Gram + Bacteria T02 Flashcards
Staphylococci are Gram positive __________, usually arranged in ___________.
cocci;
clusters
(may show Gram-positive cocci in pairs, short chains or small clumps)
Which of the following about Staphylococci is/are correct?
A. It grows best at 37 degrees Celcius B. They are catalase-positive C. They are motile D. They are non-spore-forming E. They may show pigmentation
All except C
they are non-motile
Staphylococcus aureus produces ___________ which
- In intro, causes plasma clot
- In vivo, deposits fibrin on the surface of the staphylococci rendering less susceptible to phagocytosis.
Coagulase
Staphylococcus aureus produces hyaluronidase which enhances __________________.
the invasiveness of staphylococci
Staphylococcus aureus produces ________, ________ and _____________ that kills exposed white cells.
Exotoxin, enterotoxin and leucocidin
Exotoxin: filtrable heat labile material which is lethal to animals on injection contains soluble hemolysins (alpha and beta)
____________ produced by Staphylococcus aureus is the cause of food poisoning.
Enterotoxins
Compared to Staphylococcus aureus, Staphylococcus epidermidis is ________________. (differential) It is a normal inhabitant of the skin and hair.
unable to produce coagulase//
unable to ferment mannitol
________________________ is a clinically important coagulase-negative species that can cause UTI (urinary tract infection).
Staphylococcus saprophyticus
After tesing 2 species of Staphylococci, they both do not produce coagulase. What further test should be done to differentiate them? Test result?
Test Novobiocin susceptibility:
Staphylococcus epidermidis: S
Staphylococcus Saprophyticus: R
Test Novobiocin susceptibility: (belly)
Staphylococcus epidermidis: S (Plumber)
Staphylococcus Saprophyticus: R (Beauty)
Mannitol fermentation test is used to differentiate _______________ among other Staphylococci. Test result is?
Staphylococcus epidemidis (non-mannitol fermenting)
Others: Man+
Other than coagulase production, Staphylococcus aurues can also be distinguished from Staphylococcus epiderminus and saprophyticus by ______________.
DNase production +ve
Others -ve
Micrococci can be differentiated from Staphylococci because they are
A. Catalase-positive
B. They are coagulase-ve
C. They cannot acidify glucose by fermentation
B and C only;
A is true, but Staphylococci are also catalase-positive!
______________ are Gram+ cocci in pairs, in short or long chains.
Streptococci
Which of the following about Streptococci are true?
A. They usually arrange themselves in clusters.
B. They are catalase -ve
C. Some produces hemolysis
D. Most species are aerobes or facultative anaerobes
All except A
- in pairs
B** distinguish from Staph
What are the different types of hemolysis produced by bacteria?
- Beta-hemolysis: complete hemolysis
- Alpha-hemolysis: incomplete hemolysis, formation of green pigement
- Gamma-hemolysis: no hemolysis
_______________ (Group A Strep) produces ________-hemolysis. To diagnose acute rheumatic fever in lab, ________ is present if it is infected by Group A Strep within 2-4 weeks.
Streptococcus pyogenes;
beta;
presence of antibodies to the streptolysin O hemolysin (ASO titre, antistreptolysin O titre)
_____________ is a useful rapid test for the presumptive diagnosis of group A stains.
Bacitracin sensitivity
all group A streptococci are sensitive to Bacitracin, where as hemolytic streptococci of other groups are resistant.
Which of the following about Group A strep is incorrect? A. They produce hyaluronidase B. They produce streptokinase C. They produce an erythrogenic toxin D. They produce one type of hemolysin
D
- 2 types of hemolysins
1. Streptolysin O (O2 sensitive)
2. Streptolysin S (O2 tolerant)
_______________ is capsulated and appears as lanceolate cocci in pairs. It is alpha-hemolytic and sensitive to optochin.
Streptococcus pneumoniae
Streptococcus pneumoniae is
- soluble/insoluble in bile solution
- S/R to optochin
- Can use _________ method to identify it, ___________can be seen after binding to antibody.
- solible
- sensitive to optochin
- Quellung method; capsule swelling
____________________ is non-capsulated, arranged in short chains or appear as elongated bacillary forms. They are alpha-hemolytic and resistant in optochin.
Viridans group of streptococci.
State for each group of Streptococci, their type of hemolysis.
Strep. pyogenes: beta Strep. agalactiae: beta Strep. pneumoniae: alpha Viridans Strep.: alpha Enterococcus faecalis (Group D) : beta/ no
How can we distinguish Group A strep from all other groups of Strep?
Presence of streptolysin
How can we distinguish Strep. pneumoniae from all other groups of Strep?
It is soluble in bile; others are not
Bacitracin is important to differentiate? Respective results?
Group A and Group B strep.
Strep. pyogenes: Bacitracin S;
Strep. agalactiae: Bacitracin R.
Optochin is important to differentiate? Respective results?
Strep. pneumoniae and Viridans Strep.
