Control of microbial growth Environment and human body
Public health standards Health care facilities Laboratories Home
Terminology of Microbial Control
Sepsis refers to microbial contamination Asepsis/Aseptic is an environment or procedure free of
contamination – specifically, absence of pathogens Aseptic surgery techniques prevent microbial
contamination of wounds
Degerming is the mechanical removal of microbes by
scrubbing/swabbing A nurse prepares an area of skin for an injection
Sterilization is the removal and destruction of all microbes Commercial sterilization
Killing Clostridium botulinum endospores
Disinfection is the use of chemicals or physical agents to kill or inhibit the growth of microbes, specifically pathogens Disinfectants are used to treat inanimate objects or surfaces
Antisepsis is the use of chemicals on skin or other tissue The chemicals used are called antiseptics
Terminology of Microbial Control
Terminology of Microbial Control
Sanitization Disinfection of places or things used by the public to
meet accepted public health standards
Pasteurization Heat is applied to
Kill pathogens Reduce the number of microorganisms that can
cause spoilage of food and beverages
Methods For Controlling Microbial Growth
There are three major methods for controlling microbial growth Physical Mechanical Chemical
Achieved with steam under
pressure (autoclave)
A temperature of 121C (15psi
of pressure) will kill all microbes and their endospores in 15 min Not prions
Time must be adjusted
according to the type of material properly placed in the autoclave
Sterilization requires T above that of boiling water
Physical Methods to Control Microbial Growth
Pasteurization
Process Treatment (Milk)
Historical pasteurization 63C for 30 minutes
High temperature short time (HTST) - pasteurization 72C for 15 seconds
Ultra high temperature (UHT) - pasteurization 135C for 1 second
Pasteurization Kills pathogens Lowers total bacterial counts
Heat resistant bacteria survive pasteurization
Unlikely to cause disease or refrigerated products to spoil
Physical Methods to Control Microbial Growth
Ionizing radiation X rays and Gamma rays
Cause damages to DNA (Mutations)
Nonionizing radiation UV, 260 nm
Cause damages to DNA (Thymine dimers)
Physical Methods to Control Microbial Growth
Non-irradiated and Irradiated food with low-level ionizing radiations
Ionizing radiation is used to sterilize pharmaceuticals plastic syringes surgical gloves catheters
UV lamps are commonly found in hospital rooms, nurseries, operating rooms (tables) or microbial laboratories (safety cabinets)
Filtration To sterilize heat-sensitive
materials
Culture media, drugs, vitamins, enzymes, antibiotic solutions or vaccines
Mechanical Methods For Controlling Microbial Growth
An ideal antimicrobial agent!!
Antimicrobial agents should be
Inexpensive
Fast-acting
Stable during storage (chemicals)
Control growth and reproduction of every type of microbe
Harmless to humans, animals, and objects
However, every antimicrobial agent has limitations, advantages and disadvantages
Terminology of Microbial Control
-stasis/-static: inhibits microbial metabolism and growth but does not kill microbes
-cide/-cidal: destroys or permanently inactivates (kill) microbes
- stasis/static - cide/-cidal
Bacteriostatic Bactericide
Fungistatic Fungicide
Virustatic Virucide
Germicides: antimicrobial agents that kill microbes including pathogens
Microbial death - permanent loss of reproductive capability is the accepted definition of microbial death
Effectiveness of antimicrobial chemical agents depends on Numbers of microbial cells Exposure time – accessibility* and type of microbe**) Concentration of the antimicrobial agent Temperature and pH
*Environment Many pathogens are associated with organic
materials Blood, saliva, vomit, or fecal material
Can interfere or inhibit accessibility of the antimicrobial agent
Factors that affect choice and effectiveness of antimicrobial agents
Factors that affect choice and effectiveness of antimicrobial agents
At least three factors must be considered
Site to be treated
**Susceptibility of microorganisms involved
Environmental conditions (contaminating organic materials, T/pH)
Evaluate effectiveness of antimicrobial chemical agents
Several methods are used including Phenol coefficient (phenol was used as an antiseptic by J. Lister
in 1867) Disk-diffusion method
Iodine (Halogens)
Tinctures: solution of antimicrobial agent in alcohol Iodophors: organic compound (containing iodine) that slowly
releases it
Betadine (Iodophor)
Antiseptic used in preparation for surgery on a hand
Pure alcohol is not an effective antimicrobial agent
Requires water to denature proteins Isopropanol Ethanol
Alcohols
Disk-diffusion test with Zephiran (quat) against Mycobacterium
Effect of concentration of the antimicrobial
Another example of quat is Cepacol (mouthwash)
Heavy Metals are bacteriostatic and fungistatic agents
Silver, mercury, copper, zinc, and arsenic
Oligodynamic action Denature proteins
Silver sulfadiazine is used
as a topical cream on burns
Silver nitrate was used to prevent blindness caused by Neisseria gonorrhoeae in newborns
The simple act of washing your hands can inhibit the spread of pathogens in health care facilities (i.e., hospitals!!!)
