Antimicrobial activity of silver‐containing dressings on wound microorganisms using an in vitro biofilm model

Abstract

Antimicrobial dressings such as those containing silver are now being used widely to control wound bioburden, and tests to demonstrate their efficacy predominantly involve in vitro models using free-living or planktonic bacteria. In this present study a wide range of antibiotic-sensitive and resistant bacteria were tested in their quasi-sessile state using a standard agar assay and a second method used a poloxamer gel (true biofilm state - poloxamer encourages microorganisms to exhibit a more clinically relevant biofilm phenotype) technique. The antimicrobial activity of two silver dressings, a silver-containing Hydrofiber (SCH) dressing and a nanocrystalline silver-containing dressing (NCS), were evaluated on a variety of microorganisms, using a zone-of-inhibition (ZOI) test. When grown on agar (presenting a quasi-sessile state of each organism), the antibiotic-susceptible microorganisms were generally more susceptible to the SCH dressing compared with the NCS. ZOIs associated with SCH dressing ranged between 5.7 and 17.5 mm; those for the NCS against the same group of organisms ranged between 1.9 and 8.6 mm. When grown on poloxamer gel, (presenting the biofilm state of each organism) the same group of microorganisms were less susceptible to both dressings. The SCH dressing was most effective against strains of Pseudomonas aeruginosa, Candida albicans and Staphylococcus aureus (ZOI range: 2.6-6 mm); the NCS was most effective against strains of Klebsiella pneumoniae, Enterococcus faecalis and Escherichia coli (i.e. ZOI range: 1-2.8 mm). Similarly to the antibiotic-susceptible microorganisms, nine of ten antibiotic-resistant bacterial strains when grown on agar were more susceptible to the SCH dressing compared with the NCS. Although the microorganisms tested were universally less susceptible to the silver dressings when in their biofilm state, in the majority of cases, the SCH dressing demonstrated greater biofilm-inhibiting activity than the NCS.

In vitro and in vivo evaluation of biologically synthesized silver nanoparticles for topical applications: effect of surface coating and loading into hydrogels

“…15 Silver attacks multiple targets in the microorganisms, and therefore decreases their ability to develop resistance. 13,16,17 AgNPs exhibit higher toxicity to microorganisms than mammalian cells.…”

Silver Oxynitrate, an Unexplored Silver Compound with Antimicrobial and Antibiofilm Activity

“…Again, Ag 7 NO 11 had a low MBC against planktonic populations, prevented biofilm formation, and eradicated established biofilms at lower concentrations than those of AgNO 3 and CuSO 4 . Certainly, Ag has been explored as a strategy to control infection by uropathogens (72) as well as to combat and control antibioticresistant pathogens, including MRSA (67,(73)(74)(75)(76). The results from this study demonstrated variable sensitivities of the planktonic and biofilm populations to CuSO 4 , AgNO 3 , and Ag 7 NO 11 .…”

Nanosilver: Potent antimicrobial agent and its biosynthesis

“…Nanosilver is an effective killing agent against a broad spectrum of Gram negative and Gram-positive bacteria Wijnhoven et al, 2009;Yin et al, 1999) including antibiotic-resistant strains (Percival et al, 2007;Wright et al, 1998). Silver nanoparticles show potential antimicrobial effects against infectious organisms including Escherichia coli, Bacillus subtilis, Vibrio cholera, Psuedomonas aeruginosa, S.typhus, and Staphylococcus aureus.…”