Clinical Microbiology Open-Ended Predictions

Why is Mycoplasma pneumoniae resistant to penicillin?

Penicillin and other β-lactam antibiotics kill bacteria by inhibiting cell wall synthesis. Since Mycoplasma pneumoniae has no peptidoglycan cell wall, there is no target for penicillin to attack, making the bacterium naturally resistant.

Compare using soap & water vs alcohol based sanitizer

Soap & water:

- Reduces microbial load below the ID

- solubilizes microbes, washes down drain

- Effectiveness depends on time and friction/scrubbing

Alcohol-based sanitizer:

- ~70% ethanol

- acts as an antiseptic/disinfectant

- endospores remain largely unaffected

- less effective against naked virus (ex. norovirus)

Why are cultures performed?

1. To identify the pathogen (e.g., Gram+ vs. Gram−).

2. To determine its phenotype, including antibiotic susceptibility/resistance.

Compare G(+) vs G(-) cell wall structure

Gram (+)

- thick layers of peptidoglycan

- teichoic acid-lipid

- no outer membrane

Gram (-)

- thin layer(s) of peptidoglycan

- outer membrane (phospholipid bilayer)

- lipoproteins + porins

- lipopolysaccharide = Lipid A = endotoxin

- periplasm (periplasmic space)

*plasma membrane is not included for G(-)

Lysozyme (14Kd enzyme in tears, saliva, sweat) degrades peptidoglycan. Will gram (+) or gram (-) be more affected? Why?

Gram-positive bacteria are more susceptible to lysozyme because they have a thick, exposed peptidoglycan layer, whereas Gram-negative bacteria have a thin peptidoglycan layer protected by an outer membrane.

Penicillin, cephalosporin & vancomycin antibiotics prevent peptidoglycan synthesis. Why are G(+) cell wall more sensitive?

Gram(+) because peptidoglycan makes up a much larger portion of their cell wall and is directly exposed. In Gram-negative bacteria, the peptidoglycan layer is thin and protected by an outer membrane, making these antibiotics less effective.

What are the mechanisms to move materials across cytoplasmic membrane in Prokaryotic cells?

Mechanisms to move materials across

the cytoplasmic membrane in

Prokaryotic cells

• 1. Simple Diffusion (from high to low conc.)

• 2. Facilitated Diffusion (permeases)

• 3. Active Transport (requires ATP/energy)

• 4. Group Transport -special form of active

transport that occurs exclusively in

prokaryotes. The substance is chemically

altered during transport across the membrane

What are the mechanisms to move materials across cytoplasmic membrane in Eukaryotic cells?

Mechanisms to move materials across

the membranes in Eukaryotic cells

• 1. Simple Diffusion (from high to low conc.)

• 2. Facilitated Diffusion (permeases)

• 3. Active Transport (requires ATP/energy)

• 4.

- Endocytosis -surround material with

plasma membrane, enclose it and bring into

cell as a membrane bound vesicle

(phagocytosis -engulf particles, pinocytosis -

capture liquids)

- Exocytosis (excretion)

How do prokaryotic and eukaryotic cells transport materials across the membrane?

Both:

Simple diffusion

Facilitated diffusion

Active transport

Prokaryotes only:

Group transport (substance is changed during transport)

Eukaryotes only:

Endocytosis (into cell)

Exocytosis (out of cell)

What is a facultative anaerobe?

Uses O₂ if available but can grow without it

What are the start and end amino acids in translation?

Start: AUG (met)

End: UAA, UAG, UGA

What are the sources of genetic diversity in bacteria?

- Mutation (changes in DNA sequence)

- Horizontal gene transfer

- Transformation (uptake of naked DNA)

- Transduction (DNA transferred by bacteriophages)

- Conjugation (DNA transferred through direct cell-to-cell contact)

What does it mean when bacteria are described as "hyperpromiscuous"?

They readily exchange genetic material with other bacteria (often across species) through horizontal gene transfer, rapidly acquiring traits like antibiotic resistance and new virulence factors.

How do bacteria form a capsule (phenotype)?

A capsule forms when bacteria express genes that produce and secrete polysaccharides (or polypeptides) outside the cell wall, creating a protective outer layer that helps with adhesion and immune evasion.

What are the mechanisms that bacteria use to acquire antibiotic resistance?

- Mutation

- Gene transfer

- Conjugation (plasmid mediated)

- Transformation (naked DNA)

- Transduction (virus/phage)

- Transposons ("jumping genes")

What is the difference between naked and enveloped viruses?

Naked viruses have only a protein capsid (capsomeres) and are more stable in the environment (e.g., norovirus, polio).

Enveloped viruses have a lipid membrane around the capsid and are less stable because the envelope is easily damaged (e.g., HIV, influenza, herpes, HBV).

What is the difference between antigenic drift and antigenic shift?

