Gram negative bacteria.docx

**Gram-negative species (Except Enterobacteriaceae & Campylobacter)** - Pseudomonas spp. - Acinetobacter spp. - Chryseobacterium spp. - Haemophilus spp. Bacteria Proteobacteria Gammaproteobacteria Pseudomonadales Pseudomonadaceae Pseudomonas 141 species, 10 subspecies - Pseudomo...

**Gram-negative species (Except Enterobacteriaceae & Campylobacter)** - Pseudomonas spp. - Acinetobacter spp. - Chryseobacterium spp. - Haemophilus spp. Bacteria Proteobacteria Gammaproteobacteria Pseudomonadales Pseudomonadaceae Pseudomonas 141 species, 10 subspecies - Pseudomonas aeruginosa - Pseudomonas fluorescens ***Pseudomonas aeruginosa*** \- Gram-negative rod bacterium. \- Obligate aerobe (uses oxygen for metabolism). \- Non-lactose fermenting. \- Non-spore forming. \- Catalase, citrate, and oxidase +ve \- Encapsulated with a mucoid exopolysaccharide capsule. \- Possesses flagellum for motility and pili for adhesion. \- Multi-drug efflux pumps and various drug-resistance enzymes. Distinct colony morphology - spreading and flat with serrated edges No smooth edge - often shows metallic sheen, Depending on the media - bluish-green, red, or brown Yellowy green on NA (dramatic and noticeable) - often β-haemolytic Not best test to identify **Drug Resistance Mechanisms:** 1\. Efflux Pumps: Pump antibiotics out of the cell. 2\. Beta-lactamases: Degrade beta-lactam antibiotics (e.g., penicillin). 3\. Aminoglycoside-modifying enzymes: Inactivate aminoglycosides -- a different class of antibiotics. **4. Biofilm Formation:** \- Encapsulation in mucoid layer. So the antibiotics cannot get to you \- Dormant state inside the biofilm reduces the effectiveness of antibiotics targeting protein synthesis, cell wall synthesis, or DNA replication. **Virulence Factors:** - Glycocalyx -- which makes Mucoid substance - Good for Adhesion; **biofilm formation** -- this in particular is very important for *Pseudomonas -* Protects from immune cells and antibiotics. - Pili - surface protrusions - Aid adhesion to the cell surface receptor on the host epithelial cell typically in the lungs - Neuraminidase enzymes important for binding - Facilitates pili binding - Endotoxin just part of the bacteria -- but foreign substances to humans, causing host cell damage - Lipopolysaccharides LPS -- part of the cell wall - Causes symptoms of sepsis/fever/inflammation - Enough of them bloodstream =\> shock, fever, - LPS Low toxicity - Exotoxin A -- secreted toxins =\> lysis of the host cell, inhibit protein synthesis of the host cells - Specific exotoxins for *Pseudomonas aeruginosa* - Induce autolysis lysis of the host cells - Inhibits protein synthesis - Enterotoxin - Exoenzyme S - One of the enzymes that inhibits protein synthesis - Phospholipase C / Lecithinase / Haemolysin more exotoxins - destruction of cytoplasmic membrane of host cells Causing cell lysis - Inactivates opsonins host immune proteins fighting off the infection - Elastase important if you get *Pseudomonas* infection in the eye - plays role in corneal infection - Leukocidin inhibits WBCs - inhibits neutrophil and lymphocyte functions - Pyocyanins - Pyocyanin blue pigment: Generates reactive oxygen species, causing oxidative damage. =\> cell death - Pyoverdine green compound: Iron chelator aiding bacterial growth. **Infections and Symptoms** Common Infections: \- Blood: Can lead to septic shock. \- Skin: Hot tub folliculitis (red pimply rash), Ecthyma gangrenosum (blisters progressing to necrosis). Wound infections (blue-green colour, fruity smell). \- Urinary Tract: Especially in catheter users. \- Eyes: Conjunctivitis and eye pain, often with contact lens use. \- Bones: Osteomyelitis, especially in diabetics. \- Ears: Malignant external otitis (swimmer\'s ear). \- Heart: Tricuspid valve endocarditis in IV drug users. \- Lungs: Pneumonia in cystic fibrosis patients. Symptoms: \- Systemic: Fever, elevated heart and respiratory rates, increased white blood cell count. \- Localized: Specific to