Medically Relevant Bacteria - Gram Positives - SRS Flashcards
What stain do gram positives take up?
Crystal violet is taken up by the peptidoglycan layer in the bacterial cell wall during a gram staining. This stains purple.
Streptococci are gram + cocci that are typically found in chains and are non-motile facultative or obligate anaerobes.
Name the five main groups of streptococci.
- Group A = S. pyogenes
- Group B = S. agalactiae
- Group D
- S. pneumoniae
- S. viridians
How does streptococci respond to the catalase test?
Negative
What is the Lancefield grouping based on?
Serology of cell wall C carbohydrate (18 groups)
What are the virulence factors of the streptococci?
•M proteins in S. pyogenes resist phagocytosis
•Lipoteichoic acids allow epithelial cell attachment
•Encapsulated - S. pneumoniae, S pyogenes & S. agalactiae
•Hyaluronic acid capsule - S. pyogenes
•Streptolysins, NADase, hyaluronidase, streptokinase, DNAses, erythrogenic exotoxin in S. pyogenes (causes scarlet fever rash), toxic shock syndrome toxin, pyrogenic exotoxin B (erysipelas)
Group A strep, S. pyogenes has the ability to perform beta hemolysis. What is this the number one cause of?
What can happen after the intial infection?
What are a few other things it can do?
- #1 cause of bacterial pharyngitis and tonsillitis, sinusitis, otitis, arthritis, osteomyelitis, impetigo, and cellulitis.
- Can later get rheumatic fever, rheumatic valvular disease and post-streptococcal glomerulonephritis.
- Also causes scarlet fever (toxin) and can cause pneumonia, bacteremia necrotizing fasciitis, & toxic shock syndrome (toxin).
What is group B strep the leading cause of?
neonatal septicemia, meningitis & pneumonia
What type of hemolysis does group D strep cause?
What are common infections associated with it?
ȣ or α hemolysis-urinary tract infections and endocarditis
- S. pneumoniae* is capable of α hemolysis, and is the number one cause of what conditions in…
1. adults
2. children
Adults
- bacterial pneumonia (virulence via capsule)
- Meningitis
Children
- Otitis Media
S. viridans is capable of α hemolysis and is microaerophillic, what are two things it can cause?
In what situations can this be present?
- Dental caries
- subacute endocarditis
Can be present in aspiration pneumonias and abcesses
What is the Dx criteria for streptococci?
- culture, S. pneumoniae is optochin sensitive (differentiates from α hemolytic S. viridans)
What type of hemolysis is shown on each side of the photo?
What could these cultures be?
Left: Alpha-hemolysis, S. viridans or pneumoniae
Right: Beta-hemolytic, S. pyogenes or agalactiae
What component of S. pyogenes are the antibodies targeted against that cause the problems in rheumatic fever and rheumatic valvular disease?
The M component
What is the bacteria shown here?
What is the classical description (in case he doesn’t grant us the microscopy)?
Why the clear space around them?
S. pneumoniae
Elongated pairs, lancet shaped diplococci
Apparently the clear space is associated with the capsule.
Which streptococci causes scarlet fever?
What toxin does it use in doing so?
Group A (S. pyogenes)
erythrogenic exotoxin
Enterococci are gram positive diplococci that form short chains. Previously they were categorized with one of the strep groups. If you see an out of date reference to these as such what strep group will they be referred to as?
Group D
What catalase response do you see in enterococci? What type of hemolysis do they exhibit?
Catalase negative
•ȣ hemolytic (i.e. non-hemolytic)
What are some of the virulence aspects of enterococci we should be aware of?
- Antiphagocytic capsule
- High level of resistance to antibiotics
- high capacity to transmit resistance among selves and to other bacterial populations
Enterococci are intrinsically resistant to what antibiotics?
What else are they resistant to?
•β-lactam antibiotics (penicillins, cephalosporins, carbapenems) and many aminoglycosides
VRE - vancomycin resistant enterococci
Enterococcus is normal flora in what part of the body?
Intestinal flora
Due to the proximity of the GI and UG portals, cross contamination is relatively common. If enterococcus infects the UG system what kind of fallout can occur?
- UTI
- bacteremia
- bacterial endocarditis
- meningitis
What is an example of how enterococcus can be a problem in the intestine, where it normally is all good?
If a patient has diverticulitis, and one of the pockets is fecally occluded, enterococcus can lead to an abcess.
The organism in this image was taken from a patients intestine, it demonstrates gamma hemolysis, and is non-motile.
What is the organism?
Enterococci
(This might be a bit obvious based on the order of the materials, so I recommend ranking this low initially even if you got it right, so you get another crack at it later)
What organism is depicted here?
How would you describe the arrangement?
Staphylococci
Clustered
What does S. aureus have that is characteristic for it, that the other staphylococci do not?
What does it do?
It is coagulase positive, if exposed to plasma will bind fibrinogen and cause coagulation.
S. aureus commonly infects the skin, what are the major problems that Dr. Gomez highlighted?
- Scalded skin syndrome
- pneumonia
- meningitis
- acute endocarditis
- osteomyelitis
- toxic shock syndrome
- food poisoning
How does S. aureus cause scalded skin syndrome?
