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PVS > Microbiology 4 > Flashcards

Microbiology 4 Flashcards

1
Q

Describe the mechanism of action of alkali disinfectants

A
  • Saponification of lipids in cell membranes and envelopes
  • Activity low but increases with raised temperature
  • Useful if grease is present
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2
Q

Describe problems associated with alkali disinfectants

A
  • Concentrated alkalis can burn
  • Cause corrosion
  • Correct PPE required
  • May react with water violently exothermically
  • Some strong solutions can emit fumes
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3
Q

List the main groups of alkali disinfectants used

A
  • Sodium and potassium hydroxides
  • Ammonium hydroxide
  • Sodium carbonate
  • Calcium oxide (quick lime)
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4
Q

Outline the use of sodium and potassium hydroxides

A
  • Caustic soda
  • Often used on buildings
  • Surface decontamination
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5
Q

Outline the use of ammonoium hydroxide

A

Effective against coccidial oocyts but not considered active against bacteria

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6
Q

Outline the use of sodium carbonate

A
  • Soda ash/washing soda
  • Hot solution for disinfecting buildings
  • Lacks efficacy against some bacteria and most viruses
  • At 4%w/v is approved chemical for FMDV
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7
Q

Outline the use of calcium oxide (quick lime)

A
  • Lime when mixed with water
  • After depopulation used on surfaces/group
  • Also to retard putrification of buried carcasses
  • Not effective against FMDV
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8
Q

List the microbes against which alkali disinfectants are active

A
  • Mycoplasmas
  • Gram -ve and +ve
  • Enveloped viruses
  • Some non-enveloped viruses
  • Fungal spores
  • Acid fast bacteria
  • Some bacterial spores
  • Coccidia
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9
Q

Describe the mode of action of aldehyde disinfectants

A
  • Highly effective, highly reactive
  • denature proteins and nucleic acids
  • Activity depends on humidity (optimum ca. 70%)
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10
Q

Describe some problems associated with aldehyde disinfectants

A
  • Highly toxic
  • Irritating
  • Carcinogenic
  • Restrictions on use
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11
Q

What are the 2 groups of aldehyde disinfectants?

A
  • Formaldehyde

- Glutaraldehyde

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12
Q

Outline the use of formaldehyde

A
  • Surface or soluble gas
  • Good with rough surfaces
  • Formalin solution of formaldehyde with methyl-alcohol prevents self polymerisation
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13
Q

Outline the use of glutaraldehyde

A
  • Primarily disinfection of medical equipment
  • 2% solution provides good sterilisation
  • Activity dependent on pH and temperature (poor below 7C)
  • Improved activity with organic materal than formaldehyde
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14
Q

What are the advantages of aldehyde disinfectants?

A
  • Broad spectrum

- Non-corrosive

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15
Q

List the microbes against which aldehyde disinfectants are effective

A
  • Mycoplasmas
  • Gram -ve and +ve
  • Enveloped viruses
  • Non-enveloped viruses
  • Fungal spores
  • Acid fast bacteria
  • Bacterial spores
  • Formaldehyde active against Coccidia
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16
Q

How can formaldehyde be used other than for disinfection?

A
  • Production of vaccines
  • Destruction of pathogen with formaldehyde
  • Produces inactivated vaccines once formaldehyde is removed
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17
Q

Describe the mode of action of biguanide disinfectants

A
  • Cationic compounds

- React with negatively charged groups in cell membranes altering permeability

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18
Q

Describe the problem associated with biguanide disinfectants

A
  • Limited in effectiveness against acid fast bacteria, fungi, viruses and or spores
  • Limited pH range (pH 5-7)
  • Inactivated by some soaps and detergents (anionic detergents and in organic anionic compounds)
  • Activity reduced by organic matter
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19
Q

Give an example of a biguanide disinfectant

A

Chlorhexidine aka hibiscrub

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20
Q

Outline the use of biguanide disinfectants

A
  • Alcohol based rather than aqueous based due to increased activity
  • More active vs Gram +ve than -ve
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21
Q

List the microbial groups against which biguanide disinfectants are active

A
  • Mycoplasma
  • Gram +ve, -ve
  • some enveloped viruses
  • Some fungal spores
  • Limited range of activity
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22
Q

What are the 2 groups of halogen disinfectants?

