Silver Nanorods for detection of viability and antibiotic resistance in bacterial strains

Antimicrobial resistance (AMR) is one of the major public health problems in this fast-paced world. According to the UK commission report, it is estimated that ten million people will die due to AMR infections by 2050, which outnumber the total death due to cancer. According to a report on AMR by Centers for Disease Control and Prevention USA, each year in the United States, at least 2 million people become infected with antibiotic-resistant bacteria and at least 23,000 people die each year as a direct result of these infections and diseases. Flu, food poisoning, strep throat, cold, malaria are some major infections caused by resistant microorganisms.

AMR is the ability of microbes (virus, bacteria, fungi, protozoa and some parasites) to make antimicrobials (antiviral, antibiotic, and antifungal) ineffective against themselves. When they are exposed to antimicrobial drugs, most of the microbes succumb to death, whereas, some acquire resistance and survive. These resistant microbes transfer its resistance properties to its progeny. Inappropriate use of antimicrobials compounds is one of the main cause of this. Unhygienic and improper way of treatment being taken by the hospitals, act as a carrier and it is the main reservoir of resistant microbes.

Some conventional techniques have been in practice since last few decades. The most common acceptable method for the estimation of live and antibiotic bacteria is the standard plate count (SPC) method. Although it has enough sensitivity but have some demerits e.g. labour intensive, time-consuming and need of trained operators. This method could not be used for the microbes, which do not form colonies. On the other hand, there are many other techniques like UV absorbance flow cytometry etc. Which are relatively easy but need sophisticated instruments and skilled workers. To overcome these issues a facile technique is of utmost importance in order to prevent AMR infections and diseases.

Silver is one of the most widely used material in biomedical sciences. Here, we have utilized the colourimetric and wettability properties of silver nanorods array fabricated by glancing angle deposition.

Significance of the finding:

Smartphone based non-invasive health monitoring has become a great concern in order to make human life convenient. Researchers are developing mobile based device for point of care. Here we have developed a mobile app based dual confirmatory biosensor for differentiation of live/dead and antibiotic resistant/normal bacteria by detecting hydrogen sulfide gas produced by bacteria. Observing the visible change in color and water wetting on the sensor array, one can easily distinguish live and dead as well as antibiotic resistant and normal bacteria. H2S is one the major gaseous products evolved by living organisms. It is a gasotransmitter that transmits biological signals in living system. Nitric Oxide (NO) and Carbon mono oxide (CO) are two other members of this family. This detection is based on the specific reactivity of silver nanorods with the H2S to form black colored silver sulfide (Ag2S). The color and water wetting (contact angle) properties of the silver nanorods (AgNRs) change upon the exposure of live microbes, whereas dead bacteria don’t show any change in either property. We have also developed a mobile app to make it easy, portable, user-friendly, single step and cost effective. Further, we envisage to save a great amount of time to estimate the AMR in comparison to conventional plate count method.

Expectations in the future from our research work:

The idea is quite simple and feasible. One can determine antibiotic resistance by observing the visible change in color and water contact angle on as-synthesized silver nanorods array. The change in both parameters is quite significant and easily detectable by miniaturized mobile based device. It has a potential application in health care and disease diagnosis. This cost effective and portable device can be used by a common man that would be beneficial as a diagnostic tool for the field and clinical study of antimicrobial resistance and will be helpful to prevent the spread of infectious diseases.

Thus the detection of H2S gas can be used to distinguish live and dead bacteria within 6 hours as compared to conventional SPC method, which takes about 16 to 24 h. The present approach has potential application in hospitals and clinics for the diagnosis of infections and diseases caused by antibiotic resistant and non-resistant pathogens.

Shashank Kumar Gahlaut (Senior Research Fellow)

GLAD and nano-CVD Lab

Department of Physics, Indian Institute of Technology Delhi

Hauz Khas New Delhi

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