Exfoliative A & B toxins cleave desmoglein 1 in skin.
S. aureus has two superantigens associated with it, what are they?
Toxic shock syndrome Toxin (TSST1)
Heat stable enterotoxin
What are the characteristic results that occur in a patient who has a TSST1 producing S. aureus infection?
- Fever
- Erythemetous rash
- hypotension
- shock
- multipe organ failure
- skin desquamanation
What are the characteristic virulence factors associated with S. aureus?
- Resistance to penicillins and vancomycin
- receptors for fibrinogen (clumping factor), fibronectin and vitronectin.
- polysaccharide capsule
- Surface protein A
- membrane damagin “hemolysins”
- Exfoliative A & B toxins
-
Superantigens
- TSST1
- Heat Stable Enterotoxins
How does the S. aureus surface protein A work?
Binds the Fc portion of immunoglobulins and prevents Ig mediated destruction.
What kind of problems does S. epidermidis cause?
- Subacute endocarditis (vegitations will appear on valves),
- Infection of prosthesis via biofilms
- opportunistic infections
What does the polysaccharide capsule allow S. aureus to do?
Avoid phagocytosis and adhere to artificial materials
S. epidermidis is capable of producing biofilms. What benefit do these confer?
Shield against antibiotics and other forms of immune defense
What does S. saprophyticus cause infection wise?
UTI in young females
Staphylococci are frequently encountered that are resistant to what types of antibiotics?
β lactamases - MRSA
Vancomycin - VRSA
Your patient is a state senator who recieved a package earlier in the day that sprayed white powder all over the room when openend. At this point the patient exhibits minor cold symptoms with productive cough. Sputum microscopic analysis revealed the slide attached.
What is the progression this disease would follow if you let it run its course?
This is an example of inhalation anthrax (woolsorter’s disease) - the cold symptoms are followed by hemorrhagic mediastinitis and necrosis in lymph nodes and lung, leading to ARDS, hemoptysis and death.
Your patient presents with vomiting, and diarrhea after eating fried rice with chicken at the local pay by the scoop chinese restaraunt. The attached image is a slide obtained from the patients fecal sample. What are the toxins this organisms produces that lead to the patient’s presentation?
B. cereus
Preformed enterotoxins
Vomiting - Heat stable toxin - from contaminated rice
Diarrhea - Heat labile toxin - from meat and vegetabls
What are the types of anthrax we need to be aware of?
Cutaneous
Inhalation
Gastrointestinal
B. anthracis produces a single antigenic type of capsule and several antitoxins. What is necessary for Anthrax to occur?
The bacteria must produce…
- •Polyglutamyl (amino acid) capsule (survives phagocytosis)
-
•Exotoxins
- factor A- lethal factor or edema factor (adenylate cyclase)
- protective antigen factor B
Bacillus is a gram-positive boxcar-shaped rods that are aerobe to faculatative anaerobes. What is another important characteristic these possess that helps them be viable in the environment?
They are spore formers
Your patient is a six year old boy who was running through a field and got caught on an old rusty loop of barbed wire. Later, he presented with lockjaw/trismus and convulsions.
What is the organism responsible?
What is the toxin it produces that leads to this patients constellation of symptoms and how does it work?
- C. tetani
- tetanospasmin/spasmogenic toxin/tetanus toxin fixes to gangliosides & blocks ȣ-aminobutyric acid (GABA) release leading to muscle spasms (lockjaw/trismus) and convulsions (tetanus)
Clostridia are gram-positive rods, spore formers and are obligate anaerobes. What are the types we need to be aware of?
- C. tetani*
- C. perfringens*
- C. botulinum*
- C. difficile*
What is the tennis racket shaped portion of this clostridia for? (indicated by red arrow)
This is where the spore is forming
What is the best way to deal with C. tetani?
Prevention.
Tetanus toxoid vaccines (DPT, etc) and tetanus todoid (Td) boosters every 10 years
This patient had an anaerobic mixed wound infection, that rapidly led to the myonecrosis seen on the right via bacterial endotoxins. The organism shown on the left was the primary agent in causing the damage shown.
What is the organism?
What are the exotoxins it employed to do this damage?
What are we seeing here at right?
C. perfringens
- lecithinases
- hemolysisn
- collagenases
- proteases
- lipases
Gas gangrene, which is often fatal.
C. perfringens can be a cause of mild food poisoning also, leading to brief episodes of diarrhea. What causes the diarrhea?
Enterotoxin
18 hours after eating a peach pie made with fruit canned and preserved from last years harvest, your 45 y/o female patient was brought to the clinic with diplopia, slurred, abnormally pitched speech, decreased saliva, general weakness, muscle paralysis and respiratory failure.
What is the organism?
By what mechanism is it causing the presentation we see here?
C. botulinum
Botulinum Exotoxin (types A,B,C1, C2, D, E, F, G)
Types A, B, E, and F are chromosomal and toxic to humans, they act by blocking acetylcholine release.
What is the most potent exotoxin known?
