First Aid Microbiology Flashcards
What is the treatment of choice for MRSA?
Nafcillin, a beta-lactamase resistant penicillin
Remember! Naf for Staph.
Where do the Ig binding proteins we use in lab come from?
Protein A - Staphylococcus aureus
Protein G - Streptococcal species
Alpha, beta, and gamma hemolysis
Alpha: Oxidation of hemoglobin to methaglobin, which looks greenish
Beta: Complete catabolism of heme (hence the halo)
Gamma: No hemolysis
Most common cause of endocarditis of prosthetic heart valves
Staphylococcus epidermitis
The enemy of all prosthetics. It can stick to metal because of its sticky biofilm. This biofilm also reduces immune cell and antibiotics.
Treat w/ vancomycin or novobiocin.
What is the significance of S. pyogenes protein M?
Protein M is a major virulence factor for S. pyogenes, and is the cause of rheumatic fever.
Protein M shares epitopes with cardiac myosin, resulting in the autoimmune features of rheumatic fever. This is a sequellae of strep pharyngitis, but NOT after strep skin infections, unlike PSGN which may occur after either.
Rheumatic fever is characterized by Jones criteria: Arthritis, acute heart symptoms, subcutaneous nodules, erythema marginatum, and Sydenham’s chorea.
Role of antibiotics in rheumatic fever vs PSGN
Early penicillin treatment of Strep pharyngitis can prevent rheumatic fever. However, it does not reduce the risk of PSGN.
Patient presents with bacterial skin infection. Cultures indicate that the causative organism is a bacitracin-sensitive streptococcus.
Which group of streptococci must this be?
Group A streptococci
aka Strep. pyogenes
All others are bacitracin resistant
Streptolysin O titer
Titer against a strep enzyme antibody.
Useful for retroactive diagnosis of strep infection in post-infectious sequellae, such as rheumatic fever and PSGN.
CAMP test
CAMP test + means Streptococcus agalacticae
1 cause of meningitis in neonates
Group B streptococci
aka Streptococcus agalacticae
They acquire it from their mother as they exit the vaginal canal. So, at 35 weeks pregnancy, all pregnant women are swaved and tested for GBS. If it is there, the mother is given penicillin INTRAPARTUM (during delivery) to elimiate the bacteria.
Differentiating the streptococci
Hippurate hydrolysis
+ indicates GBS is present
Streptococcus pneumoniae “MOPS” mnemonic
Meningitis
Otitis media
Pneumonia
Sinusitis
Gram + cocci growing in chains are obtained from a patient’s cultures. A sample is swaved on a blood culture plate and the below shows the results.
What tests can you do to come to a final diagnosis?
The organism is a streptococcus that is alpha hemolytic. So, it must be either Streptococcus pneumoniae or one of the viridans group Streptococci.
To differentiate these, bile solubility and optochin sensitivity may be tested. S. pneumoniae is susceptible to both, while viridans streptococci are resistant to both.
Viridans group streptococci are known to cause transient bacteremia following dental procedures. How is this possible and what are possible consequences? Can this be prevented?
Viridans group streptococci adhere to platelets via dextrans, enabling them to be swept up into the bloodstream. From here, they may colonize damaged heart valves by hopping onto platelet-fibrin aggregates at this location, causing endocarditis (most commonly the mitral valve, since mitral valve damage is highly prevalent)
This may be prevented with antibiotic prophylaxis prior to the procedure, often penicillin or a lincosamide.
Differentiating E. faecium from E. faecalis
E. faecium is rarer, but much more pathogenic and causes more severe UTIs, cardiac infections, and biliary tree infections. E. faecium is also multidrug resistant, including resistant to vancomycin, and linezolid is first-line.
Both can grow in 6.5% NaCl and are bile-resistant. (They have to be bile-resistant since they are enterococci!) They are prominent causes of nosocomial infections.
Pediatric patient presents to clinic with infection of the oropharynx. Soon after interview begins patient begins wheezing. Cervical lymphadenopathy is noted on brief physical exam, as it absent gag reflex. Patient’s family immigrated from El Salvador two years ago.
Soon after workup is begun and patient is admitted, patient develops hypotension. ECG shows ventricular fibrillation.
What other diseases is this individual at elevated risk for?
This presentation is consistent with Corynebacterium diptheriae.
Immigration status and apparent sensitivity to diptheria toxin indicates that this individual likely never received the TDaP vaccine.
Consequently, they are also at risk for tetanus and pertussis.
Pediatric patient presents to clinic with infection of the oropharynx. Soon after interview begins patient begins wheezing. Cervical lymphadenopathy is noted on brief physical exam, as it absent gag reflex. Patient’s mother reports that she has been hesitant to have the child vaccinated due to concerns over thalidomide.
What is the likely diagnosis?
Corynebacterium diptheriae infection of the oropharynx.
Pseudomembranes in the oropharynx that are not consistent with thrush should immediately make you think of diphtheria, especially in unvaccinated individuals.
If the toxin makes it to the bloodstream, it can lead to life-threatening myocarditis with arrhythmia and heart block.
Albert’s and Ponder’s stain may be used to demonstrate polar metachromatic granules. Elek’s test may be performed to evaluate whether or not strain is toxin-producing (X marks the spot, presence of toxin).
Antitoxin should be administered immediately.
Patient presents with new jaw swelling and raised erythematous lesion at the angle of the mandible. Patient has recent history of maxillofacial surgery. On exam, the abscess has draining sinus tracts under the skin.
Aspirate is taken and cultured successfully, yielding branching, filamentous, and obligate anaerobic gram positive rods. Histology of the tissue reveals sulfur granules. What is the diagnosis?
Cervicofacial actinomycosis, caused by Actinomyces israelii
Sulfur granules (shown below) and sinus tracts are pathognomonic in the context of facial abscess and recent dental/maxillofacial operation.
Treat w/ penicillin G and abscess drainage.
Patient with history of recent liver transplant, currently on immunosuppression, presents with dyspnea, chest pain, and cough productive of bloody, purulent sputum. Patient reports that they have been careful to stay home and minimize exposure to sick contacts and have instead been spending most of their time alone in their home garden.
CXR shown below. Sputum culture reveals gram positive filamentous, branching rods that grow in aerobic conditions.
What further infectious complications is this individual at risk for? What is the treatment of choice?
Patient is likely infected with Nocardia asteroides, and is at risk for encephalitis and brain abscesses. The lung CXR shows a cavitating abscess, characteristic of pulmonary nocardiasis.
Patient should be treated with sulfonamides.
Patient presents with bloody diarrhea. On CT, patient is found to have a right liver abscess. Histology from the patient is shown below.
What is the proper treatment for this patient’s condition?
This patient is presenting with entamoeba histolytica enteritis. Entamoeba histolytica is the only significant amoebal cause of dysentery (all the others are gram negative rods). It commonly causes hepatic abscesses, usually on the right, with an intraluminal consistency of “anchovy paste”. Histology shows multiple entamoebae with phagocytosed red cells.
Metronidazole is first-line. For pregnant women or following first-line treatment, paromycin is preferred. Iodoquinol may be used to treat intraluminal-limited disease, but is rarely used.
Note:Even when there is an abscess, metronidazole is preferred to surgical drainage.
Tuberculoid vs lepromatous leprosy
