Pharyngitis (or sore throat) - most common upper respiratory tract infections (URTI).
Viral pharyngitis - vast majority of cases – self-limited.
Bacteria - important etiologic agents of pharyngitis, require specific antibiotic treatment - can lead to serious complications and sequelae
Streptococcus pyogenes
Corynebacterium diphtheriae
Rare causes
Other β-hemolytic streptococci (group C and G)
Arcanobacterium hemolyticum
Fusobacterium necrophorum
Mycoplasma pneumoniae
Neisseria gonorrhoeae
Size – 0.5-1 m.
Shape – oval /elliptical.
Arrangement – in chains esp. in liquid culture media. (upto 50 cocci in a chain).
Divide in one plane.
Daughter cells do not seperate.
Gram positive
Cultures older than log phase may lose gram reaction.
Capsule –
Hyaluronic acid (group A, C). Nonimmunogenic.
Polysaccharide (group B, D ).
Nonmotile.
Nonsporing.
L-forms – cell-wall deficient, require thiol & pyridoxal for growth. Found in blood (due to antibiotics).
Aerobes & facultative anaerobes.
22-42°C; opt.37.
pH for growth –opt. 7.4.
Capnophilic – 10% CO2.
Fastidious; need blood / serum / sugar.
Liquid medium (e.g. Todd-Hewitt broth) – granular turbidity + powdery deposits.
Blood agar –
0.5-1mm, circular, low convex, -hemolytic.
Matt colonies – pathogenic
Glossy colonies – nonpathogenic.
Selective medium –
Crystal violet (1:500,000) in B.A.
Catalase – ve
Sugar fermentation –
Glucose, lactose, maltose, trehalose - . (constitutive enzymes).
Other sugars & alcohols - ,(inducible enz.).
*Ribose sugars – not fermented.
*Pyrolidonyl naphthalamide hydrolysis (PYR) - +ve (differentiates gr. A from other groups).
Delicate organism
Survives in dust in dark for many weeks.
Susceptible to heat , 54°C x 30 min.
Susceptible to common antiseptics.
Resistant to –
Crystal violet (1mg/litre) – for isolation of gr A.
Nalidixic acid (15mg/litre) for isolation of & Colistin (10mg/litre) gr. B
Bacitracin sensitive – differentiates gr. A from other hemolytic
Hyaluronic acid capsule-nonantigenic, antiphagocytic, thrombolytic.
Innermost cell wall layer peptidoglycan (NAG-NAM)
Cell-wall CHO – Group sp. Ag. Todd-Hewit growth →
Extraction by –
HCl (Lancefield)
Formamide (Fuller)
Enzyme of Streptomyces albus (Maxted)
Autoclave (Rantz & Randall).
Capillary pptn /ring pptn
M protein –
Acid extraction & Serotyping.
100 M-types.
T protein –
Typing by slide agglutination with trypsinised RBCs.
R protein –
Present in gr. B, C, G & some serotypes of gr. A (23, 28, 48).
. Antigenic cross-reactions
Capsular hyaluronic acid synovial fluid.
Cellwall CHO cardiac valves.
Cellwall peptidoglycan skin.
Cyto. membrane vascular intima & cardiac muscle.
M protein* - reqd. for invasive infection.
Receptor for fibrinogen, factor H, IgG.
Capsule - antiphagocytic
Group CHO Ag’-invasive properties.
Protein F- binds fibronectin on epi. Surface
Lipoteichoic acid loosely binds strepto’ to epi surface. F prtn, M prtn secur
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Bacterial Pharyngitis Diagnosis and Treatment
1. Introduction
▰ Pharyngitis (or sore throat) - most common upper
respiratory tract infections (URTI).
▰ Viral pharyngitis - vast majority of cases – self-limited.
▰ Bacteria - important etiologic agents of pharyngitis, require
specific antibiotic treatment - can lead to serious
complications and sequelae
7. O2 requirement
Aerobes & facultative
anaerobes
Anaerobes
Hemolysis on 5% horse B.A.
