Biofilm production and acetic acid sensitivity of Staphylococcus aureus and Escherichia coli isolated from poultry slaughterhouse environment, broiler carcasses and offal in Algeria

Abstract

The environment of poultry slaughterhouses, broiler carcasses and offal can act as reservoirs and spread various zoonotic bacterial pathogens such as Staphylococcus aureus and Escherichia coli. The objectives of this study were to determine the prevalence of S. aureus and E. coli in broiler carcasses and offal, and the environment of poultry slaughterhouses, and to evaluate the capacity for biofilm formation and sensitivity to acetic acid of certain bacterial isolates. A total of 210 samples were taken from different parts of the carcasses (wings, thighs and breasts) and offal (livers and hearts) of broiler chickens, and 19 environmental samples were collected from various compartments of poultry slaughterhouses (walls, floors and equipment) to determine the prevalence of S. aureus and E. coli. Fourteen S. aureus strains and 14 E. coli strains isolated from broiler products, as well as 14 S. aureus strains and 14 E. coli strains isolated from the environment of poultry slaughterhouses, were specifically selected to evaluate their ability to form biofilms. The tube and the tissue culture plate methods were used to evaluate biofilm forming capacity, while the minimum inhibitory concentration (MIC) of acetic acid on these bacterial isolates was determined by the agar dilution method. The total quantities of biofilm produced by the different categories of bacterial strains were compared by statistical analysis. The prevalences of S. aureus and E. coli were 100% in broiler carcass and offal samples, while in environmental samples, the prevalence of E. coli was 94.73% and that of S. aureus was 78.94%. Using the tube method, 35.71% of S. aureus strains demonstrated strong biofilm production, 50% demonstrated moderate production and 14.28% demonstrated weak production. No strain was categorized as non-biofilm producing. Similarly, for E. coli strains, 32.14% had strong biofilm production, 21.42% moderate production, and 46.42% weak production, with no strain being non-biofilm producing. Using the tissue culture plate method, 39.28% of S. aureus strains had moderate biofilm production, while 60.71% showed weak production. No isolates were identified as having strong production or being non-biofilm producers. For E. coli strains, 14.28% showed strong biofilm production, 39.28% moderate production, and 46.42% weak production, with no isolate being categorized as a non-biofilm producer. The two methods made it possible to detect biofilm production by all studied bacterial isolates. The tube method revealed a higher rate of isolates with strong biofilm production (33.92%) compared to the tissue culture plate method (7.14%). In contrast, the tube method recorded a lower rate of isolates exhibiting moderate biofilm production (35.71%) compared to the tissue culture plate method (39.28%). Similarly, the tube method showed a lower rate of isolates with weak biofilm production (30.35%) compared to the tissue culture plate method (53.57%). Regarding measures of total biofilm produced, environmental bacteria presented a not significantly higher value (total optical density (OD)=12.45) than did bacteria isolated from broilers (total OD=11.83). Likewise, the total quantity of biofilm produced by all 14 E. coli (total OD=12.78) was numerically but not significantly higher than that produced by all S. aureus isolates (total OD=11.5). Among the isolates from broilers, the 14 E. coli strains produced a numerically not significantly higher amount of biofilm (total OD=6.76) than the 14 S. aureus strains (total OD=5.07). The minimum inhibitory concentration (MIC) of acetic acid was ≤0.08% for all bacterial isolates, except for two S. aureus isolates, for which the minimum inhibitory concentration was 0.16%. In conclusion, S. aureus and E. coli are frequently present in the environment of poultry slaughterhouses and in broiler products. All bacterial isolates demonstrated an ability to form biofilms. These bacteria were very sensitive to acetic acid, which is therefore considered an ideal agent for disinfection of the poultry slaughterhouses environment and decontamination of broiler carcasses.