ID Final Exam

Yeah bro we ballin

Before antimicrobials what was the main killer of the human race?

Infectious diseases

What is the rate of death due to infectious diseases today?

1/2

What are the 3 characteristics used to describe the world of microorganisms?

Unseen, undiscovered, dominant

Rank the sizes of the following from largest to smallest: viruses, bacteria, human cells, protozoa

Protozoa > human cells > bacteria > viruses

What are some reasons that bacteria are the dominant life form on Earth?

Live in every biosphere, most diverse organisms, influence evolution, great in numbers, began life, and have many life sustaining functions such as O2 production and nutrient cycling

Why is it difficult to culture species of bacteria?

Many species are codependent on each other with many consuming the excretions of others as food sources

SATA In what way can bacteria be considered the dominant form of life on Earth?

1. Bacteria are composed of eukaryotic cells

2. Bacteria are the most abundant organisms on Earth

3. Bacterial activity has influences the evolution of other organisms

4. Bacteria inhabit all parts of the biosphere

5. Bacteria demonstrate the greatest species diversity

2,3,4,5

What are the nonliving microbials to focus on in this class

Prions, viruses

What is the genetic code for prions?

Proteins

What is the genetic code for viruses?

DNA or RNA

How do we classify bacteria?

Thickness of cell walls as determined by gram staining

What type of gram stain does a thin wall bacteria lead to?

Gram -

What type of gram stain does a thick wall bacteria lead to?

Gram +

What are the 4 eukaryotic kingdoms that microbes exist in?

Protista, Fungi, Plantae, Animale

How are protists classified?

Photosynthesizing (protozoa), non-photosynthesizing

Define magnification

Ratio of the size of an image to the size of an object

What is used to achieve magnification of specimens?

Series of lenses

How is total magnification calculated based on the lenses?

Total magnification = Magnification of each of the lenses multiplied by each other

100x= (10x)*(10x)

How is magnification calculated based on relative sizes?

Magnification = image size/actual size

(220mm/2.3mm=9.6x)

What type of microscope is this displaying?

Bright light microscope

Define resolution

the degree to which is microscope is able to produce separate images of lines that are very close together; a measure of the sharpness of an image

How is resolving power calculated?

l/(2*NA) [l= wavelength of light, NA= numerical aperture of lens]

Define numerical aperture

A measure of light refraction, proportional to the refractive index of the medium in which light is traveling in

True or false. Light with a greater wavelength would produce a greater resolution of an image.

False. l/(2*NA)

How can the numerical aperture be increased

Using immersion oil as it has a greater refractive index than are which limits the refraction of light, improving the resolution

SATA Which of the following influences the resolving power of a microscope?

1. The wavelength of light

2. The refractive index of the medium through which the light is traveling

3. The numerical aperture of the lens

4. The intensity of light

1,2,3

What are some disadvantages to bright-field miscropy?

Limitations on magnification and resolution, thin prep of specimen, staining is often required to improve contrast

What is bright-field microscopy used for?

Examining bacterial morphology or external structures or identifying eukaryotic pathogens and gram identification

What type of microscope is this?

Dark-field microscopy

What are some advantages to dark-field miscroscopy?

No staining required, able to visualize live and very thin organisms

How does dark-field microscopy work?

Light comes at an angle around an opaque disk which is reflected through condenser lenses and into the objective lens, making the image appear light

What are some advantages to fluorescence microscopy?

Fluorescent molecules can be made to only bind to specific proteins, highlights items too small to see

What is an example of a clinical application of fluorescence microscopy?

Identification of neurons infected with rabies vaccine

What type of microscope was used to view this image?

Bright-field microscope

What type of microscope was used to capture this image?

Dark-field microscope

What type of microscope was used to capture this image?

Fluorescence microscope

What were three things that changed from 1900 to now that led to fewer deaths from infectious diseases?

Sanitation, vaccination, antibiotics

What are some unintended consequences of overuse of antibiotics?

Antibiotic resistance, alterations in the microbiome leading to things such as c diff

What is a hallmark sign of infection?

Fever (>100.4F)

What can create a false positive for a fever?

