![]() ![]() Streptococcus pyogenes is a gram-positive group A cocci that can cause pyogenic infections (pharyngitis, cellulitis, impetigo, erysipelas), toxigenic infections (scarlet fever, necrotizing fasciitis), and immunologic infections (glomerulonephritis and rheumatic fever). mutans and Strep mitis found in the normal flora of the oropharynx commonly cause dental carries and subacute bacterial endocarditis (Strep. Streptococcus pneumoniae is a gram-positive, encapsulated, lancet-shaped diplococci, most commonly causing otitis media, pneumonia, sinusitis, and meningitis. saprophyticus accounts for the second most common cause of uncomplicated urinary tract infection (UTI). Staphylococcus saprophyticus is novobiocin resistant and is a normal flora of the genital tract and perineum. epidermidis commonly infects prosthetic devices and IV catheters producing biofilms. Staphylococcus epidermidis is a gram-positive, catalase-positive, coagulase-negative cocci in clusters and is novobiocin sensitive. aureus can also cause toxic shock syndrome (TSST-1), scalded skin syndrome (exfoliative toxin, and food poisoning (enterotoxin). aureus can cause inflammatory diseases, including skin infections, pneumonia, endocarditis, septic arthritis, osteomyelitis, and abscesses. Staphylococcus aureus is a gram-positive, catalase-positive, coagulase-positive cocci in clusters. It is a 20 to 80 nm thick polymer while the peptidoglycan layer of the gram-negative cell wall is 2 to 3 nm thick and covered with an outer lipid bilayer membrane. ![]() Gram-positive organisms have a thicker peptidoglycan cell wall compared with gram-negative bacteria. Also, the branching filament rods encompass Nocardia and actinomyces. Spore-forming rods that produce spores can survive in environments for many years. Bacillus and Clostridia are spore-forming rods while Listeria and Corynebacterium are not. Gram-positive bacilli (rods) subdivide according to their ability to produce spores. agalactiae (Group B), enterococci (Group D), Strep viridans, and Strep pneumonia. Streptococcus bacteria subdivide into Strep. Of course, always exceptions to these pearls, so await speciation!ĭr.Gram-positive cocci include Staphylococcus (catalase-positive), which grows clusters, and Streptococcus (catalase-negative), which grows in chains. The staphylococci further subdivide into coagulase-positive ( S. Ex: while you await speciation for that aerobic box car shaped GPR, these clues suggest Bacillus, usually a contaminant!įor Gram(–) rods, the pearl is that Pseudomonas is a ‘strict’ aerobe and ought to grow preferentially in the aerobic bottle – thus, a GNR that grows in the anaerobic bottle first is less likely Pseudomonas. For GPRs, preferential growth in the aerobic v anaerobic bottle helps organize the ‘shape’ chart. A great reason to go to micro lab and review the Gram stain!Īpply Q3) to Gram(+) rods & perhaps Gram(–) rods too. Here’s a comparative chart of GPRs to illustrate. There are some uniquely shaped Gram(–) rods too, but rare (think Fusobacterium). Can use Number of positive cx fact to your advantage – before abx, obtain more cx & increase the denominator!Īpply Q2) to Gram(+) rods since their shapes are so distinct. Time to positivity tough to interpret unless extreme (ex. Now, w/ the bugs organized, when you get that call from the micro lab, here are 3 questions to ask yourself/the lab:ġ) Number of positive bottles/cultures and time to positivity?įewer positive cultures & longer time to positivity suggests a contaminant. Remember that clinician adjudication is the ‘gold standard’ for deciding what is a contaminant! The orgs are deliberately ordered this way: Gram(+) orgs are often contaminants, Gram(–) orgs & yeast are not. Gram(+) cocci are grouped by ‘morphology’ since the lab usually tells you this: clusters, pairs, chains, etc. I arrange the potential Gram stain results that one can be called w/ as follows: Gram(+) cocci, Gram(+) rods, Gram(–) rods, Gram(–) cocci, yeast. ![]() Description Guide to Interpretation of Positive Blood Cultures ![]()
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