Control of Microbial Growth: Explore decontamination and selective toxicity (Labster Lab Manual | M) Flashcards
What is microbial load?
The # or infection pathogens on an item
For objects or items having microbial load, what should be done?
In these situations, these needs to be carefully managed
In pt care scenarios, what should be done to control the spread of infection?
Careful cleaning procedures
In cases where potentially contaminated items are invasively introduced to soft tissue or the vascular system, what should be done?
Sterilization techniques are used to prevent infection transmission
When is less stringent decontamination techniques used?
These are used to keep living organisms safe from pathogenic harm
What is Spaulding classification scheme?
It was devised as a logical way to determine the disinfection schemes required for items used during pt care
True or False.
The Spaulding classification scheme still remains the clearest and most concise way of assessing an object’s infection risk despite being over half a century old
True
What is the importance of Spaulding classification scheme?
It is important as it ensures all items receive an appropriate lvl of decontamination w/out overburdening an infection control system
Objects (via the application of Spaulding classification scheme) are split into how many categories?
3
Objects (via the application of Spaulding classification scheme) are split into 3 categories depending on what?
Depending on their normal use
What are the 3 categories (via the application of Spaulding classification scheme)?
1) Critical
2) Semi critical
3) Noncritical
What are critical items (as per Spaulding classification scheme | in terms of infection transmission)?
These items pose the highest threat of infection transmission
What are noncritical items (as per Spaulding classification scheme | in terms of infection transmission)?
These items pose the lowest threat of infection transmission
Items from different categories / classes (as per Spaulding classification scheme) go through different what?
Different decontamination processes
What are critical items?
These are objects that are designed to contact normally sterile tissue (like blood) or enter the vascular system
True or False.
Any microbial load on such an object could introduce an infection to an otherwise healthy pt
True
What should be done to critical items?
These items must be sterilized (if heat resistant)
What is the preferred method of sterilizing critical items (if heat resistant)?
Steam methods
What is the preferred method of sterilizing critical items (if heat sensitive)?
Alternate method
What are the examples of critical items?
1) Forceps
2) Scalpels
3) Bone saws
What normally sterile tissue are normally contacted w/ critical items?
Blood
What are semicritical items?
1) These items ordinarily make contact only w/ mucous membranes or the skin
2) They don’t enter open wounds or penetrate soft tissues
Does semicritical items enter open wounds or penetrate soft tissues?
No, they do not
What should be done to reusable semicritical items?
These items should be steam-sterilized (if the item can withstand such treatment)
What is the min acceptable process for reusable semicritical items?
High-level disinfection
What should be done to semicritical items prior to further decontamination processing?
These items should be thoroughly cleaned to remove debris and soil
What are the examples of semicritical items?
1) Endospores and speculums
2) Dental mirrors and other simple hand tools
3) Reusable trays for making tooth impressions
What are noncritical items?
These items only ever contact intact skin and do not touch mucous membranes
Does noncritical items pose moderate infection transmission risk?
No, it poses low infection transmission risk
What level of disinfection is routinely required for noncritical items?
Low-level disinfection
What are the examples of noncritical items?
1) Stethoscope
2) Bedpan
3) Walking crutches
What is selective toxicity (in microbiology)?
It is the idea that a chemical agent or drug can exert a toxic effect on a pathogen and leave the infected host organism unharmed
What is the action of antimicrobial drugs such as penicillin, metronidazole, and chloramphenicol?
These antimicrobial drugs interact w/ cellular components that are only found in their target organism w/c allows the agent to exert its effect only on the cells that carry the target component
What is an example of a target component being acted upon by certain antimicrobial drugs?
An enzyme involved in building a cell wall or a sp metabolic ribozyme
When and what is the cause of microorganisms becoming resistant?
As microorganisms mutate, changes to the target component may occur meaning the drug may no longer exert its toxic effect
If the antimicrobial agent is present and actively killing off unwanted competing sister cells at the time, can the mutated cell may have a survival advantage?
