Validation of a Worst-Case Scenario Method Adapted to the Healthcare Environment for Testing the Antibacterial Effect of Brass Surfaces and Implementation on Hospital Antibiotic-Resistant Strains

Abstract

The evaluation of antibacterial activity of metal surfaces can be carried out using various published guidelines which do not always agree with each other on technical conditions and result interpretation. Moreover, these technical conditions are sometimes remote from real-life ones, especially those found in health-care facilities, and do not include a variety of antibiotic-resistant strains. A worst-case scenario protocol adapted from published guidelines was validated on two reference strains (Staphylococcus aureus ATCC 6538 and Enterobacter aerogenes ATCC 13048). This protocol was designed to be as close as possible to a healthcare facility environment, including a much shorter exposure-time than the one recommended in guidelines, and evaluated the impact of parameters such as the method used to prepare inocula, seed on the surface, and recover bacteria following exposure. It was applied to a panel of 12 antibiotic-resistant strains (methicillin resistant, vancomycin-resistant, beta-lactamase, and carbapenemase producing strains as well as efflux pump-overexpressing ones) chosen as representative of the main bacteria causing hospital acquired infections. Within a 5-min exposure time, the tested brass surface displayed an antibacterial effect meeting a reduction cut-off of 99% compared to stainless steel, whatever the resistance mechanism harbored by the bacteria.

Tailor the antibacterial efficiency of copper alloys by oxidation: when to and when not to

“…Last but not the least, although it was only the antibacterial efficiency against E. coli that was investigated in the present study, copper surfaces have actually shown capability against a very broad range of bacteria [3,7,52], viruses [53][54][55], and fungi [25,52,56]. Therefore, the strategy proposed here is also encouraging in many scenarios where the general antimicrobial property is needed.…”

“…Copper and copper alloys have been extensively investigated in recent years in terms of their antibacterial activity [1][2][3]. These metallic copper surfaces are excellent candidates in many scenarios, amongst which frequently touched surfaces have been highlighted, as they can be contaminated and further transmit deadly pathogens [4][5][6][7]. In our daily lives, antibacterial surfaces installed in public environments such as in transportations and buildings would be extremely helpful since timely cleaning is not always available.…”

Bacterial survival on inanimate surfaces: a field study

“…In recent years there were innovative attempts to reduce the bacterial burden on frequently touched surfaces in hospitals, for example by coating them with layers containing direct bactericide substances or chemicals that diminish biofilm formation [ 27 – 29 ]. Another rather novel sanitation strategy is the use of (non-pathogenic) probiotic bacteria that are capable of reducing in a stable way the surface load of pathogens [ 30 ] or the use of UV-C light for surface decontamination [ 14 ].…”

Brass Alloys: Copper-Bottomed Solutions against Hospital-Acquired Infections?

“…Using C. sakazakii strains, another study showed that dry inoculation conditions (2 µL of the bacterial suspension spread on the surface and left to dry in open air) enabled a swifter reduction in viable bacterial counts than under wet inoculation conditions (25 µL of the bacterial suspension spread on the surface kept in a closed container to maintain moisture) [ 80 ]. Also, comparing a 9 µL spread inoculum with a 1 µL non-spread one, Dauvergne et al showed that the bacterial recovery was greater with the later technique [ 61 ].…”

“…The antibacterial efficacy is usually assessed after a time of exposure to the copper-containing surface using reduction in bacterial counts either compared to the initial inoculum and/or to the counts obtained on a control surface deprived of antibacterial properties such as glass, plastic or stainless steel (Figure 2). These tests were first held on food pathogens and collection strains susceptible to antibiotics [51][52][53], but publications soon moved on to report significant reductions in bacterial counts on copper and copper alloy surfaces for a range of multidrug-resistant (MDR) bacteria and/or bacteria originating from clinical settings [32,[54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69]. Indeed, the importance of testing clinical strains to evaluate whether any co-selected, cross-selected and/or co-regulated resistance between copper and antibiotics and/or detergent-disinfectants could occur soon appeared as mandatory [62].…”