Control of Microbial Growth Flashcards
Bactericide
substance capable of killing bacteria
Bacteriostatic
inhibits bacterial growth
Name four factors that affect microbial death rate:
Number of microbes
Environmental influences
Time of exposure
Microbial characteristics
Describe the ways in which microbial cell damage can occur and the distinguishing features of each mechanism:
Alteration of Membrane permeability - damage to lipids/proteins of p.m. by antimicrobial agents causes cellular contents to leak into medium & interferes with cell growth (lysis)
Damage to proteins & nucleic acids - denaturation - prevention of replication & normal metabolic functions
Used to control surgical infections in operating room & also throat losenges (carbolic acid)
Phenols
Contain molecule of phenol chemically altered to reduce irritating qualities. Usually in combination with soap.
Phenolics
Affect cell membranes; broad spectrum; G+ effective, some G- except pseudomoants, sporicidals - but some activity against enveloped viruses.
Skin and mucus membranes. Surgical hand scrub, pre-op skin prep
Biguanides
Iodine, Chlorine - impair protein synthesis & alters cell membranes…
Antiseptics - works with all kinds of bacteria, many endospores, various fungi & some viruses
Halogens
Combination of iodine & organic molecule from which iodine is released slowly - less antimicrobial activity, but do not stain and less irritating. (Betadine)
Iodophores
Kill bacteria & fungi but not endospores or non-enveloped viruses; protein nature denaturation.
Alcohols
biocidal or antiseptic - oligodynamic action
Heavy metals
Cationic detergents; most widely used as surface-active agents; fungicidal, amoebicidal, virucidal (enveloped), but not endospores or mycobacteriua.
Quaternary ammonium compounds
Solution in aqueous alcohol; alcohol helps get other things into the cell
Tincture
Which microorganisms are most resistant to biocides?
Prions, endospores, mycobacteria, protozoa, G-, fungi…
Which microorganisms are least resistant to biocides?
non-enveloped viruses, G+, viruses with lipid envelopes
Antiseptic
destruction of vegetative pathogens on living tissues
Disinfectant
destruction of vegetative pathogens on non-living surfaces
Sterilization
Destruction or removal of all forms of microbial life including endospores with possible exception of prions
Degerming
removal of microbes from limited area, such as skin or around injection site
Sepsis
bacterial contamination
Asepsis
absence of significant contamination
Moist Heat
Boiling/flowing steam or autoclaving - leads to protein denaturation
Pasteurization
heat treatment for milk - denaturation
Dry heat
direct flaming/incineration/hot air sterilization - sterilization - kills by oxidation
Filtration
separation of bacteria from suspending liquid - physical separation
Cold
Refrigeration, deep-freezing, lyophilization - decrease chemical reactions and possible changes in proteins (slows growth)
Osmotic pressure
plasmolysis - hypertonic conditions
Radiation
ionizing vs. nonionizing
Name four factors that affect chemical control of microorganisms
Manufacturer instructions
Nature of material being disinfected
pH of medium
Contact with microbes
