bactitech
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Streps are not classified by drug sensitivities. They are classified by hemolysis: alpha, beta, and gamma. This is how they appear on trypticase soy agar enriched with 5% sheep blood - a basic plate in most labs in the US and Europe (in Australia they use horse blood, which alters the hemolysis a bit I'm told). They are all catalase negative. This differentiates them right away from Staphylococci which are catalase positive. This is a BIG split. The information below comes after the catalase split.
Alpha hemolysis is a greening of the agar behind the colony; gamma is "no" hemolysis (cols look grayish and sometimes a bit alpha, but one can tell they look different than other alphas after reading plates for awhile, as the colonies are larger); beta is a clearing of the agar behind the colony. This is best observed by holding the plate up to a light source.
Alpha streps are PYR negative and bile esculin negative. If speciation is warranted (usually only on sterile body fluids and blood cultures) we use automated GPI identification cards with our Vitek instrument. Streptococci are inherently hard to speciate. Various species of alpha streps (strep viridans group) can be responsible for SBE (subacute bacterial endocarditis) when present in a series of positive blood cultures. Other bugs can also cause SBE, but SVIR are classic.
Streptococcus pneumoniae is a special alpha hemolytic strep. It can look dimpled or very mucoid, depending on strain. We use a P (optochin) disc to identify them. GPI cards can be used, but P discs are used everywhere. S. pneumo is P disc sensitive. This bug is a big time pathogen.
http://medinfo.ufl.edu/year2/mmid/bms5300/images/...
http://medinfo.ufl.edu/year2/mmid/bms5300/bugs/st...
A reagent called desoxycholate can be dropped on a colony. If, after fifteen minutes, the colony disappears from the plate (plate becomes smooth and there is no colony bumping out from the plate) this is considered a presumptive ID for S. pneumo as this shows bile solubility. Other alpha streptococci are desoxycholate negative (you can still see the colony bumping up from the plate).
Gamma streps (Group D) are divided into PYR positive streps (enterococcal) and PYR negative (non-enterococcal). PYR is a fairly new test that most micro labs use now. In the olden days, we set up bile esculin agar and 6.5% salt broth on gamma streps. Enterococcal streps are PYR +, BE +, 6.5% NaCl +. Non-enterococcal streps (in the strep bovis-equinus group) are PYR -, BE +, 6.5% NaCl -.
Beta streps include groups A,B,C, some Group D's, F, G. We identify them by latex grouping. In the near olden days, we set up A (bacitracin) and SXT (trimethoprim sulfa) discs on them. Group A is A disc sensitive and SXT disc resistant. Group B is A resistant and SXT sensitive. Groups C,F,G are all A disc negative (and mostly lumped into a "beta strep NOT group A or B" category.
We run e-test sensis on alpha streptococci if warranted (only from an inherently sterile site or blood culture) along with disc diffusion sensis (can't recall now which drugs). Penicillin is always run, and other drugs depending on site. E-test is a strip MIC (minimum inhibitory concentration) methodology used by some laboratories. An elliptical zone of inhibition shows with overnight growth. The point at which the growth bumps up against the scale preprinted on the strip gives the MIC result. We only use them in specific instances and not routinely.
http://gold.aecom.yu.edu/id/micro/mic.htm
I'm just scratching the surface of streptococci here, but this is the basic scheme microbiology labs use for identification. Hope this helps you out.
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| whitmer
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leen wrote:
can any one pl advice any good way to remember the
classification of various strepto based on sensitivity to various drugs?
I m having hard time with them
thanks
What is your profession, leen? .......................
Better to exrecise restraint if you have nothing usefull to say.
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Edited by the_holy_man on 05/24/06 - 11:48 PM. Reason: flaming
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| mjl1717
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in this arena they are classified either by Lancefield group, hemolysis, or special chemical sensitivities. of the popular ones only pyogenes and agalactiae are classified with bacitracin
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| tolito
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whitmer, i think it is essential that we maintain a decorum of respect in our posts, in short, i mean we should not be rude to others. at best, you may ask leen for clarification of his questions or you may opt not to write anything since you have not made a contribution, rather you were rude to a respected member of this forum.
