There are many television commercials and Internet advertisements recently all stating that they have instruments detrimental to the cleanliness of CPAP machines. A CPAP machine is a medical grade device used for the delivery of constant positive air pressure for the treatment and relief of sleep apnea (a type of respiratory ventilation). Anything such as this instrument used to improve quality of life should certainly be kept clean in order to avoid the introduction of infectious material into the lungs, an organ whose functional environment is of vital importance and sterility is paramount. Yet what is exactly is this infectious material that is able to survive in the plastic hoses and masks of the CPAP machine? Simply stated, the instrument plastics surfaces are susceptible to biofilms, a complex of microorganism cells that attach and proliferate on many different surfaces, both organic and inorganic, that are extremely difficult, and in some instances impossible, to remove from their attached surface. A biofilm is a cluster of cells encompassed by a matrix (predominantly a polysaccharide matrix) as opposed to cells that are planktonic, in that planktonic cells are able to float freely in their suspension and are easily rinsed away from their surrounding environments. A biofilm can consist of a single type of cell or several different types inhabiting a single matrix, studies lending strength to the hypothesis that biofilms tend to be thicker and stronger when there are more than one type of bacteria present, in that the different types of colonies lend their different strengths to the overall strength of the biofilm matrix.
Van Leeuwenhoek is credited with the discovery and the characterization of biofilms, describing their ability to grow on different surfaces, but also their ability to attach to those surfaces. These attachments occur mostly through a “solid-liquid interface” in that the surface that the biofilms seem to prefer are solid surfaces and the bacteria are introduced to those solid surfaces through an aqueous medium (for example, the CPAP machine consists of a plastic face mask, and the bacteria can be introduced by the exhalation of the person using the mask and the flux of bacteria that normally inhabit their oral cavity into the mask). Current studies, performed by the CDC and Dr. Donlan, reveal that surfaces that are not very smooth, have a tendency to be hydrophobic, and have a “conditioning film” (a hard surface that has been exposed over time consistently to a chemical medium). Also hypothesized is that bacteria that are motile are most likely to bind and create a biofilm than those cells that lack the ability of mobility.
Due to the advancements in next generation DNA sequencing, scientific evidence strongly supports that the genes of the cells in a biofilm that are up-regulated and down-regulated are very different that the regulation of the genes of planktonic cells of the same type. It is speculated that this is due to the extracellular signals that exist in the matrix encompassing the biofilm cells, favoring genes that allow the cells to thrive in an environment that is different than the environment cells are exposed to in free suspension.
A concern with the presence of biofilms, whether in medical tubing or the tissue in a chronic infection, is the tendency of biofilms to be antibiotic resistance. There are possibilities in which this antibiotic resistance could be attained by the biofilm, the first in being that the cells exist in a matrix, not allowing the flow of the antibiotics to reach the inner cells of the biofilm, only the outer ones not covered well by the matrix. A second possibility is the evidence that the cells themselves have become antibiotic resistant. With the cells contained in the biofilm being in closer proximity to each other, they are able to perform cell to cell plasmid exchange (through bacteria conjugation), thus passing potential plasmids containing genetic coding for antibiotic resistance easily from cell to cell.
Clinical and research science still have many avenues to explore for a better understanding of the formation, growth, and eradication of biofilms. Many platforms exist that will be detrimental to the study biofilms, especially that of next generation DNA sequencing in which the bacterial involved can be studied all the way to their molecular levels, and elucidation of what makes these little globules of cells so very different from their planktonic counterparts could be the key to their further study.