Microbiology Flashcards
Do bacteria have mitochondria?
No
What is an important action that takes place in mitochondria (in eukaryotes)?
Electron transport chain
Where is the site of bacteria’s electron transport chain?
Plasma membrane
What is the source of protein synthesis?
Ribosomes
What is the shape of bacteria’s DNA? Is it double stranded or single stranded?
Circular double stranded DNA
Release of LPS can cause what major life threatening syndrome? What are the symptoms/signs?
Septic shock!
Signs: Fever, hypotension, tachycardia, altered mental status.
Endotoxins will cause the body to release what molecules? What do they do and what symptom does it cause in shock?
Endotoxins cause macrophages to release: TNF-alpha, IL-1, and nitric oxide. They are all major VASODILATORS –> the hypotension found in shock.
What is one major difference between hypovolemic shock and septic shock?
Hypovolemic shock patient feels “cool and clammy” b/c of increased peripheral vascular resistance due to inc. adrenergic response. REPLACE VOLUME.
Septic shock patients will feel warm (fever) and may have flushed skin b/c of the vasodilatory response (release of TNF-alpha, IL-1, and NO).
What bacteria completely lack a cell wall?
Mycoplasma (cannot gram stain)
What special stain is needed to identify mycobacterium and why?
Contains mycolic acid - fatty acid in cell wall, causes it to be only weakly gram positive –> Must use ACID FAST STAIN to identify
Acid fast stain is used for what organisms?
Mycobacterium and Nocardia (only weakly acid fast); Cryptosporidium oocysts (protozoa)
Which organisms cannot be identified via gram stain?
“These Microbes May Lack Real Color”
- Treponema pallidum (too thin –> darkfield microscopy or fluorescent antibody staining needed to be seen)
- Mycobacteria spp. (lipids in cell wall; mycolic acid)
- Mycoplasma pneumoniae (lacks cell wall)
- Legionella pneumophila (intracellular –> immunofluorescent staining or silver staining needed)
- Rickettsia spp. (intracellular –> immunofluorescent staining needed)
- Chlamydia spp. (intracellular –> immunofluorescent staining needed)
PAS stains what structures well?
Sugars (ie glycogen in bacteria’s cell wall).
“PASs the SUGAR”
Remember: T. whippeli that causes Whipple’s disease is PAS positive (will stain bright red). Symptoms: weight loss, arthritis, abdominal pain, diarrhea.
Ziehl-Neelsen stains is used to detect what kind or organisms?
Acid fast organisms. Particularly good for mycolic acid.
What does india ink stain? What bacteria is this especially diagnostic for?
India Ink outlines the capsule of crytptococcus neoformans
What is silver stain used for?
Stains fungi, legionella, and H. pylori (appear black)
Your patient has PAS-positive macrophages on a small intestinal biopsy. What diagnosis should you consider?
Whipple’s Disease
How does selective media work?
Contains antibiotics to prevent growth of bugs other than the one of interest (i.e thayer-martin media). Thus only thing that grows on the media is the single bacteria of interest.
Thayer-Martin media is selective or differential media?
Thayer-Martin media is selective media (it contains antibiotics to prevent contaminating growth of other bugs other than neisseria gonorrhoeae or meningitidis).
Thayer-Martin media plates for what single bacteria and what antibiotics does it contain?
Neisseria gonorrhoeae or meningitidis.
“Very Typically Cultures Neisseria”
Antibiotics: Vancomycin (inhibits gram+), Trimethoprim + Colistin (inhibits gram- except Neisseria), Nystatin (inhibits fungi).
How does differential media work?
Causes bacteria of interest to change color so it can be differentiated from other bugs plated with it (ie McConkey’s agar –> lactose fermenting bugs will grow as pink colonies, the rest are colorless)
McConkey’s agar can be used to distinguish what types of bacteria? What type of media is this?
Lactose fermenting bugs (such as E.coli) will grow as pink colonies on this agar, while all other will be colorless. This is differential media.
What organisms can be distinguished on Giemsa stain?
“Certain Bugs Really Try my Patience”
Chlamydia, Borrelia, Rickettsia, Trypanosomes, Plasmodium.
