Microbiology Final (Sessions 9 - 20) Flashcards
What infections are currently at Threat Level urgent?
Clostridium difficile (C.difficile) Carbapenem-resistant Enterobacteriaceae
What infections are currently at Threat Level serious?
Vancomycin-resistant Enterococcus (VRE)
Methicillin-resistant Staphylococcus aureus (MRSA)
Drug-resistant tuberculosis
What infections are currently at Threat Level concerning?
Vancomycin-resistant Staphylococcus aureus (VRSA)
What is the meaning of generation time?
Generation time is the time required for microbial cells to double in number.
What is a culture medium usually made up of?
Water, Source of energy (sugar), Mineral nutrients (e.g. N, P, Fe), Certain growth factors (i.e. organic micronutrient) such as vitamins B1 and B12.
Explain how the number of microbial cells in a sample can be enumerated when it is cultured on a medium.
Sample (e.g. blood) is spread on a culture medium and after a few days the number of colonies are counted. Each colony represents a viable cell in the original sample.
If you work with human pathogen you must work under a …………………………………….
Biosafety cabinet
What sterilization means?
Killing all the microbes including the endospores in or on an object.
Microbial control measures fall into two categories:
Physical, Chemical
What is an autoclave?
The autoclave is a sealed device that uses steam under pressure to kill microbes and their spores. Presence of water vapor helps heat to penetrate deeper.
UV is commonly used for sterilizing …………………………….. and …………………..
Surfaces and air
A chemical that destroys all microorganisms, including endospores is called: a- Sterilant b- Sterilizer c- Sporicide d- a,b,c e- a,b
e - a, b
What is the definition of Fungistatic.
Prevent the fungus from growing but does not kill or lyse it.
What is the mode of action of Actinomycin?
It prevents RNA elongation (i.e. RNA production).
Give an example of a narrow-spectrum antibiotic.
Isoniazid (to make it easier, in Figure 27.21 only Tetracycline is a true broad spectrum)
Explain how Interferons can be used as an antiviral drug.
Interferons alarm healthy cells about an existing viral infection in the body so uninfected cells can get ready to prevent viral infection. They also inform the immune system to kill the virus.
Explain how Etest is used as an antibiotic sensitivity test (explain the procedure).
Etest is a non-diffusion-based technique that employs a preformed and predefined gradient of an antimicrobial agent immobilized on a plastic strip. Unlike paper disc, this technique is not prone to the effect of molecular structure of antibiotic (molecular structure of the antibiotic does not affect the inhibition zone).
Why is microbial control important in healthcare?
What you want is to get rid of pathogens
E.g. sterilizing surgical tools
Reducing the spread within a health care setting
Define decontamination.
Treating microbes associated with an item or material so that it is safe to handle.
What is the difference between sterilization, disinfection, and pasteurization?
Sterilization is when all of the microbes are killed, including endospores. Disinfection is when most but not all are killed, enough for it to be safe to handle. Doesn’t mean endospores are killed. Pasteurization is using moderate heat to inhibit the growth of microbes in food or liquid.
What are the main types of physical control methods?
Physical control methods include heat (dry heat sterilization, autoclave, incineration), radiation and filtration. Chemical control methods include cold sterilization, sterilant, disinfectant, antiseptic/germicides.
There are also self-disinfectants (like copper and silver)
What are the general temperatures for each of the physical control methods?
Dry heat sterilization (200) - metal and glass
Wet heat sterilization (121)
Incineration (1000) - prions and medical waste
Describe how radiation works as a disinfectant.
It destroys the genome of the pathogen. Best used on surfaces and air.
Describe how filtration works.
(think vitamins and antibiotics) - uses a filter to screen out the pathogen - it can’t fit through.
How does cold sterilization differ from autoclave?
Uses gases to sterilize objects within an enclosed device. Used for things that can’t be heated up.
Are health-care associated MRSA infections increasing or decreasing?
Decreasing
What is deadlier, MRSA or MSSA related infections?
MRSA - mortality rate 5x higher than MSSA
What is the most frequent form of transmission for MRSA infection?
Skin-to-skin
What is the difference between bacteriostatic, bacteriocidal and bacteriolytic antimicrobial agents?
- static - prevents growth but the overall number stays the same
- cidal - kills living cells but dead cells remain (viable count goes down but total count remains the same)
- lytic: reduces overall count by degrading cells
What does the term selective toxicity mean?
It means that the drug will inhibit or kill the pathogen but will not adversely affect the host. Microbes are not in and of themselves difficult to kill - the challenge is not harming the host in the process.
Give me an example of a broad spectrum antibiotic.
Tetracycline
Give me two examples of narrow spectrum antibiotics.
