Antimicrobial Product Testing: Gram-positive vs. Gram-negative Bacteria

Antimicrobial testing often includes both Gram-positive and Gram-negative bacteria. These two groups differ in their biological structure, providing differences in their resistance to chemicals, environmental persistence, and ability to adapt to new environments. Including both types of bacteria in a study design can provide a more complete picture of product performance across a range of conditions and applications.

Structural and Resistance Differences

Gram-positive bacteria

• Have a thick peptidoglycan layer that provides rigidity.

• Lack an outer membrane, which makes them generally more accessible to certain antimicrobials.

• Example in testing: Staphylococcus aureus (aka staph aureus, or MRSA), commonly used to represent durable microbes that persist on treated surfaces.

Gram-negative bacteria

• Have a thin peptidoglycan layer protected by an outer membrane containing lipopolysaccharides.

• This added barrier makes them inherently more resistant to many antimicrobials.

• Example in testing: Escherichia coli (aka E. coli, EHEC), a standard benchmark organism that represents resilient environmental and enteric bacteria.

Together, these two bacterial groups help ensure that antimicrobial claims hold up in real-world conditions where a product may encounter both types.

Why Both Matter in Testing

• Healthcare and hygiene products: ASTM E2362 determination if pre-saturated wipes exhibit antimicrobial activity on hard surfaces

• Consumer Products:  Methods such as ISO 22196 / JIS Z 2801 are often applied to plastics and non-porous surfaces, helping evaluate disinfectants, coatings, and wipes.

• Textiles and treated materials: AATCC 100 is widely used to measure antibacterial finishes on fabrics, where testing both Gram-positive and Gram-negative bacteria supports claims of broad activity.

• Consumer and industrial applications: Dynamic-contact methods like ASTM E2149 are used for polymers, liquids, and coatings, providing insight into performance under use-like conditions.

• Food and packaging sectors: Both Gram-positive and Gram-negative bacteria are included in standards assessing treated packaging and surface sanitation, helping demonstrate risk reduction across production environments.

Across industries, the inclusion of Gram-positive and Gram-negative bacteria is not limited to a single test method but is a common requirement in many standards. This approach ensures that results are both scientifically robust and aligned with regulatory and market expectations.