Strep. pneumoniae: optochin sensitive
Viridans Strep: optochin resistant
Which 2 of the 5 kinds of Strep will show growth on MacConkey agar? (this question does not relate to lactose fermenting or not)
Strep. agalactiae and Enterococcus faecalis (Group D)
Aesculin hydrolysis +ve Strep?
Group D Strep and Enterococci species
___________ has Gram+ diplococci with abundant white cells in the background.
Strep. pneumoniae
___________ have alpha-colonies, is optochin sensitive with mucoid colonies.
Strep. pneumoniae
_____________ may cause superficial bacterial infections including impetigo (pyoderma - honey crusted lesions) and cellulitis.
Staph. aureus
What is the most common cause for osteomyleitis?
Staph aureus infection
A patient is diagnosed with pneumonia after a viral infection. X-ray shows patchy infiltrates with salmon-colored sputum.
Likely diagnosis?
Staph aureus infection
Other clinical manifestations: with cavitation, effusion, empyema & resp. failure
Give an example of fulminating generalized disease caused by Staph. aureus.
Either one:
- Endocarditis: in IVDA (IV drug abuse), more acute onset compared to Strep Viridans and Enterococcus
- Septicaemia: source from IV catheter, cellulitis, wound, organ infection
- Meningitis:unusual, often a complication of neurosurgical procedure
List the toxin-associated diseases due to Staph aureus infection.
- Scalded skin syndrome (SSS): due to exofoliative toxins; diffuse epidermal peeling, DDx drug allergy
- Toxic shock syndrome (TSS): exotoxin F and toxic shock syndrome toxin (TSST-1) due to infrequently changed tampon
- Food poisoning: 2-6h after ingestion (potato salad) due to enterotoxins ; Dx clinical not culture; Sx: salivation, n/v, retching with mild diarrhoea, no fever
CoNS = coagulase -ve Staph infections
Give an example for Staph. epidermidis infection.
- prosthetic infection (at interface)
- shunt infection
- subacute endocarditis (SBE)
- Catheter infection
Give an example of a disease caused by Staph. saprophyticus.
UTI (MC in sexually active females)
Treatment for Staphalococcus infections?
- incision and drainage
- MSSA: cloxacillin (add fusidic acid in osteomyelitis)
- MRSA: vancomycin
What is the most common cause for neonatal meningitis?
What other diseases it may cause? (2)
Group B Strep. (Strep. agalactiae) infection.
- neonatal sepsis, pneumonia
What are the 3 MC diseases caused by Enterococcus?
- UTI
- SBE
- Biliary tract infection
(Do U <3 tree)
Group D strep may cause _________ and arthritis in pork handlers.
meningitis
Patient with abrupt onset of sore throat, fever, headache, tonsillar abscess, tender ant. cervical LN. Also experienced scarlet fever.
Probably diagnosis?
Strep throat (pharyngitis) caused by Strep. pyogenes infection
What are the clinical manisfestations of scarlet fever?
sandpaper rash, circumoral pallor, strawberry tongue
Strep. pyogenes are associated with skin infections like __________ and ___________.
Impetigo (Pyoderma) and Cellulitis
Which of the following about Strep A is incorrect?
A. It can cause necrotising fascilitis
B. It can be the cause of acute endocarditis which is rapid and fatal
C. It is associated with biliary tract infection
D. Acute glomerulonephritis (AGN) is one of the post-infection disease
C
- should be Enterococcus
D: Acute glomerulonephritis (AGN): follow pharyngitis (7-10d) or pyoderma (3w), type III HSR against GBM (glomerular basement membrane) > haematuria, proteinuria, HT, oedema
Other than Acute glomerulonephritis (AGN), list another post streptococcal disease. How can it be diagnosed?
Rheumatic fever.
follow only pharyngitis, type II HSR against cardiac muscles and valves > Jones criteria symptoms
JONES: Joint: polyarthritis <3: Heart problems: valve, myocarditis, etc N: subcutaneous nodules E: Erythema nodosum S: (Sydenham’s) Chorea
How to assess Group A Strep? (2)
- check ASOT > 200 (not increased in pyoderma ∵ASO degraded by oil in skin)
- anti-DNase B titres
Which group of Strep is related to patients infected after dental procedures?
What disease it may progress to?
Viridans Streptococcus
Dental caries > SBE (subacute bacterial endocarditis) with predisposing damaged/prosthetic heart valves
List all the diseases related to Strep. pneumoniae.
CMOPS
Conjunctivitis, adult Meningitis, AOM (acute Otitis media) , typical Pneumonia (rusty sputum, high fever, usually lower lobe), Sinusitis
– all as MC cause
Treatment for Group A strep?
beta- lactam
Macrolide if allergy
Treatment for Group B strep?
Ampicillin
Treatment for S. pneumoniae?
M: ceftriaxone or cefotaxime
O: amoxicillin
P: Augmentin
Treatment for Enterococcus ?
Ampicillin
Vancomycin
Linezolid for VRE (Vancomycin resistant enterococcus;MC species: E. faecium )
Treatment for Viridans group?
Penicilin + Gentamicin
Which of the following about Bacillus anthracis is incorrect?
