Corynebacterium diphtheriae is a nonmotile, noncapsulated, club-shaped, gram-positive bacillus. Toxigenic strains are lysogenic for one of a family of corynebacteriophages that carry the structural gene for diphtheria toxin, tox. Corynebacterium diphtheriae is classified into biotypes (mitis, intermedius, and gravis) according to colony morphology, as well … Read more
The antigen used to define serological test of Salmonella include Somatic O antigen, Flagellar H antigen and Vi antigen (Capsular antigen). Some of the differences between O Antigen and H Antigen are as follows: S.N. Characteristics O Antigen H Antigen 1. Types Somatic Antigen Flagellar … Read more
S.N. Characteristics S. pneumoniae Viridans Streptococci 1. Morphology Lanceolate diplococci Oval or round cells in chain 2. Capsule Capsulated Non-capsulated 3. Quellung Test Positive Negative 4. Bile solubility Bile soluble Bile insoluble 5. Inulin fermentation Positive Negative 6. Optochin sensitivity Sensitive Resistant 7. Pathogenicity in … Read more
Rapid plasma reagin (RPR) is macroscopic, non treponemal, flocculation card test used to screen for syphilis caused by Treponema pallidum. RPR is simple test can be done within few minutes. This test is less sensitive than treponemal test in early syphilis infection. Two types of … Read more
Scrub Typhus is an acute febrile illness which is caused by an obligate intracellular pathogen called Orientia tsutsugamushi, which is transmitted by the bite of infected larval stage trombiculid mite, Leptotrombidium spp. (Chiggers). The name scrub typhus was applied after discovery of increased frequency of … Read more
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 encourages the growth of a group of certain bacteria while inhibiting the growth of others. It is a selective … Read more
CAMP test is used to distinguish the species Streptococcus agalactiae from other species of beta-hemolytic Streptococcus. S. agalactiae, a member of the Lancefield Group B streptococci, is one of the causative agents of mastitis in cows. CAMP is an acronym for the authors of this … Read more
S.N. Characteristics Anthrax Bacilli Anthracoid Bacilli 1. Motility Non-Motile Generally Motile 2. Capsule Capsulated Non-Capsulated 3. Shape Grow in long chains Grow in short chains 4. Medusa Head Colony Present Not Present 5. Growth in Penicillin Agar (10 units/ml) No Growth Grow Usually 6. Hemolysis … Read more
A. Cell Wall Associated Virulence Factors Functions Peptidoglycan – Pyrogenicity – Complement Activation – Inhibition of leukocyte migration Techoic Acid – Adherence to mucosal surfaces Capsule – Diffusion Barrier – Prevents Phagocytosis – Capsular serotypes 5 and 8 are most frequently associated with bacteremia and … Read more
Neisseria gonorrhoeae and Neisseria meningitidis are both Gram Negative Bacteria. They are diplococci, non-sporing, non-motile and oxidase positive. But they have some differences which are as follows: S.N. Characteristics Neisseria gonorrhoeae Neisseria meningitidis 1 Referred as Referred to as gonococcus. Referred to as meningococcus. 2 … Read more
Staphylococcus and Streptococcus are both Gram positive organisms and cocci in shape. They are Non-motile, Non-Sporing and Facultative anaerobes. But they possess some of the differences which are as follows: S.N. Characteristics Staphylococcus Streptococcus 1 Arrangement Grape-like clusters. A chain of round cells. 2 Division Staphylococci divide in various … Read more
Lowenstein-Jensen (LJ) is the selective medium which is used for the cultivation and isolation of Mycobacterium species. It was developed by Lowenstein who incorporated congo red and malachite green to inhibit unwanted bacteria. The present formulation, a glycerated egg-based medium, is based upon Jensen’s modification. Jensen’s version eliminates … Read more
Vibrio cholerae is a gram-negative bacilli bacteria with a “comma” shaped body and a flagella for the movement. V. cholerae and V. mimicus are the only Vibrio spp. that do not require salt for growth. The string test may be performed on a glass microscope slide … Read more
Differentiation of Streptococcus pneumoniae from other viridans streptococci depends on demonstrating optochin susceptibility, bile solubility, reaction with a specific DNA probe, or detection of species-specific capsular polysaccharides. Most clinical microbiology laboratories today depend on the optochin susceptibility test. Although optochin susceptibility was first described for … Read more
Bacteremia is the simple presence of bacteria in the blood while Septicemia is the presence and multiplication of bacteria in the blood. Septicemia is also known as blood poisoning. S.N. Bacteremia Septicemia 1. Bacteremia is the simple presence of bacteria in the blood. Septicemia is … Read more
Many bacteria produce toxins, enzymes and pigments. Toxins and enzymes play important role in pathogenecity. Toxins are of two types: Exotoxins are usually heat labile proteins secreted by certain species of bacteria which diffuse into the surrounding medium. Endotoxins are heat stable lipopolysaccharide-protein complexes which … Read more
S.N. Characteristics Gram Positive Gram Negative 1 Gram Reaction Retain crystal violet dye and stain blue or purple Can be decolorized to accept counterstain (safranin) and stain pink or red 2 Cell Wall Cell Wall is 20-30 nm thick. Cell Wall is 8-12 … Read more
Bacteria are prokaryotic, unicellular microorganisms, which lack chlorophyll pigments. The cell structure is simpler than that of other organisms as there is no nucleus or membrane bound organelles. Due to the presence of a rigid cell wall, bacteria maintain a definite shape, though they vary … Read more
Hemolysis is the breakdown of red blood cells (RBC). A substance that causes hemolysis is a hemolysin. Brown (1919) introduced three terms alpha, beta and gamma to indicate three types of streptococci based on haemolytic reactions observed on blood agar plates. Beta-hemolytic Streptococci Beta-hemolysis (β-hemolysis) is … Read more
Habitat Mucous membrane of the upper respiratory tract of humans. Found in the nasopharynx of approx. 75% of healthy peoples. Cell Morphology Slender, short, gram negative rods or coccobacillus 3-0.5 um X 0.5-1 um with rounded ends. Prolonged counterstaining for 5-15 minutes with very dilute … Read more
1. They are aerobic and facultative anaerobes. 2. They grow best at 37 degree Celsius. 3. Group D grow well at between 10 degree Celsius and 45 degree Celsius. 4. Growth is poor on solid media or broth. 5. Grow well in media containing blood … Read more