Health Stream Literature Summary

Health Stream Literature Summary - Issue 58 - June 2010

Beverages obtained from soda fountain machines in the U.S. contain microorganisms, including coliform bacteria.
White, A.S., Godard, R.D., Belling, C., Kasza, V. and Beach, R.L. (2010) International Journal of Food Microbiology, 137(1); 61-66.

Advancements in public health and hygiene have greatly decreased the occurrence and severity of waterborne illness, however waterborne disease continue to cause human morbidity and mortality. The U.S. Environmental Protection Agency (US EPA) drinking water regulations to reduce the risk of waterborne illness, require than no more than 500 heterotrophic plate count (HPC) bacteria/ml be present in potable water, no more than 5% of monthly water samples test positive for coliform bacteria and all samples must test negative for Escherichia coli . In the U.S., municipal water system are monitored and are required to comply with the drinking water regulations, however there is no regular monitoring of beverages sold prepackaged in plastic bottles or dispensed from soda fountain machines. Studies suggest that water from water dispensers may be contaminated with pathogenic bacteria. In most fast food establishments in the U.S., soda fountain machines are commonly used to dispense beverages. These machines contain plastic dispensing lines which have a high surface-to-volume ratio, providing an environment that encourages the development of biofilms. These biofilms may contain many opportunistic pathogens. This study was conducted to examine the pattern and composition of microbial contamination of beverages dispensed from self-service and personnel-dispensed soda fountain machines found in fast food establishments in the Roanoke Valley region of Virginia, U.S. Also ice dispensed from soda fountain machines was examined for microbial contamination.

There were 90 beverage samples collected from 30 different fast food establishments in the Roanoke Valley between 09:30 and 13:00 on May 6, 2009. Beverages from 20 establishments were self-dispensed and those from the remaining 10 establishments were dispensed by employees (personnel-dispensed) working at drive-through windows. Establishments in the study were intentionally selected to represent the diversity of the region and varied in terms of socioeconomic and geographic characteristics. Three different beverages were sampled from each soda fountain (a sugar soda, a diet soda and water). 7 ml of each beverage was collected and analysed. There were 23 Cokes, 7 Pepsi Colas, 23 Diet Cokes, 7 Diet Pepsi Colas and 27 waters (3 machines did not dispense water and lemonade was collected as a substitute). As controls, plastic bottles of 6 sugar sodas, 6 diet sodas and 6 water beverages were purchased from a grocery store and tested for microbial contamination. Fountains at 6 different fast food establishments were observed on four occasions to assess levels of customer contact with dispensing nozzles as a possible source of contamination.

A second study was conducted on June 22, 2009 in order to determine if microbial density in beverages decreased with higher levels of use of the machines. The 3 beverage types were collected from 9 self-dispensed soda fountains between 08:00 and 09:00 and again between 13:00 and 14:30. The pH of 5 samples of each beverage type was also determined. Ice was collected from each of the nine soda fountains also and allowed to completely melt before being processed.

All bacteria identified from beverage samples were tested for antibiotic sensitivity to 11 antibiotics. Bacteria were then classified as being susceptible, intermediately susceptible, or resistant following guidelines published by Clinical Laboratory Standards Institute for zones of inhibition for each antibiotic.

No microbial growth was seen on the media control plates or on plates inoculated with beverages from plastic bottles. However bacterial growth occurred in 70% (64 of 90) of the soda fountain beverages samples collected in May. Many of the beverages exceeded U.S. drinking water standards including 20% with an HPC greater than 500 cfu/ml, 48% with coliform bacteria and 6.7% with E. coli. Of the soda fountain machines sampled, 13% had at least one beverage that tested positive for E. coli, 77% had at least one beverage with coliforms and 43% had at least one beverage with an HPC greater than 500 cfu/ml. There was no difference between the number of sugar sodas, diet sodas and water samples with an HPC greater than 500 cfu/ml, nor any difference between the number of HPC bacteria between the beverage types, despite sugar sodas having a significantly lower pH. It appeared that fewer sugar sodas were contaminated with coliform bacteria, however this difference only approached statistical significance. There was also a trend toward sugar sodas having the lowest number of coliform cfus/ml when compared to diet sodas and water. Opportunistic pathogens were detected in several beverage samples and ice samples.

There were no significant differences found in the levels of microbial contamination between self and personnel-dispensed beverages which indicates that contact with consumers may not be an important source of contamination in these machines. There were 281 individuals observed using the machines and only 5 individuals were observed touching the dispensing nozzle when obtaining a beverage and 47 were observed refilling a used cup.

Beverages sampled in the morning were more likely to have an HPC greater than 500 cfu/ml and to have coliform bacteria than when resampled in the afternoon. HPC microbes were also in significantly greater number in the morning collections of beverages than in the afternoon. Of the ice samples, 8 of 9 showed microbial contamination, however none of the samples had an HPC greater than 500 cfu/ml or contained coliform bacteria. Ice samples also had a significantly lower number of HPC microbes when compared to water collected from the same machine in the morning.

The only bacterial species that were quantified in every beverage were C. meningosepticum and E. coli. There were a total of 11.8% of beverages (11 of 93) that tested positive for E. coli during the study period and over 17% contained C. meningosepticum. Other opportunistic pathogenic microorganisms isolated from the beverages included Klebsiella, Staphylococcus, Stenotrophomonas, Candida and Serratia. In addition, from the ice samples Pseudomonas, Staphylococcus, Corynebacterium, Bacillus and Micrococcus were identified. All of the bacteria obtained from soda fountain beverages were susceptible to the antibiotics Chloramphenicol and Ciprofloxacin, while at least one bacterium showed intermediate susceptibility to Trimethoprim/Sulfamethoxazole and Tetracycline. There were also 7 antibiotics toward which one or more bacteria exhibited resistance (Amoxicillin/Clavulanic Acid, Ampicillin, Erythromycin, Imipenem, Polymyxin B, Streptomycin, Vancomycin).

It is likely that the dispensing nozzles as well as the fittings that connect the soda fountain machine to the municipal water distribution network and/or beverage source may act as a conduit for the introduction of microbes. The data from this study suggests that the internal architecture of soda machines provides a hospitable environment for the growth of the introduced microbes. The large number of beverages and soda fountain machines containing E. coli is of great concern and indicates that faecal contamination is occurring and suggests that more pathogenic strains of bacteria could persist and grow in soda fountain machines if introduced. C. meningosepticum was also found in a larger number of beverages and it can cause pneumonia, endocarditis and meningitis in immunocompromised adults and meningitis in neonates. The source of C. meningosepticum was not identified in this study, however some studies have implicated tap water and catheter lines as the source of C. meningosepticum infections. The findings here indicate the need for increased surveillance of soda fountain machines and the development of regulations for the periodic maintenance and disinfection of these machines. Periodic flushing of waterlines and sanitizing with hydrogen peroxide for example, has been found to be an effective tool for controlling bacterial contamination of waterlines.

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