Bacterial pathogens of respiratory tract Flashcards
Microbial colonization in the RT (respiratory tract)
Upper portion: thru the trachea is NON STERILE
Lower portion: all thru the alveoli is STERILE
Entry/spread of bacteria into lower (sterile) RT and defense barriers to bacterial infections
Direct inhalation: determined by particle size
Aspiration of upper airway contents, spread along mucous membrane surface, hematogenous spread, direct penetration (intratracheal tube)
Ability to filter particles based on size (air flow and vibrissae), mechanical restriction (epiglottis and cough reflex), mucociliary escalator (propel materials away from lungs), Respiratory tract secretions (antimicrobial peptides, lactoferrin/transferrin, sIgA antibodies, lysozyme), localized immune cells and other host factors (phagocytes, immunoglobulins, complement)
Strategies used by bacterial pathogens of the RT to overcome/subvert host barriers
Adherence and/or invasion to/of RT tissues: pili, fimbrae, adhesins
Secretion of tissue damaging enzymes: lysins, proteases, elastases
Factors that inhibit or neutralize host defense mechanisms: proteases, capsule
Toxins that alter/inactivate host cell functions ribosylate G proteins and EF 2, phospholipases
Factors that overstimulate immune response: superAg Form microcommunities (biofilms) to resist elimination overproduce polysaccharides
Bacterial pathogens
Upper: Bordetella pertussis, Cornebacterium diptheria, n meningitidis, step pyogenes, staph aureas
Lower: strep pneumo, H. flu, mycoplasma pneumoniae, pseudomonas, legionella, mycobacteria TB
Morphology and staining characteristics
Gram positives: coccus: Staphylococcus clusters, streptococcus chains. Rods: cornyebacterium
Acid fast Rod: mycobacterium
No cell wall, pleomorphic: mycoplasma
Gram negatives: coccus: neisseria, Coccobacillus: bordetella, RODs: pseudomonas, legionella, haemophilus
Bordetella pertussis
Important features: gram-coccobacillus, Strict Aerobe; adheres to cilia of respiratory epithelium; produces pertussis toxin (PTx); expresses several adhesins including FHA, pertactic, pili; bacterium is highly infectious and transmittable, primarily disease of the young, and adults are often asymptomatic carriers
Diseases associated with infection of the RT: whooping cough (perussis), 3 phases : catarrhal, paroxysmal, and convalescence. Vaccine is available (acellular against PTx, FHA, pertactin) waning in efficacy
MOA: Bacteria binds to ciliated epithelium, secretes PTx which alters adenylate cyclase activity. ADP-ribosylates Gia, induces elevated cAMP production–> increase secretion and mucus production. And other factors damage mucocilliary escalator–> whooping cough
Cornyebacterium diptheriae
disease by toxin
Important features: Gram positive, pallisades, main virulence is diptheria toxin, ADP-ribosylates EF2 (inhibits protein synthesis, produces pili for colonization of Upper RT
Non-toxin producing strain elicit a localized infection resulting in pseudomembrane. Toxin-producing strains capable of causing sytemic disease. Toxin carried on lysogenic bacteriophage, FEVER sore throat, malaise
Pili mediate adherence of bacteria to respiratory epithelium, extensive bacterial replication at surface of epithelium, 2 stages: localized invasion and systemic disease (toxin producing strains)
Formalin inactivated diptheria toxin, also carrier for conjugate vaccine (hib) -CRM 197 a point mutation within DT that inactivates the toxin
neisseria meningitidis
Gram negative diplococci; oxidase positive, catalase positive,polysaccharide capsule; produce pili, common inhabitant of the nasopharynx of healthy individuals
Pharyngitis, pneumonia: usually preceded by respiratory tract infection, often seen in individuals with underlying disease or in kids, greatest concern is progression to meningits
MOA:
Capsule- prevent phagocytosis and complement fixation
Type 4 pili- allow colonization of the nasopharynx
LOS (lipooligosaccharide): similar to LPS but no repeating O antigens, has endotoxin activity
Vaccine- polysaccharide capsule, given over 2 years, and conjugate given under 55, capsule vaccine over 55
Strep pyogenes (group A step)
Group A strep, Gram positive cocci arranged in chains, beta hemolytic, possesses M protein and has a hyaluronic acid capsule, expresses multiple virulence factors, catalase negative
Diseases associated with infection: pharyngitis (strep throat): redness and edema of the mucous membranes, fever, purulent exudate, tonsilitus
Scarlet fever: streptococcal pharyngits and an erythematous punctiform rash
MOA: Surface proteins (M protein, F protein, LTA) promote adherence in pharynx, localized tissue destruction due to secreted enzymes, Scarlet fever is secondary complication, due to pyrogenic eexotoxins, superantigens, not bacterial dissemination
Pharyngitis
Rapid strep test or rapid antigen detection test,
Sample goes in the dot, membrane contains rabbit anti-strepA antibody.
Staphylococcus aureus
Gram positive Cocci often in clusters, catalase positive, produces a polysaccharide capsule, surface coated with protein A, produces many different toxins and cytopathic enzymes
Diseases associated with infection of the RT: pneumonia- seen in the very young and the very old with pulmonary disease, acquired via aspiration of oral secretion or hematogenous spread from distant infection site
MOA: normal component of nasopharyngeal flora, pulmonary tissue destruction due to secreted enzymes , can spread to other sites. Capsule (prevents phagocytosis), LTA (binds epithelium), Protein A (binds Fc receptos)
Streptococcus pneumoniae
Gram positive cocci often in pairs (diplocci), alpha hemolytic, virulent strains produce polysaccharide capsule more than 90 different capsular serotypes recognized (basis of vaccine)
Diseases associated with infection of the RT: lobar pneumonia, sinusitis, otitis media
MOA: lings fill with fluid due to tissue damage and over activation of the immune response. Pneumolysin (destroy ciliated epithelium, capsule antiphagocytic)
Vaccine at risk: 23 valent polysaccharide capsule vaccine, for youngens give 13 valent PVC13
Haemophilus flue
Small gram negative rods, require heme and NAD for growth, invasive species posses polysaccharide capsule, uses pili and omps to bind respiratory epithelial cells
Pneumonia, otitis, non encapsulated strains colonize upper RT
MOA: attaches to respiratory epithelium through pili and OMPS, gain access to underlying submucosa by invading between epithelium, cause induction of localized pro inflammatory response, concern is systemic infection and spread to CNS
Vaccine to Hib (type B)
Mycoplasma pneumoniae
No cell wall, coccoid but can be pleiomorphic bound by triple layered membrane containing sterols, obligate aerobe, small prokaryote, lifestyle produces P1 adhesins
Tracheobronchitis and atypical pneumonia
MOA: Associates with upper airway epithelial cells thru major adhesins: P1, Close association causes local accumulation of toxic metabolites, oxidation of lipids. Binding destroys cilia and inhibits clearance by normal mechanisms resulting in shedding of the bacterium in respiratory secretions. Induces inflammatory response which enhances cell damagevia over secretion of cytokines
Pseudomonas Aeruginosa
Gram negative rod, single polar flagella, oxidase positive, biofilm on surfaces and inanimate objects, opportunist pathogen, produces multiple virulence determinant including exotoxins
Diseases associated with infection: lung infections of cystic fibrosis pateints
Opportunistic=must breach normal host defense barriers, biofilms formation allows bacteria to resist immune mediated clearance. Produces pilins and other adhesins which promote association with respiratory epithial cells, produces numerous ecreted proteins (Proteases exotoxins, endotoxins DNAse) directly damage or inactivate host cells
