G+ Cocci
This catalase positive, coagulase negative organism is a famous biofilm former on medical devices and can be distinguished from similar species by its gamma hemolytic activity and sensitivity to the Novobiocin antibiotic. Who’s that bacteria?
Staphylococcus epidermidis
This true zoonotic pathogen is famous for its newsworthy spores! What structural virulence factor is also unique to this organism? (Oh! And WHO’s that bacteria?) BONUS: What toxin does this organism produce that MUST BE PRESENT for its other toxins to take effect?
Bacillus anthracis - it has a protein based capsule, while most capsules are carbohydrate based. BONUS: Protective antigen (PA) - otherwise EF and LF will be ineffective.
(This question pertains to differentiating between two species of Gram negative cocci) You decide to first test for the respective species virulence factors. In your first test you decide to see if either species have endotoxic activity and find that they do, but that the endotoxin’s molecular makeup is different than that most gram negative bacteria. What is this toxin?
Lipo-oligosaccharide (LOS) similar to LPS, but without the O antigen.
This non-invasive species secretes two toxins with differing heat sensitivities, and is known to cause Traveler’s Diarrhea. Who’s that bacteria?
ETEC (Enterotoxigenic Escherichia coli). (Secretes heat labile AND heat stable enterotoxins (LT, ST))
A patient has recently come down with an infection after an extensive stay at a hospital after treatment of a wound. You, an ambitious microbiologist, want to find out the bacteria responsible as soon as possible so you can go home and watch game of thrones. You first begin with coagulase and catalase tests of your swab and find that it is positive for both. Additionally, you gram stain this organism and find it to be purple spherical shapes that form clusters. Despite your best efforts to leave early, your boss makes you stay and culture the sample to a blood agar plate with a disc of novobiocin and a Mannitol Salt agar plate. What will be the results of these tests? Who’s that bacteria?
Staphlyococcus aureus. It will have beta hemolysis on the BAP and Novobiocin sensitivity, and will turn the MSA yellow for positive fermentation.
This organism can cause sepsis/meningitis in newborn babies following a vaginal birth. It shows beta-hemolytic activity on blood agar, and is negative for coagulase. What is the confirmatory test for this organism, and how does it work? And WHO is that bacteria?
Streptococcus agalactiae. It can be confirmed by a CAMP test, which will show an increased zone of beta hemolysis near a culture of Staphylococcus aureus.
You’re attempting to differentiate between two weird looking specimens in the lab. When you look at them under the microscope, they have long branching filaments that resemble fungal hyphae. What’s up with that?! Luckily you remember your microbiology, and you decide to do a catalase test. One organism tests positive (let’s call it organism A), and one tests negative (We’ll call this one organism B). Bingo! You also test organism ‘A’ and find that it tests positive for Cord factor, an antiphagocytic agent. Who are these bacteria?
Organism A: Nocardia asteroides; Organism B: Actinomyces
You accidentally mislabel your tubes of Neisseria species in your lab and you need to determine which culture is which (without drinking either of them and contracting either an STD or meningitis). What outer membrane protein (virulence factor) could you theoretically test for, that only one species would have? (3)
Opa (opacity protein) is an outer membrane protein that is only present in Neisseria gonorrheae and would thus differentiate between the two.
This pathogen canNOT tolerate pH below 6, but it CAN tolerate some high salt levels! This motile, facultative anaerobe is primarily found in water and can grow over a broad temperature range - and it has a nasty toxin that causes “rice-water stool”. Who’s that bacteria, and what is the name and general MECHANISM of this toxin?
Vibrio cholerae; Cholera toxin - an A/B toxin that increases cAMP, which leads to watery diarrhea.
A unvaccinated baby presents in the hospital with meningitis. You culture the organism and find a gram negative rod. On further testing you find that it has a prominent capsule with ribose, ribitol, and phosphate present. However, it doesn’t seem to grow on the plates you left in the incubator. What two growth factors are needed for this pathogen to grow? Who’s that bacteria? BONUS: Name two other virulence factors of this bacteria.