Penicillin, echinocandins, streptomycin, Isoniazid
Give me an example of an antibiotic that kills fungi.
Echinocandins
Name the two antifungal drugs and how they work.
Echinocandins act to inhibit cell wall synthesis and ergosterol inhibitors target the unique fungal plasma membrane component ergosterol. This results in the cell membrane not working the way that it should work.
Define minimum inhibitory concentration (MIC)
The smallest amount of an agent needed to inhibit growth of a microorganism.
Define Multidrug Resistance (MDR), Extensively drug resistant (XDR), and Pandrug resistance (PDR) and provide an example for each.
MDR: “MDR was defined as acquired non-susceptibility to at least one agent in three or more antimicrobial categories (e.g. Methicillin-resistant Staphylococcus aureus (MRSA))
XDR: non-susceptibility to at least one agent in all but two or fewer antimicrobial categories (i.e. bacterial isolates remain susceptible to only one or two categories)” [1]. Certain strains of Mycobacterium tuberculosis Extensively Drug-Resistant Tuberculosis (XDR TB)
Pandrug resistance: “non-susceptibility to all agents in all antimicrobial categories.” [1]. Klebsiella pneumoniae - can use colistin as an antibiotic but it can have harsh side effects
Where are most drug resistant genes located and how are they transferred?
Located on plasmids and are transferred to other bacteria through horizontal gene transfer.
What are two short-term solutions to address drug resistance?
Drug combinations, management and limit use in agriculture (only use as appropriate with medical confirmation)
Name one drug combination that can help overcome antibiotic resistance.
Combining a beta-lactam antibiotic with a beta lactamase inhibitor, the antibiotic resistance of staphylococcus species can be overcome.
What does decolonization involve?
Eradication of the pathogen from living tissue It usually involves the use of topical antibiotic - mupirocin.
Sources of antimicrobial drug resistance genes are:
Nature, mutation
The primary cause of antimicrobial drug resistance is:
overuse of antibiotics
Saquinavir is a …… …………………….. inhibitor that is used against HIV.
protease
List five main strategies to control MRSA in healthcare systems:
Surveillance for MRSA.
B. Proper infection control measures during patient care.
C. Cleaning and disinfection of the patient care environment and equipment.
D. Proper biosafety training of medical staff and other healthcare workers.
E. Dedicated single patient application of medical equipment
F. Decolonization therapy.
There are a few mechanisms that enables microorganisms to become naturally resistant to certain antibiotics, list two of them:
The organism is (become) impermeable to the antibiotic (i.e. prevents the drug from getting inside the cell).
• Using certain enzymes, the microbe can alter the chemical structure of the drug (drug does not function anymore).
• Organism may be able to pump out the antibiotic (efflux)
• The microbe may develop a resistant biochemical pathway
What VRSA stands for?
Vancomycin Resistant Staphylococcus aureus
How decolonization of MRSA is done?
Decolonization of MRSA means eradication of the pathogen from living tissues. It usually involves the use of a topical antibiotic (most commonly mupirocin).
CDC has some tips for healthcare provides dealing with MRSA patients list four of them:
Know what types of drug-resistant infections are present in your facility and patients.
• Request immediate alerts when the lab identifies drug-resistant infections in your patients.
• Alert receiving facility when you transfer a patient with a drug-resistant infection.
• Follow relevant guidelines and precautions at every patient encounter.
Name a bacterial disease outbreak and a viral disease outbreak that cannot be
controlled by alcohol based hand sanitizers
Bacterial - C.difficile
Viral - norovirus (Causes most forms of gastroenteritis)
Is MRSA considered a sexually transmitted disease?
No, MRSA is not considered a sexually transmitted disease
Can MRSA be transmitted to others through sex?
Yes - it is passed by skin-to-skin contact, which is not limited to sexual activity but that can be transmitted by sexual contact
Explain how MRSA screening is done?
The actual test is often done via a swab taken from the nasal area. This is then evaluated in the laboratory. Some times swabs will be taken from other areas including active skin infections, the under arm area or around the groin.
List three areas of the body that are tested for MRSA colonization.
Nasal area, under arm area or groin area
True or false: Each time we use a given antibiotic it becomes less effective in us and in others.
True
According to the video, how many people per year are killed by antibiotic resistance worldwide?
700,000 - projected to be 10 million
For what purposes microbial cultures are used in medical microbiology?
Determine the type of organism, its abundance in the sample being tested, or both.
It is one of the primary diagnostic methods of microbiology and used as a tool to determine the cause of infectious disease by letting the agent multiply in a predetermined medium.
For decades, eggs have been considered an ideal culture medium for flu virus and is used in flu vaccine production process. However, it is shown that the flu vaccines that are produced through egg culture of most types of flu viruses are not as efficient as the original virus. Can you think of any reason for this issue? Any alternative solution?