Yes
What is the cause of antimicrobial resistance?
The proliferation of mutant cells
When can the action of antimicrobial resistance be worst?
If the resistant gene is transferred to other microorganisms
Answer the ff questions:
a) Is disinfectant selectively toxic?
b) What are the targets of disinfectant?
a) No
b) All proteins, lipids, organic compounds, etc., no sp target
Answer the ff questions:
a) Is antiseptic selectively toxic?
b) What are the targets of antiseptic?
a) No
b) All proteins, lipids, organic compounds, etc., however safe for external use on skin
Answer the ff questions:
a) Is antimicrobial selectively toxic?
b) What are the targets of antimicrobial?
a) Yes
b) Binds or is activated by a sp target found only in target organism. Safe for internal administration
Is antiseptic not safe for external use on skin?
No, because it is safe for external use on skin
Is antimicrobial safe for internal administration?
Yes
What are the principles of sterilization?
1) It is a type of decontamination where no microbial load remains on an item
2) There are 0 bacteria, fungi, spores, or even proteins present to transmit infection
What is the highest lvl of decontamination an object can receive?
Sterilization
In healthcare settings, what is recommended to be done to critical and semicritical items?
These items should be sterilized
What are the most common sterilization techniques in the lab?
1) Wet Heat (steam)
2) Dry Heat
3) Chemical
4) Irradiation
What is the other term for wet heat (steam)?
Steam sterilization
What is steam sterilization considered and what is its principle?
It is the gold std method of inactivating all organic pathogens including spores and prion proteins
What are the components (or organisms that are included) that are inactivated by steam sterilization?
Including spores and prion proteins
What should be done to some items that are heat or pressure-sensitive (in terms of sterilization)?
These items should be sterilized using an alternative appropriate methodology
What sterilization technique is commonly used for metal tools and heat resistant plastics?
Steam sterilization
What machine is used in steam sterilization?
Autoclave
What principle is an alternative to wet heat sterilization?
Baking objects in an oven where an object may be intolerant of moist conditions
True or false.
The temp and cycle time of dry heat sterilization is higher than an autoclave
True
What is the temp and cycle time in dry heat sterilization?
Temp: 160 - 190 DC
Cycle time: up to 2 hrs
In dry heat sterilization, give an example of how an object may be intolerant of moist conditions?
Due to corrosion
What is the principle of action of chemical sterilants?
These react w/ proteins and membranes to destroy organic pathogens
What type of sterilants can also be used to achieve high-lvl disinfection?
Liquid sterilants
What are the methods that eliminate the need for a high temp?
The use of chemical sterilants and liquid sterilants
Chemical and liquid sterilants can be a useful alternative to what techniques?
To wet and dry heat techniques
What is the principle of ethylene oxide chambers (for chemical sterilization)?
It applies the use of toxic ethylene gas to kill organic pathogens
At what objects can the principle of action of ethylene oxide chambers useful?
Useful for:
1) moisture and
2) heat-sensitive objects
What are the effects of the byproducts of the principle of action of ethylene oxide chambers?
The byproducts of the process of ethylene oxide chambers are very environmentally damaging, carcinogenic, and explosive
What is the length of time of long degassing times (for chemical sterilization)?
< 24 hrs
The principle of long degassing times (for ethylene oxide chambers) is reserved for what?
Long degassing times alongside toxicity issues is reserved for objects where no other techniques can be used
What are the examples of liquid sterilants?
1) Paracetic acid
2) Glutaraldehyde
What is the requirement for objects to be acted upon by liquid sterilants?
The objects are required to be completely immersed for a verified period of time to achieve sterilization
What are the results if metals are in acid for a prolonged period of time?
1) It can cause corrosion
2) Glutaraldehyde will bind blood and proteins irreversibly to the surface of a processed obj
What are the 2 types of irradiation (sterilization technique)?
1) Non-ionizing radiation
2) High energy ionizing radiation techniques
What is the principle of the 2 types of sterilization via irradiation?
