The post-antibiotic era: An apocalypse waiting to happen?

Dr Shakti Laishram *

Before the discovery of antimicrobial agents, many people died of 'curable' illnesses. In fact the majority of deaths during the First World War were due to infections rather than war injuries. However, things changed with the discovery of sulfa drugs in 1930s and subsequently other antimicrobial agents in the next few decades. It appeared as if human had finally won this war against the micro-organisms. But it was not long before we realised our foes are able to change faster than we thought and many started developing resistance to the usual antimicrobials.

We, on the other hand have not been able to keep up with the rate these organisms are mutating. The rate of discovery of newer antimicrobial agents has dwindled, with very few new antibiotics in the pipeline. With the increasing resistanceto even the highest end drugs, it is not long before we go into the post-antibiotic era where organisms are resistant to all available antibiotics, and common infections and minor injuries can kill. This is particularly true for hospital-acquired infections where these organisms are found to be resistant to all groups of antibiotics.

What do resistance or susceptibility to an antimicrobial agent imply?

When an organism is labelled resistant to an antibiotic, it means treatment with the agent will likely fail or produce no response. If an organism is tested susceptible, it means there is high possibility of response to treatment with appropriate dosage and regimen of the antibiotic. Drug resistance leads to use of higher end antibiotics which are often more costly and more toxic. Treatment failure may also translate to death.

What is driving this increasing rate of resistance?

Misuse of antimicrobial agents is the major driving force behind the development of resistance. This includes availability of over-the-counter antibiotics and self-medication, inappropriate dose and duration of treatment, use of broad spectrum antibiotics and excessive use of higher end antibiotics.

Excessive use of antibiotics in the poultry and animal husbandry practices has also led to development of resistance among organisms residing in these animals. These resistant bugs in turn either cause direct infection to human by entering the food chain, or pass on their genes responsible for resistance to related organisms causing disease in human.

How can resistance be detected?

In order to detect resistance, the organisms needs to be first grown in culture. Resistance among bacterial agents can be detected by either the disc diffusion method or an MIC (minimum inhibitory concentration) method. With the disc diffusion method, the culture of the organism is coated on an agar plate surface and discs seeded with antimicrobial agents are placed over the plate.

If the organism is resistant, it will be able to grow around the antimicrobial disc, and if susceptible the growth will be inhibited around the disc. With the MIC method the actual lowest concentration of the agent which can cause inhibition of growth of the organism is tested by exposing the organism to various concentrations of the same drug.

Why is it necessary to test for antimicrobial susceptibility?

Antimicrobial susceptibility is necessary for the appropriate choice of therapy for the patient. Not only for the individual patient, knowledge of the antimicrobial susceptibility patterns for common pathogens is necessary for choice of empirical therapy.

The WHO (World Health Organisation) in its global antimicrobial resistance surveillance noted large gap in knowledge regarding local resistance pattern, lack of standards for methodology and data sharing. This is especially alarming, as the patterns can differ from nation to nation and even with the same country based on local prescribing practices. The WHO also observed very high rates of resistance among bacteria causing common community-acquired as well as hospital acquired infections.

What is MDR (multi-drug resistant), XDR (extensively drug resistant) and PDR (pan drug resistance)?

MDR refers to resistance to three different groups of antibiotics. XDR organisms are resistant to all except agents in one or two groups of antibiotics, while PDR organisms are resistant to all groups of antibiotics.

Which antibiotic to use?

The choice of empiric therapy (when the susceptibility pattern is not yet known) should be based on local susceptibility data. Empiric therapy should always be changed to definite therapy with appropriate antibiotic and dosage once the culture and the susceptibility report is ready. The site of infection will also determine the choice of drug as every drug has differing tissue distribution. For XDR and PDR organisms, old drugs with renewed interest like colistinis used.

What is the way forward?

The way forward lies inrational use of available antibiotics. Over the counter dispensing of antibiotics need to be stopped. Compliance to the prescribed dosage and duration has to be emphasised. While the main responsibility lies with the prescribing doctor for well informed choice in antibiotic therapy, support of patients and the general public is no less to control this menace.

In conclusion, judicious use of antibiotics is the need of the hour to prevent the post-antibiotic era from becoming a reality. For this, we need adequate investigations for infections and continuous surveillance which cannot be realised without support from doctors and the general public.