A
  • Iodine

- Chlorine

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23
Q

Describe the mode of action of chlorine disinfectants

A

Electronegative nature, denaturing proteins

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24
Q

Give examples of uses of chlorine disinfectants

A
  • Water treatment
  • Food industry
  • Bleaching (chlorine dioxide)
  • Chloramine used for drinking water
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25
Q

What are the advantages of halogen disinfectants?

A
  • Broad spectrum
  • Low toxicity
  • Low cost
  • Easy to use
  • Best use on cleaned surfaces
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26
Q

Describe some problems associated with halogen disinfectants

A
  • Lose potency over time
  • Not active above 43C
  • Reduced activity above pH9
  • Lose activity in presence of organic matter, sunlight and m=some metals
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27
Q

List the microbial groups against which chlorine disinfectants are active

A
  • Mycoplasmas
  • Gram -ve and +ve
  • Enveloped viruses
  • Non-enveloped viruses
  • Fungal spores
  • Acid fast bacteria
  • Bacterial spores
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28
Q

What is the main problem with chlorine disinfectants?

A

Cannot be mixed with acids or ammonia as this will generate chlorine gas

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29
Q

Describe the use of iodine disinfectants

A
  • Broad spectrum
  • Often formulated with soaps and considered safe
  • Less active than chlorine but more tolerant of organic materials
  • Often dissolved in ethyl alcohol
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30
Q

What is the mode of action of iodine disinfectants?

A

Denatures proteins

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31
Q

What are the problems associated with iodine disinfectants?

A
  • May be irritant at high concentrations
  • Can stain skin, cloth etc.
  • Can be inactivated by QACs and organic debris
  • Can have poor stability
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32
Q

What are iodophores?

A

Iodine complexes with increased solubility and sustained release of iodine

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33
Q

What is the advantage of iodophores over elemental iodine?

A

Improved activity in the presence of organic material, and increased free iodine and activity, reduced problems associated with free iodine

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34
Q

Give an example of a common use of iodophores

A

Teat dip

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35
Q

List the microbial groups against which iodine disinfectants are active

A
  • Mycoplasmas
  • Gram +ve and -e
  • Enveloped viruses
  • Some non-enveloped viruses
  • Fungal and bacterial spores
  • Acid fast bacteria
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36
Q

Describe the mode of action of phenolic compound disinfectants

A

Denature proteins and especially affect cell permeability

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37
Q

Describe the use of phenolic compound disinfectants

A
  • Coal-tar extract or synthetic formulations
  • Usually have milky/cloudy appearance
  • Often formulated with soaps to increase penetration
  • 5% v/v solutions considered bacteriocidal, fungicidal, active against enveloped viruses
  • Active in hard water
  • Active with organic material
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38
Q

Describe the problems associated with phenolic compounds disinfectants

A
  • Can cause irritation to skin
  • Environmental concerns so being phased out
  • Can taint food so not used in food industry
  • Concentration above 2% highly toxic to animals especially cats
  • Not active against spores, non-enveloped viruses
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39
Q

List the microbial groups against which phenolic compounds are active

A
  • Mycoplasma
  • Gram +ve, -ve
  • Some enveloped viruses
  • Fungal spores
  • Some acid fast bacteria
  • Coccidia
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40
Q

Give an example of a phenolic compound disinfectant

A

TCP

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41
Q

What are QACs?

A

Quarternary Ammonium Compounds

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42
Q

Describe the mode of action of QACs

A
  • Cationic detergents
  • Attack negative charges on surfaces of microorganisms
  • Irreversibly bind to phospholipids and proteins affecting cell permeability
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43
Q

Outline the use of QACs

A
  • Non-toxic, non-staining
  • Used in food industry
  • Most common is benzalkonium, is both bactericidal and fungicidal
  • Active neutral to alkaline, lose activity below pH 3.5
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44
Q

Describe the problems associated with QACs

A
  • Not effective against non-enveloped viruses, mycobacteria, spores (but are sporostatic)
  • Inactivated by organic matter, detergents, hard water
  • Toxic to fish
  • Some Gram -ve bacteria can grow in QAC solutions
45
Q