These inactivates microorganisms by damaging their DNA either directly or indirectly
How are the 2 types of sterilization via irradiation employed?
Microorganisms are inactivated by damaging their DNA either directly or indirectly
What is used in non-ionizing radiation?
Ultraviolet (UV) light
Compare non-ionizing radiation and high energy ionizing radiation techniques
Non-ionizing radiation is a lower energy process than high energy ionization radiation techniques
What is used in high energy ionizing radiation techniques?
Gamma rays or X-rays
Can non-ionizing UV radiation penetrate objects and can be used to sterilize surfaces?
No, non-ionizing UV radiation can’t penetrate objs but it can only be used to sterilize surfaces
How are microbes inactivated via the use of UV bulb (or UV light)?
Any microbes in the direct sightline of the UV bulb will be inactivated due to DNA damage
Is UV light considered carcinogen to humans and other animals? If yes, why? If no, why not?
UV light is considered a carcinogen to humans and other animals because its action is inactivation of microbes due to DNA damage
What is the result if skin cell (of humans) are damaged (or exposed) by solar UV irradiation?
The skin cell DNA damaged by solar UV irradiation is linked to development of skin cancers
Irradiation techniques are operated at what temps?
At low temps
Are irradiation techniques useful for heat-sensitive items? Why or why not?
Yes, because irradiation techniques operate at low temps
What are the 2 types of indicators to determine if the sterilization run was successful?
1) Biological indicators
2) Chemical indicators
What are biological indicators and what is its principle (in terms of indication of a successful sterilization run)?
These are often small sxs of microorganism spores that should be inactivated if the sterilization method is successful
What component of a microorganism is used as a biological indicator (for a sterilization run)?
Spores of microorganisms
What should be done to the spores (used as biological indicators) after a sterilization run?
The spores are plated onto the growth medium and checked to see if they produce new cells
Provide a result (after a sterilization run) for the use of biological indicator and provide its interpretation
If spores that are putted onto the growth medium does not grow new cells or fails to grow, it is an indication that the sterilization run done is good and successful
What are the principles of use of chemical indicators (for determining if a sterilization run was successful)?
1) These indicators take the form of color-changing compounds that react if the sterilization conditions are met for the right length of time
2) These can include ink patches on sterilization pouches that change from pink / yellow to brown / black
3) adhesive tape that does the same and can be applied to bottles and paper-wrapped parcels
When does color-changing compounds formed (for chemical indicators | for a sterilization run)?
If the sterilization conditions are met for the right length of time
What is the principle of color change of ink patches (present on sterilization pouches)?
The ink patches present change from pink / yellow to brown / black
Where can adhesive tape be used?
It can be applied to bottles and paper-wrapped parcels
What is the aim of all disinfection processes?
To reduce the microbial load of a processed item
What are the 3 lvls (to see how effective is the disinfection method done) pf disinfection?
1) High-level disinfection (HLD)
2) Intermediate-level disinfection (ILD)
3) Low-level disinfection (LLD)
What is the goal of HLD?
To kill all but the most resistant of spores
What is not killed via HLD?
The most resistant of spores
What are the techniques that can be used in HLD?
Either heat or liquid immersion techniques (depending on the item to be processed)
What should be done for liquid immersion technique (for HLD) to be successful?
Objs must be completely immersed in a verified high-lvl disinfectant solution for a predetermined period of time
Provide examples of application of liquid immersion technique (for HLD)
1) 0.2 % glutaraldehyde solution can be used for up to 45 mins
2) 0.2 % peracetic acid solution can be used for 12 mins
What is the result if there is a long contact time bet metal objs and acidic solutions?
It can cause corrosion
What is pasteurization?
The process of heat processing for HLD
What is the principle of action of ILD?
Most bacteria and fungi are inactivated including slow-growing Mycobacterium tuberculosis, however, some infectious spores may remain after processing
Can infectious spores still remain after ILD?
