Researchers sought to replicate a food processing environment and say the chicken juice helped the bacteria attach to surfaces.
The presence of chicken juice created a protein-rich layer, making it easier for Campylobacter to attach to the surface, and also provided a rich food source.
A protective biofilm
Campylobacter is usually found in the intestinal tract of poultry. It is not very resilient, but during biofilm formation the bacteria protect themselves with a layer of slime. This makes them more resistant to antimicrobials and disinfection treatments.
A problem in food processing areas is ineffective removal of organic material. Runoffs from carcasses contain carbohydrates, proteins, lipids and sugars, providing a good environment for bacteria to thrive in.
Researchers say build-up of an organic layer – a ‘conditioning layer’ - alters physiochemical properties of the surface. This assists bacterial attachment, and also attracts bacteria because of the increased nutrient availability.
“We investigated the effect of chicken juice on the attachment of C. jejuni to surfaces and subsequent biofilm formation,” said Helen Brown, PhD student and leader of the study. “In the presence of chicken juice, C. jejuni biofilm formation is increased and this increase in biofilm levels is not simply due to increased cell numbers within the suspensions, but to an increase in attachment to abiotic surfaces.
“This increase in attachment is due to the ability of chicken juice to condition abiotic surfaces relevant to food processing environments.
“To date, most studies on C. jejuni biofilms have been performed in laboratory conditions, which do not mimic the conditions encountered in the processing environment. It is important to ensure studies are designed to allow accurate interpretation and extrapolation of laboratory-obtained results to the food industry.”
In the study, whole chickens were thawed overnight at room temperature, and the exudate (or ‘chicken juice’) collected.
Single-use glycerol stocks of C. jejuni were thawed, inoculated onto Skirrow plates, and grown overnight at 37 degrees in microaerobic conditions. These were added to portions of brucella broth, burcella broth supplemented with 5% chicken juice, or 100% chicken juice.
The samples were added to sterile borosilicate glass test tubes, 24 well polystyrene tissue culture plates, or polystyrene tissue culture plates with sterile stainless steel coupons.
Samples were incubated at 37 degrees under microaerobic or atmospheric air conditions for 48 hours.
“Supplementation of brucella broth with chicken juice resulted in an increase in biofilm formation compared to brucella broth alone in both microaerobic and aerobic conditions," said Brown.
“Replacement of medium by 100% chicken juice gave the highest level of biofilm formation, and this was not due to differences in viability, since cultures incubated in brucella broth, brucella broth with 5% chicken juice, and 100% chicken juice had similar levels of viable planktonic cells."
“To differentiate between growth and biofilm formation, we assessed growth of C. jejuni NCTC 11168 in brucella broth, brucella broth supplemented with 5% chicken juice, and 100% chicken juice in shaking cultures.
"There was no statistical difference between growth in brucella broth and media supplemented with 5% chicken juice over a 24 hour period, and thus the increase in biofilm formation in the presence of chicken juice is likely to be solely due to increased attachment of Campylobacter to the abiotic surface.”
Some additional experiments were done with surfaces pre-coated with chicken juice. When C. jejuni in unsupplemented brucella broth was added, this resulted in a ‘significant increase’ in levels of biofilm formation compared to brucella broth under both aerobic and microaerobic conditions.
Chicken juice: ‘an adhesive foundation’
“In this study we investigated the effect of meat exudates on C. jejuni biofilm formation and show that chicken juice is able to enhance biofilm formation compared to brucella broth," said Brown.
"Our data show this is mediated by the ability of chicken juice to provide a conditioning layer on abiotic surfaces, providing an adhesive foundation onto which a C. jejuni biofilm can establish itself and grow.
“This is observed in both isolates capable of forming biofilms in brucella broth and isolates that are otherwise poor biofilm formers. In an industrial food setting, this means that the presence of meat exudates can aggravate the problem of contamination by food-borne pathogens such as C. jejuni.”
November 2014, 80 (22). doi: 10.1128/AEM.02614-14
'Chicken Juice Enhances Surface Attachment and Biofilm Formation of Campylobacter jejuni'
H. Brown et al.