Gram Positive Bacteria

Gram positive phyla

Actinobacteria and Firmicutes

Gram negative phyla

Proteobacteria and Bacteroidetes

Gram Stain Procedure

Heat fixed smear flooded with crystal violet. Wash with iodine then alcohol. Safranin added for Gram negative stain.

Gram positive cell walls

up to 90% peptidoglycan. Usually contain embedded teichoic acids

lipoteichoic acids

teichoic acids covalently bound to membrane lipids

Morphology

Refers to the shape of bacterial cells, with major types being coccus (spherical), rod (cylindrical), and spirillum (spiral), including variations like spirochetes and filamentous bacteria.

Corynebacterium, Arthrobacter

group made up of 30 taxonomic families, may be very simple or complex eg C. diptheriae and C. glutamicum, the latter which produces MSG.

Mycobacteria

Rod-shaped bacteria with mycolic acids in their cell walls, including pathogens like M. tuberculosis and M. leprae causing granuloma formation.

M. leprae

Causes leprosy and is very difficult to grow in a lab, partly due to very slow growth. Can be grown in armadillo foot.

Streptomyces and Nocardia

Filamentous bacteria producing 70% of antibiotics, transitioning from spore to hyphae, found in soil.

Mycoplasmatota

Lack cell walls, include genera like Mycoplasma and Spiroplasma. Some of smallest organisms capable of autonomous growth. Animal and plant parasite. Lack key peptidoglycans

Lactobacillus and Streptococcus

Firmicutes producing lactic acid through fermentation. Can grow in pH 4 and grow in chains

Enterococcus

pathogenic Streptococcus → UTIs, bacteraemia, endocarditis, diverticulitis and meningitis

Streptococcus viridians

scarlet fever

Streptococcus pyogenes

strep throat and necrotising fasciitis

Staphylococcus

Nonsporulating Bacillales bacteria, common commensals eg S. epidermidis, with S. aureus associated with various infections and antibiotic resistance (MRSA and vancomycin resistant MRSA)

Bacillus and Clostridium

Sporulating low GC content Firmicutes found in soils

B. anthracis spore cycle

spores in soil taken up when cows consume grass → bacteria germinate and multiply, producing toxins, stress factors and spores. Spores excreted and cycle continues.

cutaneous anthrax

best prognosis, comes from infected insect bite/cut etc

pulmonary anthrax

poor prognosis, comes from inhaling spores

gastrointestinal anthrax

intermediate prognosis, comes from eating contaminated meat

vegetative B. anthracis

have both a capsule and S layer which allows them to avoid being killed

Clostridium

anaerobic, produce ATP via substrate level phosphorylation and some perform Stickland reactions - metabolism of a pair of amino acids. Found in anaerobic pockets in soil and mammalian intestinal tract

AB Toxins

Toxins with A (enzymatic) and B (binding) regions, requiring both for toxicity, working through proteolytic cleavage or separate assembly of polypeptides.

Anthrax Toxins

Primary Antigen (PA) released by B. anthracis and binds receptors, leading to LF and EF entry into cells, affecting MAPKKs, cAMP levels, and cytokine production.

EF

edema factor, remains associated with the membrane, greatly increasing cAMP conc and influencing cytokine production. May also increase host susceptibility.

LF

enters cytosol and cleaves the N terminal portion of mitogen activated protein kinase kinases (MAPKKs).

MAPKKs

involved in signalling pathways responsible for cytokine release, TNF and interleukin and induce cellular necrosis and toxin induced shock.

What happens when PA binds?

cleaved into 20 kDa and 63 kDa fragment. 63kDa fragment forms heptamer exposing LF and EF.