Yes
What are the examples of intermediate (occasionally low) lvl disinfectants?
1) Bleach
2) Alcohols
What are the 2 main types of bleach?
1) Oxygen-based bleaches
2) Chlorine-based bleaches
What is the main active ingredient used by oxygen-based bleaches?
Hydrogen peroxide
What are used by chlorine-based bleaches?
Chlorine liberating compounds like sodium hypochlorite to do the cleaning
What is the result if oxygen-based and chlorine-based bleaches are combined?
It can result in large volumes of chlorine gas being quickly released
What is the result if oxygen-based and chlorine-based bleaches are mixed in a small enclosed space (like bathroom)?
It can kill a person
Are people (probably the maintenance) advised to mix cleaning mats?
No, because adverse effects may happen if done
What is LLD?
It is the most basic form of disinfection
What is the other terms (sometimes) for LLD?
Sanitization
What is the principle of action of LLD?
Many bacteria are inactivated but M. tuberculosis may survive as may some fungi and spores
What bacteria may survive from LLD?
M. tuberculosis
What other microorganisms aside from bacteria may survive from LLD?
Fungi
What component of bacteria or fungi may survive from LLD?
Spores
What is the principle of cleaning?
It is the simple removal of surface soil and debris from an object (like doing the washing up)
What is the action of surface soil?
It can impede the ingress of steam or chemical sterilants, making sterilization process ineffective
Simple cleaning serves as what?
It serves as the foundation for all other decontamination processes
True or False.
Washing items in water and detergent can not be a simple and effective technique
False, because washing items in H2O and detergent can be a simple and effective technique
If enzymes are used during disinfection, what temp is used?
Lower temp
Why washing up gloves are important?
Because of the presence of enzymes in biological detergents
Can biological dish soap wreak havoc on the skin? Why or why not?
Yes, because of the presence of enzymes
Answer the ff questions:
Given agent (disinfectant): Glutaraldehyde
a) What is the disinfection lvl?
b) What are the comments?
a) High
b) 0.2 % concentration required for HLD. Can irreversibly bind proteins to the surface of processed objs, thorough washing required before sterilant treatment
Answer the ff questions:
Given agent (disinfectant): Peracetic acid
a) What is the disinfection lvl?
b) What are the comments?
a) High to intermediate
b) 0.2 % concentration required for HLD. Corrosion of metal objs can occur w/ long contact time. Environmentally safe waste produced after processing
Answer the ff questions:
Given agent (disinfectant): Bleach
a) What is the disinfection lvl?
b) What are the comments?
a) Intermediate to low
b) 10 % concentration required. 2 types of bleach: chlorine (hypochlorite containing) and peroxide. Both peroxide and chlorine bleaches can corrode metal objs if left in contact for too long. Can irritate skin and mucous membranes
Answer the ff questions:
Given agent (disinfectant): Alcohol (e.g. isopropanol)
a) What is the disinfection lvl?
b) What are the comments?
a) Intermediate
b) Used on hard surfaces as a disinfectant or on the skin as an antiseptic. Greater than 70 % v/v solution required. Denatures cell membranes and dehydrates cells
Answer the ff questions:
Given agent (disinfectant): Iodophor
a) What is the disinfection lvl?
b) What are the comments?
a) Low
b) Iodine containing. Used at 0.1 - 0.2 % concentration. Some iodine-containing disinfectants can also be used as antiseptic agents
Answer the ff questions:
Given agent (disinfectant): Detergent (bio or non-bio)
a) What is the disinfection lvl?
b) What are the comments?
a) Basic cleaning
b) Biological detergent contains enzymes, non-biological does not. Used to remove soil and surface debris from items
What is the required concentration of glutaraldehyde for HLD?
0.2 % concentration
What disinfecting agent can irritate skin and mucous membranes?
Glutaraldehyde
What is the required concentration of peracetic acid for HLD?
0.2 % concentration
What is the required concentration of bleach?
10 % concentration
What are the 2 types of bleach?
