Microorganisms possess many virulence factors which are usually decided by their genetic makeup. Not many virulence determinants of bacteria are expressed phenotypically. Capsule is one such bacterial organelle which displays many functions that include adherence, resistance to immune clearance, protection against environmental factors and many others including the typing of bacteria based on their specific capsular antigen and rapid diagnosis of capsulated bacterial infections using monoclonal/polyclonal anti-capsular antibodies
Key words: Bacterial capsule, Virulence determinants, functions of capsule.
1. INTRODUCTION
Identification of the bacteria isolated from clinical specimens and performing its antimicrobial susceptibility testing forms …show more content…
Capsules are among the first known bacterial virulence determinants, which were initially demonstrated by Griffith in 1928 in his rat experiments. This experiment has proved that suspensions of smooth colonies of bacteria able to produce capsule can kill a mice, where as suspension of rough colonies of bacteria devoid of capsule caused no mortality. Slime is an extracellular polymer loosely attached to the cell wall which can be easily washed off where as capsule is a compact, thick and gelatinous structure adhered to cell which is made of glycocalyx polysaccharide, glycopeptides etc.,. Capsules are usually polysaccharide in nature, may be homo/mono polymer of (glucans, dextrans, levans) or hetero/polymer of (hexose and pentose sugars plus ribitol/glycerol/other sugar alcohols) and capsule can also be composed of phosphoesterases. Capsule is also made of repeating oligonucleotide of more than one monomer. Many exopolysaccharides are acidic in nature due to heavy carbonyl groups either from acidic sugars such as uronic acids/neuraminic acid or from non-sugar subunits such as pyruvyl, acetyl and formyl group.Capsules are either synthesized at the level of cell membrane or extracellularly as done by Streptococcus mutans using extracellular enzyme glucosyltransferase in the oral cavity. Individuals infected with capsulated bacteria like Streptococcus pneumonia, Klebsiella pneumonia, Neisseria meningitides, Haemophilus influenza, Bacillus anthracis, Yersinia pestis and others show anti-capsular antibodies in their serum. Capsule is impermeable to biological dyes routinely used, therefore they cannot be stained. Negative staining which colours the background is employed to demonstrate the capsule. India ink and Nigerosin are the two stains used for staining the background and later a simple stain like safranin or crystal violet is applied to stain the
Key words: Bacterial capsule, Virulence determinants, functions of capsule.
1. INTRODUCTION
Identification of the bacteria isolated from clinical specimens and performing its antimicrobial susceptibility testing forms …show more content…
Capsules are among the first known bacterial virulence determinants, which were initially demonstrated by Griffith in 1928 in his rat experiments. This experiment has proved that suspensions of smooth colonies of bacteria able to produce capsule can kill a mice, where as suspension of rough colonies of bacteria devoid of capsule caused no mortality. Slime is an extracellular polymer loosely attached to the cell wall which can be easily washed off where as capsule is a compact, thick and gelatinous structure adhered to cell which is made of glycocalyx polysaccharide, glycopeptides etc.,. Capsules are usually polysaccharide in nature, may be homo/mono polymer of (glucans, dextrans, levans) or hetero/polymer of (hexose and pentose sugars plus ribitol/glycerol/other sugar alcohols) and capsule can also be composed of phosphoesterases. Capsule is also made of repeating oligonucleotide of more than one monomer. Many exopolysaccharides are acidic in nature due to heavy carbonyl groups either from acidic sugars such as uronic acids/neuraminic acid or from non-sugar subunits such as pyruvyl, acetyl and formyl group.Capsules are either synthesized at the level of cell membrane or extracellularly as done by Streptococcus mutans using extracellular enzyme glucosyltransferase in the oral cavity. Individuals infected with capsulated bacteria like Streptococcus pneumonia, Klebsiella pneumonia, Neisseria meningitides, Haemophilus influenza, Bacillus anthracis, Yersinia pestis and others show anti-capsular antibodies in their serum. Capsule is impermeable to biological dyes routinely used, therefore they cannot be stained. Negative staining which colours the background is employed to demonstrate the capsule. India ink and Nigerosin are the two stains used for staining the background and later a simple stain like safranin or crystal violet is applied to stain the