Put human virus in chicken
Virus has to use the chicken to replicate
Virus has to change a little bit (e.g. receptors)
Has to or won’t be able to replicate
When you give the chicken egg virus to human it works, but not as well as the human virus
Vaccine won’t create 100% immunity
Potential solution is to grow human cells and then introduce viruses
This is easier said than done
How high pressure inside an autoclave helps the process of sterilization?
Pressure within an autoclave allows water to boil beyond 100 Celsius; about 20 degrees beyond its boiling point
Pressure allows heat to get deeper into the substance; helps it penetrate into the object/medium
Mostly water vapour inside the chamber
Where are microbes usually found on the human body?
- skin
- oral cavity
- GI tract
- Respiratory tract
- urogenital tract
At times, host and the microbial microflora can be collectively referred to as what?
super-organisms
Define microflora.
combined microbial communities that live in a specific environment (e.g. human gastrointestinal microflora)
Define dysbiosis.
alternation or imbalance of an individual’s microflora relative to healthy state
What are the three groups of human body microorganisms?
- benign or neutral
- beneficial
- opportunistic pathogens
Describe the benign group of human microorganisms and provide 2 examples of pathogens that they indirectly protect against.
- most common group
- indirectly help human health by preventing pathogens from growing (e.g. compete for space or resources)
- normal skin flora suppresses MRSA growth
- certain neutral skin microbes boost immunity against s. aureus
Describe beneficial microbes.
Some microbes produce certain nutrients that are used by the body. (e.g. vitamins)
Describe opportunistic pathogens.
Can cause diseases when conditions are favourable to them, such as when a person is immunocompromised or their microflora has been damaged.
Example: s. Epidermidis can cause issues if it finds its way into the inner tissue, instead of on the skin’s surface.
True or False: Microbes can survive on the skin’s surface without triggering an immune response.
True. It seems that normal skin microflora is not only able to survive despite the immune system, it is able to communicate with it.
How many different genera of bacteria and fungi including a few yeast species live on our skin?
200
Why are gram positive bacteria better able to survive on our skin?
they are better able to survive in a relatively dry environment that is sometime salty
Microbial colonization begins at birth. What defines the type of microbes that will be found on the baby’s skin?
Primarily defined by the delivery mode. Vaginal birth will result in colonization by microbes present in the mother’s vagina. C sections will result in colonization by microbes present on the mother’s skin.
In a case study of microflora on hands, what seemed to influence the composition of microbes?
- gender
- time since last hand wash
- dominant hand
- family member in same household
- pet owners
What are the two groups of skin microflora?
resident microflora and transient microflora
What is the composition and diversity of skin microflora primarily based on?
- moisture
- weather
- health condition (e.g. HIV patients can have elevated levels of Candida colonized on their skin - can lead to serious infection)
- age (children can carry more potentially pathogenic gram negative bacteria)
- personal hygiene
Where is most of the microflora in the body found?
human GI tract
Where in the GI tract is the density of microbes very high?
The large intestine
What are some key products of the intestinal microflora?
- vitamin K
- vitamin B12
- some steroids are produced by the liver but first released into the GI and the GI microflora modifies them so that they can be absorbed and used by the body
- some essential amino acids
List some factors that may affect gut microflora.
- antibiotics (can lead to diarrhea and giving the advantage to antibiotic resistant strains of staph, c difficile, and candida)
- illness
- stress
- diet
- age
Recent studies have identified what range of bacterial species living inside the human gut?
3500 to 35,000
True or false: An individual’s GI microbial community varies greatly throughout his or her life.
False. An individual’s GI microbial community is relatively stable during his/her life.
In what unique circumstances do we see changes in microflora? Give a brief description of each.
- GI microflora and obesity
certain bacteria are able to produce more fatty acids that are absorbed by the host - these are more abundant in obese people - GI microflora and pregnancy
period between 1st and 3rd trimester microbial colony of GI tract changed because there will be an increase in body fat; body prepares for that. - GI and cancer (suggested that changes in the balance of human GI can be associated with certain types of cancer)
diets high in fats and proteins can result in more cancerogenic compounds produced by GI microflora while diets high in fiber may benefit the host - human inflammatory bowel disease
not caused by a pathogen but rather disruption of homeostasis in the GI microflora
Also, some studies suggest GI microflora can affect mood
Name two potential new therapies involving GI microflora.
- promoting the growth of beneficial microbes through probiotics
- fecal transplants from health to diseased individuals
True or false: The bladder and kidney in healthy people is sterile.