1) Chlorine
2) Peroxide
What is the component of chlorine bleach?
Hypochlorite
What types of bleach can corrode metal objs (if left in contact for too long)?
Both peroxide and chlorine bleaches
What disinfecting agent can irritate skin and mucous membranes?
Bleach
What disinfecting agent can be used as a disinfectant or antiseptic on the skin?
Alcohol (e.g. isopropanol)
What is the required % in v/v of alcohol?
Greater than 70 % v/v solution
What disinfecting agent can denature cell membrane and dehydrates cells?
Alcohol (e.g. isopropanol)
What disinfecting agent contains iodine?
Iodophor
Iodophor is used at what concentration?
At 0.1 % - 0.2 % concentration
Can some iodine-containing disinfectants also be used as antiseptic agents?
Yes
What are the 2 types of detergent?
1) Biological
2) Non-biological
What type of detergent contains enzymes?
Biological detergent
What type of detergent does not contain enzymes?
Non-biological
What disinfecting agent is used to remove soil and surface debris from items?
Detergent
What is the principle of antisepsis?
It is the process of reducing the antimicrobial load on skin to prevent the spread of infection
When are antiseptics used?
Cleansing of the skin’s microbial flora prior to an operation
What antiseptic agent can be used prior to an operation?
Iodine solution
What is the action of antimicrobial mouthwash (as an antiseptic agent)?
To prevent infection following a tooth extraction
What are the examples of antiseptic agents?
1) Clorhexidine
2) Iodophor
3) Alcohol (e.g. isopropanol)
Can some disinfecting agents be also used as an antiseptic? How are these disinfecting agents used as antiseptics?
Yes, at lower concentration
Answer the ff questions:
Given antiseptic agent: Clorhexidine
a) What is the preparation?
b) What are the examples of use?
a) 2 % or 4 % solution
b) Prophylactic mouthwash against oral infection or helping to control existing infection
Answer the ff questions:
Given antiseptic agent: Iodophor
a) What is the preparation?
b) What are the examples of use?
a) 10 % active iodine
b) Pre-operative treatment for skin prior to surgery
Answer the ff questions:
Given antiseptic agent: Alcohol (e.g. isopropanol)
a) What is the preparation?
b) What are the examples of use?
a) ~ 70 %
b) Cleansing of wounds and grazes prior to dressing, cleansing of skin prior to injection
What are the uses of prophylactic mouthwash (as an antiseptic agent)?
1) Against oral infection or 2) helping to control existing infection
What is the use of iodophor (as an antiseptic agent)?
Pre-operative treatment for skin prior to surgery
What are the uses of alcohol (e.g. isopropanol) (as an antiseptic agent)?
1) Cleansing of wounds and grazes prior to dressing
2) Cleaning of skin prior to injection
What is the principle of action of antibiotics?
These are type of antimicrobial that are effective in treating bacterial infections
What is the principle of the term ‘antimicrobial’?
It is a term used to cover many different compounds that can halt the growth of microbial cells
Can antimicrobial compounds be non-selective?
Yes
What are the antimicrobial compounds that can be non-selective?
1) Disinfectants
2) Sterilants
Can antimicrobial compounds be selectively toxic?
Yes
What is the principle of action of antimicrobial compounds being selectively toxic?
They target a sp type of microorganism
What are the terms used for non-selective antimicrobials?
They’re loosely termed as:
1) Sterilants
2) Disinfectants
3) Antiseptics
What are the 3 types of antimicrobial?
1) Sterilant
2) Disinfectant
3) Antiseptic
Answer the ff questions:
Given type of antimicrobial: Sterilant
a) What or how is the efficacy employed?
b) What its intended uses?
a) Inactivates all living organisms
b) To eliminate all potential pathogenic spp. Used on inanimate objs only
Answer the ff questions:
Given type of antimicrobial: Disinfectant
a) What or how is the efficacy employed?
b) What its intended uses?
a) Inactivates most organisms, but spores can survive
b) To reduce infection risk, used on inanimate objs
Answer the ff questions:
Given type of antimicrobial: Antiseptic
a) What or how is the efficacy employed?
b) What its intended uses?
a) Reduces microbial load, varied efficacy
b) To reduce microbial load on skin surface and around wounds. Used on living organisms
What are the intended uses of sterilant?
