Microbiology 4 Flashcards
Describe the mechanism of action of alkali disinfectants
- Saponification of lipids in cell membranes and envelopes
- Activity low but increases with raised temperature
- Useful if grease is present
Describe problems associated with alkali disinfectants
- Concentrated alkalis can burn
- Cause corrosion
- Correct PPE required
- May react with water violently exothermically
- Some strong solutions can emit fumes
List the main groups of alkali disinfectants used
- Sodium and potassium hydroxides
- Ammonium hydroxide
- Sodium carbonate
- Calcium oxide (quick lime)
Outline the use of sodium and potassium hydroxides
- Caustic soda
- Often used on buildings
- Surface decontamination
Outline the use of ammonoium hydroxide
Effective against coccidial oocyts but not considered active against bacteria
Outline the use of sodium carbonate
- 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
Outline the use of calcium oxide (quick lime)
- Lime when mixed with water
- After depopulation used on surfaces/group
- Also to retard putrification of buried carcasses
- Not effective against FMDV
List the microbes against which alkali disinfectants are active
- Mycoplasmas
- Gram -ve and +ve
- Enveloped viruses
- Some non-enveloped viruses
- Fungal spores
- Acid fast bacteria
- Some bacterial spores
- Coccidia
Describe the mode of action of aldehyde disinfectants
- Highly effective, highly reactive
- denature proteins and nucleic acids
- Activity depends on humidity (optimum ca. 70%)
Describe some problems associated with aldehyde disinfectants
- Highly toxic
- Irritating
- Carcinogenic
- Restrictions on use
What are the 2 groups of aldehyde disinfectants?
- Formaldehyde
- Glutaraldehyde
Outline the use of formaldehyde
- Surface or soluble gas
- Good with rough surfaces
- Formalin solution of formaldehyde with methyl-alcohol prevents self polymerisation
Outline the use of glutaraldehyde
- 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
What are the advantages of aldehyde disinfectants?
- Broad spectrum
- Non-corrosive
List the microbes against which aldehyde disinfectants are effective
- Mycoplasmas
- Gram -ve and +ve
- Enveloped viruses
- Non-enveloped viruses
- Fungal spores
- Acid fast bacteria
- Bacterial spores
- Formaldehyde active against Coccidia
How can formaldehyde be used other than for disinfection?
- Production of vaccines
- Destruction of pathogen with formaldehyde
- Produces inactivated vaccines once formaldehyde is removed
Describe the mode of action of biguanide disinfectants
- Cationic compounds
- React with negatively charged groups in cell membranes altering permeability
Describe the problem associated with biguanide disinfectants
- 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
Give an example of a biguanide disinfectant
Chlorhexidine aka hibiscrub
Outline the use of biguanide disinfectants
- Alcohol based rather than aqueous based due to increased activity
- More active vs Gram +ve than -ve
List the microbial groups against which biguanide disinfectants are active
- Mycoplasma
- Gram +ve, -ve
- some enveloped viruses
- Some fungal spores
- Limited range of activity
What are the 2 groups of halogen disinfectants?
- Iodine
- Chlorine
Describe the mode of action of chlorine disinfectants
Electronegative nature, denaturing proteins
Give examples of uses of chlorine disinfectants
- Water treatment
- Food industry
- Bleaching (chlorine dioxide)
- Chloramine used for drinking water
What are the advantages of halogen disinfectants?
- Broad spectrum
- Low toxicity
- Low cost
- Easy to use
- Best use on cleaned surfaces
Describe some problems associated with halogen disinfectants
- Lose potency over time
- Not active above 43C
- Reduced activity above pH9
- Lose activity in presence of organic matter, sunlight and m=some metals
List the microbial groups against which chlorine disinfectants are active
- Mycoplasmas
- Gram -ve and +ve
- Enveloped viruses
- Non-enveloped viruses
- Fungal spores
- Acid fast bacteria
- Bacterial spores
What is the main problem with chlorine disinfectants?
Cannot be mixed with acids or ammonia as this will generate chlorine gas
Describe the use of iodine disinfectants
- Broad spectrum
- Often formulated with soaps and considered safe
- Less active than chlorine but more tolerant of organic materials
- Often dissolved in ethyl alcohol
What is the mode of action of iodine disinfectants?
Denatures proteins
What are the problems associated with iodine disinfectants?
- May be irritant at high concentrations
- Can stain skin, cloth etc.
- Can be inactivated by QACs and organic debris
- Can have poor stability
What are iodophores?
Iodine complexes with increased solubility and sustained release of iodine
What is the advantage of iodophores over elemental iodine?