- hemolytic
(viridans)
- hemolytic
(pathogens)
- or non-hemolytic
(fecal streptococci)
Serogrouping by Rebecca Lancefield (1933) -
based on cell wall cabohydrate, A-W (except I & J)
Group A – Strepto. pyogenes
Serotyping based on M, T, R proteins. >100 Griffith types
7
13. Blood agar –
• 0.5-1mm, circular, low
convex, -hemolytic.
• Matt colonies –
pathogenic
•Glossy colonies – nonpathogenic.
Selective medium –
•Crystal violet (1:500,000) in B.A.
13
14. Biochemical reactions
Catalase – ve
Sugar fermentation –
Glucose, lactose, maltose, trehalose - . (constitutive
enzymes).
Other sugars & alcohols - ,(inducible enz.).
*Ribose sugars – not fermented.
*Pyrolidonyl naphthalamide hydrolysis (PYR) - +ve
(differentiates gr. A from other groups).
14
15. Resistance / viability
Delicate organism
Survives in dust in dark for many
weeks.
Susceptible to heat , 54°C x 30 min.
Susceptible to common antiseptics.
Resistant to –
Crystal violet (1mg/litre) – for isolation of gr A.
Nalidixic acid (15mg/litre) for isolation of & Colistin
(10mg/litre) gr. B
Bacitracin sensitive – differentiates gr. A
from other hemolytic streptococci. 15
17. Cell-wall CHO – Group sp. Ag. Todd-Hewit growth →
Extraction by –
HCl (Lancefield)
Formamide (Fuller)
Enzyme of Streptomyces albus (Maxted)
Autoclave (Rantz & Randall).
Capillary pptn /ring pptn
17
18. M protein –
Acid extraction & Serotyping.
100 M-types.
T protein –
Typing by slide agglutination with trypsinised RBCs.
R protein –
Present in gr. B, C, G & some serotypes of gr. A (23, 28, 48).
18
20. Virulence factors
A) cellular
M protein* - reqd. for invasive infection.
Receptor for fibrinogen, factor H, IgG.
Capsule - antiphagocytic
Group CHO Ag’-invasive properties.
Protein F- binds fibronectin on epi. Surface
Lipoteichoic acid loosely binds strepto’ to epi
surface. F prtn, M prtn secures adhesion.
20
21. Virulence factors
B) Exotoxins
Streptococcal pyrogenic exotoxins (SPE) / erythrogenic
toxins / Dick toxins – A, B, C.
Act as superantigens.
Excessive release of cytokines & interleukins from T-cells
→ inflammatory shock (TSS).
Hemolysins – Streptolysin O & S.
21
22. Streptolysin O
Oxygen labile
Broth culture + sod.
hydrogen sulphite
Cardiotoxic
Freely secreted
Antigenic
ASO titer imp. in
rheumatic fever
Streptolysin S
Oxygen stable
Broth culture + RNA
Nephrotoxic
Cell bound
Nonantigenic
Stimulates release of
lysosomal enzymes. But
exact pathogenic role
unknown
22
23. Virulence factors
C) Enzymes
Streptokinase –
dissolves fibrin wall around site of
inflammation → spread of streptococci.
Hyaluronidase –
Helps in spread. (spreading factor).
Nuclease /DNAse /Streptodornase
Dissolve thick pus & help in spread.
Neuraminidase – helps in mucosal
colonisation.
23
24. Host defenses
First line defense / nonspecific defense –
Barrier of skin
Mucociliary defense in resp. tract.
Cough & sneeze reflex.
Second line defense –
Complement activation.
Antistrepto. antibodies in serum.
Opsonization & phagocytosis.
Autophagy of phagocyte if killing impossible.
24
25. Epidemiology
Reservoirs – widely distributed in
nature. + Part of normal flora.
Sources – patients & carriers.
Transmission –
a) droplets / contaminated dust
→ URTI;
b) Milk → bovine mastitis;
c) fomites, insects (eye gnats) →
skin infn.
Age – two peaks; a) 5-8 yrs. b) at
12-14 yrs.