1) To eliminate all potential pathogenic spp
2) Used on inanimate objs only
What are the intended uses of disinfectant?
1) To reduce infection risk
2) Used on inanimate objs
What are the intended uses of antiseptic?
1) To reduce the microbial load on skin surface and around wounds
2) Used on living organisms
Among the 3 types of antimicrobial agents, what is the only agent that is used on living organisms?
Antiseptic
What are the examples of selective agents (or antimicrobials)?
1) Antibiotic drugs
2) Antifungal drugs
What is the intended use of antibiotic and antifungal drugs?
For systemic use
Selective agents (or antimicrobials) only interact to what?
To components found only in the target microorganism
What is the result if the target of a sp antimicrobial is not expressed in a particular microorganism or if the target has become altered?
The drug will not exert an effect on that organism
What are the examples of antimicrobial agents?
1) Penicillin
2) Clindamycin
3) Metronidazole
4) Mebendazole
5) Acyclovir
Answer the ff questions:
Given antimicrobial agent: Penicillin
a) What is the type of antimicrobial?
b) What are the target organisms?
c) What are the toxic mechanisms employed by the antimicrobial agent?
a) Antibiotic
b) Gram (+) bacteria
c) Inactivates key transpeptidase enzyme in cell wall manufacture
Answer the ff questions:
Given antimicrobial agent: Penicillin
a) What is the type of antimicrobial?
b) What are the target organisms?
c) What are the toxic mechanisms employed by the antimicrobial agent?
a) Antibiotic
b) Gram (+) bacteria
c) Inactivates key transpeptidase enzyme in cell wall manufacture
Answer the ff questions:
Given antimicrobial agent: Clindamycin
a) What is the type of antimicrobial?
b) What are the target organisms?
c) What are the toxic mechanisms employed by the antimicrobial agent?
a) Antibiotic
b) Most bacteria
c) Interferes w/ protein translation by binding to ribosome
Answer the ff questions:
Given antimicrobial agent: Metronidazole
a) What is the type of antimicrobial?
b) What are the target organisms?
c) What are the toxic mechanisms employed by the antimicrobial agent?
a) Antibiotic / Antifungal
b) Many bacteria and fungi
c) Activated only in microbial cells then causes irreparable DNA damage
Answer the ff questions:
Given antimicrobial agent: Mebendazole
a) What is the type of antimicrobial?
b) What are the target organisms?
c) What are the toxic mechanisms employed by the antimicrobial agent?
a) Antihelminthic
b) Parasitic pinworms
c) Binds key cytoskeletal enzyme preventing worm growth and replication
Answer the ff questions:
Given antimicrobial agent: Acyclovir
a) What is the type of antimicrobial?
b) What are the target organisms?
c) What are the toxic mechanisms employed by the antimicrobial agent?
a) Antiviral
b) Herpes virus
c) Inhibits viral DNA synthesis, preventing replication
How does clindamycin interfere w/ protein translation?
By binding to ribosome
What is the principle (or how is the principle done) in disc diffusion assay?
In this assay, filter paper discs are treated w/ a test antibacterial cmpnd and then placed onto a bacteria inoculated agar plate
What are the discs needed in disc diffusion assay?
1) Discs treated w/ (+) control
2) Untreated disc [(-) control]
What is the component of (+) control disc?
Usually a high effective disinfectant
What is the principle of zone of inhibition?
It is the size of the area around the disc where bacteria can’t grow w/c gives an indication of the cmpnd’s antimicrobial efficacy
What are the purposes of (+) controls?
1) Used to demonstrate that an exp is capable of working
2) These would let you know that the bacteria have grown on an agar plate and what inhibition growth on that plate looks like
What should be done if the (+) control doesn’t turn out as expected?
