Gram positive bacterial pathogens

(review) What is Gram-Positive Bacteria

Bacteria that stain purple, thick peptidoglycan, no OM when Gram-stained and can include opportunistic pathogens.

2 major groups:

Low G + C (guanine-cytosine) bacteria,

High G + C bacteria

when did anti-biotic resistance begin?

It’s always been present as bacteria have evolved over time to resist naturally occurring anti-biotic compounds / organisms

what do Group A Streptococci such as S. pyogenes cause?

Group A Streptococci (GP) such as S. pyogenes cause a range of infections including strep throat, scarlet fever, and skin infections.

They can also lead to more severe conditions like rheumatic fever and necrotizing fasciitis.

what are some examples of Gram + pathogens?

what are some defining features of Staphylococcus?

– Gram-positive cocci, nonmotile, facultative anaerobes

— Catalase positive

– Grape-like clusters

– Salt-tolerant i.e can tolerate salt on human skin

--Tolerant of desiccation

– Survive on environmental surfaces

What is the difference b/w Staphylococcus aureus and Staphylococcus epidermidis?

S. aureus: A virulent strain of Staphylococcus that can cause a variety of infections depending on the site.

S. epidermidis: apart of normal skin microbiome is a coagulase-negative strain generally less virulent and often associated with opportunistic infections, particularly in immunocompromised individuals.

what are the 3 disease categories of staphylococcus?

1. Noninvasive

• Food poisoning

• Due to ingestion of enterotoxin-contaminated food

2. Cutaneous

• Various localised skin conditions *due to use of coagulase

• Scalded skin syndrome, impetigo, folliculitis

3. Systemic

• Variety of infections when bacteria invade deeper tissues eg bacteremia, pneumonia, endocarditis, osteomyelitis.

what are the 3 main mechanisms of how Staphylococcus become pathogenic?

1. Evading phagocytosis

2. Production of enzymes i.e coagulase, staphylokinase

3. Production of toxins

how do staphylococcus evade phagocytosis?

• Protein A coats the cell surface which interferes with humoral immune responses

• Inhibits complement cascade

• Bound coagulase allows for fibrin clots hide the bacteria from phagocytic cells

• Synthesize polysaccharide slime layers (capsules)

• Inhibit leukocyte chemotaxis and phagocytosis

• Enables attachment of Staphylococcus to surfaces

what are the 5 main enzymes of staphylococcus?

1. Cell-free Coagulase

2. Staphylokinase

3. Hyaluronidase

4. Lipases

5. B-lactamase

what does cell-free coagulase and staphylokinase do?

Converts fibrinogen to fibrin, facilitating the formation of blood clots.

This process helps the bacteria evade the host's immune response by cloaking themselves in fibrin.

Dissolves fibrin threads in blood clots – Allows S. aureus to free itself from clots

what do Hyaluronidase do?

Breaks down hyaluronic acid

– Enables the bacteria to spread between cells

Exofoliative toxins

Cause skin cells to separate and slough off produced by certain Staphylococcus species, leading to skin conditions such as impetigo and scalded skin syndrome.

Enterotoxins

Toxins produced by certain bacteria, affect the stomach lining such as Staphylococcus aureus, stimulate symptoms of food poisoning.

What are the general steps of biofilm formation?

1. Initial attachment of bacteria to a surface.

2. Microcolony formation as bacteria multiply

3. Maturation of biofilm structure.

4. Dispersion of cells to colonize new surfaces.

Methicillin-resistant Staphylococcus aureus (MRSA)

A strain of Staphylococcus aureus that is resistant to ALL methicillin and other beta-lactam antibiotics

• Breaks down the B-lactam ring in Penicillin into Penicilloic acid by penicillinase

Opportunistic pathogens

Microorganisms that normally do not cause disease in healthy individuals but can cause infections in immunocompromised hosts.

Phagocytosis evasion

Mechanisms employed by pathogens, like Staphylococcus, to avoid being engulfed by immune cells.

Normal microbiota

Microorganisms that are normally found in the human body and may include opportunistic pathogens.

Bacteremia

The presence of bacteria in the blood, often leading to serious infections.

what are some features of Clostridia and some examples?

• Gram-positive, anaerobic, endospore-forming bacillus

• Ubiquitous in soil, water, and gastrointestinal tracts of animals and humans –

  *Endospores allow for survival in harsh conditions – eg: C. perfringens , C. difficile – C. botulinum – C. tetani

what does Clostridium perfringens cause?

*endospores are only produced under certain conditions, NEVER by GN

Clostridium botulinum + botulism

The bacterium that produces botulinum toxin, leading to botulism and paralysis, used for cosmetic purposes in small doses and as a treatment for various medical conditions.

• Anaerobic, endospore-forming, Gram-positive bacillus

• Common in soil and stagnant water

• Botulism results when the endopsores germinate and produce botulism toxins

What is Clostridium tetani?

– Ubiquitous in soil, dust, and GI tract of animals and humans

– Tetanus results when endospores germinate and produce tetanus toxin

Mechanism:

Clostridium difficile

– Common member of the intestinal microbiota

– Opportunistic in patients taking broad-spectrum antimicrobial drugs

Minor infections causes self-limiting explosive diarrhea

– Serious cases: Pseudomembranous colitis

– Life-threatening

C. difficile associated disease (CDAD)

A disease caused by Clostridium difficile, following broad spectrum antibiotic treatment, leading to severe diarrhea and colitis.

- Produces enterotoxins that damage intestines

• Increasingly more common in community-acquired diarrhea

what is the life cycle of C. difficle

• Contraction from healthcare settings, animals, the environment

• Spore formation by elimination of vegetative cells, survive gastric acid and digestive enzymes

• Germination, outgrowth and dissemination in the duodenum

• Colonisation in the colon, toxin production and inflammation

how does C. difficile cause disease in the large bowel?

• Production of toxins A and B, which damage intestinal epithelial cells, leading to inflammation, diarrhea

• Formation of pseudomembranes where mucous and cellular debris are expelled into the lumen, resulting in symptoms associated with pseudomembranous colitis.

  

Diagnosis, treatment, and prevention of Clostridium difficile

• Discontinue causative antimicrobial drug to resolve minor infections

• Serious cases treated with antibiotics treatment (selected carefully)

• Prevention- proper hygiene to limit nosocomial infections