True
What kind of bacteria usually colonize the urethra?
facultative aerobic bacteria
What opportunistic pathogens are the common causes of urinary tract infections in women and what change in conditions can lead to the infection?
E.coli and P. mirabilis. pH change.
Explain the different microbial communities in the vagina as an adult, pre-puberty and post menopause.
As an adult, the vagina is weakly acidic. A bacterium called lactobacillus acidophilus produces lactic acid and the acidic condition is believed to reduce infections.
In pre-puberty, L. acidophilus is rare and vagina doesn’t produce glycogen. pH is neutral. Microflora includes streptococci, staphylococci and e.coli.
After menopause, glycogen production ceases and the vagina microflora is similar to pre-puberty.
What microbes are present in the adult vagina?
lactobacillus acidophilus, candida, streptococci, and e.coli
What can cause vaginosis and why is it important to determine the cause?
exogenous pathogens, bacteria, fungi (yeast), or protists (protozoa). Important to identify in order to be able to treat properly.
Define microbial pathogenesis.
The process by which a pathogen causes disease in a host.
Define disease.
The tissue damage or injury to the host caused by a pathogen or other factor, that impairs host function.
Define pathogen.
A microorganism that grows in or on a host and causes disease. Basically the pathogen benefits at the expense of the host.
Define pathogenicity.
The ability of a pathogen to cause disease in the host.
Define virulence.
A measure of pathogenicity of the pathogen or the relative ability of a pathogen to cause disease.
How is a pathogen’s virulence defined?
Primarily by its genotype.
True or false. One strain of a pathogen could be highly virulent while another strain of the species is not.
True
How can you measure virulence?
Virulence can be estimated from experimental studies of the LD50 (lethal dose50).
- The number of pathogen cells that kills 50% of the host in a test group
- Less number of a highly virulent pathogen is required to kill 50% of the target population.
True or false: Highly virulent pathogens show little difference in the number of cells required to kill 100% of the population as compared to 50% of the population
True
Define attenuation
Attenuation is the decrease or loss of virulence especially when microorganisms are kept in laboratory condition for a long time.
Why does attenuation happen?
Attenuation happens because weakly virulent mutants grow faster on culture medium where virulent pathogens have no advantage.
Can attenuated microbes regain their virulence? If so, how?
Sometimes they can, if they are inoculated to a host.
Describe the high level sequence of events that result in microbial pathogenesis.
First, exposure to the pathogen.
Infection phase includes:
- adherence
- invasion
- multiplication
The disease process includes:
- toxicity, or:
- invasiveness
Both lead to tissue or system damage.
Describe the adherence stage of microbial pathogenesis.
Adherence to skin or mucosa.
Bacterial adherence can be facilitated by
- Extracellular structures such as slime layer, capsule, fimbriae, and pili
Describe the invasion phase of microbial pathogenesis.
The ability of a pathogen to enter into a host cell or tissue.
Describe the multiplication phase of microbial pathogenesis. Give an example of how bacteria can overcome the challenges of finding resources to reproduce.
The growth of a microorganism within the host, whether or not the host is harmed. The initial inoculum of a pathogen is insufficient to cause host damage, therefore pathogen needs to reproduce. Nutrients are a major limiting factor in microbial reproduction (growth) inside the host. A good example is Iron. Transferrins is a glycoprotein in the human body that carries Iron in the human body. To be able to retrieve iron for their reproduction, some bacteria produce siderophores that have a higher affinity for iron than Transferrins. This enables the pathogen to retrieve iron from the host cells.
True or false: Most pathogens produce virulence factors compounds that directly or indirectly promote their pathogenicity
True
What are some examples of virulence factors that pathogens produce to promote their pathogenicity?
Enzymes such as protease and lipase that help pathogen to degrade host structures and helps the pathogen to spread through the body.
Using Salmonella as an example, provide examples of the diversity of virulence factors.
- siderophores (iron uptake)
- Type 1 fimbriae (adherence)
- virulence plasmid
- flagellum (motility)
- H antigen ( adherence; inhibits phagocyte killing)
- anti-phagocytic proteins induced by oxyR
- Endotoxin in LPS layer/fever)
Describe the microbial pathogenesis factor of toxicity.
the ability of an organism to cause disease by means of a toxin that inhibits host cell function or kills host cells
Toxins can travel to sites within the host that are not infected by the pathogen.
List the two groups of toxins in microbial pathogenesis.
exotoxin
endotoxin
What are exotoxins?
Toxin (usually a protein) is released from the pathogen cell as it grows.
Exotoxins are divided into more specific groups such as:
AB toxins
Enterotoxin
What is an endotoxin?
The lipopolysaccharide portion of the outer membrane of certain gram-negative bacteria, is released as bacterial toxin.
