Chapter 7: The Control of Microbial Growth
Hydroxyl radicals
most reactive of the toxic forms of oxygen cause DNA damage
Iodine
stains, irritating,
Answer: E Iodophors
7) Iodophors differ from iodine (I2) in that iodophors A) Don't stain. B) Are less irritating. C) Are longer lasting. D) Are combined with a nonionic detergent. E) All of the above.
Answer: C) c
Assume that one culture is a freshly opened package of dried yeast with 0.1% moisture, another culture is the same yeast with 7.5% moisture, and the third culture is a package of yeast mixed with water. Each culture was exposed to 130°C in a hot-air oven. Which graph in Figure 7.1 most likely shows the yeast with 0.1% moisture? A) a B) b C) c D) a and b E) b and c
surfactants
A contraction of surface active agents; substances that allow oil and water to mix, or emulsify.
Answer: E
A suspension of 106 Bacillus cereus endospores was put in a hot-air oven at 170°C. Plate counts were used to determine the number of endospores surviving at the time intervals shown. 23) In Figure 7.2, the thermal death point for this culture is A) 15 min. B) 50°C. C) 30 min. D) 170°C. E) Can't tell from the data provided.
Iodophors
Complex of iodine and alcohol Have replaced free iodine solutions in medical antisepsis
Ethanol
Bactericide. Alcohol made by converting starches and sugars from plant material into alcohol and CO2.
Answer: E) Pressure cooker at 121°C for 15 minutes
If you were preparing nutrient agar at home and didn't have an autoclave, what could you use to sterilize the nutrient agar? A) Bleach B) Boiling for 1 hour C) Hydrogen peroxide D) Oven at 121°C for 1 hour E) Pressure cooker at 121°C for 15 minutes
Answer: B 60 min
In Figure 7.1, what is the thermal death time for culture (a)? A) 150°C B) 60 min. C) 120 min. D) 100°C E) Can't tell
Answer: B 15 min.
In Figure 7.2, the decimal reduction time (D value) for the culture is approximately A) 0 min. B) 15 min. C) 30 min. D) 45 min. E) 60 min.
Answer: E
In Figure 7.2, the thermal death time for this culture is A) 0 min. B) 10 min. C) 20 min. D) 40 min. E) 60 min.
Ag
Silver helps with burns
Answer: E
Table 7.1 A disk-diffusion test using Staphylococcus gave the following results: Disinfectant Zone of inhibition (mm) A 0 B 2.5 C 10 D 5 In Table 7.1, which compound was the most effective against E. coli? A) A B) B C) C D) D E) Can't tell
Answer: B Sodium Benzoate
Table 7.2 The fate of E. coli O157:H7 in apple cider held at 8°C for 2 weeks, with and without preservatives, is shown below: Bacteria/ml Cider only 2.2 Cider with potassium sorbate 2.0 Sodium benzoate 0 Sorbate + benzoate 0 32) In Table 7.2, which preservative is most effective? A) Sorbate B) Sodium Benzoate C) Sorbate + benzoate D) No preservative
Answer: A. Doom
Table 7.3 The following data were obtained by incubating gram-positive bacteria in nutrient medium + disinfectant for 24 hr, then transferring one loopful to nutrient medium (subculturing). (+ = growth; - = no growth) Doom K.O. Dilution Initial Subculture Initial Subculture 1:16 - + + + 1:32 - + + + 1:64 - + + + 1:128 + + + + Mortum Sterl Dilution Initial Subculture Initial Subculture 1:16 - - - + 1:32 - + + + 1:64 + + + + 1:128 + + + + 36) In Table 7.3, which disinfectant is the most effective at stopping bacterial growth? A) Doom B) K.O. C) Mortum D) Sterl E) Can't tell
Answer: C
Table 7.3 The following data were obtained by incubating gram-positive bacteria in nutrient medium + disinfectant for 24 hr, then transferring one loopful to nutrient medium (subculturing). (+ = growth; - = no growth) Doom K.O. Dilution Initial Subculture Initial Subculture 1:16 - + + + 1:32 - + + + 1:64 - + + + 1:128 + + + + Mortum Sterl Dilution Initial Subculture Initial Subculture 1:16 - - - + 1:32 - + + + 1:64 + + + + 1:128 + + + + In Table 7.3, which disinfectant was bactericidal? A) Doom B) K.O. C) Mortum D) Sterl E) Can't tell
Answer: B Glutaraldehyde
Which of the following substances is NOT an oxidizing agent? A) Chlorine B) Glutaraldehyde C) Hydrogen peroxide D) Iodine E) Ozone
Answer: A Alcohol
Which of the following substances is NOT effective against nonenveloped viruses? A) Alcohol B) Chlorine C) Ethylene oxide D) Ozone E) All are equally effective.