The effectiveness of hand washing depends on: Type of soap used Time taken
Hospitals use germicidal soaps because they are very
effective at preventing transmission of pathogen associated with nosocomial infections
Household soaps can be effective if enough time is taken
to wash your hands thoroughly
HAND WASHING
Introduction to antimicrobial drugs
Spectrum of action Narrow-spectrum versus broad-spectrum antimicrobials
Selective toxicity of antimicrobials Targeting the pathogen and not the host cells!!!
Antibiotics
Antibiotic: a substance produced by certain microorganisms that in small amount inhibits the growth of another microorganism
Administration of antibiotics and side effects
External infections Topical or local administration
Internal infections
Oral Intramuscular (IM) – hypodermic needle Intravenous (IV) – needle or catheter
Factors to keep into consideration include
Allergies Dosage and toxicity Disruption of the normal microbiota
Natural and semisynthetic penicillins
Chemical modification of the side group of the b-lactam ring can change Susceptibility of the
antibiotic to enzymes called b-lactamases
Spectrum of activity of
the antibiotic
Resistance to antibiotics
MRSA (Methicillin resistant Staphylococcus aureus)
Health care-associated MRSA
Community-associated MRSA
The widespread use of vancomycin to treat S. aureus infections
has led to the appearance of
VRE (Vancomycin resistant enterococci) Opportunistic Gram positive pathogens
Cause problems particularly in hospital settings
Strains of S. aureus have become resistant to vancomycin
(VISA/VRSA) as well!!
MDR-TB and XDR-TB (Mycobacterium tuberculosis)
Resistance to antibiotics Bacteria become
resistant to antibiotics through
mutations or genetic exchange
Resistance to antibiotics
The therapeutic life span of a drug is based on how quickly resistance develops Important factors that contribute to resistance Overuse of antibiotics (the more an antibiotic is used, the
more quickly resistance occurs) Patients should always complete the full regimen of their
antibiotic prescription
Resistance to antibiotics
The therapeutic life span of a drug is based on how quickly resistance develops Important factors that contribute to resistance Hospitals and nursing homes (multiple resistance and cross
resistance)
Broad-spectrum antimicrobials increase the chance that the antibiotic will cause resistance among the patient’s normal flora
Testing for susceptibility to antibiotics
To treat infectious diseases, physicians must know which antibiotic
is most effective against a given pathogen
Kirby-Bauer Test (disk-diffusion method)
Compares the relative
effectiveness of different
antibiotics
Based on the size of the
inhibition zones, organisms
are classified as:
Susceptible
Intermediate
Resistant
Synergism or antagonism
Synergism occurs
when the effect of
two drugs together
is greater than the
effect of either
alone
Antagonism
occurs when the
effect of two drugs
together is less than
the effect of either
alone
The combination has a broader
spectrum of action and reduces the
emergence of resistant strains
Testing for susceptibility to antibiotics
The E test is a more advanced diffusion method and it allows to calculate the minimum inhibitory concentration (MIC)
The plastic-coated strip contains an increasing concentration gradient of the antibiotic. The MIC can be read from the scale printed on each strip