Chemical control

Microbial control part 2

Lani Manahan January 27,2012

Chemical Agents

1. PHENOLICS

2. ALCOHOLS

3. HALOGENS

4. HEAVY METALS

5. QUATERNARY

AMMONIUM

COMPOUNDS

6. ALDEHYDES

7. STERILIZING GASES

Chemical Agents

Chemical agent Effectiveness against

Endospores Mycobacteria

Phenolics Poor Good

Quats None None

Chlorines Fair Fair

Alcohols Poor Good

Glutaraldehyde Fair Good

PHENOLICS

• First widely used antiseptic and disinfectant

• Joseph Lister (1867): reduced the risk of infection during

operations

• Act by denaturing proteins and disrupting cell membranes

• Phenol / Phenolics: Lysol

• Bisphenols: Hexachlorophene, Triclosan

PHENOLICS

• ADVANTAGES: effective in the presence of organic material

and remain active on surfaces long after application

• DISADVANTAGE: disagreeable odor and can cause skin

irritation and in some instances brain damage

(hexachlorophene)

PHENOLICS

• Ethanol, Isopropanol (70-80% concentration)

• Act by denaturing

proteins and possibly by

dissolving membrane

lipids

• 10-15 soaking in alcohol

is sufficient to disinfect

thermometers and small

instruments

ALCOHOLS

• Iodine

– Kills by oxidizing cell constituents and iodinating cell

proteins

– Kill spores at high concentrations

– DISADVANTAGE: a stain may be left (answer = iodophor)

• Chlorine

– Usually for water supply

– Kills by oxidation of cellular materials and destruction of

vegetative bacteria, fungi

– Will not kill spores

– Death within 30 minutes

HALOGENS

• Mercury, Arsenic, Zinc, Copper

• Used as germicides

• How do they Kill:

– Heavy metals combine with proteins, often with their

sulfhydryl groups and inactivate them

– May also precipitate cell proteins

HEAVY METALS

• DETERGENTS

– Amphipathic (both polar and non-polar ends)

– Kill by disrupting microbial membranes and denature

proteins

– ADVANTAGE: stable, non-toxic

– DISADVANTAGE: inactivated by hard water

QUATERNARY AMMONIUM COMPOUNDS

Soap Degerming

Acid-anionic

detergents Sanitizing

Quaternary ammonium compounds Cationic detergents

Bactericidal, Denature proteins, disrupt plasma membrane

• FORMALDEHYDES

– Very reactive molecules that combine with proteins and

inactivate them

– Sporicidal and can be used as sterilants

ALDEHYDES

PHENOL COEFFICIENT TEST

– Best-known disinfectant screening test

– Potency of a disinfectant is compared with that of phenol

– The highest dilution that killed bacteria after a 10 minutes

exposure are used to calculate phenol coefficient

– The higher the phenol coefficient value, the more effective

the disinfectant under this conditions

• The reciprocal of the appropriate test disinfectant dilution is

divided by that for phenol to obtain the coefficient

• Example: phenol dilution = 1/90 and the maximum effective

dilution for disinfectant X = 1/450

• Phenol coefficient = 5

EVALUATION OF ANTIMICROBIAL AGENT EFFECTIVENESS

THE USE DILUTION TEST

– Metal rings dipped in test bacteria are dried

– Dried cultures placed in disinfectant for 10 min at 20°C

– Rings transferred to culture media to determine whether

bacteria survived treatment

EVALUATION OF ANTIMICROBIAL AGENT EFFECTIVENESS

EVALUATION OF ANTIMICROBIAL AGENT EFFECTIVENESS

• Disk diffusion

Chemotherapy

Chemotherapeutic agent:

Antibiotic

• An antibiotic is a product produced by a microorganism or a

similar substance produced wholly or partially by chemical

synthesis, which in low concentrations, inhibits the growth of

other microorganisms

– Antibiotics are medicines used to treat infections caused by

bacteria only

– Infections are usually caused by bacteria or viruses

– Antibiotics, therefore, do not cure all infections

– Many infections like the common cold, flu, mild sore throat

or diarrhea are caused by viruses

ANTIBIOTICS

Susceptibility Tests

1. Broth dilution - MIC test

2. Agar dilution - MIC test

ANTIBIOTICS

32 ug/ml 16 ug/ml 8 ug/ml 4 ug/ml 2 ug/ml 1 ug/ml

Sub-culture to agar medium

MIC = 16 ug/ml

Minimal Inhibitory Concentration (MIC)

ANTIBIOTICS

Susceptibility Tests

3. Agar diffusion

Kirby-Bauer Disk Diffusion Test

ANTIBIOTICS

Susceptibility Tests “Kirby-Bauer Disk-plate test” Diffusion depends upon:

1. Concentration

2. Molecular weight

3. Water solubility

4. pH and ionization

5. Binding to agar

(cont’d)

ANTIBIOTICS

Susceptibility Tests “Kirby-Bauer Disk-plate test”

Zones of Inhibition (~ antimicrobial activity) depend upon:

1. pH of environment

2. Media components

– Agar depth, nutrients

3. Stability of drug

4. Size of inoculum

5. Length of incubation

6. Metabolic activity of organisms

(cont’d)