What is an alternative screening stain that can be used instead of Ziehl-Neelsen (carbol fuchsin)? What bacteria is this used for? Why is it used for screening?
Alternative is auramine-rhodamine stain for screening (inexpensive, more sensitive but less specific). This is used for acid fast bacteria (mycobacterium, nocardia, Cryptosporidium oocysts (protozoan)).
What media is used to plate for H. influenzae and what does it contain?
Chocolate agar. Contain factors V (NAD+) and X (hematin).
What bacteria is plated on chocolate agar?
H. influenzae
What does chocolate agar contain?
Factors V (NAD+) and X (hematin)
Neisseria gonorrhoeae and Neisseria meningitidis are plated on what media? What does this media contain?
Thayer-Martin agar. Vancomycin, Trimethoprim, Colistin, Nystatin. “Very Typically Cultures Neisseria”
What is Bordetella pertussis formerly and currently plated on? What is contained within these plates?
B. pertussis in the past was plated on Bordet-Gengou agar which contained potato extract, blood, glycerol, and an antibiotic. “Bordet” think “Bordetella”
Now it is plated on Regan-Lowe medium which contains charcoal, blood, and an antibiotic.
What plate is composed of charcoal, blood, and antibiotic?
Regan-Lowe medium used for B. pertussis.
What is C. diphtheriae plated on?
Tellurite agar or Loffler medium
What bacteria is distinguished by tellurite agar or loffler medium?
C. diphtheriae
What bacteria is distinguished by Eaton agar? What does this agar require?
Mycoplasma pneumoniae. Requires cholesterol.
Mycoplasma pneumoniae is plated on what agar and what does this agar require?
Eaton agar and it requires cholesterol.
E.coli is plated on what type of agar? What type of media is this and what visually occurs to distinguish the bacteria?
Eosin-methylene blue (EMB) agar. This is a differential media and causes the E.coli colonies to grow with a green metallic sheen.
Eosin-methylene blue (EMB) agar plates for what?
EMB agar grows E.coli in green metallic sheen covered colonies.
Legionella is plated on what type of medium?
Charcoal yeast extract agar buffered with cysteine and iron.
Legionella is plated on a charcoal yeast extract agar buffered with what?
cysteine and iron
What is plated on a charcoal yeast extract agar buffered with cysteine and iron?
Legionella
Fungi are plated on what type of agar to distinguish it from bacteria?
Sabouraud agar. “Sab’s a FUN GUY”
What is plated on sabouraud agar?
Fungi “Sab’s a FUN GUY”
Which bacteria are obligate aerobes?
Obligate Aerobes
Nagging Nettlesome Pests Must Love B-B-Breathing
Nocardia, Neisseria, Pseudomonas, Mycobacterium tuberculosis, Legionella, Bacillus cereus, Bordetella, Brucella
obligate anerobes have what enzymes that help them survive in oxygen rich environments?
THey contain antioxidents/enzymes catalase, peroxidase, and superoxide dismutase.
What enzymes do obligate anaerobes lack that cause them to be unable to survive in the presence of oxygen?
Catalase, superoxide dismutase, and peroxidase
What organisms are ogligate anaerobes?
“Anaerobes Frankly Can’t Breath Air”
Fusobacterium, Clostridium, Bacteroides, and Actinomyces
What is fusobacterium?
Fusobacterium is a genus of anaerobic, Gram-negative bacteria, similar to Bacteroides. Individual cells are rod-shaped bacilli with pointed ends. Strains of Fusobacteriumcause several human diseases, including periodontal diseases, Lemierre’s syndrome, and topical skin ulcers.
In contrast to Bacteroides spp., Fusobacterium has a potent lipopolysaccharide.
Clindamycin was the most active antibiotic against Fusobacterium species, followed by chloramphenicol, carbenicillin, and cefoperazone (which were about equally active) and then cefamandole.
Why can’t aminoglycosides be used with clostridium, bacteroides, actinomces, or fusobacterium?
