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

Chemical methods to control the growth of microbes on living tissue and inanimate objects

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

Cellular targets of antibiotics

Antimicrobial drugs are either bactericidal or bacteriostatic

Inhibition of synthesis of bacterial cell wall by penicillin

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

Determining the MIC using the broth dilution test

The broth dilution test allows determination of the minimum bactericidal concentration (MBC)