of acid under anaerobic conditions by some micrococci. Enterotoxin
production is adversely affected by anaerobic conditions far more than
growth.
Staphylococcus aureusis a typical mesophile with a growth tempera-
ture range between 7 and 48 1 C and an optimum at 37 1 C under otherwise
optimal conditions. The range of temperature over which enterotoxin is
produced is narrower by a few degrees and has an optimum at 35–40 1 C
(Table 7.8). The organism has unexceptional heat resistance with a
D 62 of 20–65 s and a D 72 of 4.1 s when measured in milk using
Figure 7.10 Staphylococcus aureusattached to stainless steel.
(Photo M.Lo)
Table 7.8 Factors permitting growth and enterotoxin production byStaphylo-
coccus aureus
Growth Enterotoxin Production
Factor Optimum Range Optimum Range
Temperature, 1 C 35–37 7–48 35–40 10–45
pH 6.0–7.0 4.0–9.8 Ent. A. 5.3–6.8
others 6–7
4.8–9.0NaCl 0.5–4.0% 0–20% 0.5% 0–20%
Water activity 0.98– 4 0.99 0.83– 4 0.99 4 0.99 0.86– 4 0.99
Atmosphere Aerobic Aerobic-
Anaerobic
5–20% DO 2 Aerobic-
Anaerobic
Eh 4 þ200mV o–200 to
4 þ200mV
4 þ200mV?Chapter 7 253