It is because aminoglycosides cannot be used with obligate anaeorbes. Aminoglycosides require oxygen in order to eneter into a bacterial cell, so since these organisms live in non-oxygenated areas, aminoglycosides will be ineffective.
Which bacteria are obligate intracellular bugs? Why?
“Obligate Intracellular Bugs stay inside (cells) when it is Really CHilly and COld.”
Rickettsia, CHlamydia, and COxiella
They all rely on host for ATP (cannot synthesis it themselves)
Which bugs are facultative intracellular organisms?
Some Nasty Bugs May Live FacultativeLY.
- Salmonella spp
- Neisseria spp
- Brucella
- Mycobacterium spp
- Listeria monocytogenes
- Francisella tularensis
- Legionella penumophila
- Yersinia pestis
What bug causes osteomyalitis in sickle cell patients?
Salmonella
What chronic disease state allows salmonella to cause osteomyalitis in these patients?
Sickle cell disease –> low spleen function
A child with a history of sickle cell disease comes in with salmonella osteomyelitis. What should he be vaccinated against?
Streptococcus pneumoniae, haemophilus flu, and Neisseria meningitidis.
Why
B/c of his sickle cell, he is functionally aspenic (which is why the osteomyelitis occurred). Therefore you need to protect him against encapsulated organisms such as those above. There are other encapsulated organisms, but they don’t have vaccines.
What are the 3 main blood disorders that are treated by splenectomy? What organisms are these patients now more susceptible to?
Sickle Cell Disease, hereditary spherocytosis, and those with a B cell immune deficiencies (ie. Bruton’s agammaglobulinemia anemia).
They are susceptible to encapsulated bacteria (remember SHiNE SKiS).
What is the body’s main line of defense against encapsulated organisms?
B cells (antibody mediated defense).
A six month old boy comes in with recurrent strep pneumo infection. What is one possible disease state he may have?
Bruton’s agammaglobulinemia. This is a B cell immune deficiency –> puts the child more at risk for encapsulated bacterial infections (SHiNE SKiS). It occurs at six months b/c this is the natural time when the circulating mother’s IgG decreases –> reveals deficiency. It is more likely to be a boy because the disease is X-linked recessive.
What are examples of encapsulated bacteria?
SHiNE SKiS.
- Streptococcus pneumoniae
- Haemophilus influenxae type B
- Neisseria meningitidis
- Escherichia coli
- Salmonella
- Klebsiella pneumonia
- Group B Strep
What is urease?
urease is an enzyme that catalyses the hydrolysis of urea to carbon dioxide and ammonia.
What important bacteria that infiltrates the GI uses urease and why does it?
H. pylori
Uses urease to produce ammonia which neutralizes the gastric acid allowing it to survive.
Thus can use a urease breath test to test for H pylori infection
What is a test you can do to see if the patient is infected with H. pylori?
Urease breath test.
Test works by swallow radioactive urea which then combines with h20 to form CO2 and ammonia, then detect the radio active carbon in the now CO2
Which organisms are urease positive?
“CHuck norris hates PUNKSS”
Cryptococcus neoformans
H. pylori
Proteus mirabilis
Ureaplasma urealyticum
Nocardia asteroides
Klebsiella pneumoniae
Staphylococcus epidermidis
Staphylococcus saprophyticus
Proteus mirabilis can form what kind of kidney stones?
Struvite stones (magnesium ammonium phosphate) - precipitates in alkaline urine.
Urease + organisms (like proteus mirabilis) will alkalinize the urine causing struvite stones to precipitate out
Remember: they are coffin shaped
What is catalase and what does it do?
Catalase degrades hydrogen peroxide (H2O2) into H2O and O2. Is one of the mechanisms of protection that obligate and facultative anaerobes have to survive in oxygen rich areas.
Which are the catalase positive bacteria?
“Cats Need PLACESS to hide”
[cats = catalase]
- Nocardia
- Pseudomonas
- Listeria,
- Aspergillus
- Candida
- E. coli
- Staphylococci
- Serratia
A patient has a draining abscess of the jaw. Microscopy reveals yellow sulfur granules. What is the organism?
Actinomyces israelii
Remember: A. israelii has yellow “sulfur” granules, which are composed of filaments of bacteria.
