several studies have shown that MDR-TB can be cured by a combination of second-line drugs. Among them, Ofloxacin (OFX) is one of the potent fluoroquinolone (FQ) recommended for use as prophylaxis treatment of patients exposed to MDR-TB (defined as simultaneously resistant to at least isoniazid and rifampicin), for treatment of proven MDR-TB, for empirical treatment of TB disease in settings with high rates of MDR-TB and for patients with severe adverse reaction to first-line agents. , Clinical trials have demonstrated their efficacy in combination with other drugs for treatment of MDR-TB strains. 
They have excellent pharmacokinetic profiles, achieve good tissue and cellular distribution with minimal adverse effects. , But over the past decade, the increased use of FQ in the community, especially to treat other respiratory infectious diseases caused their decreased susceptibility in Mycobacterium tuberculosis (M. tuberculosis) strains. ,
As SLDs susceptibility testing is performed only in few reference laboratories in India, therefore the data on OFX resistance trends is limited. There were some data ,,,, on OFX susceptibility which showed variable performance of the drug and highlighted significant increase in OFX resistance in last 5 years. It is therefore critically important to determine the potential of OFX before they would be used as second-line anti-TB agent in the management of drug-resistant TB. This is especially important for those patients with recurrent TB after treatment, those with MDR-TB as well as those who have previously received FQ therapy. With this objective, a study was undertaken to assess the status and extent of OFX resistance in M. tuberculosis strains in a defined population.
| ~ Materials and Methods|| |
This study was undertaken in the tertiary care center (approx. 1700 bedded) of New Delhi (India) during April 2008 - September 2009. A total of 102 (n=102) fully characterized M. tuberculosis strains (47 susceptible to first-line drugs and 55 resistant to at least Isoniazid (INH) and Rifampicin (RIF) irrespective to other drugs), isolated from individual patients clinical samples from 2006 to 2009, were studied for susceptibility testing of OFX with a critical concentration of 2 μg/ml by Lowenstein Jensen (LJ) proportion method. Stock solution of OFX (Sigma Chemical Co., USA) was prepared in distilled water acidified with minimal volume of 1N HCL to facilitate the dissolution. 
Bacterial suspension of approx. 4mg/ml (2-3 loopful growth) was prepared.  This suspension was inoculated on drug-free (control) as well as drug-containing LJ slant media with the help of loop. These slants were incubated at 37 0 C and first reading were taken after 14 days then on 28 th day and final reading was on 42 nd day. The reading was done by counting the colony-forming units (CFU) and compared with control culture. An isolate was considered resistant if it yielded a growth of 20 colonies or more on drug-containing media. The standard strain of M. tuberculosis H37Rv was also tested which were found to be sensitive at <1 μg/ml levels for OFX.
| ~ Results|| |
Out of the 47 (n=47) susceptible isolates studied, 40 (85.1%) isolates were showed inhibition at OFX at 2 μg/ml while in 55 (n=55) MDR isolates, 34 (61.8%) isolates showed susceptibility to OFX. The results are summarized in [Table 1]. On performing Fisher`s exact test [Table 2], MDR patients had significant (P-value: 0.0136) 1.377-fold increased risk to (95% confidence interval) become resistant to OFX than susceptible isolates.
| ~ Discussion|| |
India is one of the prominent destinations with the highest rate of FQ abuse and resistance in the world. The acquisition of FQ resistance by susceptible M. tuberculosis strains was facilitated due to a selection pressure from their widespread use in the treatment of TB and possibly other infections in the community, , which is hyperendemic for tuberculosis. Resistance to OFX was considered to be a risk factor related to treatment failure and relapse in MDR-TB. In the present study, we observed 14.9 % OFX resistance in first-line drug susceptible isolates and 38.2% in MDR isolates. Thus, an increase in frequency of OFX resistance in both susceptible as well as MDR isolates was found. These findings were consistent with the data reported by earlier Indian study,  which showed OFX resistance of 11.2% in non-MDR cases and 54.5% in MDR isolates. Other investigators , have disputed these findings by finding this increased trend only in MDR isolates. These differences might be explained by when the studies were conducted in relation to the time FQ were introduced for treatment of TB and to differences in the geographical regions from which the strains were isolated. These inclinations of MDR isolates to become OFX resistant could be due to many factors. OFX and other FQ are often part of many other regimens and MDR cases are often belonging to Cat II or relapse/failure category thus has a greater chance of getting exposed to FQs. Also FQs. are bulky molecules and there efficacy is affected by cell permeability and INH is known to reduce cell permeability by blocking cell wall synthesis.
There were also reports of OFX-resistant strains of M. tuberculosis or the acquiring OFX resistance during treatment. ,, Retrospective studies have shown that empiric antituberculous treatment with FQ or FQ use for misdiagnosed pneumonia delayed diagnosis of tuberculosis in an endemic area and impaired outcomes.  Research studies , from Philippines and Taiwan experienced marked increase in resistance to OFX in the later phase as compared to early period of the treatment. Therefore, it was observed that exposure to OFX and other FQ for the treatment of other bacterial diseases does appear to be predominantly responsible for the increasing trend of resistance. Therefore, strong guidelines need to be mentioned in the TB control program to keep FQ as the last line therapy when no other agents are active or tolerable. By delaying the emergence of resistance, the process of transformation from MDR strains into XDR strains could be slow down.
Our finding highlights the general risk of acquiring resistance to OFX, jeopardizing the potential for these drugs to be used as second-line anti-TB agents in the management of drug-resistant TB and creating incurable TB strains. But, it is alarming that the rate of resistance to FQ significantly increased with time, indicating the capability of these isolates to survive under selection pressure.
There also seems to be a great degree of cross-resistance among various derivatives. , So, there is a scope for further studies with the other quinolones. A potential solution may be replacement of the recommended second line quinolones with C-8 methoxy substituted FQ like moxifloxacin which shown to have good bactericidal activity in murine tuberculosis and in human patients. 
In conclusion, we recommend that as OFX showed significantly decreased susceptibility in tuberculosis, FQ susceptibility should be routinely assessed for clinical isolates of M. tuberculosis, especially for drug-resistant isolates, and when patients have a prior history of TB or prior use of anti-tuberculous drugs, so that the most optimal agents can be prescribed.
| ~ Acknowledgment|| |
We acknowledge the financial grant (Senior Research fellowship) provided by Indian Council of Medical Research (ICMR) to one of our author, Jitender Singh Verma for the study.
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[Table 1], [Table 2]
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