Surfaces with instant and persistent antimicrobial efficacy against bacteria and SARS-CoV-2

Abstract

Surfaces contaminated with bacteria and viruses contribute to the transmission of infectious diseases and pose a significant threat to global public health. Modern day disinfection either relies on fast-acting (>3-log reduction within a few minutes), yet impermanent, liquid-, vapor-, or radiation-based disinfection techniques, or long-lasting, but slower-acting, passive antimicrobial surfaces based on heavy metal surfaces, or metallic nanoparticles. There is currently no surface that provides instant and persistent antimicrobial efficacy against a broad spectrum of bacteria and viruses. In this work, we describe a class of extremely durable antimicrobial surfaces incorporating different plant secondary metabolites that are capable of rapid disinfection (>4-log reduction) of current and emerging pathogens within minutes, while maintaining persistent efficacy over several months and under significant environmental duress. We also show that these surfaces can be readily applied onto a variety of desired substrates or devices via simple application techniques such as spray, flow, or brush coating.

Keywords: COVID-19; SARS-COV-2; antimicrobial; antiviral; durable; gram-negative; gram-positive; instant kill; long-lasting; persistent.

Graphical abstract

Figure 1

Dichotomy of instant and persistent antimicrobial technologies Escherichia coli kill rates using instant and non-persistent disinfection methods including UV, Cl₂ gas, liquid disinfectants, and aqueous Ag+ ions., , In this study, comparison is made with non-instant but more persistent antimicrobial solid surfaces comprising pure copper, its alloys,^, heavy metal-based nanoparticles,^, and surfaces. Error bars for literature data were not extractable from literature sources.

Figure 2

Controlling the speed of disinfection against Gram-negative and Gram-positive bacteria (A) Survival of an initial inoculum (green dashed line) of ∼3 $\times$ 10⁶ CFU/cm² of E. coli (UTI89) on surfaces with different fractions of AT, plotted against time, at room temperature (similar to ISO 22196). PU+60%AT showed a rapid ∼3.5-log and ∼5.8-log reduction in CFUs of E. coli in 30 s and 2 min, respectively. Gray dashed line at 5 CFUs/cm² represents limit of detection. (B–D) Survival of (B) E. coli, (C) P. aeruginosa, and (D) MRSA on surfaces with AT, CMA, and their combinations. Similar to E. coli, larger fractions of AT were effective against P. aeruginosa and MRSA as well. PU+35%AT-CMA (3:7) displayed a faster kill rate against P. aeruginosa compared with PU+35%AT and PU+35%CMA, indicating synergistic action. Error bars represent 1 SD; N = 3 independent experiments with triplicate measures.

Figure 3

Persistent antimicrobial efficacy (A) Eight successive E. coli contamination cycles highlighting the continuous, rapid bactericidal properties of PU+35%AT. In each cycle, the surfaces were contacted with ∼10⁶ cells/cm². (B) Total CFUs/cm² of E. coli and MRSA recovered from control (PU and PS) and test surfaces after 24 h at 37°C from an initial broth inoculum of ∼10⁶ cells/mL (green line). No CFUs were detected for PU+35% AT (limit of detection = 5 CFUs/cm²) showing a ∼5.3-log reduction. The graph also shows persistent antimicrobial performance of PU+35%AT after exposure to extreme conditions of mechanical and chemical (Clorox) abrasion, UV exposure, freezing conditions, and accelerated aging under air flow for up to 5 months. After 6 months, the surface’s efficacy is maintained against MRSA but reduced against E. coli. Error bars represent 1 SD; N = 3 independent experiments with triplicate measures.

Figure 4

Survival and inactivation of SARS-CoV-2 on different surfaces (A) Comparison of SARS-CoV-2 inactivation on different surfaces in the literature^, and this work. Error bars represent SD; N = 2–3 independent experiments with three technical replicates each. (B) Infectivity of SARS-CoV-2 (starting viral load of 2.5 × 10⁷ TCID50/mL) on PU+35%AT and PU+70%AT surfaces plotted against the contact time of the virus with the surface. The speed of inactivation of the virus on the surface increases with the fraction of AT. Within just 10 and 30 min, a 1.7-log and 4.3-log reduction, respectively, was observed for PU+70%AT. The PU+70%AT surface maintained its 4.3-log reduction in 30 min even after environmental exposure for 1- and 2-week periods without any external disinfection. Error bars represent 1 SE of mean; N = 2–3 independent experiments with three technical replicates each. The gray dashed line represents the limit of detection of the TCID50 assay (2 Log10 TCID50/mL).

Figure 5

Applications of the fabricated surfaces (A) Uncoated and spray-coated keyboards with PU+35%AT are contacted with gloved fingers contaminated with MRSA. Ten minutes post contamination, bacterial colonies on the keyboard were enumerated. The coated keyboard showed a 3.1-log or 99.9% reduction with respect to the uncoated keyboard. Scale bar, 23 mm. The spray-coated keyboard retained its electronic function. (B) A cutting board, half brush coated with BM+35%AT, was contacted with thawed chicken. Scale bar, 12 mm. Approximately 4 $\times$ 10⁶ CFU were recovered from the swabs for the uncoated side of the board, while the coated side showed only 15 CFUs, a 5.4-log reduction after 20 min. (C) Cell phones with an uncoated and a PU+35%AT-coated screen protector. Gloved thumbs with ∼1.5 $\times$ 10⁵E. coli cells were contacted in a specific pattern (Figure S14) over the phones. After 2 min, the uncoated screen showed a total of ∼6,000 CFUs while no CFUs were detected on the coated surface. Scale bar, 16 mm. (D) Uncoated and coated medical gauze with BM+60%AT-CMA (3:7). The inset shows 2 cm² pieces of the respective gauze after 24 h of incubation (37°C) in a broth culture containing P. aeruginosa. The coated gauze displayed an ∼8.2-log reduction compared with the uncoated dressing. Scale bar, 11 mm. All images of colonies represent a 5-fold dilution of the recovery solution.