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A Review of Standardized Antibacterial Material Testing Methods

Microorganism causes disease after reaching out to a potential host. They move around the environment in various but typically passive ways such as aerosols, direct contact between two animated objects and fomites. Certain microbes can retain their pathogenic potential whilst outside their host for a longer period of time. According to studies, they can survive from days to few weeks on inanimate surfaces like metals and plastics which are usually considered hygienic surfaces. Most common examples of such materials are door handles, light switches, lift buttons, digital locks, etc.

Microorganism causes disease after reaching out to a potential host. They move around the environment in various but typically passive ways such as aerosols, direct contact between two animated objects and fomites. Certain microbes can retain their pathogenic potential whilst outside their host for a longer period of time. According to studies, they can survive from days to few weeks on inanimate surfaces like metals and plastics which are usually considered hygienic surfaces. Most common examples of such materials are door handles, light switches, lift buttons, digital locks, etc.

Both clinical and non-clinical settings are prone to growth of microorganisms. Various methods are used to control microorganisms on surfaces in those settings. In clinical environments, methods to chemically disinfect surfaces are often used, but may be performed inadequately, (through poor adherence to cleaning protocols), allowing pathogens to be spread more rapidly throughout wards, following recontamination of disinfected surfaces via contact with fomites. Antimicrobial testing laboratory is need of the hour to take on microorganisms.

Testing the Efficacy of Antimicrobial Materials (AMM)

Standardized test methods are required and considered inevitable in the development of a unique antimicrobial material. In order to define a material as antimicrobial, efficacy should be evaluated under reproducible conditions that mimic later in-use environments. In case the set threshold is not satisfied, the surface then cannot be taken as antimicrobial.

The method needs to enable them who have special interest in AMM to establish a confidence in their material, offering some positive data that bolsters further exploration for testing the material either under conditions more precise to the intended point of use or even in practice. Let's say, bacterial inocula utilized in standardized testing (~105–108 CFU/mL) are considerably higher than that found in the most potential end-use settings (e.g., ~102–104).

In addition, renowned microbial testing laboratory performs the relevant standardised test method to validate the reproducibility of an antimicrobial material and achieve results that are all within the natural error range for such test. The validity of data resulted from individual test method should be acknowledged. On the other hand a growing need exists for accurate and reproducible methods, as many different AMM fall short when being tested by independent reviewers.

Standardised Tests for AMMs in Vitro

Here are the five general categories of test for an antimicrobial material in vitro:

1. High surface area to volume ratio tests - Such methods focus on maximising the contact between the surface and the microorganism, so the cells and the surface are essentially always touching and interacting. Here the bacteria are kept between the test sample and the sterilised non-antimicrobial material such as glass or plastic. The most used test method for antimicrobial materials in this category is ISO 22196:2011 (and similar methods such as JIS Z 2801).

2. Agar zone of inhibition tests - Methods that utilise zones of inhibition, for which there are two existing standardized methods, are relatively quick and simple but may provide only an indicator of whether any antimicrobial effect might be present under permanently wet conditions. The first, ISO 20645:2004 is based on a disk diffusion method, where the AMM is placed on top of an inoculated nutrient agar plate, incubated at the required temperature for a set time depending on the requirements for the bacteria being tested (such as at 37 °C for 24 h for E. coli).

3. Suspension tests - Suspension methods focus on inoculating and incubating bacteria in a liquid medium containing the antimicrobial surface, and then determining the remaining viable CFUs by taking an aliquot of this liquid and performing a dilution plate count using it. The process evaluates the materials that exhibit antimicrobial-release properties. However, due to the inoculum not being placed directly on the material, only surfaces that release antimicrobials can get tested.

4. Adhesion tests - Such tests intend to find the bacteria count that can adhere to an antimicrobial material. Generally the testing is performed by two ways. The first requires that the test surface is inoculated with the bacteria and incubated for 1 to 4 h. Non-adhering bacteria are detached and either the surface with attached cells is added to a liquid medium or an agar slab is kept on the top of the surface and incubated (for counting CFUs), or the microorganisms can be stained (e.g., live-dead staining) to know cells per unit area.

