cell phone

Cell Phone Study 2006-2009
Dr. Petersen & Dr. Sehmi
Biology Department
Queensborough Comunity College


Background of the Study | Explanation of Methods | Summary of Results | For More Information

Participants, please enter your code here to view the results from your cell phone:




The purpose of this study was to determine if cellular phones could carry the bacterial species Staphylococcus aureus (SA). We wanted to find out:
1. Is Staphylococcus aureus (SA) found on cell phones of Queensborough students?
2. Is the SA found on cell phones resistant to antibiotics?
3. Is there a difference between students who work in hospitals and those that don’t (in terms of
whether or not SA is found on their phones)?

Staphylococcus aureus is a type (species) of bacteria that is commonly found on the skin. However, some strains of these bacteria can cause very serious infections. In addition, many of these strains are resistant to antibiotics (for example, Methicillin-resistant Staphylococcus aureus or MRSA), making them difficult to treat. We wanted to find out if cell phones could be a possible source for the spread of these bacteria.


Here is a brief description of the tests that we used to detect SA on the samples taken from cell phones.

1. Mannitol salt agar (MSA): this media is used to screen for SA. The media is selective because only bacteria that can grow in a high-salt environment (like Staph) would grow here. In addition, SA produces a yellow colored colony on this plate, which distinguishes it from other Staph species that would appear white.

What it means if bacteria are growing on this plate: it means that your phone possibly carried bacteria in the Staphylococcus genus (not necessarily SA). Other types of bacteria can grow on these plates as well. Also, many bacteria cannot. Therefore not all bacteria that were present on your phone necessarily grew on this plate.

The individual results for your phone give the total number of bacterial colonies, plus the ones that were yellow in color that could be SA. Since we were specifically looking for SA we did not identify the other types of bacteria.

2. ChromAgar (CA): this media uses a color reaction to identify different types of bacteria from environmental samples. SA should appear as a mauve-colored colony on this plate. We used these plates as an early stage of identifying possible SA colonies. Colonies that had a different color appearance (blue, white, pink, etc…) were presumed to not be SA and were not tested.

3. Hemolysis test: uses Blood Agar plates: (BA): bacteria were plated on media containing 5% sheep’s blood to determine if the bacteria could produce an enzyme (hemolysin) that breaks down red blood cells. If the bacteria break down the blood, there is a clear zone around the growth. A greenish discoloration around the growth indicates that the bacteria could partially break down hemoglobin (considered a negative result for this study).

4. Coagulase test: most pathogenic (disease-causing) strains of SA make an enzyme called coagulase to help protect them from your immune system. To test for this enzyme, bacteria are mixed with latex. The appearance of clumps indicates that the bacteria are coagulase-positive.

5. Oxacillin resistance screening: bacteria that were positive on chromagar and blood agar were plated on a media that contained oxacillin (an antibiotic similar to methicillin and penicillin). If the bacteria grew on this plate that means that they might be resistant to antibiotics, and should be further tested.

6. API identification: this is a group of metabolic tests that confirms whether or not the bacteria tested are SA or some other type of bacteria. This test was only done on a few of the isolates (ones that tested positive in other tests).

7. Antibiotic resistance confirmed (disk diffusion assay): isolates that were positive for other tests were tested against 10-12 antibiotics, including penicillin, ampicillin. oxacillin and vancomycin using the Kirby-Bauer method. In this test antibiotic disks are placed on a Petri dish that contains the bacterial being tested. In general, if the bacteria can grow close to the disk, this indicates that the bacteria are resistant to that particular antibiotic.
This test was only done with a few isolates (presumed to be SA and showing possible resistance on oxacillin screening test).

Summary of Results

We sampled 166 cell phones of Queensborough students (82 from students working on hospitals; 84 from “control” students who do not work in hospitals.

16 cell phones (8 each from control and experimental groups) gave initial results that indicated the possibility of antibiotic resistant SA. Isolates from 6 phones were eliminated when additional tests were negative.

14 isolates from 10 phones were further tested to see if they could be pathogenic SA. From these samples, 5 were confirmed to be SA, 4 were confirmed Staphylococcus epidermidis (another species that is usually non-pathogenic). The remaining isolates either could only be identified to the Staphylococcus genus, or were another type of (non-pathogenic) bacterium.

Most of the isolates tested with the disc diffusion assay did appear to be resistant to penicillin and ampicillin, but not to other most antibiotics. However, antibiotic resistance tests were not conclusive due to variability in repeated tests.

At least some bacteria found on almost every cell phone we sampled. The number of colonies ranged from 0-to too many to count (over 200). However, most of these bacteria were not SA.

There was no detectable difference in the appearance of SA on cell phones of hospital workers vs. non-hospital workers. Also the average number of colonies for each group was about the same.

For more information:

If you would like to know more about your results or the results of the study in general, please contact either Dr. Petersen (718-631-6048; JPetersen@qcc.cuny.edu); or Dr. Sehmi (718-281-5503; SSehmi@qcc.cuny.edu); or Dr. Gorelick (718-631-6335; MGorelick@qcc.cuny.edu)

Thank you for your participation in this study.