POD Bacteriology

Bacteria

Unicellular organisms with DNA and RNA, replicate by binary fission

Cell Envelope

Includes inner cell membrane and cell wall, may contain virulence factors, targeted by diagnostic methods and antibiotics

Flagella and Pili

Filamentous protein structures anchored in the cell wall, act as virulence factors

Plasmids

Extrachromosomal genetic elements encoding 'fitness factors', transferable between bacteria, act as virulence factors

Gram Positive Bacteria

Stain purple, thinner cell envelope, more teichoic acids and peptidoglycans

Gram Negative Bacteria

Stain red/pink, thicker cell envelope, more lipid, lipoproteins, two layers of membrane, less peptidoglycans

Strain

Specific variant or subtype of a bacterial species, differs in characteristics like virulence, antibiotic resistance

Serotype

Groups within a single species of bacteria, classified based on distinct surface structures, can cause differences in virulence and diseases

ESKAPE Bacteria

Group of multi-drug resistant bacteria causing nosocomial infections: Enterococcus, Staphylococcus, Klebsiella, Acinetobacter, Pseudomonas, Enterobacter

Virulence Factors

Mechanisms or molecules produced by bacteria to survive and cause disease, including endotoxins, exotoxins, adhesins, M Protein, capsules, flagella, spores, secretion systems, iron acquisition systems

LPS Endotoxin

Virulence factor in outer membrane of highly pathogenic gram negative bacteria, composed of Lipid A, oligosaccharide, O antigen, causes severe host immune responses

MecA

Gene in staph that makes it resistant to B-lactam antibiotics (MRSA and MRSP)

Exotoxins

Molecules secreted from bacteria, including hemolysins, cytotoxins, enterotoxins, extracellular enzymes, superantigens

Streptolysin

Exotoxin produced by Strep, causes complete lysis of red cells (B hemolysis), resulting in necrosis

Enzymes

Include DNAase, lipase, elastase, hyaluronidase, coagulase, help with host tissue penetration

Toxic Shock Syndrome Toxin (TSST)

Superantigen causing cytokine storm leading to uncontrolled immune response and sepsis

STI (ETEC)

Reduces NaCl absorption leading to reduced water absorption (fluid loss)

STII (ETEC)

Increases secretion of Na+ and Cl- and HCO3- leading to fluid loss

LT (ETEC)

Reduces Na+ absorption that is irreversible, leading to fluid loss

Shiga Toxin (EHEC/STEC)

Causes damage to endothelial cells in blood vessels of colon and kidney

RTX Leukotoxin

Exotoxin produced by M. haemolytica, destroys pulmonary macrophages to allow bacteria to multiply unrestricted

Biofilms

Complex communities of bacteria forming plaques, very difficult to treat

Spores

Dormant form of bacteria, resistant to disinfection, minimal metabolism and respiration

Secretion Systems

Apparatus used to deliver proteins, toxins, DNA into host cells

SPI-1 Type 3 Secretion System

Used by Salmonella enterica, allows uptake by enterocytes, causes apoptosis and inflammation

SPI-2 Type 3 Secretion System

Used by Salmonella enterica, allows survival within macrophages

Iron Acquisition Systems

Methods to scavenge iron from host proteins or molecules to help with bacterial survival

Gram Stain

Quick method helpful in determining antibiotic to use, differentiates between gram positive and negative bacteria

Bacterial Culture

Growing microorganisms on various media to determine bacterial infection, diversity, and density

Biochemical Reactions

Includes catalase and coagulase tests

Molecular Methods

Advanced methods to determine specific bacterial species, strain, serotype etc.

Immunological Methods

Identify bacteria specific antibodies or antigens

Serotyping

Differentiate serotypes using antisera for specific antigens

Pathotyping

Detect specific virulence genes in a bacterial genome

MALDI-TOF

Used to identify species of suspect colonies based on their mass

MacConkey Agar

Indicator and selective medium, differentiates between gram negative lactose fermenters and non-lactose fermenters

Oxidase Test

Tests for the presence of cytochrome c oxidase in G- bacteria, helpful in differentiating bacteria

Antimicrobial Susceptibility Testing

Standardized methods to determine which antibiotics work on bacteria, and the minimum inhibitory concentration

Kirby Bauer method

Paper disks soaked in specific concentration of antibiotic placed on agar plate containing a lawn of bacteria

E Test (MIC Strip)

Paper strip with a concentration gradient of antibiotic placed on agar with bacterial lawn

Gram Positive Aerobic Cocci

Staphylococcus, Streptococcus, Enterococcus

Gram Positive Aerobic Rods

Bacillus, Listeria, Trueperella, Actinomyces

Gram Negative Aerobic Enterobacterales Rods

Escherichia, Klebsiella, Enterobacter, Salmonella, Proteus, Yersinia

Gram Negative Coccobacilli

Pasteurellaceae: Pasteurella, Manheimia, Actinobacillus, Glaesserella, Histophilus and Alcaligenaceae: Bordetella, Taylorella