Gram -ve bacteria

Quorum Sensing

• Bacteria communicate with each other based on population density, coordinating activities when enough are present.
• This process involves adjusting gene expression in response to cell density, allowing bacteria to act collectively and enhance survival and virulence.

Iron Acquisition

• Acinetobacter spp. extract iron from the environment, crucial for growth and survival.
• Iron extraction from host's body can cause damage to host cells.
• They are highly resistant to serum and complements, components of the immune system.

Environmental Survival

• Bacteria survive in the environment by resisting drying out.
• They are resistant to disinfectants and antibiotics via biofilm formation.

Virulence Factors

• Not much is known about the pathogenicity and virulence of Acinetobacter.
• Pseudomonas is associated with sepsis, while Acinetobacter is associated with endocarditis and meningitis.

Acinetobacter baumannii

• OmpA: outer membrane protein.
• Pili assembly/fimbria.
• Biofilm-associated proteins.
• Phospholipase D: resistant to human serum, evades epithelial cell defenses, and contributes to pathogenesis.
• Phospholipase C: toxic to epithelial cells.

Chryseobacterium

• 125 species.
• Gram-negative rods, non-motile, with yellow pigment on BA.
• Strictly aerobic, oxidase-positive, and catalase-positive.

Chryseobacterium Virulence Factors

• Protease: breaks down proteins, damaging tissues and evading immune response.
• DNase: breaks down DNA, spreading infection and evading immune defenses.
• Phosphatase: regulates enzyme activity by removing phosphate groups.

Haemophilus influenzae

• Gram-negative, pleomorphic, small bacilli (coccobacillus).
• Non-motile, non-spore former, facultative anaerobe.
• Oxidase-positive, catalase variable.
• Capsulated forms are called Type B (super virulent form).

Haemophilus influenzae Growth Requirements

• Cultivation medium: Chocolate agar, requires Factor X (hemin) and Factor V (NAD).
• Alternative growth method: Blood agar with Staphylococcus aureus colonies providing Factor V via red blood cell haemolysis.

Haemophilus influenzae Classification

• Encapsulated strains: six serotypes based on capsular antigens (a, b, c, d, e, f).
• Unencapsulated strains: non-typeable, lacking a polysaccharide capsule.

Haemophilus influenzae Virulence Factors

• Capsule: pentose sugar + ribitol-phosphate Endo.
• Pili: adhesion to mucosal cells.
• Exotoxins: IgA1 protease, evading mucosal resistance to infection.
• Adhesins: adhesion to epithelial cells.
• Exotoxins: bacteriocin (haemocin), helping to fight off other bacteria.

Pseudomonas Aeruginosa Characteristics

• Gram-negative rod bacterium
• Obligate aerobe, meaning it requires oxygen for metabolism
• Non-lactose fermenting and non-spore forming
• Catalase, citrate, and oxidase positive
• Encapsulated with a mucoid exopolysaccharide capsule
• Possesses flagellum for motility and pili for adhesion
• Multi-drug efflux pumps and various drug-resistance enzymes

Colony Morphology

• Spreading and flat with serrated edges, no smooth edge
• Often shows metallic sheen, depending on the media
• Bluish-green, red, or brown color, with a yellowy green color on nutrient agar (NA)

Drug Resistance Mechanisms

• Efflux pumps: pump antibiotics out of the cell
• Beta-lactamases: degrade beta-lactam antibiotics
• Aminoglycoside-modifying enzymes: inactivate aminoglycosides
• Biofilm formation: encapsulation in mucoid layer, reducing antibiotic effectiveness

Virulence Factors

• Glycocalyx: produces mucoid substance, aiding adhesion and biofilm formation
• Pili: surface protrusions aiding adhesion to host epithelial cells
• Neuraminidase enzymes: facilitate pili binding
• Endotoxin (LPS): part of cell wall, causing host cell damage and symptoms of sepsis
• Exotoxin A: secreted toxin, inhibiting protein synthesis and causing host cell lysis
• Other exotoxins: enterotoxin, exoenzyme S, phospholipase C, and leukocidin