Improved activity in the presence of organic material, and increased free iodine and activity, reduced problems associated with free iodine
Give an example of a common use of iodophores
Teat dip
List the microbial groups against which iodine disinfectants are active
- Mycoplasmas
- Gram +ve and -e
- Enveloped viruses
- Some non-enveloped viruses
- Fungal and bacterial spores
- Acid fast bacteria
Describe the mode of action of phenolic compound disinfectants
Denature proteins and especially affect cell permeability
Describe the use of phenolic compound disinfectants
- 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
Describe the problems associated with phenolic compounds disinfectants
- 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
List the microbial groups against which phenolic compounds are active
- Mycoplasma
- Gram +ve, -ve
- Some enveloped viruses
- Fungal spores
- Some acid fast bacteria
- Coccidia
Give an example of a phenolic compound disinfectant
TCP
What are QACs?
Quarternary Ammonium Compounds
Describe the mode of action of QACs
- Cationic detergents
- Attack negative charges on surfaces of microorganisms
- Irreversibly bind to phospholipids and proteins affecting cell permeability
Outline the use of QACs
- 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
Describe the problems associated with QACs
- 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
Outline the generations of QACs
Later more active,, less foaming, more tolerant
Describe the mode of action of peroxygen compounds
Denature proteins and lipids and react with DNA
Describe the use of peroxygen compound disinfectants
- Broad spectrum
- Peroxide based
- Vary in range of activity
- Good on hard surfaces and equipment
List the main groups of peroxygen compounds
- Peroxide
- Peracetic acid
- Virkon
- Ozone
Describe the problems associated with peroxygen compounds
- Dilute considered safe, but can be irritating esp in powder form
- Can damage clothing surfaces in concentrated form or after prolonged use
Outline tolerance mechanisms to perozygen compounds
- Some bacteria have catalases and peroxidases, increase tolerance at low concentration
Outline how resistance to QACs may occur
Efflux systems in bacteria allow QACs to be pumped out of the cell
List the microbial groups against which hydrogen peroxide is active
- 5-20% concentration is bacteriocidal, virucidal and fungicidal
- At 30% is sporicidal
- LImited activity in mycobacteria
List the microbial agents against whic peracetic acid is active
- Bacteriocidal (including mycobacteria)
- Fungicidal
- Sporicidal
- Virucidal
- Also active against algae
Describe the formulation of peracetic acid
- Formulation of hydrogen and acetic acid
- Produces peracetic acid and water
Describe the mode of action of Virkon-S
- Peroxygen molecule
- Organic acid
- And surfactant combination
Give some problems associated with peracetic acid
- Corrosive and hazardous
- May be carcinogenic
Give some problems associated with Virkon-S
- Dust and sprays can be irritant
- Some people can be sensitive
Compare the activity of peroxygen compounds in organic material
- Hydrogen peroxide: limited
- Peracetic acid: some, better cf hydrogen peroxide
- Virkon-S: some activity in organic material
Describe the mode of action of ozone disinfectants
Hyper oxygen species reacts with proteins and nucleic acids
Outline the use of ozone disinfectants
- Often used in water systems for feeders
- Bacteriocidal, virucidal, sporicidal
Outline the disinfection methods to remove prions
- Highly resistant, poor activity
- Autoclaving at higher temperatures for longer
- Soaking in sodium hypochlorite or sodium hydroxide
- Use disposables and incineration of waste
What factors affect the efficacy of disinfectant?
- Dilution
- Contact time
- Temperature
- Activity against microbe being targeted
- Humidity
- Application
- Presence of organic matter
- Biofilms
- Other agents used that may inactivate
What is pasteurisation?
Rapid heating and then cooling of a liquid in order to reduce number of sensitive viable pathogens
Outline the efficacy of pasteurisation
- Not sterilisation, reduces number of sensitive viable pathogens
- 90% effective against vegetative bacteria (non-sporulating)
Define surgical site infection
An infection that develops at the operative site within 30 days of surgery, or up to a year after surgery if implants were placed
What are the subclassifications of surgical site infections?
- Incisional infection (can be superficial or deep)
- Organ/space infection
List Halstead’s principles of good surgical practice
- Gentle tissue handling
- Strict asepsis
- Haemostasis
- Preservation of blood supply
- No tension on tissues
- Good approximation of tissues
- Obliteration of dead space
Outline how a surgical site infection can develop
- 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
What are the potential sources of bacteria in surgical infections?