Antigenic drift: Small, gradual changes in viral surface proteins due to mutations over time; causes seasonal flu changes.

Antigenic shift: Large, sudden change due to reassortment of viral genome segments (usually in influenza A); can create a new virus subtype and cause pandemics.

You are a microbiologist and your uncle asks your opinion on whether or not he should get the flu shot. What do you tell him from a scientific view?

The flu vaccine works by exposing the immune system to influenza antigens without causing disease. This stimulates the production of antibodies and memory cells, allowing the immune system to recognize and respond more quickly if exposed to the actual virus in the future. So yes, it is recommended, especially because it reduces the risk of influenza infection and decreases the likelihood of severe disease, hospitalization, and death.

You are a microbiologist and your uncle asks your opinion on whether or not he should get the Gardasil vaccine. What do you tell him from a scientific view?

I would recommend the Gardasil vaccine because it protects against several types of the human papillomavirus (HPV) that can cause cervical cancer, other cancers, and genital warts. The vaccine exposes the immune system to HPV antigens, stimulating the production of antibodies and memory cells without causing disease. This allows the immune system to quickly recognize and neutralize HPV upon future exposure.

Will there be another flu pandemic at some point?

- Influenza viruses, especially influenza A, undergo antigenic drift (small mutations) and occasionally antigenic shift (major genetic reassortment).

- Antigenic shift can create a new influenza subtype that most people have little or no immunity against.

- Influenza viruses circulate in animals such as birds and pigs, providing opportunities for new strains to emerge.

- Past pandemics, such as the 1918 Influenza Pandemic, 1957 Asian Flu Pandemic, 1968 Hong Kong Flu Pandemic, and 2009 H1N1 Influenza Pandemic, occurred when novel influenza viruses spread through a population with limited immunity.

How do we account for pandemics?

Caused by reassortment of RNA segments in a mixed infection of two different flu strains creating a new combination of H&N flu virus.

Compare and contrast the Salk and Sabin polio vaccines

Salk

- First polio vaccine (1955)

- grown in African Green Monkey kidney cells

- Killed virus

- Shot

- Requires boosters (not lifelong immunity)

- used exclusively in U.S. since 2001

Sabin

- Second polio vaccine (1961)

- attenuated polio (weakened)

- grew in African Green Monkey cells

- Oral live virus vaccine

- replicated in vaccinated individuals

- vaccination can spread to others (fecal oral transfer)

- strong response, doesn't require booster

- mutation: can revert to neurovirulence and cause vaccine associated polio paralysis

Explain the protection provided by Gardasil 9 and why vaccination is recommended at a young age.

Protects against HPV 16, 18, 6, 11, 31, 33, 45, 52, and 58

HPV 16 & 18 cause ~10% of cervical cancers

HPV 6 & 11 cause ~90% of genital warts

Prevents ~90% of:

- Cervical cancer

- Anal cancer

- Vulvar cancer

- Vaginal cancer (`85%)

- Genital warts

-HPV can also cause penile, head & neck, and oral cancers

- Does not protect against HPV 35, 63, or 66 (more common in black women)

- Older individuals may still benefit because protection against the remaining HPV strains is possible even if exposed to one strain already

- Girls are often vaccinated at ages 10–12 before sexual activity begins to prevent future HPV infections and HPV-related cancers

- Boys may also be vaccinated to reduce HPV transmission, protect future sexual partners, and lower their own risk of HPV-related cancers

What are the major criteria used to classify bacteria?

- Cell wall structure (Gram+ vs. Gram−)

- Cell shape (coccus, bacillus, spirillum)

- Metabolism

- Biochemical characteristics

- Genetic analysis (DNA/rRNA sequences)

What are the major criteria used to classify viruses?

- Type of nucleic acid (DNA or RNA)

- Single-stranded or double-stranded genome

- Capsid symmetry/structure (helical, icosahedral, complex)

- Presence or absence of an envelope

- assembled in host cell nucleus or cytoplasm

- virion size (10's of nm: 10⁻⁹)

What are the major criteria used to classify fungi?

- Morphology (yeast, mold, dimorphic)

- Reproductive structures/spores

- Sexual and asexual reproduction

- Genetic characteristics

What are the major criteria used to classify protozoans?

- Method of locomotion

- Pseudopodia

- Flagella

- Cilia

- Nonmotile

- Life cycle characteristics

- Morphology

- Genetic characteristics

Can a child get shingles from an older person who has shingles?

No. A child cannot get shingles from someone with shingles. However, if the child has never had chickenpox or the chickenpox vaccine, they can get chickenpox from contact with the shingles rash because both diseases are caused by the varicella-zoster virus (VZV).

*shingles is specifically the reactivation of VZV, cannot be reactivated if never exposed before

What does MMWR stand for and which government agency produces it?

Morbidity & Mortality Weekly Report; CDC