Chemical control of Microbial growth

1
Chemical control of Microbial growth

• Few agents achieve sterility
• Most reduce microbe population to a safe level or
  removes the vegetative state pathogens
• Selecting the agent to be used is based on the
  premise that no one agent is appropriate in all
  instances

2
Disinfection

• Label generally notes the organisms that it is
  effective against
• Concentration affects its action
• Ph
• Is a gradual process

3
Phenol

• Lister was the first to use phenol to control
  surgical infections in operations
• Phenol coefficient test- standard against which
  other disinfectants are rated
• Used in throat lozenges for local anesthetic
  effect but rarely used today due to its
  disagreeable odor , is skin irritant and must be
  used at concentrations higher than 1
• Phenolics- phenol derivatives contain an altered
  phenol molecule which increases its antibacterial
  activity in combination with a soap or detergent
• Remain effective in the presence of organic
  molecules
• O-phenylphenol , a cresol, is the main
  ingredient in Lysol
• Cresols are good surface disinfectants

4
Halogens

• Iodine and chlorine are effective antimicrobial
  agents either used alone or in combination with
  other compounds
• Iodine has long been used as an antiseptic
  against all bacteria, some viruses and fungi and
  some endospores
• Available as a tincture (in solution in aqueous
  alcohol)
• Available as an iodophor (a combination of iodine
  and an organic molecule from which the iodine is
  slowly released)
• Betadine and Isodine are povidone( improves
  wetting action and serves as a reservoir for free
  iodine) -iodides, used as a scrub, is not
  sporocidal, causes less skin irritation and less
  staining
• To treat water, iodine tablets can be added or
  water can be passed through iodine-treated filter

5
Halogens

• Chlorine
• As a gas or in combination with other chemicals
• Germicidal when chlorine is added to water
  forming hypochlorous acid (neutral charge that
  allows it to diffuse across cell membrane like
  water) ? hypochlorite ion
• Hypochlorous acid is the most effective form
• Strong oxidizing agent that prevents cellular
  enzyme reactions
• Municipal drinking water is disinfected using
  compressed chlorine gas
• Bleach or sodium hypochlorite (Clorox) is used as
  a household disinfectant, hemodialysis systems,
  food processing systems
• Two drops of bleach added to a liter of water can
  be used in an emergency to consider water safe
  for consumption

6
Alcohols

• Effectively kill bacteria and fungi but not
  unenveloped viruses and endospores
• Denatures proteins
• Disrupts and dissolves membranes
• Evaporate rapidly when skin is swabbed (degermed)
  before injection
• Actually, microbial effectiveness comes from
  wiping away skin oils along with dirt and
  microorganisms
• Unsatisfactory for antiseptic when applied to
  wounds (because it coagulates proteins under
  which bacteria are still able to grow)

7
Alcohols

• Ethanol and isopropyl alcohol are the two most
  commonly used, often used to enhance
  effectiveness of other chemical agents
• 70 ethanol is most recommended although
  concentrations from 60- 95 are effective (pure
  alcohol is less effective, cannot be denatured
  without water)
• Isopropyl or rubbing alcohol is slightly
  superior, cheaper, less volatile and easier
  acquisition
• Usually 70 but conc can be 40-80
• Used for needle sticks
• Spore-resistant

8
Heavy metals

• Can be antiseptic or biocidal
• Small amounts of heavy metals effect
  antimicrobial activity (oligodynamic action)
• Copper, zinc, silver and mercury
• Mercury-
• mercurochrome antiseptic, an organic mercury
  compound used at home
• Mercurial used to control mildew in paint

9
Heavy metals

• Zinc-
• Zinc chloride is used in mouthwashes
• Zinc oxide ointment as an antifungal treatment
• Silver
• 1 silver nitrate used as an antiseptic
• Formerly required by many states to prevent the
  transmission of gonorrhea to newborn infants
  (antibiotics have now replaced that)
• Silver-sulfadiazine used as a topical cream for
  burns
• Incorporated in indwelling catheters, a common
  source of hospital infections

10
Heavy metals

• Copper
• Copper sulfate commonly used to destroy green
  algae in reservoirs, swimming pools and fish
  tanks
• Used to prevent mildew in paint

