Journal of Food Research; Vol. 6, No. 4; 2017
ISSN 1927-0887 | E-ISSN 1927-0895
Published by Canadian Center of Science and Education
Bacterial Transfer Associated with Blowing Out Candles on a Birthday Cake
Paul Dawson¹, Inyee Han¹, Danielle Lynn¹, Jenevieve Lackey¹, Johnson Baker¹ & Rose Martinez-Dawson²
¹ Department of Food, Nutrition and Packaging Sciences, Clemson University, Clemson, SC 29634, USA
² Department of Mathematical Sciences, Clemson University, Clemson, SC 29634, USA
Correspondence:
Paul Dawson, Department of Food, Nutrition and Packaging Sciences, Clemson University, Clemson, SC 29634, USA.
Tel: 1-864-656-1138
E-mail: pdawson@clemson.edu
Received: March 24, 2017
Accepted: April 10, 2017
Online Published: May 22, 2017
DOI: 10.5539/jfr.v6n4p1
Abstract
This study examined the potential spread of bacteria when blowing out candles on a birthday cake. Preliminary tests of blowing on nutrient agar indicated that bioaerosols in human breath expelled from the mouth may be a source of bacteria transferred to cake surfaces. To test aerosol transfer to cake, icing was spread evenly over foil then birthday candles were placed through the foil into a Styrofoam™ base. After consuming pizza, test subjects were asked to extinguish the candles by blowing. Icing samples were sterilely recovered then surface plated to determine the level of bacterial contamination. Blowing out the candles over the icing surface resulted in 1400% more bacteria compared to icing not blown on. Due to the transfer of oral bacteria to icing by blowing out birthday candles, the transfer of bacteria and other microorganisms from the respiratory tract of a person blowing out candles to food consumed by others is likely.
Keywords: birthday candles, aerosolized bacteria, blowing, bacterial transfer
1. Introduction
1.1 Blowing Out Birthday Candles
The tradition of blowing out birthday candles has different theories as to its origin. Some theorize the practice began in Ancient Greece related to bringing cakes with lit candles to the temple of the goddess of the hunt, Artemis. Other ancient cultures believed the smoke from candles carried their wishes and prayers to the gods. A written account reported birthday candles matching the age of Count Ludwig Von Zinzendorf being presented at the Count’s birthday celebration in Germany in the 1700’s (Frey, 1753). This tradition has become commonplace in many parts of the world.
1.2 Spread of Bacteria
Bacteria are an unavoidable part of life, present in and on almost everything humans contact. Whether benign or pathogenic, it is important to understand how bacteria are transferred and become familiar with measures for avoiding contamination. Illnesses related to pathogenic bacteria, which can spread rapidly throughout the population, are a major public health concern in today’s society.
Bioaerosols and poor air hygiene can have adverse effects on human health (Douwes, Thorne, Pearce & Heederik., 2003; Xu et al., 2011). Respiratory droplets expelled by coughing and sneezing are sources of normal human flora, as well as pathogenic bacteria (Obeng, 2008; Houk, 1980) and viruses (Loosli, Hertweck & Hockwald, 1970). The respiratory tract can be colonized with pathogenic organisms that can then be aerosolized in the breath of an infected individual (Couch et al., 1969; Knight, 1973).
The spread of respiratory diseases including SARS (Yu et al., 2004) and H1N1 avian influenza (Baker et al., 2010) have been attributed to oral airborne transmission. Influenza virus particles have been detected in the exhaled breath of infected individuals through coughing, breathing, and talking (Fabian et al., 2008; Stelzer-Braid et al., 2009; Huynh et al., 2008; Lindsley et al., 2010).
When respiratory droplets are released, they may spread infection directly from person to person or by contamination of surfaces then touched by others (Obeng, 2008). The bacteria may originate from respiratory droplets expelled directly onto surfaces or indirectly as droplets coating hands that are transferred to surfaces.
