Baird Parker Agar- Composition, Principle, Preparation, Results, Uses

Baird Parker Agar

Baird Parker Agar was developed by Baird Parker from the Tellurite-glycine formulation of Zebovitz et al for isolation and enumeration of Staphylococci in food and other material since it allows a good differentiation of coagulase-positive strains. Sodium pyruvate was added as a selective growth stimulant, and egg yolk emulsion as a differentiation agent. The medium allows the growth of Staphylococcus aureus and selectively inhibits the growth of most other bacteria. It is thus considered as a selective and diagnostic medium for … Read more

Mannitol Salt Agar (MSA)- Composition, Principle, Preparation, Results, Uses

Results on Mannitol Salt Agar (MSA)

Mannitol Salt Agar (MSA) is used as a selective and differential medium for the isolation and identification of Staphylococcus aureus from clinical and non-clinical specimens. It is recommended for the detection and enumeration of coagulase-positive Staphylococci in milk, food, and other specimens and encourages the growth of a group of certain bacteria while inhibiting the growth of others. Principle of Mannitol Salt Agar (MSA) Mannitol Salt Agar contains beef extract and proteose peptone, which makes it very nutritious as they provide essential growth … Read more

Staphylococcal food poisoning (SFP)- Staphylococcus aureus enterotoxins

Staphylococcal food poisoning

Staphylococcal food poisoning (SFP) is one of the most probably occurring food-borne diseases which cause intoxication from the consumption of food containing preformed staphylococcal enterotoxins (SEs). Staphylococcal enterotoxins are mainly produced by Staphylococcus aureus which is enterotoxigenic strains of coagulase and Thermo nuclease (TNase) positive staphylococci. While occasionally SFP causing coagulase-negative staphylococcus species are Staphylococcus intermedius, Staphylococcus hyicus, Staphylococcus lutrae, Staphylococcus agnetis, and Staphylococcus schleiferi subsp. coagulans. Similarly, one of the exceptional cases of TNase negative coagulase-positive staphylococci is Staphylococcus … Read more

Biochemical Test of Staphylococcus aureus

Biochemical Test of Staphylococcus aureus

Biochemical Test of Staphylococcus aureus ­Basic Characteristics Properties (Staphylococcus aureus) Capsule Non-Capsulated Catalase Positive (+ve) Citrate Positive (+ve) Coagulase Positive (+ve) Gas Negative (-ve) Gelatin Hydrolysis Positive (+ve) Gram Staining Positive (+ve) H2S Negative (-ve) Hemolysis Positive (+ve)- Beta Indole Negative (-ve) Motility Negative (-ve) MR (Methyl Red) Positive (+ve) Nitrate Reduction Positive (+ve) OF (Oxidative-Fermentative) Fermentative Oxidase Negative (-ve) Pigment Mostly Positive (+ve) PYR Negative (-ve) Shape Cocci Spore Non-Sporing Urease Positive (+ve) VP (Voges Proskauer) Positive (+ve) Fermentation … Read more

Staphylococcus aureus- An Overview

Staphylococcus aureus

Image Source: ASM and Bacteria in Photos. Habitat of Staphylococcus aureus The natural habitat is mammalian body surfaces. They are normal flora of the skin and mucous membrane. Also present in the nose / the anterior nares. They can also be found in Pharynx. Found in stratified epithelial cells or mucous or serum constituents associated with these cells. Found in skin/nasal passage and axillae of humans. They act as a benign or symbiotic relationship with the hosts. Enterogeneric strains of S. aureus … Read more

Coagulase Test- Principle, Procedure, Types, Result, Uses

Coagulase Test

Coagulase Test Definition A coagulase test is a biochemical test that is used to differentiate Staphylococcus aureus from other Staphylococci species like S. epidermidis and S. saprophyticus on the basis of the ability to produce the coagulase enzyme. The coagulase test is an important test that differentiates the species of the genus Staphylococci into two groups; Coagulase positive Staphylococci and Coagulase Negative Staphylococci. The coagulase enzyme acts as a virulence factor in some organisms as it interacts with the fibrinogen … Read more

Catalase Test- Principle, Procedure, Types, Results, Uses

Catalase Test- Slide Method

What is Catalase Test? The catalase test is a biochemical test for aerobic organisms that detects the production of catalase enzyme in the organism. Catalase enzyme is a common enzyme that is found in all living beings that survive in oxygen and catalyzes the decomposition of hydrogen peroxide, releasing water and oxygen. Catalase is an essential enzyme in pathogenic organisms as it protects the organism from oxidative damage from the reactive oxygen species. The enzyme neutralizes the bactericidal effects of … Read more

Biochemical Test of Bacteria

Biochemical Test of Bacteria

Biochemical reactions are very important in the identification of bacterial isolates and in the identification of different bacterial species. These tests depend on the presence of certain enzymes, such as catalase, oxidase, urease, gelatinase, etc., produced by the bacteria. Different bacteria produce varying spectra of enzymes. For example, some enzymes are necessary for the bacterium’s individual metabolism, and some facilitate the bacterium’s ability to compete with other bacteria or establish an infection. Tests that measure single bacterial enzymes are simple, … Read more

Methicillin Resistant Staphylococcus aureus (MRSA)

Methicillin Resistant Staphylococcus aureus (MRSA)

MRSA is mediated by the mecA gene; which is chromosomally coded. It alters penicillin-binding protein (PBP) present on S. aureus cell membrane to PBP-2a: PBP is an essential protein needed for the cell wall synthesis of bacteria. β lactam drugs bind and inhibit this protein, thereby inhibiting cell wall synthesis. The altered PBP2a of MRSA strains has less affinity for β lactam antibiotics; hence MRSA strains are resistant to all β lactam antibiotics. BORSA strains (Borderline Oxacillin resistant S. aureus): … Read more

Aerobic and Facultatively Anaerobic Gram-Positive Cocci

Aerobic and Facultatively Anaerobic Gram-Positive Cocci

Enterococcus faecalis and Enterococcus faecium Clinical Features Urinary tract infections, peritonitis, bacteremia, endocarditis Virulence Factors Relatively avirulent Staphylococcus aureus Clinical Features Suppurative infections: impetigo, folliculitis, furuncles, carbuncles, wounds Disseminated infections: bacteremia, endocarditis, pneumonia, empyema, osteomyelitis, septic arthritis Toxin-mediated infections: toxic shock syndrome, scalded skin syndrome, food poisoning Virulence Factors Possess thick peptidoglycan layer, capsule, protein A, various toxins (cytotoxins, exfoliative toxins, enterotoxins, toxic shock syndrome toxin, Panton- Valentine leukocidin) and hydrolytic enzymes Staphylococcus, coagulase-negative Clinical Features Wound infections, urinary tract … Read more