(Draft) Bacterial Structure & Its Functions

Bacterial Structure & Function

3 Levels of Bacterial Structure

1. External Structures

2. Cell Envelope

3. Internal Structures

External Structure Categories

Appendages (Flagella, Fimbriae, Pili) and Glycocalyx

Cell Envelope Components

Cell wall, Cell membrane, Periplasmic space

Internal Structure Components

Chromosomes, Plasmids, Cytoplasmic granules and inclusions

Bacterial Cell Wall Primary Functions

• Morphology determinant (cocci, coccobacilli, bacilli, curved, fusiform, spiral)

• primary basis of bacterial classification

Bacterial Cell Wall Peptidoglycan Composition

• N-acetyl-D-glucosamine (NAG)

• N-acetyl-D-muramic acid (NAM)

Bacterial Outer Membrane Function & Composition

initial barrier to environment

• composed of Lipopolysaccharide (LPS) → negative charge

Bacterial Inner Membrane Functions

• Permeability barrier

• cell wall synthesis

• site of energy/ATP synthesis (counterpart of mitochondria)

Periplasm / Periplasmic Space

contains gel-like substance that captures nutrients and detoxifies environmental solutes like antibiotics

Bacterial Plasmid

Extrachromosomal DNA that carries antibiotic resistance genes

Bacterial Nucleoid

Contains bacterial chromosome (circular DNA complexed with RNA)

Bacterial Ribosome Size & Function

• 70S in Bacteria (80S in Fungi)

• site of protein synthesis

Endospore Composition & Resistance

• Made of Calcium dipicolinate

• resistant to heat, chemicals, nutrient deprivation, and drying

Bacillus anthracis Endospore Location

Bacteria w/ Center (Central) Endospore

Clostridium tetani Endospore Location

Bacteria w/ Terminal Endospore

Clostridium botulinum Endospore Location

Bacteria w/ Subterminal Endospore

Bacterial Cytosol

Has thousands of enzymes and is the site of protein synthesis

Glycocalyx

Outermost covering found outside the bacterial cell wall (not present on all bacteria)

Slime Layer Characteristics & Function

Loose, unorganized layer; for adhesion to surfaces and biofilm formation (e.g., Staph epidermidis on prosthetic heart valves)

Capsule Composition & Appearance

Tightly bound, well-organized layer; consists of polysaccharide/carbohydrates (except B. anthracis which is D-glutamic acid / amino acid / protein); contributes to colonization and mucoid layer on agar

Capsule Primary Function

Attachment and anti-phagocytic

Encapsulated Bacteria Examples

N. meningitidis, S. pneumoniae, K. pneumoniae, H. influenzae, Cryptococcus neoformans

Capsule Lab Diagnosis

Neufeld-Quellung reaction (Capsular swelling) and K or Vi Ag typing

Fimbriae Morphology & Function

Short, numerous appendages around the bacterium; used for attachment

Pilus / Pili Morphology & Categories

Long and fewer in number than fimbriae; divided into Common/Somatic pili and Sex pili

Common / Somatic Pili Function

For attachment

Sex Pili (F factor, F pilus) Function

For gene transfer (conjugation)

Pathogenicity Islands (PAIs) Definition

Genomic regions in which virulence factors are encoded

Biofilm Composition & Properties

Consists of monomicrobic or polymicrobic group of bacteria housed in a complex biochemical matrix; adheres to implants and prosthetic devices; contributes to antibiotic resistance

Persister Cells Definition & Properties

Starved, nutrient-deprived, slow-growing state of cells in a biofilm; displays reduced susceptibility to antimicrobial agents

Common Biofilm Producers

S. aureus, CONS, Streptococcus, Listeria monocytogenes, P. aeruginosa, Acinetobacter, Aeromonas, Aggregatibacter spp., Salmonella spp., Enterobacter, Enterococcus, Escherichia coli, Klebsiella, Proteus, Serratia, Citrobacter koseri, Candida albicans