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Micro - Corynebacteria (i) (C Diphtheriae (pharyngeal/tonsillar diphtheria…
Micro - Corynebacteria (i)
intro
gram +ve coccobacilli, small, club-shaped (V/L/chinese letter shapes)
aerobic (some also facultative anaerobes)
catalase +ve (bubbling)
non-spore forming
non-motile
ubiquitous in plants + animals (skin, upper resp tract, GUT)
Albert stain
differential
metachromic granules (dye changes colour)
C Diphtheriae
human only
world-wide distribution
was a significant cause of infant death prior to vaccine
Tx
give diphtheria toxoid vaccine when in convalescence (recovery)
threshold for herd immunity = 85%
natural infection does not reliably induce immunity
routine in many countries
high dose (D) @ 2,4 + 6 months with booster @ 4/5 yrs
low dose (d) booster @ 12-14 yrs
antitoxin
produced by horse
10% get serum sickness
not prophylaxis
only neutralises unbound toxin
penicillin G/erythromycin
ECG
airway + neuro management
do follow-up cultures to ensure eradication
@ risk: children, unvaccinated, overcrowding
droplet spread via cases + asymptomatic nasal carriers
3 biotypes (based on colonial appearance + biochem profile)
gravis
intermedius (rarely pathogenic)
mitis
disease = resp or cut
may involve skin/any mucous membranes (genitals, eyes, mouth)
incubation period = 1-10 (usually 2-6) days
classified based on infection site (ant nasal, tonsillar, pharyngeal, laryngeal, cut, ocular, genital)
pharyngeal/tonsillar diphtheria
insidious/gradual onset
severe exudative pharyngitis + tonsillitis
inflamm + exudate spreads over 2-3 days
forms thick adherent pseudomembrane (made up of exudate, bacteria, fibrin, dead cells, plasma cells, lymphocytes)
risk of resp obstruction + hypoxia
low grade fever
locally produced toxin rarely is absorbed into blood + has systemic effects - damages distant organs (esp heart, NS, kidneys + adrenals)
"bull neck" - oedema, tenderness, local lymphadenopathy
Dx
ddxs = GAS, EBV
not routine, so communicate with lab
take travel + vaccine Hx
pharyngeal swab + culture on selective media
takes up to 48hrs
must be selective to prevent overgrowth of normal commensals that are abundant in pharynx
Loeffler's serum slope potassium tellurite agar
grey/brown/black colonies
PCR
exotoxin
not produced by all strains
produced by tox gene
tested for using Elek test (filter paper saturated with antitoxin) or PCR of A subunit of tox gene
introduced to bacteria via transduction from lysogenic phages
identical in all strains
causes disease
cleaved into 2 protein molecules
remain attached via a disulphide bind
A terminates host cell ribosome protein synthesis
B binds to the heparin-binding EGF R (in many cells, esp in heart + Ns)
complications
mostly due to exotoxin
severity depends on extent of local disease
most common = myocarditis + neuritis
death in 5-10% from resp obstruction/paralysis or arrhythmia
cut diphtheria
infection via break in skin/after contact with an infected person
papule may form
chronic non-healing ulcer sometimes covered in a grey membrane
often mistaken for anthrax (caused by bacillus anthracis)
systemic disease if exotoxin present
IPC (infection prevention + control)
notifiable
screen close contacts
droplet precautions
outbreak in all ages in Soviet Union countries in 1990 (due to conflict - breakdown in vaccine programme)