Exhaled breath contains 693 to 6,293 CFU of bacteria per cubic meter (Xu et al., 2012). Qian et al. (2012) also reported that humans emit bacteria at a rate of approximately 37 million gene copies per person per hour. Thus, when a person forcibly exhales, such as while blowing out birthday candles, bacteria or viral particles can become aerosolized from the respiratory tract.
1.3 Research Objective
The purpose of this research was to evaluate the level of bacterial transfer to the top of a cake when blowing out candles on a birthday cake. Scientific data from this investigation may help raise awareness of possible health risks associated with birthday celebrations and encourage preventive measures to reduce bacterial spread.
2. Methods
2.1 Blowing Out Candles
A sheet of foil cut in a circular shape with a diameter of 149 mm was placed on a Styrofoam™ disc of the same size. 18 g of icing was spread in a thin layer on the foil. Seventeen candles were evenly spaced into the Styrofoam, passing through the icing and foil layers.
Each test subject was asked to smell and consume a piece of hot pizza to simulate a meal-dessert sequence. After lighting the candles, subjects were instructed to blow until all candles were extinguished on the mock cake (Figure 1). For each testing session a control sample was collected where the procedure was followed but candles were not blown out.
Figure 1. Styrofoam™ base and candle apparatus with icing used to test bacterial transfer when blowing out candles.
2.2 Enumeration of Bacteria
After candles were blown out (blow) or not blown out (no-blow), the candles and holders were removed from the Styrofoam base without touching the icing. Using sterile forceps, the foil was folded with the icing layer inside and placed in a stomacher bag.
Fifty milliliters of 0.1% sterile peptone solution were added. The bag was placed in a stomacher at 230 rpm for 1 minute. Duplicate samples of 1 ml and 0.1 ml were aseptically removed, serially diluted, and plated on plate count agar.
Samples were incubated at 37°C for 48 hours. Colony forming units (CFU) were counted and converted to CFU per sample and log₁₀ CFU per sample.
2.3 Research Design and Statistical Analysis
The experiment was replicated three times on separate days by 11 subjects, yielding 33 observations per treatment. Statistical analysis was performed using SAS (2010) to obtain mean, median, range, and standard deviation. A Student’s t-test and GLM analysis were used to determine significant differences between blowing and non-blowing treatments.
3. Results and Discussion
Blowing out candles over icing resulted in 15 times more bacteria recovered compared to icing not exposed to blowing (Table 1). The variation in bacterial recovery was 100 times greater in the blow treatment. The median and maximum transfer of bacteria increased 300% and 12,000%, respectively.
Previous studies on airborne droplets from the oral cavity date back to Flügge (1899) and later research confirmed that droplets released during breathing, coughing, and sneezing can remain airborne for extended periods (Duguid, 1946).
More recent research indicates that over 2,000 moisture particles may be released per breath, most smaller than 5 µm (Wan et al., 2014). These droplets are capable of carrying both bacteria and viruses.
Normal respiratory aerosols may include:
Staphylococcus spp.
Streptococcus spp.
Corynebacterium spp.
Haemophilus spp.
Neisseria spp.
Some pathogenic species such as Streptococcus pneumoniae and Staphylococcus aureus may cause illness through aerosol transmission and contaminated surfaces.
Birthday celebrations commonly involve blowing out candles on cakes. Considering the presence of oral bioaerosols, the results of this study suggest that this practice may significantly increase bacterial contamination of the cake icing.
Table 1
Mean, median, range and standard deviation of bacterial counts for cake icing exposed to blowing out candles and not blowing out candles
¹ No-blow = cake icing not exposed to blowing out candles
² Blow = cake icing exposed to blowing out candles
³ CFU/sample = colony forming units per cake icing sample
N = 33
Means with different superscripts are significantly different (p ≤ 0.0001).
Log CFU/sample = log₁₀ of colony forming units per cake icing sample.
Acknowledgments
This research was supported by the Creative Inquiry Program at Clemson University.
Technical Contribution No. 6547 of the Clemson University Experiment Station.
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