BackMicrobial Growth and Control in Microbiology
08:59
Terms in this set (28)
Microbial growth is an increase in the number of cells, not just cell size, through cell division producing daughter cells.
Binary fission is an asexual process in most prokaryotes where a single cell divides into two genetically identical cells.
Budding is asexual reproduction where a cell elongates and forms a smaller outgrowth (bud) that separates, seen in some fungi and bacteria.
Biofilms form when planktonic bacteria adhere to surfaces, produce a polysaccharide matrix, and develop a mixed microbial community with nutrient channels.
Generation time is the time it takes for a microbial population to double by cell division, varying by species and conditions.
1) Lag phase: adjustment, no growth
2) Log phase: exponential growth
3) Stationary phase: growth rate equals death rate
4) Death phase: exponential cell death
A chemostat maintains constant bacterial growth by continuously adding fresh medium and removing waste and excess cells.
Psychrophiles thrive at −20°C to 10°C; psychrotrophs grow at 0–30°C and are linked to foodborne illness.
Mesophiles grow best at 10°–50°C and include most human pathogens.
Acidophiles grow below pH 5; alkaliphiles grow in pH 9–11 environments.
Halophiles require high salt (up to 35% NaCl); facultative halophiles tolerate high salt but may not grow well.
Obligate aerobes require oxygen; obligate anaerobes cannot grow in oxygen and may die from exposure.
Superoxide dismutase converts superoxide ions to hydrogen peroxide; catalase converts hydrogen peroxide to water and oxygen.
Growth factors are essential substances a microbe cannot synthesize and must obtain from the environment.
Defined media have known chemical compositions; complex media contain undefined ingredients like extracts and support fastidious organisms.
Selective media encourage growth of certain bacteria while suppressing others, e.g., Mannitol Salt Agar (MSA).
Differential media allow visual distinction of microbes based on metabolic traits, e.g., Blood Agar showing hemolysis types.
Samples are serially diluted and plated; colonies formed are counted to estimate living cell numbers as colony-forming units (CFU).
Sterilization eliminates all microbes including endospores, required for medical instruments and lab media.
An autoclave uses steam heat at 121°C and 15 psi pressure for at least 15 minutes to sterilize.
Pasteurization applies moderate heat below boiling to kill pathogens and reduce spoilage microbes, e.g., 72°C for 15 seconds (HTST method).
Alcohol denatures proteins and disrupts cell membranes, killing many microbes.
Bactericidal agents kill bacteria; bacteriostatic agents inhibit bacterial growth.
HEPA filters remove 99.97% of airborne particles ≥0.3 micrometers, including many microbes and allergens.
Biofilms have a protective matrix, slow-growing cells, and persister cells, making them harder to kill than planktonic cells.
Ethylene oxide gas alkylates proteins and DNA, sterilizing heat-sensitive medical equipment.
Disinfection reduces microbes on inanimate objects; antisepsis reduces microbes on living tissue.
Catalase breaks down hydrogen peroxide into water and oxygen, producing bubbles; used to identify aerobic bacteria.