11
Detergentsand Soaps

• Surface active agents or surfactants decrease
  surface tension among a liquids molecules
• Soaps and detergents
• Little value as antiseptics but rather
  mechanically remove microbes
• Soap emulsifies oily film on skin and water and
  soap lift the debris off skin
• Deodorant soaps contain triclocarban effective
  against gram bacteria
• Acid-anioic surface-active sanitizers act on a
  wide array of microbes and are important for
  cleansing dairy equipment and utensils
• Pseudomonas can grow in soap dishes

12
Detergents and soaps

• Quats (quaternary compounds) are cationic
  surfactants
• Ammonium compounds are strongly bacteriocidal
  against gram bacteria mostly
• Also fungicidal, amoebicidal and virucidal
  against enveloped viruses
• Do not kill endospores or mycobacteria
• Zephiran (benzalkonium chloride) AN D Cepacol
  (cetylpyridinium chloride) are two popular quat
  compounds
• Pseudomonas not only survives in quats but
  actively grows in them

13
Formaldehyde

• Aldehydes are effective antimicrobials
• Formaldehyde and glutaraldehyde are two examples
• Inactivate proteins by forming cross-links with
  functional groups
• Formaldehyde gas is a superior disinfectant
• Commonly available as a 37 aqueous solution of
  the gas
• Glutaraldehyde is less irritating and more
  effective
• Used in hospitals to disinfect instrumentation
  especially respiratory therapy equipment
• A 2 solution is bacteriocidal, virucidal,
  tuberculocidal in 10 minutes and sporicidal in 10
  hours
• Can be considered a sterilizing agent as well as
  a chemical disinfectant
• Both formalin and glutaraldehyde are used in the
  funeral industry for embalming

14
Peroxigens

• Oxidize cellular components
• Ozone (O3) is used to supplement chlorine in
  water disinfection
• Hydrogen peroxide and peracetic acid are most
  used
• H2O2 is commonly found in home medicine cabinets
  and hospitals
• Is a good disinfectant and even sporicidal but is
  not a good antiseptic on open wounds where it is
  quickly broken down into water and oxygen by
  catalase
• Used for aseptic packaging in food industry
• Contained in the cleansing solution for contact
  lenses

15
Peroxigens

• Oxidizing agents are good for deep wound
  irrigation
• Inhibits growth of anaerobic bacteria
• Benzoyl peroxide useful in treatment of wounds
  infected by anaerobes but more familiar as an
  acne OTC (acne caused by an anaerobic bacterium
  which infects hair follicles)
• Peracetic acid- effective liquid chemical
  sporicides, considered a sterilent (kills
  endospores and viruses in 30 minutes and
  vegetative fungi and bacteria in less than 5
  minutes)
• Disinfectant in food-processing and medical
  equipment

16
Chemical food preservatives

• Common additives are simple organic acids or
  salts of organic acids
• Sodium benzoate (used in cheese and soft drinks)
• Sorbic acid or potassium sorbate (also used in
  acidic foods)
• Calcium propionate (used in breads as a
  fungistat)
• Sodium nitrate and nitrite which preserve food
  color and inhibit germination and growth of
  botulism endospores in meats (ham, bacon, sausage
  and hot dogs)
• concern about nitrosamines, cancer causing

17
Gaseous chemosterilizers

• Ethylene and propylene oxide gases
• Denatures proteins by alkylation
• After a lengthy exposure (14-18 hours), kills all
  vegetative and endospore forms
• Mixed with nonflammable gas since it is both
  explosive and toxic in pure form
• Sterilizes without heat and penetrates deeply
• Used on medical supplies and equipment, dried
  fruits and spices
• Often find ethylene oxide chambers in hospitals
• Are suspected carcinogens

18
Chemotherapeutic agents

• Goal is to find drugs that treat the patient
  without harming them
• Selective toxicity
• Kills the microorganism without damaging the host
• Most chemotherapeutic agents fall short
• Side effects which are undesirable
• Elimination of normal bacterial flora
• Formation of antibiotic strains