25
26. Sex – males > females.
Season –
winter in temperate climates; all seasons in tropics.
Predisposing factors –
Crowding
Medical problems
Immunity – associated with antibody to M-protein.
26
27. Diseases
A) Suppurative
Pharyngitis , tonsillitis,
URTI.
By earlier serotypes.
Swollen, red post.
pharyngeal wall.
Complications –
peritonsillar & retro-
pharyngeal abscess,
sinusitis, otitis media,
mastoiditis etc.
27
Streptococcal sore throat, with enlarged tonsils
covered with white fibrinous exudate
28. Skin & soft tissue infections
By later serotypes. Common in small children.
Impetigo –
Small papules, vesicles, pustules → thick crusts
Ecthyma –
Ulcerated lesion
(staphylococcal lesions produce larger vesicles & bullous ulcers.)
28
29. Erysipelas
In older children.
Red, swollen, edematous, indurated skin with sharply demarcated
lesions.
Repeated attacks.
Due to SPE- B & C.
29
30. Cellulitis –
In skin with breach in continuity.
Lesion –
Red, swollen, painful
Not raised or demarcated.
Lymphangitis, bacteremia common.
30
31. Necrotizing fascitis / streptococcal gangrene –
Skin with breach in continuity.
1-2 days – erythema & purple bullae.
7-10 days –
Demarkated lesion.
Skin breaks open.
Underlying necrosed tissue seen.
31
32. Streptococcal toxic shock syndrome –
Wound infections of skin due to type M1, M3.
Due to SPE- A, B, C.
Super antigens. → inflammatory shock, renal failure & ARDS.
Extensive necrosis of skin & s/c muscles.
32
33. Other invasive infections –
Puerperal sepsis.
Anaerobic infections cause sepsis.
Abscess formation in kidney, brain & other organs.
33
34. Diseases
B) Nonsuppurative
Acute rheumatic fever & glomerulonephritis.
Both seen 1-3 weeks after ac. strepto. infn.
RF seen after pharyngitis but not after cut. Inf.
GN seen after dermal infections
No virulence factor of streptococcus is solely responsible
for both the diseases.
34
35. Rheumatic fever
Pathogenesis
Molecular mimicry & autoimmunity –
M protein Heart
Membrane antigen Skin & joints
Group sp. CHO Brain
Genetic predisposition of some B-alloantigens
Pathology
Thick mitral, aortic & tricuspid valves.
Thick chordae tendinae.
Thick myocardium.
35
36. Thick mitral valve.
Thick chordae tendinae.
Thick myocardium.
Thickened &
calcified Aortic
valves due to RHD.
36
37. Histopathology
Aschoff nodule
In interstitium
around vessels
Rosette of
giant cells
around central
necrosis.
37
41. Differences ACUTE RHEUMATIC
FEVER
ACUTE
GLOMERULONEPHRITIS
Site of infection Throat Throat / skin
Prior sensitization Essential Not necessary
Serotypes Any Pyodermal types
Immune response Marked Moderate
Complement level Unaffected Lowered
Genetic susceptibility Present Not known
Repeated attacks Common Absent
Penicillin prophylaxis Essential Not indicated
Course Progressive / static Spontaneous resolution
Prognosis variable good
42. Differential diagnosis
▰ Diphtheria and Viral pharyngitis
▰ Scarlet fever: Mediated by streptococcal
pyrogenic exotoxins (e.g. SPE-A, B, and C)
▰ Characterized by pharyngitis and rashes (with
sandpaper feel), strawberry tongue (enlarged
papillae on a coated tongue). Rashes in the skin
folds - Pastia’s lines
43. Laboratory diagnosis
Specimens –
Throat swabs, pus, blood, CSF/body fluids, infected
tissues from cellulitis/ erysepelas.
Collection –
Under vision with aseptic precautions in a sterile
container.
Transport –
Immediate / immediate plating on B. A.
Transport medium – Pike’s medium (B.A.+ C.V. +Na-
azide).
43
44. Smears (Gram stain) –
Pus & body fluids. No value for throat & genital specimens.