ANTIBIOTICS

Antibiotic Mechanisms of Action

Transcription

Translation

Translation

Alteration of Cell

Membrane

Polymyxins

Bacitracin

Neomycin

• When bacteria are exposed to an antibiotic, they either

die or adapt

• Those that survive carry genes that protect them

against the antibiotic and pass those genes on to other

bacteria

• Since bacteria multiply very quickly and can be easily

spread among people, resistant bacteria can easily

occur in places like hospitals and nursing homes, where

a lot of people are gathered and antibiotic use is high

ANTIBIOTICS

New Resistant Bacteria

Emergence of Antimicrobial Resistance

Susceptible Bacteria

Resistant Bacteria

Resistance Gene Transfer

Resistant Strains

Rare

Resistant Strains

Dominant

Antimicrobial

Exposure

Selection for Antimicrobial-

Resistant Strains

Resistance

Physiological Mechanisms

1. Lack of entry – tet, fosfomycin

2. Greater exit

– efflux pumps

– tet (R factors)

3. Enzymatic inactivation

– bla (penase) – hydrolysis

– CAT – chloramphenicol acetyl transferase

– Aminogylcosides & transferases

4. Altered target

– RIF – altered RNA polymerase (mutants)

– NAL – altered DNA gyrase

– STR – altered ribosomal proteins

– ERY – methylation of 23S rRNA

5. Synthesis of resistant pathway

– TMPr plasmid has gene for DHF reductase; insensitive to TMP

Resistance to β-Lactams – Gram pos.

Mechanism of Action CELL WALL SYNTHESIS INHIBITORS

(cont’d)

Resistance to β-Lactams – Gram neg.

Mechanism of Action CELL WALL SYNTHESIS INHIBITORS

(cont’d)

Danger of spread of antibiotic resistant bacteria

Danger of spread of antibiotic resistant bacteria

• Antibiotics revolutionised medicine

• The first antibiotic, penicillin, was discovered by Alexander

Fleming in 1929

• It took less than 20 years for, bacteria to show signs of

resistance

• Staphylococcus aureus, which causes blood poisoning and

pneumonia, started to show resistance in the 1950s

• Today there are different strains of S. aureus resistant to

every form of antibiotic in use (MRSA)

Danger of spread of antibiotic resistant bacteria

Where do we get antibiotic resistant bacteria

• If a patient taking a course of antibiotic treatment does not

complete it

• Or forgets to take the doses regularly, then resistant strains

get a chance to build up

• When antibiotics are used on a person, the numbers of

antibiotic resistant bacteria increase in other members of the

family

• In places where antibiotics are used extensively

e.g. hospitals and farms

antibiotic resistant strains increase in numbers

0

10

20

30

40

50

60

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

Perc

en

t R

esis

tan

ce

Methicillin (oxacillin)-resistant

Staphylococcus aureus

0

5

10

15

20

25

30

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

Perc

en

t R

esis

tan

ce

Vancomycin-resistant

enterococci

Non-Intensive Care Unit Patients

Intensive Care Unit Patients

Antimicrobial Resistance Among Pathogens Causing

Hospital-Acquired Infections

Source: National Nosocomial Infections Surveillance (NNIS) System

0

2

4

6

8

10

12

14

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

Perc

en

t R

esis

tan

ce

3rd generation cephalosporin-

resistant Klebsiella pneumoniae

0

5

10

15

20

25

30

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

Perc

en

t R

esis

tan

ce

Fluoroquinolone-resistant

Pseudomonas aeruginosa

Non-Intensive Care Unit Patients

Intensive Care Unit Patients

Antimicrobial Resistance Among Pathogens Causing

Hospital-Acquired Infections

Source: National Nosocomial Infections Surveillance (NNIS) System

Link to: NNIS Online at CDC

Myths & Facts about Antibiotics and Respiratory Illness

Myths and Facts

• Myth: Taking antibiotics means I or my child

can return to work or childcare sooner

• Fact: Antibiotics do not shorten the duration

of viral illnesses

Everyone should stay home until they are

fever-free and well enough to participate in

activities whether they have a viral or

bacterial illness.

Myths and Facts

• Myth: Cold and flu symptoms will feel better

or get better faster on antibiotics

• Fact: Antibiotics cannot ease the symptoms

of viral illnesses; these infections resolve on

their own

Children and adults need extra rest and care,

extra fluids…not antibiotics, symptomatic

relief is helpful

Myths and Facts

• Myth: Illnesses with the same symptoms

require antibiotics

• Fact: Illnesses with similar symptoms can be

caused by different germs

Let a healthcare provider decide if the illness is

caused by a virus or bacteria - and if antibiotics

are needed

Myths and Facts

• Myth: If I take an antibiotic, I won’t spread my

illness to others

• Fact: Viral illnesses (colds, flu, etc.) usually

spread from person to person before the onset

of symptoms; before a person appears ill

Antibiotics cannot stop the spread of viral

illnesses

How do we Stop Antibiotic Misuse?

• Don’t ask for antibiotics – let your doctor

decide if you need them

• Always take antibiotics exactly as prescribed

• Finish the whole prescription - do not stop

when you feel better

• Never save antibiotics for a future illness –

or share with others

ANTIMICROBIAL RESISTANCE: KEY PREVENTION STRATEGIES

Optimize Use

Prevent

Transmission

Prevent

Infection

Effective

Diagnosis

and

Treatment

Pathogen Antimicrobial-Resistant Pathogen

Antimicrobial

Resistance

Antimicrobial Use

Infection

Susceptible Pathogen

12 Steps to Prevent Antimicrobial Resistance: Hospitalized Adults

1. Vaccinate

2. Get the catheters out

3. Target the pathogen

4. Access the experts

5. Practice antimicrobial control 6. Use local data 7. Treat infection, not

contamination 8. Treat infection, not colonization 9. Know when to say “no” to vanco 10. Stop treatment when infection

is cured or unlikely 11. Isolate the pathogen 12. Contain the contagion

Diagnose and Treat

Infection Effectively

Prevent Infection

Use Antimicrobials Wisely

Prevent Transmission