Haemophilus influenzae B - it must be incubated with NAD+ and Hemin to grow in vitro. BONUS: Adhesins for attachment to epithelial cells/mucin; immunoglobulin A1 proteases
This coagulase and catalase positive organism can easily be found on your skin and mucous membranes, but if it finds its way into your food, your bloodstream, or that gnarly paper cut, you’re in trouble! It can cause Toxic Shock Syndrome, Pneumonia, and Gastroenteritis due to its multiple virulence factors. Who’s that bacteria? BONUS: Name a virulence factor unique to this organism!
Staphylococcus aureus; BONUS: TSST-1 Toxin, Protein A (antiphagocytic) (there are probably some other ones, but these are the ones that were most emphasized)
A patient in the hospital presents with a strange looking papule on the skin that has progressed to a non-healing ulcer. You culture it and it tests positive for an A/B toxin that you remember from your microbiology class binds to a protein called Elongation Factor 2 (EF2). The patient worriedly tells you as you leave the exam that they have not gotten a TDaP vaccine in over 15 years. Who’s that bacteria, and what test should you do to confirm?
This is likely Corynebacterium diphtheriae, which is usually immunized against in the TDaP vaccine. In order to confirm, you should do a Tellurite agar culture. If this is the correct ID, the organism will show gray - black colonies indicating reduction of tellurite to tellurium. (You could also do an Elek test or methylene blue stain)
A woman has recently brought her baby into the hospital with meningitis. When you take a swab of the suspected organism, you use microscopy to determine that it is a gram negative species, but you can’t see the morphology clearly enough because your microscope is old and the lens is smeared. What agar-based test could you do to confirm that a gram negative cocci species is causing this illness? How would you know for sure that it’s confirmatory (i.e, what is the nature of the test)?
To confirm a gram negative cocci based meningitis, you should culture the organism on Thayer martin agar. This agar contains 3 antibiotics: Vancomycin (which would kill all G+), Colistin (which kills all G- except Neisseria species), and Nystatin (which kills all fungi); thus you would confirm your diagnosis.
This pathogen is a Zoonotic, through rat fleas. It caused the black death back in the day, probably due to its intracellular growth ability and Type III Secretion system. Who’s that bacteria, and What special temperature range can this bug grow at?
Yersinia pestis, which can grow at 1-4C.
2 patients come into the hospital with STDs, anxious for a diagnosis and hopefully some antibiotics. Luckily, these are two STDs that were in your micro lectures. You take cultures from both. Patient 1 has painful genital ulcers, and Patient 2 has painful genital ulcers with discharge. You decide that a simple gram stain and look at the morphology should be enough to determine the species and distinguish between these two patients’ infections. What is each patient infected with? What will the gram stain show?
The gram stain of Patient 1 will show gram negative RODS, indicative of chancroid caused by Haemophilus ducreyi. Patient 2’s stain will show gram negative cocci, indicative of gonorrhea from Neisseria gonorrheae.
This catalase negative organism can cause pneumonia, middle ear infections (otitis media), bacteremia or even meningitis! It is in fact, the most common cause of bacterial pneumonia AND bacterial meningitis! It has multiple virulence factors, but what is the major one that helps it evade phagocytes? And Who’s that bacteria? BONUS: Name the other two enzymatic virulence factors!
Streptococcus pneumoniae - main VF is its capsule. BONUS: Pneumolysin, Secretory IgA protease
This spore forming organism can often causes soft tissue infections such as cellulitis and gas gangrene, but can also be a cause of gastroenteritis from food poisoning. It has a very unique hemolytic activity… Whos that bacteria, and what does it look like on a blood agar plate? BONUS: What is the confirmatory unique test for this organism? Double BONUS: Name this organism’s 5 toxins!