“Israel has YellowSand (sulfur granules)”
What is the main antibody method of infection clearance in the respiratory track? What virulence factor prevents this and allows bacteria to colonize the respiratory mucosa?
IgA
IgA protease cleaves IgA allowing bacteria to colonize.
These bacteria are: SHiN
- Strep pneumo
- H. influenza type B
- N. meningitidis
Note: all of these organisms are encapsulated
What bacterial virulence factor binds the Fc region of IgG? What does this do? What bacteria expresses this?
Protein A
Prevents opsonizationa and phagocytosis
Expressed by Staphylococcus aureus
What virulence factor does staph aureus have and how does it work?
Protein A
Prevents opsonization and phagocytosis by binding to the Fc region of IgG and effectively blocking where neutrophils and macrophages would normally bind.
Which bacteria have IgA protease as a virulence factor? How does it work?
SHiN
- Streptococcus pneumoniae
- Haemophilus influenza type B
- Neisseria meningitidis
Cleaves IgA which is the main antibody protection in the respiratory system –> these encapsulated bacteria can no colonize repiratory mucosa.
How does M protein act as a bacterial virulence factor? Who express this?
Helps prevent phagocytosis and is expressed by group A streptococci.
Which are the pigment producing bacteria? What pigments do they produce?
Actinomyces israelii—yellow “sulfur” granules, which are composed of filaments of bacteria.
Israel has yellow sand (sulfur granules).
S. aureus—yellow pigment.
Aureus (Latin) = gold.
Pseudomonas aeruginosa—blue-green pigment.
Aerugula is green.
Serratia marcescens—red pigment.
Serratia marcescens—think red maraschino cherries.
Which virulence factor shares similar epitopes to human cellular proteins? What is this known as? What autoimmune response is this virulance factor thought to underlie?
M protein
Molecular mimicry
Possibly underlies autoimmune response seen in rheumatic fever.
Name 2 toxins that inhibit elongation factor 2. What is the mechanism?
Diptheria toxin (Corynebacterium diphtheriae) and Exotoxin A (Pseudomonas aeruginosa)
Mechanism: ADP ribosylation of EF-2
Which toxins over stimulates adenylate cyclase? Which bugs release them?
- Heat-labile toxin released from Enterotoxigenic E.coli (ETEC) - permenantly activate Gs –> stim adenylate cyc –> inc cAMP
- Cholera toxin released from Vibrio cholerae permenantly activate Gs –> stim adenylate cyc –> inc cAMP
- Pertussis toxin released from Bordetella pertussis; inhibits Gi –> nothing downregulating adenylate cyc –> inc cAMP
What toxin overstimulates guanylate cyclase? What releases it?
Heat-stable toxin released by Entertoxigenic E.coli (ETEC); permenantely activate Gs –> overactives guanylate cyclase –> inc. cGMP
Which toxin can mimic adenylate cyclase activity? What releases this and what will it cause?
Edema factor released by Bacillus anthracis and causes an inc. cAMP
What toxins cleave the SNARE protein complex? What does this do? Which bacteria release these?
Tetanospasmin - clostridium tetani
Botulinum toxin - clostridium botulinum
SNARE protein is necessary for proper neurotransmitter release.
What neurotransmitters does tetanospamin inhibit? What does this cause?
Tetatnospamin (clostridium tetani) cleaves the SNARE protein complex –> inhibits GABA and Glycine (inhibitory neurotransmitters) –> unopposed muscle contraction & rigidity occur.
Prevent w/ TDaP vaccine
What neurotransmitters does botulinum toxin inhibit? What does this cause?
Botulinum toxin (Clostridium botulinum) cleaves the SNARE protein complex necessary for proper neurotransmitter –> inhibits Ach (stimulatory neurotransmitter) from presynaptic nerve terminals –> flaccid paralysis (“floppy baby syndrome”) –> admit to hospital b/c need to monitor/help w/ breathing b/c diaphragm is a muscle!
Other symptoms: anticholinergic symptoms –> blurred or double vision, difficulty speaking or swallowing, constipation, ptosis (droopy eyelid), muscle weakness
Paralytic effects develop in a descendng fashion!
