MICRO Flashcards
7 species included in the Enterobacteriaceae
E. coli Salmonella Shigella Klebsiella Enterobacter Serratia Proteus
5 lab characteristics of Enterobacteriaceae
Capsular K antigen – virulence Flagellar H antigen All ferment glucose Oxidase -
Does ETEC cause a fever?
Nope. It does not invade the intestinal wall.
Most common cause of gram negative sepsis
E. coli (#2 is Klebsiella)
Most common cause of food-associated diarrhea in developed countries
Salmonella enterica and enteridis Poultry, eggs, reptiles
Which bug do you avoid treating with antibiotics?
Salmonella –may prolong carrier state in salmonella GI tract infections
Bug associated with causing Reiter syndrome
Shigella flexneri
Diarrhea caused by gram - nonmotile organism that does not ferment lactose
Shigella
2 organisms associated with rice-water stools
Vibrio cholera ETEC
Diarrhea transmitted from pet feces
Yersinia enterocolitica
Diarrhea caused by gram - motile organism that does not ferment lactose
Salmonella
Diarrhea caused by gram - lactose fermenting bacteria with no fever
E. coli
2 organisms associated with diarrhea + recent ingestion of water from a stream
Giardia lamblia Entamoeba histolytica
4 organisms known to cause infections in the mouth of AIDS patients
Candida albicans HSV CMV EBV (oral hairy leukoplakia)
3 structural genes that code for HIV proteins
pol (Reverse transcriptase env (gp120, gp41) gag (p24)
32 y.o. male patient went camping in northern CA 2 weeks ago, had a 2 day stint of diarrhea and now presents with sx of liver damage and jaundice. Whats the infecting organism?
Entamoeba histolytica
Classic triad associated with congenital Toxoplasmosis
Chorioretinitis Hydrocephalus Intracranial calcifcations
Organism associated with hemoptysis
Paragonimus westermani
2 organisms that can lead to microcytic anemia
Acylostoma Necator
Organism associated with pigmented gallstones, cholangiocarcinoma
Clonorchis sinensis (undercooked fish)
Organism associated with liver cysts and how is it acquired
Echinococcus granulosus Ingestion of eggs from dog feces
Associated with Eosinophilic Loeffler’s pneumonitis and how it is treated
Ascaris Lumbricoides Treated with bendazoles or pyrantel pamoate
Most common cause of pneumonia in children 1-year-old or younger
RSV
Most commo ncause of pneumonia in the neonate (B-28 days)
Group B strep or E. coli
Common cause of pneumonia in patients with other healt hproblems
Klebsiella pneumonia
Common bacterial cause of COPD exacerbation
H. influenzae
Intra-alveolar exudate is found on CT. What is the causative organism?
S. pneumo usually Klebsiella This is LOBAR pneumonia.
Patchy distribution of acute inflammatory infiltrates involving >1 lobe. What are the 4 most likely causative organisms?
S. pneumo S. aureus H. influenzae Klebsiella
Diffuse patchy inflammation localized to interstitial areas involving >1 lobe. What are the 4 most likely causative organisms?
Viruses (influenza, RSV, adenoviruses) Mycoplasma Legionella Chlamydia
Air fluid levels are seen on CXR in an epileptic. What is the dx and what are the most causative organisms?
Lung abscess due to S. aureus or anaerobes (Bacteroides, Fusobacterium, Peptostreptococcus)
6 organisms that do not take gram stain.
These Rascals May Microscopically Lack Color. Treponema Rickettsia Mycobacteria (high lipid content in cell wall detected by carbolfuchsin in acid fast stain) Mycoplasma Legionella Chlamydia
Which bacteria are encapsulated? (6)
Some Killers Have Nice Shiny Bodies S pneumo K pneumo H influenzae B N meningitidis Salmonella Group B strep
What does the alpha toxin of S. aureus do?
Hemolysis
What does the beta toxin of S aureus do?
Sphingomyelinase
Which exotoxin contains a lecithinase that causes gas gangrene?
Alpha toxin of C. perfringens. The alpha toxin is a phospholipase that degrades tissue and cell membranes. The degradation of PLC causes myonecrosis and hemolysis (double zone of hemolysis on blood agar.)
This exotoxin destroys leukocytes.
Leukocidin of S. aureus
This exotoxin blocks the release of the inhibitory neurotransmitter glycine
Tetanospasmin
What 5 bacteria secrete enterotoxins (exotoxin that causes water and electrolyte imbalances of intestinal epithelium resulting in diarrhea)?
Vibrio cholera ETEC Staph aureus Salmonella Shigella
Name 5 bugs that stain with giemsa.
Certain Bugs Really TRY My Patience Chlamydia Borrelia Rickettsia TRYpanosomes Plasmodium
What does PAS stain?