- Exogenous
- Endogenous
- Nosocomial
Define nosocomial
- Subgroup of exogenous
- Occur during period of hospitalisation and are more likely with extended hospital stays and catheterisation
Outline patient factors that affect surgical infection establishment
- 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)
List surgical factors that affect surgical infection establishment
- Aseptic technique
- Duration
- Reactive materials
- Suture tightness
- Implants
What are the classifications of surgical cleanliness?
- Clean
- Clean-contaminated
- Contaminated
- Dirty
What is the aim of surgical aseptic technique?
Minimise exposure to bacteria to as low as possible (number, virulence and duration of contamination)
Outline the relationship between surgical duration and infection rate
- Every hour of surgery doubles the infection rate
- prolonged anaesthesia also independently increases risk
Which suture materials minimise risk of infection?
Synthetic and monofilament - reduced reactivity and wicking
Outline how implants can lead to infection
- Can themselves be contaminated
- Also provide surface for biofilm formation, which protects pathogens and encourages bacterial colonisation
- Increases difficulty of treating infection
Describe biofilm structure
- Glycocalyx film (tissue protein)
- Community of bacterial cells, self-produced polymeric matrix adherent to inert or living surface
Explain how biofilms facilitate the development infection
- 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
Outline how surgical technique increases the chance of infection
- 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
List peri-operative factors that increase risk of infection
- Anaesthesia
- Drugs
- Wound ischaemia
- Reduced oxygen supply
- Poor nursing hygiene
- Hospitalisation
Outline how ischaemia increases infection risk and how this can be avoided
- Reduced supply of immune cells
- Need to keep PCV above 20% pre- and intr-op
- Shock and trauma potentiates infection
- Avoid peripheral vasoconstriction
Outline how hospitalisation can lead to increased infection risk
- Movement between patients passing infections
- Increased intervention required, likely to have lower immune strength
Outline the significance of MRSA
- 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
Describe what is meant by a clean procedure/wound
- 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
Are antibiotics required for a clean surgical procedure?
No, unless very prolonged, lots or implants used or lots of tissue trauma
Describe what is meant by a clean-contaminated surgical procedure
- 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
Are antibiotics required following a clean-contaminated surgical procedure?
Yes, reduces infection rates from Staphs, Gram -ve, Enterobacteriaceae
Describe what is meant by a contaminated surgical procedure
- 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%
Are antibiotics required following a contaminated surgical procedure?
Yes, high risk of infection from pyogenic wounds, GIT, UG tract and anaerobes from lower GI particular worry
Describe what is meant by a dirty surgical procedure
- 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%
Are antibiotics required following a dirty surgical procedure?
Yes, based on culture and sensitivity
List the signs of surgical infection
- Pain/tenderness
- Localised swelling, redness, heat
- Discharge or drainage from incision
- +/- systemic signs
- +/- wound breakdown
- Abscessation
- Positive bacterial culture
What are the consequences of post-operative infection?
- Patient suffering
- Delayed healing
- Wound breakdown
- Failure of surgery
- Systemic illness
- Prolonged hospitalisation
- Increased risk of nosocomial infection
- major client dissatisfaction and increased costs
Describe the principles of surgical wound monitoring
- 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
Outline the treatment of orthopaedic infections
- 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
Outline the administration of antibiotics for antibiotics in a clean surgical procedure
- Single intravenous peri-surgical dose of broad spec antibiotics where prolonged surgery
Outline the administration of antibiotics for a clean-contaminated surgical procedure
- Single IV dose peri-operatively at time of surgery
- Prevents contamination developing to infection
Outline the administration of antibiotics for a contaminated surgical procedure
Peri-operative IV and course of post-op antibiotics
Outline the administration of antibiotics for a dirty surgical procedure
- Peri-operative IV
- Post-operative
- Is therapeutic treatment, not prophylactic
Compare prophylactic and therapeutic use of antibiotics
- Therapeutic: where infection is present
- Prophylactic: in order to prevent development of infection and depends on likelihood of infection and likely pathogen causing contamination
When is it best to administer antibiotics for surgical infections and why?
- Before surgery IV
- Ensures that tissue concentrations will be high when contamination is likely to occur, therefore preventing colonisation
- Predictable peak and complete bioavailability
When is repeat dosing with antibiotics for surgical infections indicated?
- 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
Outline the selection of antibiotics for surgical infection
- Prophylactically use broad spectrum
- Therapeutically use specific agent based on culture and sensitivity
Describe some special considerations for dental procedures and infection
- 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)
Outline some special considerations when performing GI procedures
- 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)
What factors may influence antibiotic choice (for example, in the case of otitis externa)?
- 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
What is metaphylaxis?
Timely mass medication of groups of animals to eliminate or minimise an expected outbreak of disease
