Growth and Survival of Acid-Resistant and Non-Acid-Resistant Shiga-Toxin-ProducingEscherichia coliStrains during the Manufacture and Ripening of Camembert Cheese

Abstract

Growth and survival of acid-resistant (AR) and non-acid-resistant (NAR) Shiga-toxin-producing Escherichia coli (STEC) strains were investigated during the manufacture and ripening of microfiltered milk Camembert cheeses. The induction of acid resistance of the STEC strains in cheeses was also studied. Six different mixtures of AR and/or NAR STEC strains were inoculated separately into microfiltered milk at a level of 103 CFU mL−1. The STEC counts (AR and NAR) initially increased by 1 to 2 log10 CFU g−1 during cheese-making. Thereafter, the populations stabilized during salting/drying and then decreased during the early stages of ripening. Exposing the STEC strains in artificially inoculated cheeses to simulated gastric fluid (SGF - pH: 2.0) reduced the number of NAR strains to undetectable levels within 40 minutes, versus 120 minutes for the AR STEC strains. AR and NAR STEC were able to survive during the manufacture and ripening of Camembert cheese prepared from microfiltered milk with no evidence of induced acid tolerance in NAR STEC strains.

An Overview of Molecular Stress Response Mechanisms in Escherichia coli Contributing to Survival of Shiga Toxin-Producing Escherichia coli during Raw Milk Cheese Production

“…Therefore, the growth and survival of pathogens vary greatly depending on the technology parameters. Variation in behavior also occurs among strains of E. coli and STEC in cheeses (98,133).…”

“…At present, studies considering the stress responses of STEC strains are very limited and mainly focused on strains of serotype O157:H7 (2,48,133,193).…”

“…Hard cheeses are considered to present a relatively lower risk for growth and survival of pathogens (114). Although STEC loads increase remarkably during the manufacture of cheese, levels generally are expected to decrease during raw milk cheese ripening (124,133,154,195); however, some organisms can survive even in hardripened uncooked raw milk cheeses for several months, clearly indicating that the ripening time alone is not sufficient to control STEC (34,79,175,196). Cooking temperatures of 53°C and higher result in a rapid decrease FIGURE 1.…”

A review of the microbiological hazards of dairy products made from raw milk

“…4.2 log cfu g À1 in curd at pressing 3.8 log cfu g À1 in cheese at day 7; 0 cfu g À1 in cheese at week 10 Jørgensen et al (2005) Inoculation of 4 log cfu g À1 of L. monocytogenes in sheep milk Decrease after 6 wk; log reduction at 4 C: 2.10 at day 91, 3.19 at day 101, presence at day 111, absent at day 114; log reduction at 12 C: 1.74 at day 77, 2.90 at day 91, presence at day 98, absent at day 104; log reduction at 22 C: 1.76 at day 54, 2.45 at day 67, 4.02 at day 70, presence at day 74, absent at day 77 Valero et al (2014) Soft cheese Inoculation of 4 log cfu mL À1 of E. coli O157:H7 and L. monocytogenes; growth of both pathogens during production Storage at 2 C for 75 d; E. coli O157:H7: highest count at day 10, decrease after 10 d, count at day 75 higher than inoculum; L. monocytogenes: survival, count at day 75 higher than inoculum Ramsaran, Chen, Brunke, Hill, and Griffiths (1998) Inoculation of 4 log cfu mL À1 of E. coli O157:H7 and L. monocytogenes; growth of both pathogens during production Storage at 2 C for 65 d; E. coli O157:H7: highest count after 24 h, decrease after 24 h, count at day 65 higher than inoculum; L. monocytogenes: survival, count at day 65 higher than inoculum Ramsaran et al (1998) Inoculation of 3 log cfu mL À1 of VTEC; increase of 1 e2 log cfu g À1 during production; stabilisation during salting/drying Storage at 4 C; decrease during early stages of ripening Montet et al (2009) Inoculation of 3.6 log cfu mL À1 of Brucella abortus in milk;…”

Fates of Acid-Resistant and Non-Acid-Resistant Shiga Toxin-Producing Escherichia coli Strains in Ruminant Digestive Contents in the Absence and Presence of Probiotics

“…The AR and AS non-O157:H7 STEC strains used in this study (Table 1) have been described previously (43,44) and were used to examine whether acid resistance conferred a growth or survival advantage during manufacture of fermented raw meat sausages and raw milk Camembert cheeses (30,31). E. coli O157:H7 strain EDL933 was isolated from ground meat during an outbreak in the United States (33).…”