How to Differentiate Gram-Positive Cocci - PDF

How to Differentiate Gram Positive Cocci in a Simple Distinguishing different types of gram-positive cocci is crucial for accurate diagnosis and treatment. This section provides a Way straightforward approach to help laboratory technicians quickly identify these medically important bacteria. b...

How to Differentiate Gram Positive Cocci in a Simple Distinguishing different types of gram-positive cocci is crucial for accurate diagnosis and treatment. This section provides a Way straightforward approach to help laboratory technicians quickly identify these medically important bacteria. by Heba Rashed  Characteristics of Gram Positive Cocci Gram Positive Staining Cluster Formation Chain Formation Gram positive cocci stain Many gram positive cocci, Other gram positive cocci, purple due to the thick such as Staphylococcus, such as Streptococcus, peptidoglycan layer in their tend to grow in grape-like divide in a single plane and cell wall, which retains the clusters due to their form long chains of crystal violet dye during the division in multiple planes. individual cells.  Staphylococcus Species Staphylococci Staphylococcus are spherical, species are a leading cause of gram-positive bacteria that skin and soft often form tissue infections, as clusters well as more resembling serious grapes. conditions like pneumonia and sepsis. The primary way to differentiate Staphylococcus species is through the Catalase and Coagulase tests. Differentiating Staphylococcus Aureus Catalase Positive 1 Staphylococcus aureus is catalase positive, which helps differentiate it from streptococci. Coagulase Positive 2 Staphylococcus aureus is coagulase positive, clotting plasma, unlike coagulase negative s Mannitol Fermentation 3 Staphylococcus aureus can ferment mannitol, turning mannitol salt agar yellow. Pigment Production 4 Staphylococcus aureus produces a golden-yellow pigment on nutrient agar. Identifying Staphylococcus aureus is crucial as it is an important human pathogen responsible for a variety of infections, from skin and soft tissue to more severe invasive diseases. Differentiating it from other gram-positive cocci relies on key biochemical tests. Differentiating Coagulase Negative Staphylococci Catalase Positive 1 Coagulase negative staphylococci are catalase positive. Coagulase Negative 2 Unlike Staphylococcus aureus, they do not produce the coagulase enzym Novobiocin Susceptibility 3 Staphylococcus Epidermidis sensitive to novobiocin. Staphylococcus saprophyticus resistant to Coagulase negative staphylococci (CoNS) are a diverse group of Gram-positive cocci novobiocin. that can be differentiated from Staphylococcus aureus by their lack of coagulase production. They are commonly found on the skin and mucous membranes of humans and animals. Proper identification is important for distinguishing contaminants from  Streptococcus Species Overview Pathogenicity Key Species Identification Streptococcus is a Many The clinically Accurate genus of Gram- Streptococcus important identification of positive, spherical, or species are Streptococcus Streptococcus ovoid bacteria that opportunistic species include S. species is crucial arrange in chains or pathogens, pneumoniae, S. for targeted pairs. They are a causing a wide pyogenes, and S. antibiotic common cause of range of diseases agalactiae, which treatment and infections in humans like pharyngitis, have distinct infection control and animals. pneumonia, characteristics and measures. endocarditis, and disease necrotizing associations. fasciitis. Differentiating Streptococcus Pyogenes Beta-Hemolysis Streptococcus pyogenes, also known as Group A Streptococcus (GAS), exhibits complete or "beta" hemolysis on blood agar plates. Chain Formation Streptococcus pyogenes forms long chains of cocci when examined under a microscope after Gram staining. Bacitracin Sensitivity Streptococcus pyogenes is typically sensitive to bacitracin, which helps differentiate it from other Streptococcus species. Differentiating Streptococcus Agalactiae Beta-Hemolysis 1 Complete hemolysis of red blood cells = form narrow clear zon Bacitracin Sensitivity 2 Group B Streptococcus resistant to Bacitracin CAMP Test 3 Synergistic hemolytic reaction with Staphylococcus aureus Streptococcus agalactiae, also known as Group B Streptococcus (GBS), is an important human pathogen that can cause serious infections in newborns, pregnant women, and immunocompromised individuals. Differentiating GBS from other Streptococcus species relies on key phenotypic tests such as beta-hemolysis, and the CAMP