Category archives for Bacteriology

Types of flagellar arrangement in bacteria

While reading bacterial structures, you might have known that flagella are the organ of locomotion in bacteria. If bacteria do not possess flagella then they are non motile. For example, Klebsiella spp Shigella spp do not possess flagella hence they are nonmotile while those psoosessing flagella are Bacteria (especially gram negative bacilli) possess flagella with […]

Colony characteristics used for identification of bacteria

Colony characteristics are observed after the primary isolation bacteria in solid culture medium. The appearance of bacterial colony on culture medium is usually characteristic and helps in preliminary identification. It is described under following headings: Size: diameter of the colony is measured in millimeters Shape: Shape refers to the general form of the colony which […]

Diene’s stain for identification of Mycoplasmas

Mycoplasma colonies can be identified by observing typical fried egg colonies on culture medium. Visualization is facilitated by application of Diene’s stain directly to the agar surface. Diene’s stain is a nonspecific stain that imparts a contrasting appearance to Mycoplasma colonies on agar. It allows easy visualization of colony morphology and characteristics. Composition of Diene’s […]

X and V factor test: Identification test for Haemophilus

Members of the genus Haemophilus are fastidious in nature. i.e. they require extra nutritional supplements in order to grow.  Some Hemophilus require only X factor (haemin-which is present on blood agar)  or only V factor (Nicotinamide-adenine dinucleotide, NAD- which is present within the blood cells) or a combination of both. So,  Haemophilus influenzae grows only […]

Sodium Polyanethol Sulfonate (SPS) disk for differentiation of anaerobic cocci

Principle Sodium polyanethol sulfonate (SPS) is a commonly used anticoagulant. It is also known as Liquoid. It can inhibit the growth of certain anaerobic bacteria such as Peptostreptococcus anaerobius as well as aerobic Gardnerella vaginalis. So, this property of SPS can be used as a tool for differentiating P. anaerobius from other anaerobic cocci. For […]

List/Classification of Coagulase Negative Staphylococci (CoNS)

There are more than 40 recognized species of CoNS. Most of these species have been isolated from humans, usually from the skin and mucous membranes. Certain species are found in very specific sites, such as the head (Staphylococcus capitis) or ear (Staphylococcus auricularis). Others have been isolated from animals and animal products. CoNS are classified into different […]

General characteristics of Staphylococci

Staphylococci are gram-positive cocci arranged in cluster (grape-like fashion). The genus name, Staphylococcus, is derived from the Greek term staphle, meaning “bunches of grapes.” On gram stained smears, they appear as gram positive spherical cells (0.5 to 1.5 μm) arranged singly, in pairs, and in clusters. Although the Staphylococci can be identified on the basis […]

Methods/Ways/Media that can inhibit swarming of Proteus

There are various methods/ways/media to inhibit swarming of Proteus spp. We can either increase the concentration of agar (2.5-3.0% w/v) or incorporate growth inhibitors like chloral hydrate (1 in 500), sodium azide (1 in 5000), boric acid (1 in 100) and sulphonamide. Use of these chemicals may inhibit the growth of other pathogenic bacteria too […]

Normal flora

By Normal flora, we mean the population of microorganisms residing in  the skin and mucous membranes of  healthy normal individuals without causing any harm to them. There are more numbers of bacteria (1014) in human body than the number of cells (1013). These bacterial populations constitute the normal microbial flora of human body. The normal flora is […]

Oxidation Fermentation (OF) test: Principle, Procedure and Result Interpretation

Oxidation Fermentation (OF) test is used to differentiate those organisms that utilize carbohydrates aerobically (Oxidation) such as Pseudomonas aeruginosa, from those that utilize carbohydrates anaerobically (Fermentation) such as members of the Enterobacteriaaceae and those that do not utilize carbohydrates at all (Non fermenters) such as Alcaligenes faecalis  . This test was developed by Hugh and […]

Tween 80 hydrolysis test

Tween 80 hydrolysis test is used mainly to differentiate slow–growing Mycobacterium (Scotochromogens) with similar colony appearance, M. gordonae (positive) and M. scrofulaceum (negative). This test is also useful in identifying M. kansasii (positive results within 24 hours). Those Mycobacterium spp that produce lipase hydrolyse the detergent Tween 80 (polyethylene derivative of sorbitan mono-oleate) with the production of oleic acid and polyoxyethylated […]

Hanging drop test/preparation

Hanging drop test is a confirmatory test to identify if an organism is motile or non motile. It can also be used for the presumptive identification of organism on the basis of its characteristic motility like Vibrio cholerae which has a darting type of motility in stool sample of patients with cholera. This test is prepared […]

Hydrogen sulphide (H2S) production test

Hydrogen sulphide (H2S) production test is used for the detection of hydrogen sulphide (H2S) gas produced by an organism. It is used mainly to assist in the identification of members of family Enterobacteriaceae and occasionally to differentiate other bacteria such as Bacteroides sps and Brucella sps. H2S is produced when sulphur – containing amino acids […]

