PA614 Microbiology: Growth/Detection & Microbial Structures/Virulence

Bacteria and viruses are both capable of growing within a human host and causing disease. Which one of the following statements most accurately describes the features of bacteria and viruses?

Viruses can only replicate within a cell, whereas bacteria can replicate independently of host cells.

Bacteria, fungi (yeasts and molds), viruses, and protozoa are important causes of human diseases. Which one of the following microbes contains either DNA or RNA but not both?

Viruses

Which one of the following contains DNA that is not surrounded by a nuclear membrane?

Bacteria

What are three structural differences between prokaryotes and eukaryotes?

Eukaryotes are multicellular, have membrane bound organelles, and contain a nucleus.

What do bacterial cell walls contain?

Peptidoglycan

What are two virulence factors Streptococcus pyogenes causes?

Hyalauronidase and Streptokinase

What does hyalauronidase do?

Break down connective tissue

What are the three species of Staphylococcus that are important?

S. aureus, Staphylococcus epidermidis, and Staphylococcus saprophyticus

What is the most common species of Staphylococcus?

S. aureus

Describe the relationship between virulence and infectious dose.

High virulence pathogens require a lower infectious dose to cause disease.

What distinguishes exotoxins from endotoxins in terms of their chemical composition and secretion?

Exotoxins are peptides secreted by bacteria whereas endotoxins are lipid A from LPS.

How do encapsulated bacteria such as Step Pneumoniae evade the immune system?

The capsule prevents phagocytosis and protects against immune attack.

What is the primary advantage of having normal flora in the human body?

It provides colonization resistance and primes immune response.

During which stage of HSV infection would a viral culture likely yield a positive result?

Clinical phase once the characteristic skin lesions appear.

Why are antifungal drugs that target ergosterol considered relatively safe for humans?

Ergosterol is absent from human cell membranes

How does protein A in Staph aureus help the bacteria evade immune response?

It binds to IgG which prevents complement opsonization and phagocytosis

What distinguishes acid fast bacteria from other types?

They can not be visualized using standard gram staining techniques.

What is an example of an acid fast bacteria?

Mycobacterium tuberculosis

What are some features of eukaryotes that make them differ from prokaryotes?

They are larger, have membrane bound organelles, and a have a nucleus.

What is the difference in gram negative and gram positive bacteria based on their cell walls?

peptidoglycan layer is much thicker in gram-positive bacteria. Gram-positive bacteria also have fibers of teichoic acid that protrude outside the peptidoglycan, whereas gram-negative bacteria do not have teichoic acids.

What is the clinical significance of the E. Coli serotype O157:H7?

It is a highly virulent strain that can cause hemorrhagic diarrhea

What is pathogenesis?

The process by which an organism causes disease in a host

What is the primary function of the LPS O antigen in gram negative bacteria?

It serves as a fingerprint for bacterial serotype identification.

The initial step in the process of many bacterial infections is the adherence of the organism to mucous membranes. The bacterial component that mediates adherence is the:

pilus

In the process of studying how bacteria cause disease, it was found that a rare mutant of a pathogenic strain failed to form a capsule. Which one of the following statements is the MOST accurate regarding this unencapsulated mutant strain?

It was nonpathogenic primarily because it was easily phagocytized.

Mycobacterium tuberculosis stains well with the acid-fast stain, but not with the Gram stain. Which one of the following is the most likely reason for this observation?

It has a large amount of lipid that prevents entry of the purple dye.

Of the bacterial components, what exhibits the most antigenic variation?

capsule

β-Lactamases are an important cause of antibiotic resistance. Which one of the following is the most common site where β-lactamases are located?

Within the periplasmic space

What is the most accurate description of the structural differences between gram-positive bacteria and gram-negative bacteria?

Gram-positive bacteria have a thick peptidoglycan layer, whereas gram-negative bacteria have a thin layer.

Bacteria that cause nosocomial (hospital-acquired) infections often produce extracellular substances that allow them to stick firmly to medical devices, such as intravenous catheters. Which one of the following is the name of this extracellular substance?

Glycocalyx

Lysozyme in tears is an effective mechanism for preventing bacterial conjunctivitis. Which one of the following bacterial structures does lysozyme degrade?

Pilus

Several bacteria that form spores are important human pathogens. Which one of the following is the most accurate statement about bacterial spores?

They are metabolically inactive, yet can survive for years in that inactive state.

What is colonization resistance?

The ability of commensal organisms to prevent pathogen establishment.

What is the primary mechanism by which beta lactam antibiotics like penicillin kill bacteria?

They inhibit the enzyme transpeptidase which inhibits the peptidoglycan crosslinking.

What is the primary purpose of bacterial endospores?

To enable bacteria to survive harsh conditions in a dormant state.

What are two types of bacteria that form endospores?

Bacillus and Clostridium

Why are fungi more difficult to target with drugs as opposed ot bacteria?

Fungi are eukaryotic organisms with similarities to human cells.

Why is autoclaving necessary to kill endospores?

They are resistant to heat, desiccation, and most chemicals

What are benefits provided by the human microbiome?

Synthesizing vitamins, aiding in nutrient absorption, helping the adaptive immune response, and providing colonization resistance.

What role do pilli play in bacterial pathogenesis?

They enable bacteria to attach to surfaces and host tissue.

Why do bacteria develop beta lactamase enzymes?

To destroy beta lactam antibiotics and resist their effects

Why are bacterial ribosomes good antibiotic targets?

They are structurally different from human ribosomes- prokaryotic organisms have 70S ribosomes while eukaryotes have 80S.

How do dimorphic fungi such as Candida change their morphology?

They transform from yeast to mold form when conditions allow overgrowth.

