February 6, 2015

The Microbial Burden on Common Hospital Surfaces: A Pilot Study in Preparation for the Surfaces to be Replaced by Antimicrobial Copper

Miranda Chimzar '15

In the United States in 2002, 1.7 million people suffered from hospital acquired infections (HAI), which caused almost 10,000 deaths and lead to 176.4 million days in the hospital. The Centers for Disease Control and Prevention has guidelines for minimizing the outbreaks of HAI. One way to lower the number of microbes causing these infections is through the use of antimicrobial copper. Before hospital surfaces can be replaced with copper it is important to know which surfaces have the highest microbial burden, or largest amounts of bacteria, viruses, and fungi. It is also important to look at the cost of changing these surfaces to copper in comparison to the impact they would make on the number of HAI. This pilot study assesses the microbial burden on a number of hospital surfaces by counting the colony forming units per square centimeter (CFU/cm2), using Kirby-Bauer Diffusion assays to test for antibiotic resistance and sequencing microbial DNA. Samples were taken at an acute care hospital with 64 beds, following the procedure from Attaway (2012). It was found that bedrails had the highest CFU/cm2 followed by the wound cart, a cart that traveled from room to room treating patients with open wounds; bedside tables; computer mice; and chair arms. Samples were tested for the genus Staphylococcus. The bedrail was the only surface containing Staphylococcus aureus that was further tested using a Kirby-Bauer Diffusion Assay, which suggested resistance to ampicillin, penicillin, and potentially tetracycline. Colony Polymerase Chain Reaction (PCR) was performed on the wound cart and the DNA was purified for sequencing. Bacteria on the wound cart was found to be from the bacillus and possible sporosarcina genera. Based on these results, changing the bed rails to copper would have the greatest impact on HAI. Bed rails, because of their irregular shape are expensive to replace. For those hospitals that cannot afford to replace bedrails, correct glove and hand sanitizing should be emphasized and patients should wash or sanitize their hands before eating to prevent the spread of these microbes.

Individuals afflicted by iron overload diseases are susceptible to infection by ferrophilic bacteria like Vibrio vulnificus because the excess iron in their blood facilitates its growth and reproduction. Ferrophilic bacteria take advantage of the excess iron through the secretion and internalization of siderophores, high-affinity iron chelators. Fortunately, iron overload diseases are treatable by iron chelation therapy. However, deferoxamine, the iron chelator predominantly used, is known to facilitate the growth of V. vulnificus and other ferrophilic bacteria. This was believed to be due to its containing hydroxamate moieties, functional groups characteristic of bacterial siderophores. Assuming the receptors for siderophore uptake of V. vulnificus depend on the presence of the hydroxamate moiety, then chelators containing them should be able to be internalized through those receptors. Two iron chelators, deferasirox and deferiprone, are being tested as viable alternatives for deferoxamine because they are just as efficacious as deferoxamine at chelating iron, but because they lack the hydroxamate functional groups, should not facilitate ferrophilic bacterial growth. To assess these alternative chelators, V. vulnificus was grown in a medium designed to mimic iron in the blood at three different concentrations of deferasirox, deferiprone, and deferoxamine to determine which, if any, of these chelators would inhibit V. vulnificus growth. The results indicated that both deferasirox and deferiprone inhibited V. vulnificus growth at all tested concentrations while deferoxamine facilitated growth at all concentrations. It turns out that deferoxamine supports V. vulnificus growth not solely because it expresses hydroxamate functional groups. Instead of one general receptor for siderophore uptake based on hydroxamate moieties, V. vulnificus has many specific receptors for distinct siderophores. One of these receptors is specific for deferoxamine, which happens to be a Streptomyces siderophore, not a Vibrio one. This case exemplifies siderophore piracy in which ferrophilic bacteria evolved to internalize heterologous siderophores to better compete for iron, a rare and essential nutrient in their natural estuarine environment. Since deferasirox and deferiprone are synthetic iron chelators that are not derived from bacterial siderophores, it is not surprising that they do not facilitate V. vulnificus growth and reproduction.