The paralytic effectos of botulinum toxin develop in an ascending or descending fashion?
Descending!
What is the mechanism of alpha toxin and what bug releases this exotoxin?
Clostridium perfringens releases alpha toxin which is a lecithinase – or an enzyme that degrades lecithan (a phospholipid found in the outer cell membrane in all human cells) –>Alpha toxin lyses cell membranes causes degradation of tissues and blood vessels –> gas gangrene (myonecrosis)
What may be seen on an imaging study of someone with a profound necrotic clostridium perfringens infection?
Since clostridium perfringens can cause gas gangrene, pockets of free air may be apparent in the tissue
If Clostridium perfringes is grown on blood agar what will happen? What other requirements are necessary for growth?
C. perfringens grows readily on blood agar plate in anaerobic conditions, and often produces a double zone of beta hemolysis.
What special about neisseria’s endotoxin ?
It is a LipoOLIGOsacharide (LOS as opposed to LPS) it does not possess the O antigen/O specific side chain, but still has the lipid A endotoxin.
A young boy is admitted to the hospital for nose bleed. Nasal packing is placed in the ED. 6 hours later, the boy develops fever, hypotension, and rash. What is your diagnosis?
Toxic Shock Syndrome (likely from staph aureus - b/c naturally found in the nose)
What is the mechanism of action of Toxic shock syndrome toxin and streptococcus pyogenes exotoxin A?
These are superantigens. They cause non-specific proliferation by binding to the outside of MHCII and T-cell receptor complex –> overwhelming proliferation of T & B cells –> huge immune response –> release of inflammatory and vasodilatory cytokines (IL-1, IL-2, IFN-gamma, TNF-alpha) –> shock
Which exotoxins increase cAMP?
cAMP
- Cholera (Vibrio Cholera)
- Anthrax (Bacillus anthracis)
- Montezuma’s revenge (E.coli)
- Pertussis (Bordetella pertussis)
What are the major mechanisms for transfer of antibiotic resistance?
Conjugation and transposition!
Exchange can occur between unrelated bacteria as well as related.
What two gram positive alpha hemolytic species can be differentiated by optochin?
Strep. viridans (resistant)
Strep. Pneumo (sensitive)
Remember: OVRPS (overpass)
- O- optochin
- V-viridans
- R - resistant
- P- pneumo
- S - sensitive
What is the most common cause of the “24 hour bug” –> vomiting and watery diarrhea?
Staph. aureus preform toxin
Ingestion of the preform toxin –> nausea and vomiting in ~ 6hrs and resolves in 1 day
A family comes in with vomiting and watery diarrhea. They had been at a picnic earlier this morning where they served potato salad and cole slaw. What is the cause of their symptoms?
Staph. aureus preform toxin
Why: sitting out mayonnaise, most comon cause of 24 hour stomach bug, onset is usually in ~6hrs, usually resolves in a day
What is a common antimicrobial used against MRSA?
Vancomycin
If someon gets a skin infection in the hospital setting, while waiting for culture how should you treat the patient?
Treat with something that treats MRSA (ie vancomycin), until culture comes back negative, better to treat as if has resistant bug.
Impacted nose or left in tampons, what should you think?
Toxic shock syndrome from TSST toxin from staph aureus
A child comes in after the parents gave birth in a taxi and cut the umbilical cord with a scissor the driver had. The baby skin is red with fluid filled blister. What is the disease and what is the mechanism?
Scalded Skin Syndrome
Caused by staph aureus release of exfoliatin exotoxin that breaks down epidermal layer by targeting desmoglein/desmosomes –> looks scalded
Strong history or physical exam with IV drug abuse (ie track marks, evidence of skin popping), must consider what bug?
Staph aureus –> endocarditis.
Manitol salt agar is a selective media for what type of bacteria?
The salt is selective for staphylococcus.
Then depending upon whether the specific species of staph is a manitol fermenter the agar will either stay pink (not a fermenter) or turn yellow (fermenter!)
Staph aureus is a manitol fermenter –> turns agar yellow.