Outline the generations of QACs

A

Later more active,, less foaming, more tolerant

46
Q

Describe the mode of action of peroxygen compounds

A

Denature proteins and lipids and react with DNA

47
Q

Describe the use of peroxygen compound disinfectants

A
  • Broad spectrum
  • Peroxide based
  • Vary in range of activity
  • Good on hard surfaces and equipment
48
Q

List the main groups of peroxygen compounds

A
  • Peroxide
  • Peracetic acid
  • Virkon
  • Ozone
49
Q

Describe the problems associated with peroxygen compounds

A
  • Dilute considered safe, but can be irritating esp in powder form
  • Can damage clothing surfaces in concentrated form or after prolonged use
50
Q

Outline tolerance mechanisms to perozygen compounds

A
  • Some bacteria have catalases and peroxidases, increase tolerance at low concentration
51
Q

Outline how resistance to QACs may occur

A

Efflux systems in bacteria allow QACs to be pumped out of the cell

52
Q

List the microbial groups against which hydrogen peroxide is active

A
  • 5-20% concentration is bacteriocidal, virucidal and fungicidal
  • At 30% is sporicidal
  • LImited activity in mycobacteria
53
Q

List the microbial agents against whic peracetic acid is active

A
  • Bacteriocidal (including mycobacteria)
  • Fungicidal
  • Sporicidal
  • Virucidal
  • Also active against algae
54
Q

Describe the formulation of peracetic acid

A
  • Formulation of hydrogen and acetic acid

- Produces peracetic acid and water

55
Q

Describe the mode of action of Virkon-S

A
  • Peroxygen molecule
  • Organic acid
  • And surfactant combination
56
Q

Give some problems associated with peracetic acid

A
  • Corrosive and hazardous

- May be carcinogenic

57
Q

Give some problems associated with Virkon-S

A
  • Dust and sprays can be irritant

- Some people can be sensitive

58
Q

Compare the activity of peroxygen compounds in organic material

A
  • Hydrogen peroxide: limited
  • Peracetic acid: some, better cf hydrogen peroxide
  • Virkon-S: some activity in organic material
59
Q

Describe the mode of action of ozone disinfectants

A

Hyper oxygen species reacts with proteins and nucleic acids

60
Q

Outline the use of ozone disinfectants

A
  • Often used in water systems for feeders

- Bacteriocidal, virucidal, sporicidal

61
Q

Outline the disinfection methods to remove prions

A
  • Highly resistant, poor activity
  • Autoclaving at higher temperatures for longer
  • Soaking in sodium hypochlorite or sodium hydroxide
  • Use disposables and incineration of waste
62
Q

What factors affect the efficacy of disinfectant?

A
  • Dilution
  • Contact time
  • Temperature
  • Activity against microbe being targeted
  • Humidity
  • Application
  • Presence of organic matter
  • Biofilms
  • Other agents used that may inactivate
63
Q

What is pasteurisation?

A

Rapid heating and then cooling of a liquid in order to reduce number of sensitive viable pathogens

64
Q

Outline the efficacy of pasteurisation

A
  • Not sterilisation, reduces number of sensitive viable pathogens
  • 90% effective against vegetative bacteria (non-sporulating)
65
Q

Define surgical site infection

A

An infection that develops at the operative site within 30 days of surgery, or up to a year after surgery if implants were placed

66
Q

What are the subclassifications of surgical site infections?

A
  • Incisional infection (can be superficial or deep)

- Organ/space infection

67
Q

List Halstead’s principles of good surgical practice

A
  • Gentle tissue handling
  • Strict asepsis
  • Haemostasis
  • Preservation of blood supply
  • No tension on tissues
  • Good approximation of tissues
  • Obliteration of dead space
68
Q

Outline how a surgical site infection can develop

A
  • All surgical wounds are contaminated by bacteria
  • Infection occurs if >10^8 bacteria present/gram of tissue
  • depends on bacterial factors, host defences, wound environment
  • Level of contamination above that which the patient can control
69
Q

What are the potential sources of bacteria in surgical infections?