Answer: A) Biguanides
Which of the following substances is NOT used to preserve foods? A) Biguanides B) Nisin C) Potassium sorbate D) Sodium nitrite E) Sodium propionate
Answer: C Chlorhexidine
Which of the following substances is used for surgical hand scrubs? A) Phenol B) Chlorine bleach C) Chlorhexidine D) Soap E) Glutaraldehyde
Answer: D They are equivalent treatments.
Which of the following treatments is the most effective for controlling microbial growth? A) 63°C for 30 min. B) 72°C for 15 sec. C) 140°C for 4 sec. D) They are equivalent treatments. E) None is effective.
Answer: A) Boiling
Which of the following will NOT destroy prions? A) Boiling B) Incineration C) NaOH + autoclaving at 134°C D) Proteases E) All of the above destroy prions.
Answer: C) High pressure
Which of the following will NOT inactivate endospores? A) Autoclave B) Chlorine dioxide C) High pressure D) Plasma E) Supercritical CO2
Answer: D
Which of the following will NOT preserve foods? A) Desiccation B) High pressure C) Ionizing radiation D) Microwaves E) Osmotic pressure
Answer: C Bisphenols
Which of these disinfectants acts by denaturing proteins? A) Alcohols B) Aldehydes C) Bisphenols D) Halogens E) Phenolics
Answer: A -Acid-anionic detergents
Which one of the following does NOT belong with the others? A) Acid-anionic detergents B) Benzoic acid C) Supercritical CO2 D) Pasteurization E) Peracetic acid
Answer: D Hydrogen peroxide
Which one of the following does NOT belong with the others? A) Beta-propiolactone B) Glutaraldehyde C) Ethylene oxide D) Hydrogen peroxide E) Propylene oxide
Answer: C) Mycobacteria
Which one of the following is most resistant to chemical biocides? A) Gram-negative bacteria B) Gram-positive bacteria C) Mycobacteria D) Protozoan cysts E) Viruses with lipid envelopes
Answer: E) Ultraviolet radiation - desiccation
Which one of the following pairs is mismatched? A) Ionizing radiation - hydroxyl radicals B) Ozone - takes electrons from substances C) Plasma sterilization - free radicals D) Supercritical fluids - CO2 E) Ultraviolet radiation - desiccation
Heat-labile solutions
are typically sterilized by filtration.
Prions
infectious protein particles that do not have a genome
ionizing radiation
radiation with enough energy to knock electrons off some atoms of a bombarded substance to produce ions
Thermal death time (TDT)
shortest length of time required to kill all test microbes at a specified temperature
Mycobacterium tuberculosis
tuberculosis
hypochlorous acid (HOCl)
bleach The antimicrobial activity of chlorine is due to
desiccation
dehydration; the process of being rendered free from moisture
gamma radiation
High-energy radiation emitted by the nuclei of radioactive atoms.
Answer: C Ethylene oxide
Which of the following substances can sterilize? A) Alcohol B) Phenolics C) Ethylene oxide D) Chlorine E) Soap
organic acids/carboxylic acids
- food preservation R--COOH (carboxyl group), prepared by mild oxidation of aldehydes, simpliest is methanoic acid (in ants, bees, etc), add -oic to alkane stem
Mycobacteria
Acid Fast; fever, night sweats, wt loss, hemoptysis M. tuberculosis: TB, M. kansasii: TB-like sx M. avium-intracellulare: AIDS prophyl: Azithromycin
Glutaraldehyde (Cidex)
Antiseptic and Germicidal and disinfectant for hospitals. Its safe, acts quickly, attacks all mirobes, not hampered by organic materials
Answer: E) Supercritical fluids.
Bone and tendons for transplant are decontaminated by A) Ethylene oxide. B) Glutaraldehyde. C) Peroxygens. D) Plasma sterilization. E) Supercritical fluids.
Bisphenols
Denaturate protiens, disrupt plasma membranes, Hexacholorphene, triclosan
Ultraviolet Radiation (UV)
Electromagnetic waves between visible light and X-rays in the electromagnetic spectrum.
Answer: B
Figure 7.3 Assume 109 E. coli cells/ml are in a flask. Which graph in Figure 7.3 best depicts the effect of placing the culture in an autoclave for 15 min. at time x? A) a B) b C) c D) d E) e
Answer: A Stains and corrodes
Glutaraldehyde is considered one of the most effective disinfectants for hospital use. Which of the following statements about glutaraldehyde is false? A) Stains and corrodes B) Is safe to transport C) Acts rapidly D) Is not hampered by organic material E) Attacks all microorganisms
Membrane filtration
Liquid media containing heat-sensitive components would best be sterilized by
Quats (Quaternary Ammonium Compounds)
Low-Level disinfectant. Cationic, incompatible with soap. denatures essential cell protein, and disrupts cell membranes. Environmental sanitation of non-critical surfaces such as floors, walls, & furniture. Not the disinfectant of choice for use in central service.
H2O2 (hydrogen peroxide)
Organic Peroxides are great for open wounds
Autoclave
Piece of equipment used to sterilize articles by way of steam under pressure and/or dry heat.