A. They appear as large rods on Gram smears
B. They have virulent strains that are mucoid
C. They are highly resistant to penicillin
D. They grow on blood agar with 2-5mm colonies
E. They have endospores that are central to subterminal
F. One of the features is that they have large medusa head colonies
C
C- highly susceptible to penicillin
What disease is Bacillus cereus assoicated with? How is it diagnosed?
Food poisoning due to the production of enterotoxins.
Diagnosed by quantitative cultures to determine the number of organisms per gram of food sample.
- may be present in normal stool samples too
- Short food poisoning: fried rice syndrome, by emetic toxin
- Long food poisoning: by diarrheal toxin
Name the bacteria.
- It is a short, G+, non-spore-forming rod
- It has a characteristic tumbling motility at 22 degrees Celcius but not at 37 degrees Celcius.
What diseases it may cause?
Listeria monocytogenes.
- sepsis and meningocephalitis
Corynebacterium species are bacteria that are: A. Gram+ rods B. Pleomorphic C. in angular arrangements D. produce endospores
All except D
- they do not produce endospores
Corynebacterium diphtheriae causes diphtheria.
It appears black on _________ medium. Metachrmatic granules are observed on microscopic examination of smeras stained with Albert’s stain.
tellurite
What test that can be done to identify Corynebacterium diphtheria other than tellurite medium?
Elek test (perpendicular double diffusion of antibody and antibody)
An 8 y/o boy had a sore throat a month ago and was treated with penicillin for an unknown period of time. You susect that he may have post-streptococcal diseases. What laboratory test(s) would you request?
Group A Strep is most likely, pharyngitis (virus60%-70% cases; bacteria 20-30%, within bacteria Group A is MC)
ASOT (Anti-streptlysin O titre) >200 - antibodies quantitatively
Listeria monocytogenes is related to the ingestion of?
Diary products like unpasteurized milk, cheese –> systemic reaction
A dairy farmer has recently had an ulcer in his neck and it developed into a black necrotic central eschar. Gram +.
What is the bacteria and what is the probable diagnosis?
Bacillus anthracis;
Dx: Cutaneous anthrax
Other than the eschar with erythematous border, fever, painful lymphadenopathy, B. anthracis will also cause ______________ if untreated.
Fatal septicaemia
What is the clinical significance of B. anthracis having spores?
Woolsorter’s disease: Inhlation of spores is life-threatening, hemorrhagic pneumonia may occur, together with pleural and pericardial effusions, septicaemia
1st line treatment for B. anthracis infection?
Fluoroquinolones such as ciprofloxacin/ Doxycycline
How is B. cereus caused food poisoning treated?
Food poisoning is self-limited
- they are R to beta lactams antibiotics, therefore chloramphenicol, aminoglycosides, clindamycin and vancomycin effective
A 3 y/o male from Russia suffered from an inflamed tonsil Culture from the throat swab on potassium tellurite agar is shown black, Elek Test is done. What is the causative organism?
Corynebacterium diphtheriae.
S. aureus changes mannitol salt agar from _____to________ because?
pink to yellow, it produces acid when fermenting mannitol
List the results when 3 different types of Staph are put to Novobiocin test.
Sensitive:
S. aureus
S. epidermidis
R:
S. saprophyticus
List the results when 3 different types of Staph are put to DNase test.
Only S.aureus have clear zone = meaning that only S.aureus produces DNase;
others: no clear zone
Key test to differentiate Staph and Strep?
Catalase test
Staph: Catalase +ve
Strep: Catalase -ve
What is the mode of transmission of Corynebacterium diphtheriae?
Respiratory transmission
For patients with _____________, they present sore throat with pseudomembrane which may cause potential respiratory obstruction.
Toxin from pseudomembrane may even spread to the heart to cause myocarditis, and spread to the nerve to cause RLN palsy.
diphtheria
How can diphtheria be treated and prevented?
Tx: Diphtheria antitoxin, penicillin (limited value)
Prevention: DTaP vaccine(Diphtheria, Tetanus, and Pertuissis)
___________ is the 3rd most common cause for neonatal meningitis and the MC cause for meningitis in immunocompromized patients.
Listeria monocytogenes
Tumbling motility, cold growth
Listeria monoctogenes
Facts about Listeria monocytogenes
A. It can be transmitted from mother by asymptomatic carriage to the neonate to cause neonatal infection
B. It can cause foodborne diseases and causes diarrhea in totally healthy adults
C. It can cause stillbirth to pregnant patients
D. Pregnant patients may experience septicaemia with fever and chills
E. It is treated by ampicillin and gentamicin
All of the above.
Characeristics of Nocardia asteroides? A. Filamentous/fungi-like B. Partially acid-fast C. It can be treated by co-trimoxazole D. It does not cause pneumonia
D is wrong - it can cause cavitatory pneumonia which is similar to TB, possible spread to the brain (with multiple abscess)
B. To differentiate from TB
Other than cavitatory pneumonia, what other possible clinical manifestations can occur with Nocariosis (due to Nocardia asteroides?)
Chronic cutaneous/subcutaneous suppuration
- Traumatic implantation > cellulitis > mycetoma (subcutaneous abscess with granules)