test. Differentiating Streptococcus Pneumoniae 1 Gram Staining 2 Optochin Sensitivity 3 Bile Solubility 4 Alpha – Hemolysis 5 Capsule Production  Enterococcus Species Clinical Significance Identification Enterococci are opportunistic Enterococci are Gram- pathogens that can cause urinary positive, ovoid cocci that tract infections, bacteremia, and often appear in pairs or short endocarditis. Antibiotic Resistance chains. Many Enterococcus species are resistant to commonly used antibiotics, making them challenging to treat. Differentiating Enterococcus Morphology Faecalis 1 Enterococcus faecalis are Gram-positive cocci that typically appear in pairs or 2 Bile short Esculin chains. Test E. faecalis is bile esculin positive, indicating its ability to hydrolyze esculin in the presence of bile salts. 3 PYR Test E. faecalis is generally PYR (pyrrolidonyl arylamidase) positive, which helps distinguish it from other enterococcal Hemolysis Patterns Alpha Hemolysis Partial lysis of red blood cells, Beta Hemolysis resulting in a greenish-brown Complete lysis of red blood discoloration of the agar cells, creating a clear zone around the colony. around the colony. Gamma Hemolysis No lysis of red blood cells, with the agar remaining unchanged around the colony. Catalase Test Catalase Reaction Test Procedure Interpreting Results The catalase test is used to identify To perform the catalase test, a Catalase-positive bacteria will bacteria that produce the enzyme bacterial colony is mixed with a drop produce bubbles as the enzyme catalase, which breaks down of hydrogen peroxide. Bubbling breaks down the hydrogen peroxide, hydrogen peroxide into water and indicates a positive result, signaling while catalase-negative bacteria will oxygen. the presence of catalase. not show any reaction. Coagulase Test Definition Principle The coagulase test is a key The test detects the ability of diagnostic tool used to distinguish Staphylococcus species to clot between Staphylococcus aureus, plasma by converting fibrinogen to which produces the coagulase fibrin, indicating the presence of enzyme, and other coagulase- the coagulase enzyme. negative staphylococci. Optochin Sensitivity 1 Principle 2 Test Procedure The optochin sensitivity An optochin disk is placed test helps differentiate on a Streptococcus culture Streptococcus plate and incubated. pneumoniae from Zones of inhibition indicate other streptococcal sensitivity. species. 3 Interpretation Streptococcus pneumoniae is typically sensitive to optochin, while other streptococci are resistant. Bile Esculin Test Purpose Procedure The bile esculin test is used to Colonies are inoculated into a medium differentiate between Enterococcus containing esculin and bile salts. A species and other gram-positive cocci. It positive result is indicated by the medium helps identify Enterococcus by its ability turning black, due to the production of to hydrolyze esculin in the presence of esculetin from esculin hydrolysis. bile salts. PYR Test PYR Test Test Procedure Interpreting Results The PYR (pyrrolidonyl arylamidase) The test involves adding a reagent to A positive PYR test result helps test is used to detect the presence of a bacterial colony, which will change differentiate Enterococcus species the enzyme pyrrolidonyl arylamidase, color if the enzyme is present, from other Gram-positive cocci, which is produced by certain bacteria indicating the species. assisting in accurate identification. like Enterococcus.  Bacitracin Susceptibility Gram Positive Indicator Resistance in Other Species Bacitracin is a useful test to differentiate Streptococcus Most other gram-positive pneumoniae from other cocci, such as gram-positive cocci. Staphylococcus and Susceptibility to bacitracin is Enterococcus species, are a characteristic of resistant to bacitracin. Streptococcus pneumoniae. Interpretation Helps quickly differentiate Group A streptococci from other β-hemolytic streptococci. Streptococcus pyogenes is typically sensitive to bacitracin, which helps differentiate it from other Streptococcus species. Staphylococcus Epidermidis sensitive to novobiocin. Staphylococcus saprophyticus resistant to novobiocin. Novobiocin Susceptibility Novobiocin Susceptibility Test Differentiation Novobiocin is an antibiotic that can be The novobiocin susceptibility test Staphylococcus species are typically used to differentiate Staphylococcus involves exposing the bacterial isolate susceptible to novobiocin, while species from Micrococcus. to a novobiocin disk and observing for Micrococcus and Kocuria species are growth inhibition. resistant.