Clostridium perfringens - it will show a small area of beta hemolysis with a larger area of alpha hemolysis. BONUS: Egg yolk agar - culturing this on EYA will show a cloudy precipitate due to its presence of alpha toxin. Double BONUS: Alpha, beta, iota, epsilon, enterotoxin (heat labile)
This question pertains to differentiating between two species of Gram negative cocci. You test one of the species antigenically to try and classify it’s fimbriae. But you find that after many weeks of differing cultures, some of the colonies are testing differently, indicating that the fimbriae might have changed. Who’s this bacteria? What has happened, and how might this give this bacteria an advantage?
This would be Neisseria gonorrheae, due to the presence of fimbriae. This is called antigenic variation, where the fimbrial tip may change its antigenic activity, which can help hide the pathogen from immune cells.
This opportunistic pathogen has produces an exotoxin that binds to the same target as that of diphtheria toxin. What is the name of this target, and who’s that bacteria? BONUS: What is this organism’s antiphagocytic virulence factor?
Pseudomonas aeruginosa; bonus - Slime layer (glycocalyx)
A patient in the hospital has come down with a rather serious case of food poisoning. You’re not sure the diagnosis yet, but on first glance at your slide you can see that it is a gram negative rod shaped species, and through some magical testing you’ve found that it has intracellular growth ability. On accident, you leave your plates in a cold incubator (4C) overnight, but the culture grows as normal. Who’s that bacteria?
Yersinia enterolitica
This catalase negative organism is normally found in the throat and skin, but in the winter and spring months, can cause a throat infection that when left untreated can progress to Acute Rheumatic Fever! What are the names of this bacterium’s adhesins (3)? And Who’s that bacteria?
Streptococcus pyogenes - adhesins are M protein, F protein, and lipoteichoic acid.
A major food poisoning outbreak has occurred at a nearby restaurant. After some investigation, it is determined that the culprit was an improperly cooled dish of fried rice with meat and vegetables. After testing some patients and interviewing them, you find that they got their symptoms about 8-10 hours after consuming the food and their main symptom was vomiting. What TOXIN was responsible for these symptoms, and Who’s that bacteria that was all up in that food? BONUS: What type of toxin is this? What is the name and the type of the other toxin secreted by this organism?
Bacillus cereus; the toxin was likely a heat STABLE enterotoxin due to the symptoms and time of onset. BONUS: heat stable enterotoxin is a superantigen. The other toxin, the heat labile enterotoxin, is an AB toxin.
Two newborn infants present in the hospital with Gram negative cocci based infections. One (Boy) has an ocular infection. The second, (Girl), has pneumonia. Their mothers are clearly big Bird Box fans. Which child is infected with which Neisseria species?
Boy - Neisseria gonorrheae; Girl - Neisseria meningitidis
This species is one of the facultative intracellular pathogens that belongs to the Enterobacteriaceae family. It is tolerant to stomach acids, and bile salts! If you get this bug in your bloodstream, you could end up with high fever, headache, abdominal pain, constipation or diarrhea (be thankful for clean water and VACCINES!) Who’s that bacteria? BONUS: What toxin does this organism produce?
Salmonella typhi; bonus - Heat labile enterotoxin
Your friend is attempting to diagnose a patient with a middle ear infection (otitis media) and after initial analysis you find that it is gram positive and spherical shaped. They culture this organism to a blood agar plate and find greenish halos around the colonies. You tell them to next test its antibiotic sensitivity, but they can’t recall the name of the right one! What antibiotic disc would be best suited to find a confirmatory identification of this bacteria? BONUS: your friend accidentally threw out all of the lab’s antibiotic discs! What other test could they do to confirm the ID?
Based on this information, this species is likely Streptococcus pneumoniae, so the ideal antibiotic to test for sensitivity would be Optochin, which S. pneumoniae is sensitive to. BONUS: your friend accidentally threw out all of the lab’s antibiotic discs! What other test could they do to confirm the ID? A: A bile solubility test (clearing will indicate S. pneumoniae, or a Quelling Reaction (positive swelling = S. pneumoniae)