Type A botulinum exotoxin
Who should never be fed bee honey?\Why?
Infants
C. botulinum will produce infant botulism
What are the common clinical presentations of exposure to botulinum exotoxin?
- flaccid paralysis
- diplopia
- dysarthria
- dysphonia
- dysphagia
- respiratory failure
- decreased saliva
- general weakness
- muscle paralysis
- Fatal ~20 % of the time
In addition to food, what other route can we see C. botulinum infection with?
Wound botulism from penetrating injuries
C. botulinum is difficult to culture even in strict anaerobic environments, what are the ways we confirm this diagnosis?
- PCR
- Immunoassays
- Mouse neutralization bioassay confirms botulism by isolating the botulism toxin.
What is the treatment protocol for botulism?
botulinum antitoxin
debridement and antibioticcs for wound botulism
C. difficile has large, oval subterminal spores and produces what two toxins?
- Toxin A - enterotoxin
- Toxin B - cytopathic agent
C. difficile, while a normal part of many people’s microflora can overgrow when antibiotics are used. What is a consequence that can occur as a result of this?
Describe this presentation a bit.
Pseudomembranous enterocolitis.
•Abdominal pain with a watery diarrhea and leukocytosis
•Can be fatal in about 27-44% if untreated
•Patients secrete large numbers of spores in feces
How is a C. difficile infection diagnosed?
- presence of pseudomembrane (necrotic bowel)
- exotoxin ELISA
- PCR
- Isolation of organism from feces
What are the three ways we treat a C. difficile infection?
- Oral Vancomycin
- metronidazole
- bacterial recolonization
Your patient presents with the image on the left, muscle weakness, pseudomembranous material in the upper respiratory tract.
1. What media would you use to culture this organism?
After successfully culturing the organism you prepare the slide seen on the right, and find gram-positive rod-like to filamentous bacteria that are non-motile and catalase positive.
2. On close inspection, what do you find in the cell wall of this organism?
3. What is this organism?
- Tellurite media - produces jet black corynebacteria colonies
- Mycolic acid (TQ alert)
- C. diptheriae
Diptheriae exists throughout the world and occasional utbreaks occur almost yearly, it colonizes the mucus membranes of the respiratory tract and produces what three harmful substances?
- Neuraminidases
- diphthin (protease that inactivates IgA)
- Tox (diptheria toxin)
Explain the mechanism by which diptheria toxin works.
- Digestion with trypsin gives two fragments, A and B
- The B (binding) fragment attaches to cells
- Proteases release the A (active) fragment into the host cell
- The C (catalytic) domain of the A fragment acts as an ADP-ribosyltransferase, which inactivates elongation factor EF-2, blocking protein synthesis
How do we prevent C. diphtheriae infections?
Treat?
- DPT vaccine formalin inactivated toxin (i.e. toxoid)
- Passive immunization with antitoxin, penicillin, erythromycin or gentamicin, vaccinate (DPT)
A woman in her second trimester of pregnancy ate a hotdog at the recent Rockies Vs. Padres game. Later, she developed a flu like illness and misscarried. The attached image is of the organism cultured from the miscarried fetus.
What organism caused this?
How did this organism cross the placental barrier?
Listeria monocytogenes
Crosses the placental and blood-brain barrier by riding in macrophages.
Listeria are small +/- intracellular gram positive bacilli that sometimes arrange in chains. They are beta-hemolytic, catalase positive, facultative. Describe their modes of locamotion both independent and cell driving.
Independent - posess tumbling motility at room temp. via 105 flagella.
Cell driving - capable of polymerizing host cell’s actin to produce motility and this allows spread from cell to cell without an extracellular stage
Listeria is a facultative intracellular parasite, describe how it manages to live inside cells.
•Listeriolysin O allows it to survive and reproduce within macrophage phagolysosome
What are the common food vectors that are associated with listeriosis.
- hot dogs
- meats
- milk
- cheese
- raw vegetables
What are the various consequences possible due to listeriosis?
- sepsis
- meningitis
- granulomatous inflammation in infected tissues
- Pregnant women…
- amnionitis
- miscarriage
- stillbirth
- neonatal sepsis (granulomatous infantiseptica and meningitis)
- death ~20%
What are the preferred treatment protocols for listeria?
- ampicillin
- trimethoprim-sulfamethoxazole
Your 23F patient complains of pain and discomfort during urination. On physical exam, unusual discharge is noted in her vagina, and a “fishy” odor is detectable.
Analysis of the tissue sample in the attached image reveals the distintive presence of what cells?
What would you give the patient to treat this case of bacterial vaginosis?
What lead to this condition?
Gardernella vaginalis
Clue cells
•Rx – metronidazole or clindamycin to kill anaerobic bacteria overgrowth
A microfloral shift lead to this, with a decrease in normal lactobacillus flora, with overgrowth of anaerobes
What is the gram stain for gardernella vaginosis?
Gram positive
What does P. anaerobius tend to infect?
Oral cavity
What does P. magnus tend to infect?
Skin and soft tissues
What organism might you find in deep organ abcesses of the GI tract or female GU?
P. magnus
