Microbiology Exam Study Guide
MICROBIAL NEEDS (FATTOM)
microbes have varying needs in food/nutrients required for growth
especially partial to high protein foods and known as “potentially hazardous” *Milk, meat, poultry,
fish provide moist + favorable environment]
Nitrogen from amino acids, carbon for energy, minerals and vitamins
prefer simple sugars
prefer complex carbohydrates
most bacteria we are concerned with grow on human body that grow best in pH that is neutral/biological
6.8~7.4. Extreme shifts in pH can damage cells. Most foods are slightly acidic.
Acidic Foods with pH lower than 4.6 such as limes, grapefruit, pickles, tomatoes, pineapple are not
considered favorable environments for microbial growth
Fungi (Yeasts + Molds)
prefer slightly acidic conditions grow best between pH 5~6 (normal human skin)
establish low pH of 3~4 not favorable for pathogens
Low Acid Foods
foods with pH 4.6~7 such as lettuce, celery, milk, meat, fish, egg white, corn.
Corn needs more heat since as the pH increases the foods become more heat resistant.
variety of temperatures but most have favorable between 60~110F. “Danger Zone” of microbial growth
40~140 °F. Most die after 140 °F, but not spores that can survive boiling.
32~45 °F can also grow as low as 19 °F if freeze they grow slower, but bacteria are not killed
130 °F they “love” “heat” and found in hot springs and compost heaps
varying among whether bacteria can grow with the presence of free oxygen or when O
is excluded. Most are
only can grow when supplied with free oxygen [
oxygen is toxic to these organisms, can only grow in vacuum [
Facultative - adaptable can use oxygen when present but can switch to anaerobic pathways in its absence
quantity of water contained in a material
measure of how efficiently water present can take part in a chemical/physical reaction
> 0.9 Bacteria + Yeast
< 0.9 Molds can tolerate lower water activity
fungi, made of tubular elements called hyphae, grow quickly look like tangled, fuzzy mass can be visible to the
naked eye. Some mold produce toxins that lead to foodborne illness known as mycotoxicoses, others are useful for
penicillin and ripening cheeses.
Mostly spoil foods, great adaptability