Microbiology

How does Streptococcus viridans appear on a Gram stain?

Gram positive cocci in chains

What is the most critical factor in the spread of nosocomial infections involving Staphylococcus aureus?

Patients in a hospital setting have compromised biological defenses, either immuno-suppressed or with new portals of entry.

Peptidoglycan is the major component of the prokaryotic cell wall. Its arrangement is one determining factor in the results of a Gram stain. What peptidoglycan structural feature is only found in Gram-positive bacteria?

Pentaglycine cross-bridges are a feature only found in Gram-positive bacteria. In Gram-negative bacteria, there is a direct cross-link between tetrapeptide chains extending off of NAM molecules. NAG molecules, NAM molecules, and tetrapeptide chains are all structural features found in both Gram-positive and Gram-negative bacteria.

A patient presenting with cyanosis, hemorrhagic mediastinitis, and meningitis is proposed to have been exposed to Bacillus anthracis endospores (anthrax). What is the most likely route of transmission?

Inhalation of aerosolized endospores

What aspect of Gram-positive bacteria allows species like Clostridium and Bacillus to form endospores?

Thick peptidoglycan layer

When adenine is the nitrogenous base on a segment of DNA, what is the other nitrogenous base it binds to on the opposite DNA strand through hydrogen bonding?

Thymine

Which of the following microorganisms is considered an obligate anaerobe?

Clostridium tetani

What is the term for a strand of nucleic acids and associated proteins that carries the genetic information of an organism?

Chromosome

Rheumatic fever is a post-streptococcal disease caused by an immunologic response to the initial infection. It may lead to migratory polyarthritis and carditis. How long after an initial infection do the symptoms of rheumatic fever appear?

2-3 weeks

How many histone proteins make up a nucleosome in the making of eukaryotic chromosomes?

8

Porin is a structural molecule in bacteriology. Which one of the following is called porin?

A protein forming a channel for transport

What is the name of the manifestation where a patient's immune response during infection with Streptococcus pyogenes produces antibodies that react with host sarcolemma, myosin, and synovium?

Acute rheumatic fever is an autoimmune state induced by streptococcal infection where antibodies produced by the host are reactive with muscle fiber sheath and the membrane in joints. Erysipelas is an infection of the skin and subcutaneous tissue. Scarlet fever is pharyngitis due to a streptococcal strain capable of producing superantigens. Streptococcal toxic shock syndrome is a very serious, rapidly progressive multisystem disease where shock and bacteremia are possible.

Which of the following bacteria is the first microorganism linked to a specific disease?

Bacillus anthracis

What is the site of action of beta-lactam antibiotics against Gram-positive organisms?

Bacterial Cell Wall

What is the standard recommended treatment in the United States for a patient undergoing secondary prevention for rheumatic fever once group A streptococcal pharyngitis is confirmed?

Benzathine penicillin once a month for several years

Which molecule acts specifically by binding to the promotor site of the lac operon so that the genes can be effectively transcribed?

Catabolite activator protein

What is a likely route of transmission of anthrax to humans?

Contact with contaminated bone meal fertilizer

Site-specific DNA inversion is made possible by inherent flexibility of enzyme and double-stranded DNA molecules. DNA inversion at secondary crossover sites is a proposed mechanism for control of gene expression, but the stochastic nature of this mechanism has also led to proposals highlighting the adaptive nature of this event. What is a potential adaptive advantage of DNA inversion within bacterial populations?

Generation of variation

What is an operon in terms of the regulation of bacterial genes?

Genes that participate in the same metabolic activity

What proteins are able to wrap DNA around them to condense the structure of DNA?

Histones

What is the primary metabolic activity controlled by the lac operon in bacterial species?

Lactose catabolism

What does the slow progression of healing of cutaneous anthrax generally lead to?

Limited systemic symptoms

What characteristic of microbes causes mutation to display a large influence within bacterial populations?

Low generation time

What structure is observed for the identification of different Gram-negative bacterial species and strains?

O Antigen

What type of mutation is a single nucleotide substitution that causes a change in the codon, resulting in production of a different amino acid?

Missense

What structures lack a cell wall?

Mycoplasmas

What type of mutation is a change in codon specifying a premature termination codon?

Nonsense

Certain bacteria are capable of generating bioluminescent chemicals under specific conditions. Which of the following refers to the ability of bacteria to share cell density information and regulate patterns of gene expression?

Quorum sensing

Scalded skin syndrome is caused by Staphylococcus aureus. What is the mechanism of the disease progression?

Release of protease

What basic bacterial shape is the bacterium Bacillus anthracis?

Rods

Bacteria have characteristics amenable to the study of spontaneous mutation, including haploidy, a highly studied and characterized genome, and what other feature?

Short generation time

What type of mutation changes the original codon into another codon that codes for the same amino acid?

Silent

Mannitol salt agar is used to culture which of the following microorganisms?

Staphylococcus aureus

A 5-year-old girl presents with sore throat, runny nose, and itchy eyes. Patient has no fever, but a rapid strep test is negative. A throat culture is sent into the lab. The patient is sent home and advised to return if there is fever or worsening symptoms. Gram stain shows a Gram-positive coccus in chains. In the following days, the culture shows alpha hemolysis, is green in color, and has small gray colonies. What is the most likely organism?

Streptococcus viridans Streptococcus viridans is an alpha-hemolytic (green incomplete hemolysis) Gram-positive coccus seen in chains. Streptococcus viridans is part of the normal flora of a human mouth. On a blood agar, it grows in small grayish alpha-hemolytic colonies. Escherichia coli is a Gram-negative rod that does not typically cause pharyngitis. E. coli can grow on a blood agar as a smooth round gray-white colony. Some strains are beta-hemolytic, or they show no hemolysis at all. Staphylococcus aureus is a Gram-positive coccus seen in clusters that does not typically cause pharyngitis. On a culture, this organism grows as a medium-sized round creamy yellow colony and shows beta-hemolysis. Streptococcus pyogenes typically causes "strep throat" and would cause a positive rapid strep test. A rapid strep test looks for Group A strep, which causes beta-hemolysis or full hemolysis on blood agar after culture. S. pyogenes also produces small grey colonies similar to Viridans strep on blood agar and is also a Gram-positive coccus in chains. The key difference is the hemolysis that was shown on the culture.

The process of nucleotide substitution (replication infidelity) occurs during DNA replication. Base pairing depends on electron distribution within nucleotides of parental and newly synthesized DNA. Short-lived physical forms (tautomers) arise and can result in mispairing of bases due to intrinsic pliability rather than a replicative misstep. What is a plausible mechanism for the process of nucleotide substitution?

Structural flexibility of enzyme and DNA molecules

What is the purpose of the cell wall in bacteria?

To prevent osmotic lysis of the cell

Which of the following antibiotics is used to treat methicillin-resistant Staphylococcus aureus (MRSA)?

Vancomycin

Which of the following microbes is the most common cause of subacute endocarditis in individuals?

Viridans group streptococcus

What species of staphylococcus commonly causes surgical wound infections of the skin?

aureus