Streptococci - Overview of Detection, Identification, Differentiation and Cultivation Techniques

Transcription

1 Return to Web Version Streptococci - Overview of Detection, Identification, Differentiation and Cultivation Techniques By: By Jvo Siegrist, Product Manager Microbiology, ivo.siegrist@sial.com, AnalytiX Volume 7 Article 3 Streptococci are non-motile, microaerophilic, Grampositive spherical bacteria (cocci). They often occur as chains or pairs and are facultative or strict anaerobes. Streptococci give a negative catalase test, while staphylococci are catalase-positive. Because they are unable to synthesize cytochromes, streptococci cannot carry out oxidative phosphorylation. They are able to ferment sugars, but the end product is always lactic acid. Therefore, streptococci are very acid tolerant and count among the lactic acid bacteria order. There are many natural sources of streptococci, including humans and diverse animals where they often colonize the mucosal surfaces of the mouth, intestinal tract, nasal passages and pharynx. The presence of streptococci in drinking water indicates fecal contamination. Food sources with high risk of contamination include milk and dairy products, eggs, steamed lobster, ground ham, potato salad, custard, rice pudding and shrimp salad. In most streptococcal food poisoning cases, the food was allowed to stand at room temperature for several hours between preparation and consumption. The contamination of the food is most often the result of poor hygiene, handling of the food by infected people, or the use of raw (unpasteurized) milk. Although they can be potent pathogens, some streptococci are commercially important for the production of cheese and yogurt. These include S. lactis, S. cremoris, S. diacelillactis and S. thermophilus, the latter being the most well-known. For detection, identification, differentiation, enumeration and cultivation of streptococci, Sigma-Aldrich provides a broad range of specific agars and broths (Table 1), Streptococci Diagnostic Tests (Table 2) and a Gram staining kit and component solutions (Table 3). Scientific classification of Streptococcus Kingdom: Eubacteria Phylum: Firmicutes Class: Bacilli Order: Lactobacillales Family: Streptococcaceae Genus: Streptococcus Grouping of Streptococci based on hemolytic activity Streptococci are divided into three groups based on their hemolytic (red blood cell lysing) activity. The hemolytic reaction can be visualized on blood agar plates, such as the non-selective Agars for Differentiation that are listed in Table 1. Table 1...Media for Streptococci Non-selective Enrichment Broths Fluka Brain Heart Broth B2551 Sigma Brewer thioglycollate medium Fluka Casein peptone Lecithin Polysorbate Broth Fluka CASO Broth Fluka Cooked Meat Broth Fluka Elliker Broth Fluka Heart Infusion Broth

2 70122 Fluka Nutrient Broth No Fluka Nutrient Broth No Fluka Peptone Water, phosphate-buffered, Vegitone Fluka Peptone Water Fluka Peptone Water, phosphate-buffered S4681 Sigma Standard Nutrient Broth No Fluka Stuart Ringertz Medium Fluka Thioglycolate Broth with Resazurine T1438 Sigma Todd Hewitt Broth Fluka Tryptic Soy Broth Fluka Tryptic Soy Broth No Fluka Tryptic Soy Broth, Vegitone T3938 Sigma Tryptone Soya Broth without Dextrose T4407 Sigma Tryptose Broth V5262 Sigma Veal Infusion Broth Selective Enrichment Broths Fluka Glucose Azide Broth Non-selective Agars for Cultivation, Enumeration and Isolation A3340 Sigma AC Agar Fluka Brain Heart Infusion Agar Fluka CASO Agar Fluka Columbia Agar D3060 Sigma Dextrose starch agar D8184 Sigma Diagnostic sensitivity test agar Fluka Milk Agar Fluka Nutrient Agar Fluka Peptonized Milk Agar Fluka Plate Count Agar Fluka Plate Count Agar according to Buchbinder et al Fluka Plate Count Agar, Vegitone Sigma Streptococcus thermophilus Isolation Agar Fluka Tryptic Soy Agar Fluka Tryptic Soy Agar, Vegitone Fluka Tryptic Soya Agar with Polysorbate 80 and Lecithin

3 51414 Fluka Tryptic Soya Agar with Polysorbate 80 and Lecithin Fluka Tryptone Glucose Extract Agar T2313 Sigma Tryptose Agar Non-selective Agars for Differentiation Fluka Blood Agar (Base) B1676 Sigma Blood Agar Base No Fluka CLED Agar Fluka Deoxyribonuclease Test Agar D2560 Sigma DNase Test Agar with Toluidine Blue Fluka LS Differential Agar Selective Agars with Differential System for Differentiation, Detection and Isolation Fluka Bile Esculin Azide Agar Fluka Kanamycin Esculin Azide Agar Fluka Mitis Salivarius Agar Media for Sensitivity Testing Fluka Mueller-Hinton Agar 2 Alpha-Hemolytic Streptococci In alpha hemolysis, the red blood cells remain intact, but the hemoglobin is converted to biliverdin. This causes a greening of the blood agar plate around the colonies. Pneumococci S. pneumoniae: Causes bacterial pneumonia, otitis media and meningitis. S. pneumoniae sensitivity to optochin (ethyl hydrocupreine hydrochloride) is the basis of a diagnostic test (Figure 1, Table 2).

