Unit 4Part 3 Streptococcal Serology

Terry Kotrla, MS, MT(ASCP)BB

Introduction

Gram-positive Beta hemolytic Spherical, ovoid or

lancet shaped Pairs or chains

Divided into Serotypes or groups Two major outer proteins M and T Interior proteins divided into 20 defined

groups known as Lancefield groupings A-H and K-T.

Streptococcus pyogenes belong to Lancefield group A

M protein chief virulent factor

Numerous Exoantigens

Exoantigens are produced and excreted and include: Streptolysin O Dnase Hyaluronidase Nicotinamide Adenine Dinucleotidase Streptokinase

Patients react to exoantigens by producing antibodies

Streptococcus pyogenes

Organism found only in man. Leading cause of oropharyngitis which may

lead to serious complications (sequelae) Rheumatic fever Acute glomerulonephritis

Culture and rapid screening tests detect early infection.

Characteristics

Two major sites of infection Upper respiratory tract Skin

Upper Respiratory

Sore Throat Tonsillar exudate Fever Chills Headache 20% school children

carriers

Skin

Pyoderma or Impetigo Lesions on extremities Commonly on face Pustular and crusty

Suppurative Complications

Suppurate -To generate pus; as, a boil or abscess suppurates.

Erysipelas Cellulitis Necrotizing fasciitis Scarlet fever Puerperal sepsis

Erysipelas Erysipelas produces a rash that is red, slightly swollen, with

very defined borders (well demarcated), warm, and tender to the touch.

In this photograph, the right cheek is involved. There may be symptoms that affect the entire body (systemic) including fever and chills.

Cellulitis

Diffuse inflammation of connective tissue with severe inflammation of dermal and subcutaneous layers of skin.

Skin on face or lower leg most common site, but can occur anywhere on body.

Necrotizing Fasciitis – rare infection of deeper layers of skin and subcutaneous tissue

Scarlet Fever

Strawberry tongue Strep bacteria

produces a toxin that causes a rash

Appears 12-48 hours after fever

Sandpapery Peels

Suppurative Complications

Septic arthritis Acute bacterial endocarditis Meningitis Toxic shock-like syndrome

Non-Suppurative Complications Inflammatory response elsewhere in the

body. Damaging sequelae to strep infection

Rheumatic Fever Post-Streptococcal glomerulonephritis

Rheumatic Fever

Only certain serotypes involved. Delayed consequence of an untreated upper

respiratory infection with group A streptococci in 2-3% of population.

Not well understood. Symptoms occur 20 days after sore throat. Causes serious, debilitating damage to the

heart. Associated with large amount of M protein

and a capsule

Rheumatic Fever

Due to immune response against Strep antigens similar to heart antigens.

Inflammation of the mitral valve the most serious.

Thirty to 60% of patients suffer permanent disability.

Rheumatic Fever

This is the heart of a 44 year old woman who had rheumatic fever and had been treated for congestive heart failure for about one year.

Poststreptococcal glomerulonephritis Follows strep infection of skin or pharynx. Occurs about 10 days following initial

infection. Characterized by damage to glomeruli of

kidneys. Inflammatory response causes damage.

Post-Streptococcal Glomerulonephritis Deposition of Ag-Ab complexes, activation of

complement. Complement activated resulting in

hypocomplementemia. Renal function impaired due to reduction in

glomerular filtration rate, results in edema and hypertension.

Renal failure not typical.

Poststreptococcal glomerulonephritis Most common in children 2-12 Symptoms:

Hematuria Proteinuria Edema hypertension

Poststreptococcal glomerulonephritis The scattered capillary wall granular deposits in

acute poststreptococcal glomerulonephritis also stain for complement (immunofluorescence with antibody to C3)

Laboratory Testing

Culture and identification Rapid Strep Tests from throat swab Detection of Streptococcal antibodies Anti-Streptolysin O (ASO) titer DNA probes

Rapid Strep Tests from throat swab Antigen from a swab is extracted. Test extracted antigens using ELISA or latex

agglutination. If negative perform C&S.

Detection of Streptococcal Antibodies Most useful in Streptococcal sequelae Organisms elaborate more than 20 exotoxins

that may invoke antibody response. Most useful antibodies are:

Anti-Streptolysin O (ASO) Anti-DNase B Anti-NADase Anti-Hyaluronidates

Detection of Streptococcal Antibodies Serological evidence of disease is based on

elevated or rising titer of Streptococcal antibodies.

Four fold (2 tube dilution) rise in titer is considered clinically significant.

Anti-Streptolysin O (ASO) titer Two of the toxins produced are Streptolysin S,

which is oxygen stable, nonantigenic and Streptolysin O (SLO), which is oxygen labile and antigenic.

SLO is a hemolysin which is toxic to many tissues, including heart and kidneys.

Evokes an antibody response (anti-SLO) which neutralizes the hemolytic action of SLO.

Specific for ASO, it does not test for antibodies to any other Streptococcal exotoxins.

Anti-DNase B Testing

May appear earlier than ASO. Increased sensitivity for detection of

glomerulonephritis preceded by streptococcal skin infections.

Macro- and micro-titer, ELISA and neutralization techniques are available.

Neutralization technique has advantage of stability of reagents.

DNA Probes

Sensitive and specific Takes less time, hours versus days Many methods developed but principle the

same. PCR Add specific primers (probes) with tag Tag gives off signal, ie, fluorescence

The End