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| mjl1717
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tolito wrote:
whitmer, i think it is essential that we maintain a decorum of respect in our posts, in short, i mean we should not be rude to others. at best, you may ask leen for clarification of his questions or you may opt not to write anything since you have not made a contribution, rather you were rude to a respected member of this forum.
i agree- and i know bachtitech is like gold around here.
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| general malaise
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 for sarcasm and disrespect go to SDN. this is a support site.
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| cyra
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mjl1717 wrote:
i agree- and i know bachtitech is like gold around here.
I concur!
Thanks for all your help bactitech!
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| leen
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I m sorry for such a post ....actually I m near my exam so much streesed out
hope u guys understand it
thanks
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| whitmer
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No need to apologize for asking a question, leen. My apologies to you - for seeming to make light of your question. I just wanted clarification as to what exactly you were asking - so I wouldn't assume and answer incorrectly.
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| leen
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wat i want to ask was how to remember which spp of strept is optochin sensitive which is resistant which is bacitracin sensitive which resistant ?n so on.....any mneumonic for that?
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| whitmer
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Streptococcus pneumoniae is sensitive to optochin. You would do this to differenciate it from other alpha-hemolytic Strep.
Streptococcus pyogenes is sensitive to bacitracin. BacitrAcin. B for Beta-hemolytic. A for group A Strep.
corny-but works for me
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| vallia
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Bactitech is the best, just want to give a simple classification (actually 2),
first there are 5 important pathogens (fur usmle purpose): s.pyogenes, s.agalactiae, s.viridans, s.pneumoniae, enterococci and non-enterococci.
beta-hemolytic (strep pyogenes, strep agalactiae), strep alfa-hemolytic (strep viridans, strep pneumoniae, ) and gamma hemolytic (means non-hemolitic, enterococci-fecalis, faecium and non-enterococci-bovis, equinus).
and the second is the Lancefield classification
3 are important pahogens-group A----strep pyogenes (beta-hem, bacitracin sensitive)
-group B-----strep agalactiae (beta-hem, bacitracin resistant)
-group D------enterococci (PYR +)and non-ennterococci (PYR -)
2 are not included in Lancefield classification
-strep viridans (alpha-hem, optochin-resistant)
- strep pneumoniae (alpha-hem, optochin sensitive), quellung reaction
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| tolito
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good job vallia. that pretty much sums it up. thank you.
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| tolito
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so putting together stuff from vallia and bactitech:
alpha hemolytic strep......green
beta..............................clear
gamma..........................gray
Gp A .. (s. pyogenes)...............bacit sens, sxt resis
Gp B (s agalact).....................bact resis, sxt sens
GpD enteroccoci.......................pyr pos, nacl pos, be pos
non-enterocci...................pyr neg, nacl neg, be pos
non lancefield
s.viridans ................................pyr neg, bile neg, optochin R
s. pneum.................................pyr neg, bile pos, optochin sens, quellung rxn
thanks guys. been meaning to compile these properties. all the questions i failed in micro had to do with id' ing the org with all these bile solubility, salt soluble ....
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| bactitech
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As an addendum: Group A is beta hemolytic; Group B is beta hemolytic MOST of the time (there are non-hemolytic group B's); Group D is mostly gamma (non) hemolytic but, again, there are a few Group D's that are beta hemolytic; Group D non-enterococcus is PYR neg, NaCl neg, BE pos whereas Strep viridans group is BE negative. The Quellung reaction is something I've read about in textbooks but I've never seen or used in 30+ years in micro. We use bile solubility for presumptive ID and optochin for confirmatory ID. We can also use Vitek GPI identification cards for identification. There are some latex agglutination reagents that can be used also.
As you can see, streptococci are complicated and I still learn new stuff about them on a regular basis. They are sometimes difficult to identify. Many of the tests are on a rule-out basis. The beta hemolytic ones are the easiest to deal with. We use latex agglutination for these nowadays, as our accrediting agencies only allow a presumptive ID with the A and SXT discs now, i.e. if we use these discs and it comes out A disc sensitive and SXT resistant, we can only report out "presumptive Group A beta strep." We cannot definitively call it Group A (S. pyogenes) without latex agglutination identification or a GPI identification card. Because we want to be able to charge for identifications (playing the reimbursement game the insurance companies put every lab through nowadays, not just ours) we use reagents that we can charge for.
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