Periodic acid Schiff stains glycogen and mucopolysaccharides (remember it stains T. whipplei)
Ziehl-Neelsen is used to stain what organisms?
Acid-fast organisms like Nocardia, Mycobacterium, Cryptosporidium, Isospora, Cyclospora, etc.
India ink stains what organism?
Cryptococcus neoformans (#1 cause of AIDS meningitis)
Silver stain is positive in what 3 organisms?
Fungi (such as Pneumocystis) Legionella H. pylori
Only gram + bacteria with an endotoxin
Listeria
Amish patient presents with her 5 year old son. Examination reveals gray pseudomembranes on the pharynx. What is the mechanism of the exotoxin used by the causative organism?
This is diphtheria toxin which inactivates elongation factor 2, inhibiting protein synthesis.
73 y.o. with severe exacerbation of COPD is on a ventilator and dies of a bacterial pneumonia. What is the mechanism of the toxin produced by the causative organism?
P. aeruginosa releases Exotoxin A which inactivates elongation factor 2, inhibiting protein synthesis and causing host cell death.
7 year old boy presents with blood and protein in the urine. CBC reveals thrombocytopenia. His mom states he had several episodes of bloody diarrhea about a week ago at a church picnic where he ate 6 hamburgers. What are the two possible causative organisms and what is the mechanism of the toxin used by these organisms?
This is HUS caused by either Shigella or EHEC (O157:H7 especially). These produce Shiga toxin or shiga-like toxin, which inactivates the 60S ribosome by removing adenine from rRNA, inhibiting protein synthesis. This enhances cytokine release, causing HUS. However, EHEC does not invade host cells while Shigella does.
Patient presents with watery diarrhea after recently visiting Mexico. Gram stain reveals gram negative rods that ferment lactose. What is the MOA of each toxin produced by this organism?
ETEC. Heat labile toxin overactivates adenylate cyclase (increases cAMP), thus increasing Cl- secretion in gut and H2O efflux. The heat-stable toxin overactivates guanylate cyclase (increases cGMP), thus decreasing the reabsorption of NaCl and H2O in the gut. These cause watery diarrhea, also known as Montezuma’s revenge. :)
Patient presents with a painless ulcer covered in black eschar on his face.
He’s a wool sorter. What is the exotoxin responsible for this lesion?
Edema factor from bacillus anthracis mimics the adenylate cyclase enzyme, increasing cAMP and causing increased fluid secretion. Characteristic edematous borders of black eschar lesion.
Patient presents with diffuse watery diarrhea for the past 3 days. Gram stain reveals gram negative curved rods that are oxidase + and grow in alkaline media. MOA of the toxin produced by the causative organism?
This is Vibrio cholerae and it produces the cholera toxin. This toxin overactivates adenylate cyclase (just like the heat-labile toxin of ETEC) by permanently activating Gs, thus increasing Cl- secretion in the gut and H2O efflux.
Amish patient presents with her 3 year old son who has a fever and a seal bark cough for the past 100 days. What is the mechanism of the exotoxin produced by the causative organism?
Bordetella pertussis produces the pertussis toxin, which overactivates adenylate cyclase (increasing cAMP) by disabling Gi, impairing phagocytosis which permits survival of the microbe. However, the toxin may not actually be the cause of the cough.
Name 4 organisms with exotoxins that increase cAMP.
CAMP.
Cholera
Anthrax
Montezuma’s revenge (ETEC)
Pertussis
A lady presents with fever, shock, and a diffuse rash over her body after realizing she left her tampon in for 6 days. What is the MOA of the toxin produced that is causing these symptoms, and name one other toxin that can cause similar symptoms.
This is toxic shock syndrome. TSST-1 from S. aureus and Exotoxin A from S. pyogenes are both superantigens that bring MHC II and TCR in proximity to outside of an antigen binding site, which causes an overwhelming release of IFN-y and IL-2.
Describe the 3 components of the main pathogenesis of endotoxins.
- Activate macrophages –> release of Il-1, TNF, and NO (cause fever and hypotension.)
- Activate complement (C3a, causing hypotension and edema; C5a, causing neutrophil chemotaxis)
- Activate tissue factor –> coag cascade – > DIC
First AID has a fun mneumonic
Edema (C3a)
Nitric oxide (hypotension; from macrophages)
DIC/Death (not that fun)
Outer membrane (where the LPS are found that contain endotoxins)
TNF-a
O-antigen
eXtremely heat stable (kind of a copout…)
IL-1 (fever)
Neutrophil chemotaxis (C5a)
What 3 organisms are most commonly implicated in sub-acute endocarditis?
Viridans strep (S mutans)
Enterococci
Coagulase negative staph (S. epidermidis)
Most common causative organism in mastitis.
S. aureus