Culture –
Sheep B. A. without NAD (H. influenzae can’t grow). Incubation in 5-10%
CO2.
Colony morphology & hemolysis.
Selective medium – sheep blood agar + cotrimoxazole or crystal violet
(1:500000).
Biochemical reactions –
Catalase –ve, 10% bile insoluble, sugar fermentation except ribose, PYR
+ve.
44
45. Grouping & typing
Bacitracin sensitivity
6 mm disc, 0.1unit of bacitracin.
Zone of inhibition, ≥ 11 mm
diameter.
Lancefield grouping
Griffith typing
Phage typing
45
46. Antigen detection in samples –
Antigen extraction by pronase / nitrous acid.
Techniques –
Latex agglutination test (LAT).
Enzyme immunoassay (EIA).
Liposome immunoassay (LIA).
Fluorescent antibody staining.
Rapid detection of Strepto. pyo.
DNA hybridization
46
47. Serological diagnosis (retrospective diagnosis in RF & GN) –
Antistreptolysin O- inhibit streptolysin O mediated RBC lysis.
Titers high in RF; low in GN.
Titers >200 Todd units significant.
AntiDNAse B – inhibits DNAse B from hydrolyzing DNA-methyl green
conjugate.
47
48. Other antibodies –
Anti NADse
Anti hyaluronidase
Anti A-carbohydrate
Rapid screening tests –
Streptozyme test
Passive hemagglutination (RBCs coated with streptococcal antigen)
48
49. OTHER TESTS FOR STR.
PYOGENES
1) Fluorescent antibody technique
2) Typing by precipitation or
agglutination
3) Rapid diagnostic test kits
available
4) ASO titre estimation
5) AntiDNAseB estimation
RAPID DIAGNOSTIC
TEST KIT
50. Prophylaxis
Life long prophylaxis for Rheumatic fever –
Prevents reinfection & further damage to heart.
Long acting penicillins, erythromycins, sulfadiazine (to
prevent recurrent attacks).
Not useful in c/o glomerulonephritis as it occurs after
single infn and there is no reinfection.
50
51. Treatment
Cellwall active agents used.
Penicillins, macrolides (erythro’, azithro’), clindamycin,
vancomycin, cephalexin.
Surgical debridement in c/o myositis, necrotizing
fascitis etc.
For pharyngitis: Benzathine penicillin G, IM single dose or
oral penicillin V for 10 days.
For recurrent pharyngitis: Clindamycin or amoxicillin-
clavulanate.
For concomitant pneumonia and empyema: Penicillin G +
drainage of empyema.
51
52. Other hemolytic streptococci
45% of total strepto. Isolates = Gr. A.
15%
,, ,, ,, ,, = Gr. B.
15%
,, ,, ,, ,, = Gr. C.
25%
,, ,, ,, ,, = Gr. G.
5 %
,, ,, ,, ,, = Gr. F.
52
53. Group B streptococci –
Identified by hippurate hydrolysis, CAMP test.
Hippurate benzene ring + serine
Overnight growth in broth
culture → Centrifuge →
Deposit → Red ppt. on
addition of FeCl3.
Colony suspension in
broth → Incubate for 4
hrs. → Purple colour on
addition of ninhydrin.
HIPPURICASE
53
56. Group C streptococci
Animal pathogens.
Strepo. equisimilis – human pathogen.
Infections of deep tissues, bones, brain & heart.
Important source of streptokinase (used in thrombolytic therapy).
Group F streptococci
Minute streptococci.
Streptococcus MG - -h streptococci in PAP. Used in diagnosis of
serological test of mycoplasma pneumonia.
56
57. Group D streptococci –
Two types –
Enterococcal group – Enterococcus fecalis, E. fecium.
Nonenterococcal group – Strepto. bovis, Strepto. equinus.
Pairs of oval cocci arranged at angles.
Dark magenta colored coloured colonies on MacConkey’s agar; black
colonies on BPT.
Grow at 45°C, at pH 9.6, in 6.5% NaCl, in 40% bile; and hydrolyse esculin.
57