A
  • Exogenous
  • Endogenous
  • Nosocomial
70
Q

Define nosocomial

A
  • Subgroup of exogenous

- Occur during period of hospitalisation and are more likely with extended hospital stays and catheterisation

71
Q

Outline patient factors that affect surgical infection establishment

A
  • General health
  • Hypoalbuminaemia is an important predictor of morbidity and mortality
  • Functional state of host defences (age, poor physical status, malnutrition, obesity, systemic disease, drug therapy)
72
Q

List surgical factors that affect surgical infection establishment

A
  • Aseptic technique
  • Duration
  • Reactive materials
  • Suture tightness
  • Implants
73
Q

What are the classifications of surgical cleanliness?

A
  • Clean
  • Clean-contaminated
  • Contaminated
  • Dirty
74
Q

What is the aim of surgical aseptic technique?

A

Minimise exposure to bacteria to as low as possible (number, virulence and duration of contamination)

75
Q

Outline the relationship between surgical duration and infection rate

A
  • Every hour of surgery doubles the infection rate

- prolonged anaesthesia also independently increases risk

76
Q

Which suture materials minimise risk of infection?

A

Synthetic and monofilament - reduced reactivity and wicking

77
Q

Outline how implants can lead to infection

A
  • Can themselves be contaminated
  • Also provide surface for biofilm formation, which protects pathogens and encourages bacterial colonisation
  • Increases difficulty of treating infection
78
Q

Describe biofilm structure

A
  • Glycocalyx film (tissue protein)

- Community of bacterial cells, self-produced polymeric matrix adherent to inert or living surface

79
Q

Explain how biofilms facilitate the development infection

A
  • Increase difficulty of host defences and antibiotics to penetrate
  • Bacteria able to communicate with each other (quorum sensing)
  • 1000x more resistant to antibiotics than free-swimming bacteria
80
Q

Outline how surgical technique increases the chance of infection

A
  • Each incision disrupts local defence mechanisms
  • Greater tissue injury leads to increased risk of infection
  • Damaged blood supply increases infection as prevents influx of immune cells
  • Drying of tissues increases risk of infection
81
Q

List peri-operative factors that increase risk of infection

A
  • Anaesthesia
  • Drugs
  • Wound ischaemia
  • Reduced oxygen supply
  • Poor nursing hygiene
  • Hospitalisation
82
Q

Outline how ischaemia increases infection risk and how this can be avoided

A
  • Reduced supply of immune cells
  • Need to keep PCV above 20% pre- and intr-op
  • Shock and trauma potentiates infection
  • Avoid peripheral vasoconstriction
83
Q

Outline how hospitalisation can lead to increased infection risk

A
  • Movement between patients passing infections

- Increased intervention required, likely to have lower immune strength

84
Q

Outline the significance of MRSA

A
  • Methicillin Resistant Staph aureus
  • Can limit spread using basic hygiene and common sense
  • Swab chronic non-healing wounds for MRSA and treat with specific antibiotic
  • Cover wound and barrier nurse or isolate patient
85
Q

Describe what is meant by a clean procedure/wound

A
  • Elective, no-traumatic, short procedure (<60-90mins
  • No break in aseptic technique
  • No acute inflammation
  • No entry into resp, GI or urogenital tract
  • 2.5-6% infection rates in SAs
  • More likely for orthopaedic surgery
86
Q

Are antibiotics required for a clean surgical procedure?

A

No, unless very prolonged, lots or implants used or lots of tissue trauma

87
Q

Describe what is meant by a clean-contaminated surgical procedure

A
  • Minor break in aseptic technique (may be iatrogenic e.g. drop equipment, contact with non-sterile surface)
  • Entry into GI, UG ro resp tract without serious contamination
  • Infection rate 2.5-9.5% in SAs
88
Q

Are antibiotics required following a clean-contaminated surgical procedure?

A

Yes, reduces infection rates from Staphs, Gram -ve, Enterobacteriaceae

89
Q

Describe what is meant by a contaminated surgical procedure

A
  • Traumatic wound <4 hours old
  • Break in aseptic technique (surgeon or instruments)
  • Spillage from viscous e.g. GIT, pyometra, UG tract
  • Infection rates 5.5-28%
90
Q

Are antibiotics required following a contaminated surgical procedure?