Answer: D 3, 2, 1
Place the following surfactants in order from the most effective to the least effective antimicrobial activity: 1-Soap; 2-Acid-anionic detergent; 3-Quats. A) 1, 2, 3 B) 1, 3, 2 C) 2, 1, 3 D) 3, 2, 1 E) 3, 1, 2
Answer: E
Table 7.1 A disk-diffusion test using Staphylococcus gave the following results: Disinfectant Zone of inhibition (mm) A 0 B 2.5 C 10 D 5 29) In Table 7.1, which compound was the most effective against Staphylococcus? A) A B) B C) C D) D E) Can't tell
Answer: E
Table 7.1 A disk-diffusion test using Staphylococcus gave the following results: Disinfectant Zone of inhibition (mm) A 0 B 2.5 C 10 D 5 In Table 7.1, which compound was bactericidal? A) A B) B C) C D) D E) Can't tell
Answer: E. Can't tell
Table 7.3 The following data were obtained by incubating gram-positive bacteria in nutrient medium + disinfectant for 24 hr, then transferring one loopful to nutrient medium (subculturing). (+ = growth; - = no growth) Doom K.O. Dilution Initial Subculture Initial Subculture 1:16 - + + + 1:32 - + + + 1:64 - + + + 1:128 + + + + Mortum Sterl Dilution Initial Subculture Initial Subculture 1:16 - - - + 1:32 - + + + 1:64 + + + + 1:128 + + + + In Table 7.3, which disinfectant was most effective against Salmonella? A) Doom B) K.O. C) Mortum D) Sterl E) Can't tell
Answer: A The formation of hypochlorous acid
The antimicrobial activity of chlorine is due to which of the following? A) The formation of hypochlorous acid B) The formation of hydrochloric acid C) The formation of ozone D) The formation of free O E) Disruption of the plasma membrane
Chlorine dioxide
Used for water treatment Used to disinfect endospores -Congress after the anthrax attacks in 2001
Answer: B 70%
Which concentration of ethanol is the most effective bactericide? A) 100% B) 70% C) 50% D) 40% E) 30%
Answer: D
Which graph in Figure 7.3 best depicts the effect of placing the culture at 7°C at time x? A) a B) b C) c D) d E) e
Answer: E All of the above
Which of the following affects the elimination of bacteria from an object? A) Number of bacteria present B) Temperature C) pH D) Presence of organic matter E) All of the above
Answer: A The cells in a population die at a constant rate.
Which of the following best describes the pattern of microbial death? A) The cells in a population die at a constant rate. B) All the cells in a culture die at once. C) Not all of the cells in a culture are killed. D) The pattern varies depending on the antimicrobial agent. E) The pattern varies depending on the species.
Answer: B Gamma radiation
Which of the following could be used to sterilize plastic Petri plates in a plastic wrapper? A) Autoclave B) Gamma radiation C) Microwaves D) Sunlight E) Ultraviolet radiation
Answer: B Pasteurization
Which of the following does NOT achieve sterilization? A) Dry heat B) Pasteurization C) Autoclave D) Formaldehyde E) Ethylene oxide
Answer: D Cell lysis
Which of the following does NOT directly result from application of heat? A) Breaking of hydrogen bonds B) Breaking of sulfhydryl bonds C) Denaturing of enzymes D) Cell lysis E) Damage to nucleic acids
Answer: E
Which of the following is NOT a factor contributing to hospital-acquired infections? A) Some bacteria metabolize disinfectants. B) Gram-negative bacteria are often resistant to disinfectants. C) Invasive procedures can provide a portal of entry for bacteria. D) Bacteria may be present in commercial products such as mouthwash. E) All of the above may contribute to hospital-acquired infection.
Answer: E Heat
Which of the following is NOT used to disinfect water? A) Ozone B) Gamma radiation C) Chlorine D) Copper sulfate E) Heat
Answer: D Cannot be used with heat-labile materials
Which of the following is a limitation of the autoclave? A) Requires a long time to achieve sterilization B) Cannot inactivate viruses C) Cannot kill endospores D) Cannot be used with heat-labile materials E) Cannot be used with glassware
Answer: C Membrane filtration
Which of the following is the best method to sterilize heat-labile solutions? A) Dry heat B) Autoclave C) Membrane filtration D) Pasteurization E) Freezing
Answer: B Alcohols - open wounds
Which of the following pairs is mismatched? A) Ag - burns B) Alcohols - open wounds C) CuSO4 - algicide D) H2O2 - open wounds E) Organic acids - food preservation
nutrient agar
a general "catch-all" agar that will grow anything
nonenveloped viruses
consist only of the nucleic acid and capsid
CuSO4
copper sulfate algicide
Proteases
enzymes that break down proteins but now prions
algicide
killer of algae
Mycobacterium leprae
leprosy (Hansen's disease)
Decimal Reduction Time (DRT)
the time, in minutes, in which 90% of a population of bacteria at a given temperature will be killed
Acid-anionic detergents
used to clean dairy equipment