Repeat exp
What is the purpose of (-) controls?
To check those things that shouldn’t affect an exp don’t produce an effect
Provide an ex of application where (-) controls are used
If you dilute a rgnt w/ a buffer, you might test that the buffer doesn’t have an effect on the exp
What is a another form of a disc diffusion assay?
Uses a commercially available item an antibiotic multi-susceptibility test ring (AMT ring)
What is the purpose of AMT ring?
To compare many antibiotics simultaneously
What are the components of AMT ring?
Many discs, each of w/c is treated w/ a different test cmpnd
What is the result if there are presence of zones of inhibition?
These gives an indication for an effective candidate antimicrobial
What is epsilometer test?
It is related to disc diffusion assay and it is commercially available
What is the principle of epsilometer test and what is its process?
Each strip of paper is impregnated w/ an increasing concentration of a candidate antimicrobial from the bottom to the top. The assay is processed by adding a test strip to a freshly bacteria-inoculated agar plate. After an incubation period, the MIC of a drug required to prevent microbial growth is determined by reading the concentration on the strip where antimicrobial growth is first inhibited
How is the MIC of a drug read?
By reading the concentration on the strip where antimicrobial growth is first inhibited (the point of the tear-shaped zone of inhibition)
What is the meaning of E-Test?
Epsilometer test
What are zones of inhibition?
These are areas where no bacteria can grow around an antibiotic cmpnd
What is a bacterial ‘lawn’?
It most often appears as a light-colored and opaque layer over a darker field of supportive agar jelly
What is the interpretation for gaps in the bacterial lawn?
Gaps represent areas where growth has failed
What are zones?
1) These are most commonly associated w/ antibiotic susceptibility tests such as diffusion disc assays
2) A zone can appear around diff test components depending on whether a component (like a doped filter disc) contains a cmpnd that can prevent bacteria from growing, replicating or simply being alive
What is the interpretation for image A (for exs of zone of inhibition)?
No antimicrobial effect
What is the interpretation for image B (for exs of zone of inhibition)?
Potential resistance or regrowth
What is the interpretation for image C (for exs of zone of inhibition)?
Ambiguous outcome
What is the interpretation for image D (for exs of zone of inhibition)?
True zone of inhibition
What is the principle for image A (for exs of zone of inhibition)?
In this image, we see that although the bg lawn of bacteria is slightly lightened, there are many bacteria growing right up to the disc. There is no recordable antimicrobial effect
What is the principle for image B (for exs of zone of inhibition)?
We can see a radius that appears to have been cleared, however, there are several colonies growing within this radius. This could represent colonies of resistant bacteria, or regrowth of bacteria following the decomposition of the antimicrobial agent. Either way, this test would normally be repeated in the lab, as there is no recordable clear zone of inhibition
What is the principle for image C (for exs of zone of inhibition)?
There does appear to be a zone here, however, the zone is very small and there does appear to be a few colonies growing next to the plate. This ambiguity would lead to a repeat test if certainty was required. There is no clear zone here.
What is the principle for image D (for exs of zone of inhibition)?
There is a very clear zone here w/ only a couple of small irregularities around the very edge of the zone. The bacteria-free area would be measured across its diameter and the distance recorded as the size of the zone
Provide an ex of beta-lactam antibiotics
Penicillin
What is the component of all beta-lactam antibiotics?
They carry a square-shaped beta-lactam ring at the core of their chemical structure
What is the purpose of the square-shaped beta-lactam ring at the core of the chemical structure of all beta-lactam antibiotics?
This highly reactive feature is responsible for the antimicrobial effects
What is the action of transpeptidase enzyme?
It is responsible for linking muramic acid side chains of peptidoglycan
What is the result of the action by transpeptidase enzyme?
This mesh-linking activity creates a strong cell wall
What are the action of penicillin?
