Microbiology-Bacterial URIs Flashcards
A patient comes to see you with a sore throat. You check her vitals, take her history and take a look at her throat. What things will help you determine if her sore throat is viral or bacterial?
Viral pharyngitis comes with more nasal discharge, less incidence of fever in adults and people are healthier than they feel. GpA Strep comes with more swelling, erythema, exudate, temperature and tender lymph nodes. Bacterial infections are typically devoid of typical viral symptoms: conjunctivitis, cough and rhinorrhea.
What pathogens cause most infections in the nasopharynx?
Mostly viruses (rhinoviruses, coronaviruses). Viruses are the most common pathogens of all pharyngitis.
What pathogens cause most infections in the oropharynx?
Strep pyogenes, diptheria, EBV (mono), adenovirus, enterovirus and acute HIV infection.
What pathogens cause most infections in the middle ear and sinuses?
Strep pneumoniae, H. influenzae non-typeable, Moraxella catarrhalis and group A strep.
What pathogens cause most infections in the epiglottis?
H. influenzae type B (Vaccine preventable Hib)
What are the lab characteristics of a group A strep culture?
Gram-positive, catalase negative, beta-hemolytic, bacitracin-sensitive and chain-forming cocci.
What are the different manifestations of suppurative streptococcal diseases?
Note that Scarlet fever and TSS only occurs after production of super antigens.
What are the different manifestations of non-suppurative streptococcal diseases?
Acute glomerulonephritis and rheumatic fever.
A 12 year old girl comes to your clinic complaining of nausea, vomiting, abdominal pain a sore throat and she has a temperature of 102. Throat culture is positive for Gram+ catalase - cocci. What complications is this patient at risk for?
She has group A strep infection. Complications of this infection include peritonsillar abscesses, scarlet fever, cervical adenines, otitis media or strep TSS.
This patient comes to see you in clinic with a temperature of 102 degrees. You treat her with antibiotics and the infection goes away, however, three weeks later she returns with acute cardiac symptoms consistent with endocarditis. Why do you prescribe the patient a life-time supply of amoxicillin?
The group A strep infection caused antibody production that can also opsinize its own tissue in the heart. Regular prophylaxis with antibiotic prevents future infection and activation of plasma cells to produce more of those self-destructive antibodies.
A 19 year old male comes to see you at the university health clinic. He and several other roommates have come down with meningitis. History reveals no vaccination in this patient. Lab results reveal the gram-negative coccobacilli shown below. Where are you most likely to find immune response against this agent?
This is H. influenzae that commonly caused bacterial meningitis before its vaccine was invented. It will be found in CSF fluid and PMNs will be phagocytosing it as seen below.
A patient comes to see you with epiglottitis. His laryngoscopy is shown below. What lab type of culture will you order from the lab?
The most common offender in epiglottitis is H. influenzae type b. Chocolate agar is heated up blood that causes them to lyse and release hemin (X) and NAD/NADP (V). H. influenzae B requires both of these things in order to grow.
What is unique to H. influenzae type B’s capsule? How does this help our body to protect against it?
It has PRP (polyribose-ribitol phosphate). This is the strain of H. influenzae that is responsible for most systemic disease in humans; however, antibody against the capsular polysaccharide can recruit complement and cause lysis because it is a gram - cocci.
What is different about the H. influenzae that causes otitis media?
It is the non-encapsulated type that is a part of our normal flora in our upper respiratory tract. This is the second most common offender only to S. pneumoniae.
What diseases is Hib commonly responsible for?
It is a very invasive bacteria that can get into the upper respiratory tract and spread throughout the body.
What is so nifty about the Hib vaccine?
It is a polysaccharide. Normally APCs cannot present a polysaccharide to a helper cell in the immune response. With Hib, the polysaccharide is coupled with a protein that allows for presentation by the APC, recognition by the T cell and activation of B cells into plasma cells that will produce antibodies against that particular antigen.
A patient comes to see you with a sore throat. You do a throat swab and culture and get the results back below. What is your next step in narrowing your diagnosis?
Diptheria can convert tellurite to a black color as seen in the image. However, that is not your concern, you are concerned if it is making toxin or not. You analyze this with PCR.
A patient comes to see you who has never received any vaccinations. You diagnose him with diphtheria after running several lab tests. How long is the incubation period in this patient and what is he at risk to die from?
2-5 day incubation period. The toxin destroys cells in the upper airway and creates a pseudomembrane that occludes the airway. The toxin also causes neuritis and myocarditis.
How does the diphtheria toxin work?
Neutralizing antibody blocks the toxin from ever binding to cells where it would normally inhibit protein synthesis.
