Grieston Fonseca
Assistant Product Manager - Microbiology,
Transasia Bio-Medicals Ltd.

Broth Dilution Is Now The Method Of Choice For The Testing Of Colistin

While a superbug may seem akin to a superhero, which combats all the evil powers, in reality it is just the opposite! Irrational and rampant use of antibiotics, has led to anti-microbial resistance (AMR) in micro-organisms, earning them the title of superbugs! These superbugs are causing difficult-to-treat, antibiotic-resistant infections and thus posing an ever-growing challenge to medical experts worldwide.

On WHO’s hit list

The WHO has issued an updated list of superbugs in 2017 and categorized them based on the threat quotient. Amongst the most critical is Carbapenem-resistant Enterobacteriaceae (CRE). This has in the recent times become a serious threat to public health due to high mortality, potential dissemination rates, and limited treatment options associated with these organisms.

The Carbapenem group of antibiotics is considered as last resort antibiotics as they offer broad spectrum cover, enabling effective treatment for severe infections. Its resistance is increasingly encountered in hospitals and healthcare facilities in India.

Countering CRE

Polymyxins (colistin and polymyxin B) are antibiotics that are used for treating CRE infections. Initially, colistin was not a drug of choice, due to concerns over high rates of nephro and neurotoxicity. However, in recent years, it has emerged as the cornerstone of therapy.

Need for MIC testing

Chromosomal and plasmid-mediated resistance to polymyxins has resulted in elevated minimum inhibitory concentration (MIC) values and treatment failure. Susceptibility testing and determination of MIC helps in confirming AMR of CREs to polymyxins and plays an important role in guiding treatment. This is crucial since the efficacy of polymyxins needs to be balanced against potential toxicities associated with this class of antibiotics.

Choosing the right MIC testing method

The CLSI and EUCAST Polymyxin Breakpoints Working Groups have defined some guidelines for MIC testing of colistin. Broth dilution testing is recommended as the reference method. These guidelines also mention the kits to be free of any surfactants, as the surfactant used in coating on most commercially available kits, acts as an interference.

Transasia Bio-Medicals Ltd. is the first company in India to offer single MIC testing strips for individual antibiotics by broth-dilution in micro-well format. In adherence with the CLSI and EUCAST guidelines, these kits are surfactant-free ensuring reliability of results. Many laboratories in major hospitals across India are now using Transasia’s kits.

AMR infections are a big threat! According to WHO, AMR infections lead to 7 lakh deaths per year, globally. By 2050, 1 million patients per year will succumb to AMR infections, worldwide. 60,000 newborn lives in India are lost each year to AMR infections.

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