the infection site, e.g., skin rash, eye pain, ear pain. **Diagnosis and Treatment** Diagnosis: \- Complete Blood Count (CBC). \- Cultures of site of infection: Blood, sputum, skin. **Treatment:** \- Serious Infections: Guided by cultures and antibiotic susceptibility testing. \- Combination Therapy: Often needed due to multidrug resistance. \- Examples: Beta-lactam with aminoglycoside or carbapenem with quinolones and aminoglycosides. **Environmental Presence and Transmission** Environmental Presence: \- Survives on dry surfaces and inanimate objects for months. \- Thrives in humid/wet conditions (e.g., hot tubs, contact lenses, catheters, medical ventilators). Transmission: \- Contact with contaminated surfaces or aerosols. \- Particularly affects high-risk individuals (e.g., those with cystic fibrosis, chronic diseases, immunodeficiencies, severe burns, deep wounds, IV drug users). Bacteria Proteobacteria Gammaproteobacteria Pseudomonadales Moraxellaceae - ***Acinetobacter*** 26 species ***Acinetobacter* General characteristics** - Gram-negative - **Short** bacilli in pairs - Non-motile - Capsulated - Strictly aerobic - Oxidase - ve - Catalase + ve ***Acinetobacter* sp. Clinical significance** - **Nosocomial infection** - Catheter associate infection - Ventilator-associated - Wound/soft tissue infection - Endocarditis - THREAT in hospital Respiratory tract causing pneumonia - Bacteraemia bloodstream - Endocarditis - Meningitis - UTI urinary tract Natural resistance to the host response and can form a biofilm Anything that has a group activity = quorum sensing -- so enough number of bacteria in one spot to turn something on. Quorum sensing: - Group activity -- Quorum sensing is a way bacteria communicate with each other based on their population density. When enough bacteria are present, they can coordinate activities. - Gene expression regulation -- this process involves adjusting gene expression in response to cell density. It allows bacteria to act collectively, which can enhance their survival and virulence. Immune system response -- The human immune system responds to infections, but sometimes the response can be too strong, causing damage to the body's own tissues. The part of the damage caused by infections can be due to the immune system's overreaction rather than the bacteria themselves. Iron acquisition: - Iron extraction -- Acinetobater spp. Can extract iron from their environment, which is crucial for their growth and survival. - Killing the host cells -- by pulling iron from the host's body, they can cuase damage to host cells. - Resistance to serum and complements -- they are highly resistant to components of the immune system, such as serum (the liquid part of blood) and complements (a group of proteins that help fight infections). Environment - Survive in the environment -- resistant to being dried out - Resistant to disinfectants and antibiotics (biofilm formation) For Pseudomonas, the worry is sepsis, the spread of infection through the bloodstream. For Acinetobacter, the worry is the infection in the heart or brain- endocarditis, meningitis **Virulence factors** -- not much is known about the pathogenicity and virulence *A. baumannii* Nosocomial infection of importance - OmpA -- outer membrane proteins - Pili assembly/fimbria - Biofilm associated proteins - **Phospholipase D** - resistance to human serum blood - epithelial cell evasion - pathogenesis - **Phospholipase C** - toxicity to epithelial cells Bacteria Bacteriodetes Flavobacteria Flavobacteriales Weeksellaceae ***Chryseobacterium*** 125 species ***Chryseobacterium* General Characteristics** Not so common, opportunistic ♣ Gram-negative rods\ ♣ Non-motile\ ♣ Yellow pigment on BA distinctive -- S. aureus can also be yellow on BA\ ♣ Strictly aerobic\ ♣ Oxidase +ve\ ♣ Catalase +ve Where can we find them? All over the place Virulence Factors: - Protease breakdown proteins -- damage tissues and evade the immune response - DNase breakdown DNA -- assist in spreading