19
History of antibiotics

• Ehrlich proposed the magic bullet that would
  destroy the pathogen without harming the infected
  host
• Tested 605 substances before treating syphilis
  with salvarsan (1910), an arsenic derivative
  (considered to offer salvation from syphilis and
  it contained arsenic)
• Before this discovery, use of quinine to treat
  malaria

20
History of antibiotics

• Fleming identified Penicillium notatum as an
  active inhibitor of bacterial growth
• Penicillin is an antibiotic produced by a fungus
• Usefulness of penicillin was not apparent until
  the 1940s when it was tested and mass-produced
• Used in WWII to significantly reduce the death of
  soldiers
• First true antibiotic because by definition an
  antibiotic is a natural substance made by an
  organism to kill microbes

21
Sulfa drugs

• Sulfonamides- among the first synthetic
  antimicrobial drugs used to treat microbial
  diseases (1930s)
• Action due to the structural similarity to PABA
• Used to treat certain urinary tract infections
• Antibiotics have replaced the broad use of sulfa
  drugs

22
Antibiotic drug dilemma

• Increasing numbers of bacteria that are becoming
  resistant to antibiotics
• MRSA
• PPNG
• VRE
• VRSA
• Reasons for this dilemma include
• 300 million prescriptions are written each year
  with 1-2 being misread or misprescribed
• Many prescriptions are written for VIRAL
  infections
• Overused in surgical prophylaxis

23
Antibiotic drug dilemma

• Used for non-medical purposes which include
  growth stimulators, bacterial plant disease,
  production of selective media (Thayer-Martin), to
  inhibit the growth of bacteria in cell and tissue
  culture
• Use of broad spectrum antibiotics (kill both
  gram /- bacteria) that can lead to
  superinfections (survivors flourish and become
  opportunistic pathogens) Example is Candida
  albicans, a fungus that proliferates when normal
  flora are killed by antibiotic. Superinfection
  also applies to a target pathogen that is no
  longer resistant to the antibiotic

24
Antibiotic drug dilemma

• Lack of culture and sensitivity performed (C
  S) to specifically target the microbe
• Outdated antibiotics are shipped out of country
  and sold OTC
• Poverty precludes use of drugs when they are
  needed preventable illnesses which may end in
  death or disability

25
Antibiotic resistance

• Occurs from
• Mutations occurring in a single bacterium that
  reproduces by binary fission so that the mutant
  genes are passed on to all future offspring
• Transmission of antibiotic plasmids from one
  bacterium to another

26
Steps to be undertaken by all health care
professionals

• Avoid the use of antibiotics for viral infections
• Dont put away a few days supply of antibiotic
  for the next time. Use the full prescription for
  that illness
• Use the optimum dose or a combination of an
  antibiotic
• If the antibiotic does not appear to be working,
  notify the doctor. Perhaps you have an
  antibiotic resistant organism

27
Criteria for selecting the appropriate antibiotic

• The etiologic agent must be determined
• Wound swab, urine sample, tissue sample
• Simultaneously identify the etiologic agent AND
  examine for the best antibiotic that will treat
  the infection
• Determine the MIC- minimum inhibitory
  concentration that will completely eliminate the
  infection
• Tube dilution method
• Agar diffusion method using Mueller Hinton agar
  called the Kirby Bauer technique
• Zone sizes are resistant, intermediate or
  sensitive
• You want a drug which shows that the microbe is
  sensitive to and killed by the antibiotic

28
Route of administration

• Antibiotics can be administered in the following
  manners
• p.o. Per os (by mouth)
• Parenteral - by injection either subq, IV or IM
• Topically- on the surface cutaneous or
  conjunctival

29
Bacterial destruction by antibiotics

• How do some common antibiotics kill bacteria?
• Either are bacteriocidal or bacteriostatic
• Bacteriostatic depends on the hosts own defenses
  such as antibody production and phagocytosis

30
Inhibition of cell wall synthesis

• Penicillin and cephalosporins
• Are known as Beta lactam antibiotics
• Work best on gram walls
• Penicillin targets the synthesis of peptidoglycan
  wall of actively growing cells
• Little toxicity to host cells (no cell wall)
• Allergic reactions are frequent

