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Cycle 43 Organism 6 48 Monte Carlo Crescent Kyalami Business Park, Kyalami Johannesburg, 1684 South Africa www.thistle.co.za Tel: +27 (011) 463 3260 Fax to Email: + 27 (0) 86-557-2232 e-mail : [email protected] Please read this section first The HPCSA and the Med Tech Society have confirmed that this clinical case study, plus your routine review of your EQA reports from Thistle QA, should be documented as a “Journal Club” activity. This means that you must record those attending for CEU purposes. Thistle will not issue a certificate to cover these activities, nor send out “correct” answers to the CEU questions at the end of this case study. The Thistle QA CEU No is: MTS-18/063. Each attendee should claim ONE CEU point for completing this Quality Control Journal Club exercise, and retain a copy of the relevant Thistle QA Participation Certificate as proof of registration on a Thistle QA EQA. MICROBIOLOGY LEGEND CYCLE 43 – ORGANISM 6 Streptococcus agalactiae Streptococcus agalactiae (also known as group B streptococcus or GBS) is a gram-positive coccus (round bacterium) with a tendency to form chains. It is a beta-hemolytic, catalase-negative, and facultative anaerobe.In general, GBS is a harmless commensal bacterium being part of the human microbiota colonizing the gastrointestinal and genitourinary tract of up to 30% of healthy human adults (asymptomatic carriers). Nevertheless, GBS can cause severe invasive infections. Streptococcus agalactiae is the species designation for streptococci belonging to group B of the Lancefield classification. GBS is surrounded by a bacterial capsule composed of polysaccharides (exopolysacharide). The species is subclassified into ten serotypes (Ia, Ib, II–IX) depending on the immunologic reactivity of their polysaccharide capsule. This is why the plural term group B streptococci (referring to the serotypes) and the singular term group B streptococcus (referring to the single species) are both commonly encountered. Signs and symptoms The GBS organism colonizes the vagina, GI tract, and the upper respiratory tract of healthy humans. GBS infection is almost always associated with underlying abnormalities. In elderly persons aged 70 years or older, GBS infection is strongly linked with congestive heart failure and being bedridden. Signs and symptoms of GBS infection include the following: GBS pneumonia: Rare with few unique features; observed in elderly people with diabetes and with neurologic deficits; fever, shortness of breath, chest pain, pleuritic pain, or cough GBS meningitis: Common manifestation of neonatal infection; uncommon in adults; almost always associated with anatomical abnormalities contiguous with, or of, the CNS, usually as a result of neurosurgery; fever, headache, nuchal rigidity, or confusion GBS bacteremia: Common; most cases have no identifiable source of infection; fever, malaise, confusion, chest pain, shortness of breath, myalgia, or arthralgia Skin and soft-tissue infection, decubitus ulcers, colonization of diabetic foot infections: Fever, malaise, localized pain, cellulitis Osteomyelitis, arthritis, discitis: Fever, malaise, localized pain, cellulitis, arthralgia, arthritis, or weakness Chorioamnionitis, endometritis, UTIs (from asymptomatic bacteruria to cystitis and pyelonephritis with bacteremia): Fever, dysuria, flank pain, or pelvic pain Page 1 of 3 48 Monte Carlo Crescent Kyalami Business Park, Kyalami Johannesburg, 1684 South Africa www.thistle.co.za Tel: +27 (011) 463 3260 Fax to Email: + 27 (0) 86-557-2232 e-mail : [email protected] Pathophysiology S agalactiae when cultured on sheep blood agar forms glistening gray-white colonies with a narrow zone of beta haemolysis. It is an invasive encapsulated organism capable of producing severe disease in immuno-compromised hosts. Group B streptococcal infection in the absence of associated co-morbid medical conditions is rare. The virulence of S. agalactiae is related to the polysaccharide toxin it produces. Immunity is mediated by antibodies to the capsular polysaccharide and is serotype-specific. These organisms are divided into 9 serotypes on the basis of capsular polysaccharides (Ia, Ib, II, and III through VIII). Serotypes Ia, Ib, II, III, and V account for approximately 95% of cases in infants in the United States. Serotype III is the predominant cause of early-onset meningitis and most late-onset infections in infants. Laboratory findings and Identification GBS grows readily on blood agar plates as colonies surrounded by a narrow zone of β-hemolysis. GBS is characterized by the presence in the cell wall of the antigen group B of Lancefield classification (Lancefield grouping) that can be detected directly in intact bacteria using latex agglutination tests. The CAMP test is also another important test for identification of GBS. The CAMP factor produced by GBS acts synergistically with the staphylococcal β-hemolysin inducing enhanced hemolysis of sheep or bovine erythrocytes. GBS is also able to hydrolyze hippurate and this test can also be used to identify presumptively GBS. Hemolytic GBS strains produce an orange-brick-red non-isoprenoid polyene pigment (granadaene) when cultivated on granada medium that allows its straightforward identification. Figure 1: β-hemolytic colonies of Streptococcus agalactiae on blood agar. Figure 2: A positive CAMP test indicated by the formation of an arrowhead where the Strep group B (Streptococcus agalactiae) meets the Staphylococcus aureus (white middle streak) Prevention There is no reliable way to prevent newborn disease currently; however prophylactic treatment with antibiotics (typically intravenous penicillin) during delivery can prevent early-onset disease. Vaccination of adolescent women is considered an ideal solution; however, though research for the development of such a vaccine is underway, a good candidate vaccine has yet to surface. Different western countries use different strategies to select which women in labour are most likely to need Page 2 of 3 48 Monte Carlo Crescent Kyalami Business Park, Kyalami Johannesburg, 1684 South Africa www.thistle.co.za Tel: +27 (011) 463 3260 Fax to Email: + 27 (0) 86-557-2232 e-mail : [email protected] antibiotics. The United States uses the most aggressive strategy: all pregnant women are screened for S. agalactiae and prophylactic antibiotics are given to all positive women. Because of this strategy, the USA has seen a marked reduction in babies born with early-onset infection. Most European countries do not generally screen, but use a risk-based strategy at time of delivery. References 1. http://microbewiki.kenyon.edu/index.php/Streptococcus_agalactiae 2. Streptococcus Group B Infections Author: Christian J Woods, MD, Fellow, Infectious Diseases Program, Department of Pulmonary Critical Care, Georgetown University Hospital, Washington Hospital 3. https://en.wikipedia.org/wiki/Streptococcus_agalactiae Questions 1. How can group B Streptococcal be identified in the laboratory? 2. How can Streptococcus agalactiae be prevented? 3. Discuss the pathophysiology of S. agalactiae. Page 3 of 3 .
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