Malignancy, drug fever, blood transfusions, recent surgery

What can create a false negative fever?

Use of antipyretics, antimicrobial therapy, overwhelming infection

What lab value is generally a confirmation of infection?

Elevated white blood cell count (>10,000)

What is a way to zero in on where an infection may be in the body?

Where pain and inflammation is occuring

What should we do before beginning antimicrobial therapy?

Start efforts to identify the pathogen- microscopy, culture, or molecular tests

What is an issue with selecting antimicrobial therapy when it comes to pre-marketing data?

Lack of comparative trials, extremely ill patients were excluded, generally all organisms are susceptible to antibiotics

If a culture is gram postive, how will it appear under a microscope?

Blue

If a culture is gram negative, how will it appear under a microscope?

Red or pink

Define MIC

Lowest concentration of antimicrobial that prevents visible growth performed with a broth dilution

Define MBC

Lowest concentration of antibiotic that kills a bacterium

What are some situations where we should determine an MIC?

Severe infection (especially when the MIC is expected to be low), unusual resistance, uncommon organisms, unexpected treatment failure, usage of a new antibiotic that isn’t normally in a culture panel

Define antibiogram

A chart made to describe susceptibility of bacteria to antibiotics for a local population (such as a hospital), used to make empiric decisions to treat infection

What’s an important thing to consider with antibiotics in terms of protein binding?

Only free drug is active

Where do most pathogens typically live if an infection is in tissue?

Extracellular fluid

How does the free drug concentration in the blood compare to the extracellular fluid concentration?

Equal

True or false. Renally eliminated antibiotics can be used to treat UTIs

False

Define bactericidal agent

An agent that kills 99% of the organism within 24 hours

Describe concentration dependent bactericidal activity

A direct relationship between antibiotic concentration and bactericidal effect

Describe time dependent bactericidal activity

Maximum suppression of an organism is achieved as long as antibiotic concentrations remain above the MIC

Define bacteriostatic

An antimicrobial that kills <99% of an organism in 24 hours; kills enough to keep growth in check

What is the practical difference between bactericidal and bacteriostatic agents?

None

What type of MIC relationship is displayed here?

Dose dependent

What type of MIC relationship is displayed here?

Time dependent

What are some major offenders for drug interactions with antibiotics?

Rifampin, HIV drugs, fluoroquinolones with antiarrhythmics, warfarin

In general, how do we manage drug interactions when it comes to antibiotics?

Weigh the potential benefit of the antibiotic and recognize the antibiotic is generally temporary

What are some factors of the patient that can affect antibiotic selection?

Age, genetic and metabolic abnormalities, pregnancy, renal and hepatic function, site of infection

What are some things to assess when you see a sick patient in an outpatient setting?

How sick are they, do they need to be stepped up in care, is this viral, have they had any other antibiotics, do they have any infectious history, do they have any real allergies, is there a diagnosis

When is the best time to obtain cultures?

Before antibiotics have been given

EM is in your hospital and has been for the last 5 weeks after a routine surgery was complicated by a wound infection. He is currently in the ICU, intubated and sedated. Today he has spiked a fever to 102.2 and his WBC is 19.1. The wound appears unchanged from previous exams, it is not erythematous and isn’t warm to the touch. His urine and bowel output is stable. What is the most likely source of new infection in this patient?

1. Urine

2. Antibiotic associated colitis (c diff infection)

3. Lung (pneumonia)

4. Surgical wound

3

A patient presents to the ED with S/S suggestive of infection including fever to 103.1, WBC 23.4, BP 97/61. Which of the following is the best course of action?

1. Initiate empiric antibiotics immediately, then take a sample for culture

2. Get a sample for culture immediately and then start empiric antibiotics right after

3. Get a sample for culture and wait to start antibiotics until culture results come back

2

In general how should you think about antibiotics?

Spectrum of gram positive and gram negative coverage along with aerobes and anaerobes

Is it better to overdose or underdose antibiotics?

Overdose- who cares if the SCr increases we want to kill the infection

What is the number one way we should follow up on when administering antibiotics?

See if cultures came back to more directly target therapy and limit collateral damage

What are Dr. Leonard’s three fundamental skills of ID?