31
Cell wall inhibition

• Vancomycin
• Used against MRSA infections
• Potentially toxic to kidneys, ototoxic also
• Some allergic response
• Bacitracin
• Topically applied
• Potentially nephrotoxic
• Isoniazid (INH)
• Used to treat mycobacterium (TB)
• Can be hepatotoxic

32
Injury to cell membrane

• Polypeptide antibiotics
• Affect cell membrane permeability
• Polymyxin B- attaches to phospholipids thereby
  disrupting cell membrane

33
Inhibition of Protein Synthesis

• Structural differences in prokaryotic and
  eukaryotic ribosomes account for the selective
  toxicity
• Erythromycin reacts with the 50S portion
• Affects mostly gram bacteria
• Doesnt cross the blood brain barrier
• Side effects include nausea, vomiting and
  gastrointestinal pain

34
Inhibition of protein synthesis

• Chloramphenicol is a broad spectrum antibiotic
• Reacts with the 50S inhibiting the formation of
  peptide bonds
• Rare cases of aplastic anemia and neurological
  damage

35
Inhibition of protein synthesis

• Tetracycline
• Reacts with the 30S portion
• Interferes with the attachment of the tRNA
  carrying the amino acids to the ribosomes
  preventing the addition of AA to the polypeptide
  chain
• Possible side effects include nausea, light
  sensitivity, bone strength and shape in young
  children

36
Inhibition of protein synthesis

• Streptomycin, a broad spectrum antibiotic
• Along with gentamycin, is an aminoglycoside
  antibiotic
• Interferes with the initial step of protein
  synthesis by changing the shape of the 30S
  portion of the ribosome
• Side effects nephrotoxic, ototoxic

37
Inhibition of nucleic acids synthesis

• May interfere with DNA replication or
  transcription
• Rifampin
• used for the treatment of TB
• Selectively interferes with mRNA synthesis
• Quinolones (ciprofloxin)
• Inhibits DNA synthesis
• Both are selectively toxic

38
Inhibition of synthesis of essential metabolites

• In the presence of sulfanilamide, the enzyme that
  normally converts PABA to folic acid will combine
  with the sulfanilamide instead
• Folic acid is an co-enzyme needed for the
  synthesis of purine and pyrimidine bases for the
  synthesis of DNA and also is needed for the
  synthesis of certain amino acids
• Other anti-metabolites include sulfones and
  trimethoprim

39
Nosocomial infections

• Fourth leading cause of death after heart
  attacks, cancer and stroke
• Derived from the Greek word meaning hospital
• Necessary to understand the processes of
  microbial growth, aseptic technique, inhibition
  of microbial growth in the allied health
  professional careers so that these infections can
  be prevented in your patients, yourself and your
  family and friends

40
Nosocomial infections

• By definition, infections that are spread in
  hospitals and other medical facilities such as
  nursing homes
• 2 million people acquire these each year with
  100,000 deaths
• According to the CDC, 5 15 of all hospital
  patients acquire them
• Occur as a result of the interaction of the
  following

41
Nosocomial infections

• Microorganisms present in the hospital
  environment
• Normal microbiota of the human body become
  opportunistic. These do not cause disease in
  healthy people
• Compromised state of the host (patient) who may
  have surgical wounds, burns, trauma, or IV
  catheterizations
• Chain of transmission in hospital
• staff ?patient, patient? patient, fomites or
  hospital ventilation systems

42
Breaking the cycle

• Proper hand washing technique- according to the
  CDC, single most important means of preventing
  the spread of infection
• Aseptic technique
• Isolation
• Reverse isolation
• Hospital disinfection/sterilization of fomites
  (non- living object involved in the spread of
  disease tissues, towels, diapers, thermometers,
  eating utensils and towels

43
Breaking the cycle

• Environmental sanitation
• Infection control committees

44
Universal precautions

• Protect yourself from the potential contamination
  by blood and body fluids
• Wash hands before and after patients
• Avoid needle and scalpel sticks
• Use a barrier for mouth to mouth resuscitation
• Workers with oozing, open lesions should not be
  involved with patient care or equipment
• Vaccination- health care frontline professionals
  should have all necessary and updated
  immunizations such as tetanus and Hepatitis B