DNase test (deoxyribonuclease test)

DNase test  is useful in the identification of Staphylococcus aureus which produces deoxyribonuclease (DNase) enzymes. This test is particularly useful when plasma is not available to perform a coagulase test or when the results of a coagulase test are difficult to interpret. Views – 12772

Definition, Classification, Morphology and cultural Characteristics of Shigella

Classification Kingdom: Bacteria Phylum: Proteobacteria Class: Gamma Proteobacteria Order: Enterobacteriales Family: Enterobacteriaceae Genus: Shigella Type species:  S. dysenteriae   Definition of Shigella: They are fermentative, facultative anaerobic non spore forming gram negative bacilli, non motile, catalase positive (except Shigella dysentriae type 1), oxidase negative, do not produce gas form carbohydrates with few exceptions. None forms […]

Pathogenesis of Shigella

Shigella is a common cause of bacterial diarrhoea worldwide, especially in developing countries. Humans are the only natural reservoir for disease. Transmission can occur via direct person-to-person spread, as well as via contaminated food and water. Infective dose is very low as 10-100 bacilli can cause disease. Once ingested, the bacteria survive the gastric environment […]

Voges Proskauer test (VP test): Principle, Procedure, Interpretation and Quality Control

Voges-Proskauer test is one of the tests used for identification of Enterobacteriaceae. It is usually performed alongside the methyl red test since both tests are performed on cultures grown in MR-VP broth.  Both tests are based on the detection of end products from the metabolism of glucose. VP test is based on the detection of […]

Oxidative/Fermentative Test (O/F test)

Oxidative/Fermentative (O/F) test is done to distinguish between aerobes and anaerobes through their ability to breakdown carbohydrates. In this test, a semi solid medium containing a carbohydrate (usually glucose) and a pH indicator is used.  If acid is produced only at the surface of the medium, where conditions are aerobic, the attack on sugar is […]

Novobiocin susceptibility test

The speciation of coagulase negative Staphylococcus is necessary in certain culture specimens. Coagulase negative staphylococci can either be resistant or susceptible to novobiocin. The one most commonly isolated novobiocin resistant coagulase negative staphylococcus from urine is Staphylococcus saprophyticus. It is one of the most common causes of urinary tract infections in sexually active young women. So, […]

Bile solubility test: Principle, Procedure and Expected results

Principle of Bile Solubility test: Bile solubility test is used to differentiate Streptococcus pneumoniae from other alpha-hemolytic Streptococci. Streptococcus pneumoniae is bile soluble whereas all other alpha-hemolytic streptococci are insoluble. Bile or a solution of bile salt, like sodium desoxycholate rapidly lyses the pneumococcal colonies. This lysis depends on the presence of intracellular autolytic enzyme. Bile […]

CAMP test and Reverse CAMP test

CAMP (Christie, Atkins, and Munch-Peterson) test is used for the presumptive identification of Group B Streptococcus (Streptococcus agalactiae). It is the only beta-hemolytic Streptococcus which yields a positive CAMP test. The test has been named after Christie, Atkins, and Munch-Peterson, who described it in 1944.  a Principle of CAMP test CAMP test is done to detect […]

Leucine amino peptidase (LAP) test for identification of catalase negative gram positive cocci

Principle of  Leucine amino peptidase (LAP) test: Leucine amino peptidase (LAP) test is used for the preliminary characterization of catalase negative, gram-positive  cocci.  This is a rapid test for detection of enzyme leucine aminopeptidase. Leucine- β- napthalamide impregnated disk serves as a substrate for the detection of leucine aminopeptidas.  This enzyme hydrolyse the substrate resulting […]

Gelatin hydrolysis test: Principle, Procedure, Interpretation and preparation of nutrient gelatin medium

Gelatin hydrolysis is helpful in identifying and differentiating species of Bacillus, Clostridium, Proteus, Pseudomonas, and Serratia.  It also distinguishes the gelatinase-positive, pathogenic Staphylococcus aureus from the gelatinase-negative, non-pathogenic S. epidermidis . Gram-positive, spore-forming, rodshaped, aerobic or anaerobic bacteria such as Bacillus anthracis, Bacillus cereus, Bacillus subtilis, Clostridium perfringens and Clostridium tetani, are also positive for […]

Hippurate hydrolysis test

Hippurate hydrolysis test can be used for presumptive identification of Gardnerella vaginalis, Campylobacter jejuni, Listeria monocytogenes and group B streptococci. Principle of Hippurate hydrolysis test Hippurate hydrolysis test is used to detect the ability of bacteria to hydrolyse hippurate into glycine and benzoic acid by action of hippuricase enzyme present in bacteria. Previously, it was tested using ferric chloride […]