Infections and Symptoms

• Common infections: blood, skin, urinary tract, eyes, bones, and ears
• Symptoms: systemic (fever, elevated heart and respiratory rates, increased white blood cell count) and localized (specific to infection site)

Diagnosis and Treatment

• Diagnosis: complete blood count (CBC), cultures of site of infection
• Treatment: not specified, but often involves antibiotic therapy and management of underlying conditions

General Characteristics of Acinetobacter

• Gram-negative, short bacilli in pairs
• Non-motile, capsulated, and strictly aerobic
• Oxidase-negative and catalase-positive

Clinical Significance of Acinetobacter

• Causes nosocomial infections, including catheter-associated, ventilator-associated, and wound/soft tissue infections
• Associated with endocarditis and a significant threat in hospital settings
• Can cause respiratory tract infections, including pneumonia, bacteraemia, and meningitis, as well as UTI

Virulence Factors

• Natural resistance to host response and ability to form biofilms
• Quorum sensing allows for coordinated activities, gene expression regulation, and enhanced survival and virulence
• Iron acquisition mechanisms enable extraction of iron from the environment, killing of host cells, and resistance to serum and complements

Environment and Survival

• Resistant to desiccation, disinfectants, and antibiotics due to biofilm formation

Comparison with Pseudomonas

• Acinetobacter is a concern for endocarditis and meningitis, while Pseudomonas is a concern for sepsis

A. baumannii

• Causes nosocomial infections of importance
• Virulence factors include:
  • OmpA (outer membrane proteins)
  • Pili assembly/fimbria
  • Biofilm-associated proteins
  • Phospholipase D (resistance to human serum, epithelial cell evasion, and pathogenesis)
  • Phospholipase C (toxicity to epithelial cells)

Chryseobacterium General Characteristics

• Gram-negative rods
• Non-motile bacteria
• Produce a distinctive yellow pigment on blood agar (BA), similar to S. aureus
• Strictly aerobic, requiring oxygen for growth
• Oxidase positive, indicating the presence of cytochrome c oxidase
• Catalase positive, allowing the breakdown of hydrogen peroxide

Habitat and Distribution

• Ubiquitous, found in a wide range of environments

Virulence Factors

• Protease: breaks down proteins, damaging tissues and evading the immune response
• DNase: breaks down DNA, facilitating the spread of infection and evasion of immune defenses
• Phosphatase: removes phosphate groups from molecules, regulating enzyme activity by turning them on or off
• Interferes with the activity of other enzymes, including kinases, which add phosphate groups to proteins or molecules through phosphorylation

Characteristics of Haemophilus influenzae

• Gram-negative, pleomorphic, small bacilli (coccobacillus)
• Non-motile and non-spore forming
• Facultative anaerobe, oxidase +ve, catalase +ve
• Encapsulated or non-encapsulated, with only capsulated forms being Type B (super virulent form)

Growth Requirements

• Chocolate agar with Factor X (hemin) and Factor V (NAD) for growth
• Alternative growth method: Blood agar with Staphylococcus aureus colonies to provide Factor V
• Haemophilus influenzae is a fastidious grower, requiring supplemented factors (X and V) for growth

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
• Pili: adhesion to mucosal cells
• Exotoxins: IgA1 protease, evading mucosal resistance to infection
• Adhesins: adhesion to epithelial cells
• Exotoxins: Bacteriocin (haemocin), fighting off other bacteria
• Outer Membrane Proteins (OMPs): Endo
• Lipooligosaccharides (LOS): Endo

Diseases Caused by Haemophilus influenzae

• Meningitis
• Otitis media
• Sinusitis
• Epiglottitis
• Pharyngitis and Laryngitis
• Bacteraemia and Endocarditis
• Cellulitis
• Conjunctivitis
• Haemophilus parainfluenzae: Endocarditis, Secondary bacteraemia, Urethritis

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, people with malignancies or complement component deficiencies, those with acute viral infections
  • Unencapsulated strains: children and immunocompromised individuals, people with chronic lung conditions

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