What component of the LPS is responsible for triggering septic shock?

Lipid A.

What is the infectious dose?

The number of organisms required to cause disease in a host.

Why is the gram stain ineffective for visualizing Mycobacterium tuberculosis?

The organism has layers of mycolic acid that prevents stain retention.

Why are enveloped viruses generally less stable than non-enveloped viruses?

They dry out easily and are not stable unless a liquid is present.

Why are non-enveloped viruses more resistant?

They have a protein coat (capsid) that is more resistant to environmental stressors.

What temperature and duration are required to kill a bacterial endospore through autoclaving?

121 celsius for more than 15 minutes under high pressure.

What two things are needed to kill a bacterial endospore?

High pressure and temperatures above 121 Celsius for more than 15 minutes.

What happens to bacterial cells when peptidoglycan crosslinking is prevented?

The cell walls fall apart and the cell dies as contents spill out.

How do collagenase and hyaluronidase contribute to bacterial virulence?

They break down connective tissue allowing bacteria to spread through tissue.

What is the primary function of bacterial slime layers in pathogenesis?

Forming biofilms that help bacteria adhere to surfaces and evade immune responses.

What is the difference between a yeast and a mold in fungal morphology?

Yeasts are unicellular while molds are multicellular and grow in chains called hyphae.

What is the approx percentage of people who are carriers of C diff?

3%

Why are people with uncontrolled diabetes more susceptible to opportunistic infections?

Hyperglycemia provides nutrients for pathogens and impairs immune functions.

What is the primary reason that testing for HSV during the incubation periods yields negative results?

The virus has not yet replicated to detectable levels in the body.

Which three encapsulated pathogens have vaccines available against them?

Strep pneumoniae, N meningitis, Haem Influenzae

What is the significance of bacteria developing a resistance to Methicillin?

They develop new transpeptidase enzymes that methicillin cannot bind to.

How does the infectious dose of Shigella compare to that of Salmonella?

Shigella requires over 100 whilst Salmonella requires over 100,000

Which enzyme does penicillin target to inhibit bacterial cell wall synthesis?

Transpeptidase.

What distinguishes Haemophilus Influenzae type B from other strains?

Type B has a capsule that increases it's virulence

What describes why the digestive tract is considered outside of the body?

Materials remain in the lumen and never actually enter any body tissues.

What is the primary structural component of fungal cell walls that distinguish them from human cells?

Chitin

What characteristic makes viruses different than bacteria and fungi?

Viruses require host cell machinery to replicate and are not considered living organisms.

What is the relationship between inoculum size and likelihood of developing disease?

Larger inoculum increases likelihood and severity of disease

What antibiotic is most commonly associated with C. diff overgrowth?

Clindamycin

What is the advantage of PCR tests compared to culture-based methods?

They provide faster results and are highly specific.

How does the doubling time of Mycobacterium tuberculosis compare to E. coli under lab conditions?

M tuberculosis doubles slower

What is the limitation of serologic testing in clinical diagnosis?

They cannot always determine infection location or activity status.

What defines a facultative anaerobe?

An organism that can grow with or without oxygen

What is the critical first step in lab identification of pathogens?

Obtaining an adequate sample from the patient

What precautions should be applied to all patients regardless of diagnosis?

Standard universal precautions.

What is the difference between disinfection and sterilization?

Disinfection kills most organisms while sterilization kills all organisms.

What requirement must be met for successful microscopy and staining of pathogens?

High pathogen density with minimal normal flora contamination

What is the molecular drawback of a PCR test?

They can only detect what they are designed to look for. If someone is testing for Chlamydia, but the patient has Gonorrhea it will not show the patient has a different infection.

What does a short doubling time indicate?

The organize can reproduce rapidly

What does the minimum inhibitory concentration measure in antibiotic testing?

The minimum antibiotic concentration needed to inhibit growth

When are contact precautions warranted in addition to standard precautions?

For non-respiratory infectious diseases like rashes or diarrhea

What additional equipment is required for airborne precautions beyond standard precautions?

Negative pressure room and N-95 mask

Which diseases require airborne precautions during specimen collection?

SARS-CoV-2, pulmonary tuberculosis, and measles

What do serologic tests fundamentally detect?

an antibody or antigen in a sample

What type of room is required when implementing airborne precautions?

Negative pressure room.

What does disc diffusion assay help determine in culture and sensitivity testing?

Antibiotic resistance patterns

What is the primary purpose of dilution plating in microbial culture?

To determine organism concentration

What condition requires contact precautions in addition to standard precautions?

MRSA skin infection

What is the doubling time of C. perfringens under optimal conditions?

10 minutes

What organism is classified as obligately intracellular and cannot be cultured easily?

Chlamydia species

Which respiratory pathogen requires droplet precautions rather than airborne precautions?

influenza virus

What is the doubling time for Candida albicans?

60 minutes.

What organism requires the complete absence of oxygen for growth?

obligate anaerobe

What follows the lag phase in microbial growth within an enclosed system?

log phase

What is a common name for serologic immunoassay test?

ELISA

What sterilization method uses ultra-toxic chemicals to eliminate all organisms?

ethylene oxide gas

What organism is classified as too fastidious to culture in a laboratory?

Treponema pallidum

What is a fastidious organism?

An organism that requires specific condition and difficult to meet growth requirement in laboratory settings.

What PPE is required for standard (universal) precautions?

hand hygiene, safe needle handling, face mask

What PPE is required for contact precautions?

disposable gloves, disposable gown, and room disinfection

What PPE is required for droplet precautions?

Face shield, googles, and room disinfection

When do you use contact precautions?

non respiratory infectious disease