Pathogenic Human Disease

Transmission of pathogenic human disease can occur under many different circumstances. One mode of transmission that is of interest to people is the transmission of microbes on surfaces. A surface for transmission can range from a doorknob to our very own hands. Nonliving surfaces involved in transmission of microbes are called fomites. Fomites are very diverse and can be essentially any non-living surface capable of spreading disease through microbial transmission. Skin and fomites are two of the most common ways to transmit disease between humans, and they are leading causes of nosocomial infections (Clause 2018). Nosocomial infections are the result of microbial transmission causing infection within a medical facility such as a hospital or doctor’s office.

These infections often happen to patients in the facility that are already sick which may leave them immunocompromised. This can greatly increase a patient’s risk of death or the amount of time they spend in the facility, therefor fomites and nosocomial infections are concerning issues. The two types of nosocomial infection are endogenous and exogenous infection. Endogenous infection usually results from opportunistic organisms infecting a weakened immune system, because endogenous infections are caused by an individual’s personal microflora. Exogenous infections, on the other hand, are caused by pathogens in the patient’s external environment. These infections are often caused by transmission from hands or fomites. Exogenous nosocomial infections are more easily prevented than endogenous because it is easy to combat transmission through hands and fomites using proper techniques of sterilization and cleaning (Muran & Inam 2016). The purpose of this experiment is to gain a better understanding of fomites and the role they play in transmission, and to understand nosocomial infections. This is accomplished by testing the effectiveness of hand washing in preventing the transmission of pathogenic Serratia marcescens. If the experiment is done properly than students should have a clear understanding of the effectiveness on hand washing against pathogenic transmission.

Methods: The experiment required some materials to begin which included: a broth culture of Serratia marcescens, 2 agar plates containing nutrients, sterile gloves and cotton swabs, hand soap and a doorknob. The procedure is simple and begins with each student being assigned a number beginning with the first student being assigned number 1 and the twelfth student being assigned number 12. Each student obtained 2 agar plates containing nutrients and labeled them with their assigned number and labeled one plate “before” and the other plate “after”. Next, each student placed a sterile glove on their right hand and was careful not to touch the fingers to any surface. An independent party used a cotton swab to apply a healthy amount of the Serratia marcescens culture to the doorknob. After the application of the culture student 1 was instructed to grasp the doorknob and rub their fingers on the agar plate labeled “before” immediately after grabbing the doorknob. After this, student 1 washed their gloved hand and proceeded to rub their fingers on the plate labeled “after” after washing their glove and drying it with a sterile paper towel. The same exact procedure was followed by each subsequent student in numerical order, i.e. student 2 went next and student 3 when after student 2 and so on. The plates were then inverted and incubated at 25̊C for 48 hours and then they were examined.

Results: The results showed that not only did the bacterial concentrations decrease on plates after the students washed their hands, but it also decreased as more students contacted the doorknob. For example, at student number 12 there was no Serratia colonies present on wither the “before” or “after” agar plates. Student number one only showed 5-10 CFUs on the “after” plate compared to an uncountable number of CFUs on the “before” plate. Students number 4 through 12 showed no growth on the “after” plate, while many of them had an uncountable number of colonies on their “before” plates.

Discussion: Transmission was very strong among the first few students to contact the door knob and became weaker as more students encountered the contaminated doorknob. Handwashing was very effective among all the students. Every student saw an extremely significant decrease in colonies between their “before” and “after” agar plates. However, this result could have been skewed by experimental error. If students did not thoroughly wash all the soap off their gloves, some soap could have been plated giving it an unfair advantage to further restrict Serratia growth. Another possible issue with this experiment is that it studied both fomites and hand transmission. When the experiment is thoroughly analyzed it appears that the hands really acted as fomites themselves because they were covered by latex gloves, so transmission was not really occurring on living tissue. This could have skewed the results because there are already microbes on human skin that would have influenced the transmission of Serratia. The hypothesis was proven despite these possible errors because students gained a better understanding of fomite and their role in transmission and nosocomial infections; students also had an excellent visual representation of the effectiveness of personal hygiene.