Survival and detection of coliforms, Enterobacteriaceae, and gram-negative bacteria in Greek yogurt

Abstract

Despite the widespread use of coliforms as indicator bacteria, increasing evidence suggests that the Enterobacteriaceae (EB) and total gram-negative groups more accurately reflect the hygienic status of high-temperature, short-time pasteurized milk and processing environments. If introduced into milk as postpasteurization contamination, these bacteria may grow to high levels and produce a wide range of sensory-related defects. However, limited information is available on the use and survival of bacterial hygiene indicators in dairy products outside of pasteurized fluid milk and cheese. The goal of this study was to (1) provide information on the survival of a diverse set of bacterial hygiene indicators in the low pH environment of Greek yogurt, (2) compare traditional and alternative detection methods for their ability to detect bacterial hygiene indicators in Greek yogurt, and (3) offer insight into optimal hygiene indicator groups for use in low-pH fermented dairy products. To this end, we screened 64 bacterial isolates, representing 24 dairy-relevant genera, for survival and detection in Greek yogurt using 5 testing methods. Before testing, isolates were inoculated into plain, 0% fat Greek yogurt (pH 4.35 to 4.65), followed by a 12-h hold period at 4 ± 1°C. Yogurts were subsequently tested using Coliform Petrifilm (3M, St. Paul, MN) to detect coliforms; Enterobacteriaceae Petrifilm (3M), violet red bile glucose agar and the D-Count (bioMérieux, Marcy-l'Étoile, France) to detect EB; and crystal violet tetrazolium agar (CVTA) to detect total gram-negative bacteria. Overall, the non-EB gram-negative isolates showed significantly larger log reductions 12 h after inoculation into Greek yogurt (based on bacterial numbers recovered on CVTA) compared with the coliform and noncoliform EB isolates tested. The methods evaluated varied in their ability to detect different microbial hygiene indicators in Greek yogurt. Crystal violet tetrazolium agar detected the highest portion of coliforms, whereas EB Petrifilm detected the highest portion of EB, as well as highest portion of total gram-negative bacteria. Additionally, the D-Count method allowed for faster detection of EB in yogurt by generating results in approximately 13 h rather than the 24 h required when using EB Petrifilm and violet red bile glucose agar. Results from this study indicate that the coliform and EB groups encompass a broad range of dairy-relevant gram-negative bacteria with the ability to survive in Greek yogurt, supporting their use as microbial hygiene indicator groups in low-pH fermented dairy products.

CONTAMINATION OF BIOAEROSOL IN THE CONFECTIONERY FACILITY WITH Enterobacteriaceae MEMBERS

“…Relationship between the enteritic coliform and the number of workers, if will be confirmed in the future studies, may be the important indicator of hygiene rate in the facility. The number of Enterobacteriaceae is used as indicator of hygiene status and quality of finished product for milk processing facilities (Hervert et al 2016). One of the main factors influences on the bioaerosol composition and concentration is outdoor air flow (Adams et al 2013).…”

Consumption of Greek yogurt during 12 weeks of high-impact loading exercise increases bone formation in young, adult males – a secondary analysis from a randomized trial

“…Greek yogurt (GY) has recently become a popular dairy product that is widely accessible and affordable (Darmon and Drewnowski 2015;Drewnowski 2018). It also contains important bone-supporting nutrients (calcium, potassium, phosphorus, and vitamin D, if fortified), and additional structural (e.g., solid vs. liquid) and constitutional features (e.g., increased protein content, lower pH, fermentation/bacterial cultures and higher casein/ whey ratio) that contribute to its uniqueness compared with milk (Van den Heuvel et al 1999;Scholz-Ahrens and Schrezenmeir 2000;Adolfsson et al 2004;Hervert et al 2017;Thorning et al 2017;Rizzoli and Biver 2018).…”

Effect of physical stresses on survivability and post-exposure antibiotic susceptibility of coliforms in environmental waters and wastewaters

“…and Enterococci sp. are commonly isolated coliform bacteria in environmental waters and their occurrence or survival are dependent on various physiological processes (1).…”