Understand the usual microbiology of various infections, be able to make an appropriate empiric recommendation based on knowledge of usual microbiology and available data and guidelines, appropriately narrow antimicrobial therapy in response to susceptibility data

Define smear for light microscopy

A suspension of a bacterial sample is spread on a slide with an inoculating loop then air dried

Define fixation for light microscopy

Process of adhering bacterial cells to a slide by coagulating carbohydrates and proteins to glass surface via heat or chemical methods

Describe a basic (pH) stain

Stain is positively charged at a neutral pH and binds to negatively charged proteins in addition to DNA

Describe acidic stains

Negatively charged at neutral pH, since bacterial surfaces tend to be negatively charged, the stain is repelled leaving a stained background and the cells themselves unstained (negative staining)`

Describe a differential stain

Use of multiple des to allow for differentiation of one microbe to another such as gram staining

What is the order of dyes and solutions used for gram staining?

Crystal violet, gram’s iodine, ethanol, safranin

What does crystal violet do?

Stain all bacterial cells with peptidoglycan in their walls

What does gram’s iodine do?

Interacts with crystal violet to form insoluble complexes

What does ethanol do in gram staining?

Decolorizes the stain, removing violet-iodine complexes from the bacteria with thin layers of peptidoglycan

What is safranin’s purpose?

Counterstain that colors the DNA of all the cells so they’ll appear red or purple

If a bacterium has a thick cell wall, what will the result of gram staining be? (color and + / -)

Purple, Gram +

What does it mean if a bacterium is red or pink after gram staining?

The bacterium has a thin cell wall, gram -

The _____ in a Gram stain removes the _____ from _____ cells.

1. EtOH; crystal violet and iodine; gram negative

2. EtOH; crystal violet and iodine; gram negative

3. iodine; crystal violet; gram negative

4. iodine; crystal violet; gram positive

5. safranin; iodine; gram negative

1

Describe acid-fast staining and how it’s used as a diagnostic tool

Process where red fuchsin is applied and heat is applied to drive the stain through specimens with a waxy wall then rinsed with an acid alcohol decolorizer, then methylene blue is applied for better visualization. This is used to diagnose diseases such as TB and leprosy where the bacteria have a thick, waxy wall

Define endospore

Resistant asexual spores that develop inside some bacteria which can help in identification and diagnosis of certain species

What type of stain is capsule staining?

Negative stain

Why would we stain flagella?

Too thin to see with a light microscope so staining helps with visualization

What type of stain is this?

1. Capsule stain

2. Acid fast stain

3. Endospore stain

4. Dark field microscopy

1

What are common features of prokaryotes and eukaryotes?

Macromolecular structure, DNA as genetic information, DNA → RNA → protein, ATP as energy, cell membrane provides structure and function, glycolysis is the energy-yielding pathway

How is genetic information stored in a prokaryote?

In a circular chromosome or in one nucleoid

What is the difference between an 80S ribosome and a 70S ribosome?

70 S has no space between ribosome components and is present in prokaryotes, 80S is present in eukaryotes and has a gap

What is the cell wall of a prokaryote made of?

Peptidoglycan

How do prokaryotes divide?

Binary fission

SATA The key feature shared by all prokaryotic cells include

1. 80S ribosome

2. True membrane-bound organelles

3. Replication via binary fission

4. Structurally complex cell wall

3,4

A _____ cell has _____ but lacks _____

1. Prokaryotic; a single circular chromosome; a nucleus

2. Eukaryotic; multiple linear chromosomes; 80S ribosomes

3. Prokaryotic; a complex cell wall; a cell membrane

4. Eukaryotic; many complex membrane-bound organelles; the ability to divide by mitosis

1

SATA How do prokaryotes help to sustain life on Earth?

1. Photosynthetic prokaryotes produce glucose and oxygen gas used by all other aerobic organisms

2. Only prokaryotes can perform nitrogen fixation

3. CH4 generating bacteria live within roots of legumes and other plants

4. Prokaryotes live in symbiotic relationships in stomachs of grazing animals to give them nutrients from plant material

1,2,4

What determines the shape of a bacterium?

Cell wall