5. Biofilm tests - A biofilm is an accumulation of microorganisms that are connected with a surface and often become encased in a matrix of polysaccharide material. They are one of the most common forms that microorganisms take on Earth and can cause many problems when they form in specific artificial environments. Owing to their impact on health, industry and the environment, the ability to either destroy a biofilm or to stop it from forming in the first instance using antimicrobial materials is a focus of rising importance.

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Three Common Microbiological Testing Methods for Food Products

Today consumers become very sensitive to their food quality.  Their growing demand for fresh and appropriate forms of foodstuffs leads to the advancement of safety practices in the food industry. Day by day outbreaks of foodborne diseases across countries rise up resulting in mounting concern and intensive investigation of foodborne pathogens. This is why the demand of for the microbiological testing of food products is fast increasing.

What's the purpose of Microbiological Testing?

The purpose of microbiological testing is to identify and contain harmful microbes that damage foods, and ensure protection from foodborne diseases. It means that the experts at microbiological testing lab must establish a thorough testing procedure to recognize all the possible threats that could lead to one of the two results: pathogen detected or not detected.

Prior to carrying out a microbiology test, the professionals need to know the importance, purpose, and primary expectations underlying the test along with the expected certainty of identifying an issue, and possible results, which may result from the test.

As a result, it will help know the sampling procedure to be conducted, the kind of samples to be gathered, the specific test method to be used, and appropriate actions to be taken before and after the test results are got.

Reasons for a Microbiology Test

The common reasons for microbiological testing are to:

Spot risk factors

Meet precise specifications for raw material, intermediate, and finished product

Process verification

Confirm that all regulatory guidelines are practiced properly

Why Microbiological Testing?

Microbiological testing is a component of the food safety system even though it cannot guarantee 100% of the product safety. Microbiological testing is a requirement and key part that must be performed to ensure food safety. It can outline essential information about a manufacturing process, processing environment, and a specific product batch. With it, one can know whether a sampling or testing procedure is properly designed and completed based on regulatory guidelines or not.

The microbiological testing mostly ensures that no pathogens are identified from the sample and/or, comprehend the levels of sensitivity and assurance given by the testing procedures and sampling plans used.

Common Test Methods

Various technologies are being used for the detection and verification of microbes. Some of the popular types are described below. Have a look at them.

1. Culture Media

2. Immunoassay

3. Polymerase chain reaction

Culture Media

A kind of medium which is used in microbial laboratory to identify various types of microorganisms is known as culturing or growing. A culture medium generally comprises of some nutrients to augment microbial growth.

Today the culture techniques witness low popularity because the modern developments of the testing methods and validation studies already confirmed that cultural methods aren't appropriate for all food groups.

Immunoassay

Immunoassay is considered as a microbiological test commonly used to measure the concentration of a macromolecule present in a solution by using an antibody or immunoglobulin. The found macromolecule from an immunoassay method is more like a protein and is broadly coined as an "analyte".

Such analytes in biological liquids are frequently measured following immunoassay test methods for different purposes. Enzyme-Linked ImmunoSorbent Assay (ELISA) i.e. “pregnancy test” or “dipstick” type method) is among the most commercially accessible immunoassay types.

Polymerase Chain Reaction (PCR)

Polymerase Chain Reaction (PCR) is the latest and revolutionary method developed during 1983. Presently PCR is used in medical and biological research laboratories as a normal and an essential technique for many applications. A PCR test identifies pieces of DNA or RNA that are likely unique to the target microbe.

Conclusion Every human being wants their edible items must be healthy and free from any kind of microorganisms that have adverse impact on our body directly or indirectly. And we cannot detect whether the items contain anything hazardous. It's the microbiology testing lab that helps us getting rid of dangerous microbes. Thus their testing methods powered by modern equipment and expertise of their microbiologists are very essential.

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