the infection and evading immune defence. - Phosphatase removes phosphate groups from molecules - Regulating the activity of other enzymes by turning them on or off -- this will be interfered - Phosphatase and kinases are two different enzymes that regulate the activity of other enzymes. - Kinase -- add phosphate groups to proteins or other molecules (phosphorylation) - Phosphatases -- remove phosphate groups from proteins or other molecules (dephosphorylation) Bacteria Proteobacteria Gammaproteobacteria Pasterellales Pasterellaceae Haemophilus - Haemophilus influenzae - Haemophilus parainfluenzae ***Haemophilus influenzae*** **Characteristics:** \- Gram-negative Pleomorphic small bacilli (coccobacillus) - Intermediate between round (coccus) and linear (bacillus). \- Non-motile. \- Non spore former \- Facultative anaerobe. \- Oxidase +ve, Catalase V \- Encapsulated or non-encapsulated Only the capsulated forms are called Type B -- super virulent form So have HIB -- H. influenzae Type B vaccine **Growth Requirements** \- Cultivation Medium: Chocolate agar, requires: \- Factor X (hemin) \- Factor V (NAD) \- Alternative Growth Method: Blood agar with Staphylococcus aureus colonies to provide Factor V via red blood cell haemolysis. **Growth factor X & V** H is a fastidious grower -- needs some factors supplemented = Factor X & V; without these, it cannot grow Right -- only grows around the disk -- X + V Left -- usually grows when factor V is supplemented because factor X is haem (already on it) **Classification** \- Encapsulated Strains: Six serotypes based on capsular antigens (a, b, c, d, e, f). \- Unencapsulated Strains: Non-typeable, lacking a polysaccharide capsule. **Virulence Factors** - capsule - pentose sugar + ribitol-phosphate Endo - Pili -- adhesion to mucosal cells - Exotoxins IgA1 protease -- evade mucosal resistance to infection, destroying IgA - Adhesins -- adhesion to epithelial cells - Exotoxins Bacteriocin -- haemocin this helps it fight off other bacteria so that it can have space to live. - Outer Membrane Proteins -- OMPs Endo - Lipooligosaccharides - LOS Endo +-----------------------------------+-----------------------------------+ | ***Haemophilus influenzae*** | ***Haemophilus parainfluenzae*** | +===================================+===================================+ | - Meningitis | - Endocarditis | | | | | - Otitis meida eye | - Secondary bacteraemia blood | | | | | - Sinusitis throat | - Urethritis | | | | | - Epiglottitis throat | | | | | | - Pharyngitis & Laryngitis | | | pharynx, larynx | | | | | | - Bacteraemia & Endocarditis | | | blood, heart | | | | | | - Cellulitis tissue | | | | | | - Conjunctivitis eye | | +-----------------------------------+-----------------------------------+ **Epidemiology** \- Transmission: Respiratory droplets and secretions. \- Colonisation Rates: \- Non-encapsulated strains: 40-80% of children and adults. \- Encapsulated strains: 3-5% of children aged 2-5 years. **Risk Factors** \- Encapsulated Strains: \- Children, especially unvaccinated. \- Individuals with spleen issues (splenectomy, sickle cell disease). \- People with malignancies or complement component deficiencies. \- Those with acute viral infections, especially influenza virus. \- Unencapsulated Strains: \- Children and immunocompromised individuals (diabetes, malignancy, HIV). \- People with chronic lung conditions (COPD, cystic fibrosis). **Diagnosis** \- Sample Cultures: Blood, CSF, synovial fluid, pleural fluid, etc. \- Serological Methods: Latex agglutination, enzyme immunoassay, coagglutination. \- Specific Tests: \- Epiglottitis: Laryngoscopy, X-ray showing \"thumbprint sign.\" \- Bronchopneumonia: Chest X-ray showing ground-glass opacities, bronchial wall thickening, consolidation. **Treatment** \- Encapsulated Strains: \- Ceftriaxone \- Chloramphenicol \- Unencapsulated Strains: \- First-line: Amoxicillin ± clavulanate. \- Alternatives: Second/third-generation cephalosporins, macrolides, fluoroquinolones.