4 Figure 1... Differentiation and identification flow chart of Gram-positive cocci Table 2... Diagnostic tests for identification and differentiation of streptococci Fluka Catalase Test Fluka Bacitracin Disks Fluka Optochin Disks Fluka PYRase Strips Viridans and Others S. mutans: Associated with dental caries. S. viridans: Causative agent for endocarditis and dental abscesses. S. salivarius: Considered to be an opportunistic pathogen. S. salivarius subsp. thermophilus: Used in the production of cheese and yogurt. Beta-Hemolytic Streptococci Beta hemolysis is a true hemolysis of erythrocytes by the enzyme hemolysin. Clear zones will appear around the colonies on the blood agar plate. Beta-hemolytic streptococci are further divided into serological groups using specific antibodies that recognize surface carbohydrate antigens (e.g. A, B, etc.). Group A S. pyogenes: Causes infections like strep throat, acute rheumatic fever, scarlet fever, acute glomerulonephritis and necrotizing fasciitis. It is sensitive to bacitracin (Fig. 1), a fact that is employed in a Streptococcus diagnostic test (Table 2). Other Streptococci species may also possess the Group A antigen but are not human pathogens. These include S. dysgalactiae subsp. equisimilis and S. anginosus strains. Group B

5 Group B S. agalactiae: Causes meningitis in neonates and the elderly. Occasionally colonizing the female reproductive tract, they increase the risk for premature rupture of membranes and transmission of the infection to the child. Group C S. equi: Causes strangles infection in horses. S. zooepidemicus: Causes infections in cattle, horses and other mammals. Group D (Enterococci) Many former Group D streptococci have been reclassified to the genus Enterococcus (e.g. S. faecalis, S. faciem, S. durans, S avium). S. bovis and S. suis: Still in the Group D streptococci. Non-Hemolytic or Gamma-Hemolytic Streptococci Gamma hemolysis is a misnomer as there is actually no hemolysis. Non-hemolytic or gamma-hemolytic streptococci rarely cause disease. Table 3... Gram staining kit and component solutions Fluka Gram Staining Kit Fluka Gram s Crystal violet Solution Fluka Gram s Decolorizer Solution Fluka Gram s Fuchsin Solution Fluka Gram s Iodine Solution Fluka Gram s Safranin Solution Materials Product # Image Description Molecular Formula Add to Cart Bacitracin Disks for Bile Esculin Azide Agar for Blood Agar (Base) for Brain Heart Infusion Agar for Brain Heart Infusion Broth for Casein peptone Lecithin Polysorbate Broth for CASO Agar for CASO Broth for CLED Agar for Columbia Agar for Cooked Meat Broth for

6 60865 Cooked Meat Broth for Deoxyribonuclease Test Agar for Elliker Broth for Glucose Azide Broth for Gram s crystal violet solution for Gram s decolorizer solution for Gram s fuchsin solution for Gram s iodine solution for Gram s safranin solution for C 20 H 19 ClN Gram Staining Kit for Heart Infusion Broth for Hydrogen peroxide solution 3%, for Kanamycin Esculin Azide Agar for LS Differential Agar for H 2 O Milk Agar for Mitis Salivarius Agar for Mueller-Hinton Agar 2 for Nutrient Agar for Nutrient Broth No. 1, for Nutrient Broth No. 3, for Optochin Disks for

7 70179 Peptone Water for Peptone Water, phosphatebuffered for Peptone Water, phosphatebuffered, Vegitone for Plate Count Agar for Plate-Count-Agar according to Buchbinder et al. for Plate Count Agar, Vegitone for Pyrase Strips for Thioglycolate Broth with Resazurine for Tryptic Soya Agar with Polysorbate 80 and Lecithin for Tryptic Soy Agar for Tryptic Soy Agar, Vegitone for Tryptic Soy Broth for Tryptic Soy Broth No. 2 for Tryptone Glucose Extract Agar for Vegitone; Casein Soya Broth for Vegitone infusion broth for