A

Yes, high risk of infection from pyogenic wounds, GIT, UG tract and anaerobes from lower GI particular worry

91
Q

Describe what is meant by a dirty surgical procedure

A
  • Infected
  • Traumatic wound >4 hours old, or with devitalised tissue or foreign bodies
  • Perforated viscus e.g. older pyometra
  • Acute bacterial inflammation or pus e.g. abscesses-
  • Infection rate 18-25%
92
Q

Are antibiotics required following a dirty surgical procedure?

A

Yes, based on culture and sensitivity

93
Q

List the signs of surgical infection

A
  • Pain/tenderness
  • Localised swelling, redness, heat
  • Discharge or drainage from incision
  • +/- systemic signs
  • +/- wound breakdown
  • Abscessation
  • Positive bacterial culture
94
Q

What are the consequences of post-operative infection?

A
  • Patient suffering
  • Delayed healing
  • Wound breakdown
  • Failure of surgery
  • Systemic illness
  • Prolonged hospitalisation
  • Increased risk of nosocomial infection
  • major client dissatisfaction and increased costs
95
Q

Describe the principles of surgical wound monitoring

A
  • Check surgical wound 24 hours later, change dressing
  • Change dressing as soon as evidence of strike through
  • Provide buster collar if animal is bothering at the wound (unless severe discomfort indicates bandaging issue)
  • Give owner clear written post-op care instructions
96
Q

Outline the treatment of orthopaedic infections

A
  • Culture and sensitivity
  • Radiographic changes appear initially in soft tissue, then bone
  • Remove implants if they are unnecessary
  • If necessary, treat with antibiotics 6wks then remove
  • Orthopaedic emergencies: joint infection, open fracture
97
Q

Outline the administration of antibiotics for antibiotics in a clean surgical procedure

A
  • Single intravenous peri-surgical dose of broad spec antibiotics where prolonged surgery
98
Q

Outline the administration of antibiotics for a clean-contaminated surgical procedure

A
  • Single IV dose peri-operatively at time of surgery

- Prevents contamination developing to infection

99
Q

Outline the administration of antibiotics for a contaminated surgical procedure

A

Peri-operative IV and course of post-op antibiotics

100
Q

Outline the administration of antibiotics for a dirty surgical procedure

A
  • Peri-operative IV
  • Post-operative
  • Is therapeutic treatment, not prophylactic
101
Q

Compare prophylactic and therapeutic use of antibiotics

A
  • Therapeutic: where infection is present
  • Prophylactic: in order to prevent development of infection and depends on likelihood of infection and likely pathogen causing contamination
102
Q

When is it best to administer antibiotics for surgical infections and why?

A
  • Before surgery IV
  • Ensures that tissue concentrations will be high when contamination is likely to occur, therefore preventing colonisation
  • Predictable peak and complete bioavailability
103
Q

When is repeat dosing with antibiotics for surgical infections indicated?

A
  • To ensure MBC is maintained
  • Every 90 mins intraoperatively
  • May add dose at end of surgery
  • Extend course if contamination occurred, drains or implants put in place
104
Q

Outline the selection of antibiotics for surgical infection

A
  • Prophylactically use broad spectrum

- Therapeutically use specific agent based on culture and sensitivity

105
Q

Describe some special considerations for dental procedures and infection

A
  • Potential for bacterial embolisation
  • Always have bacteraemia due to endogenous contamination of bacteria
  • Ideally do not perform clean surgery at the same time (e.g. spay)
106
Q

Outline some special considerations when performing GI procedures

A
  • Starve patient to reduce potential for leakage of gut contents
  • +/- enema: messy, may still have liquid faeces during surgery which poses greater risk for contamination vs normal faecolith
  • Reduce gut flora (metronidazole, oral aminoglycosides)
107
Q

What factors may influence antibiotic choice (for example, in the case of otitis externa)?

A
  • Conformation of ear
  • Concurrent issues e.g. excessive moisture, obstruction of ear canal
  • Systemic disease
  • Effects of treatment e,g. causing itching leading to secondary infection
  • Owner compliance
  • Previous use
  • Underlying allergy
  • Potential for resistance
  • Cost
108
Q

What is metaphylaxis?

A

Timely mass medication of groups of animals to eliminate or minimise an expected outbreak of disease

PVS (23 decks)

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