It can mimic a component of the side chain and as such can irreversibly bind into the enzyme’s active site, preventing it from carrying out this crosslinking work
What is the result of the action by penicillin?
Leads to degradation of the bacterial cell wall
Provide an ex of the mode of function of all beta-lactam antibiotics
Penicillin binds to the transpeptidase enzyme
What are the ways of how the bacteria can become resistant to beta-lactam antibiotics?
1) Mutation of the transpeptidase active site
2) Expression of a lactamase enzyme
3) Altered membrane permeability
4) Active efflux of the drug
What is the principle of mutation of the transpeptidase active site (way of bacteria to become resistant to beta-lactam antibiotics)?
If the antibiotic can no longer bind into the target enzyme due to a conformational change, the drug can’t exert its effect anymore
What is the principle of expression of a lactamase enzyme (way of bacteria to become resistant to beta-lactam antibiotics)?
Lactamase enzymes cleave the all-important square-shaped beta-lactam ring that is the source of this class of antibiotic’s effect. By cutting open the ring before the drug has had a chance to interact w/ its target, the enzyme can prevent any drug-target binding from taking place
What is the principle of altered membrane permeability (way of bacteria to become resistant to beta-lactam antibiotics)?
Changes to the cell wall that prevent or slow down a drug’s entry to the cell can confer a degree of resistance. If the drug can’t reach the target, it can’t have an effect
What is the principle of active efflux of the drug (way of bacteria to become resistant to beta-lactam antibiotics)?
Efflux pumps are transmembrane proteins that pump cmpnds out of the cell. If a bacteria begins to express a pump that can remove a drug quickly, the effect of that drug will be hugely reduced
What are antimicrobial targets?
These are components of microbial cells that are either not present or are present in a very different from compared to host cells (like human or animal cells)
What are the commonly targeted microbial components?
1) Bacterial transpeptidase
2) DNA gyrase
3) Bacterial ribosome
4) DNA
5) RNA polymerase
Answer the ff questions:
Given target microbial component: Bacterial transpeptidase
a) What are the drugs present?
b) What are the actions of the drugs present to the target microbial component?
c) What are the outcomes of the action brought by drug present in response to target microbial component?
a) Beta-lactams (like penicillin)
b) Prevents the production of the cell wall by inhibiting cross linking enzyme
c) Cell wall breakdown and eventual lysis
How is the production of cell wall prevented by beta-lactams to bacterial transpeptidase?
By inhibiting cross linking enzyme
Answer the ff questions:
Given target microbial component: DNA gyrase
a) What are the drugs present?
b) What are the actions of the drugs present to the target microbial component?
c) What are the outcomes of the action brought by drug present in response to target microbial component?
a) Quinolone drugs (like ofloxacin)
b) Hijack enzyme to create breaks in the DNA
c) Prevents DNA replication and growth
Answer the ff questions:
Given target microbial component: Bacterial ribosome
a) What are the drugs present?
b) What are the actions of the drugs present to the target microbial component?
c) What are the outcomes of the action brought by drug present in response to target microbial component?
a) Lincosamides (like clindamycin)
b) Prevents ribosomal translocation and protein production
c) Arrests cell growth
Answer the ff questions:
Given target microbial component: DNA
a) What are the drugs present?
b) What are the actions of the drugs present to the target microbial component?
c) What are the outcomes of the action brought by drug present in response to target microbial component?
a) Nitroimidazoles (like metronidazole)
b) Converted to reactive form only inside microorganism cells and damages DNA
c) Prevents NA formation, preventing growth and replication
What is the result of prevention of NA formation by nitroimidazoles to DNA?
Results to preventing growth and replication
Answer the ff questions:
Given target microbial component: RNA polymerase
a) What are the drugs present?
b) What are the actions of the drugs present to the target microbial component?
c) What are the outcomes of the action brought by drug present in response to target microbial component?
a) Rifamycins (like rifampin)
b) Preventing the production of RNA by inactivating polymerase enzyme
c) Arrests cell growth and replication
