Media for detection of Staphylococcus Aureus: a Spreading Bacteria

By: Jvo Siegrist, AnalytiX Volume 10 Article 2

Staphylococcus aureus is frequently a part of our skin flora but is also a cause of a broad range of illnesses. Current studies report a remarkable increase of Methicillin Resistant Staphylococcus aureus (MRSA) over recent years.

Jvo Siegrist, Product Manager Microbiology ivo.siegrist@sial.com

Staphylococci may be airborne and can occur in both animals and humans, in sewage, water, milk or food, and on environmental surfaces or food equipment. It is still one of the five most common causes of nosocomial infections, often causing postsurgical wound infections. Consequently, it poses a major concern in hospitals, especially in regard to MRSA, methicillin-resistant Staphylococcus aureus.

Staphylococcus aureus is an invasive pathogen that can cause disease in almost any tissue or organ in the human body, primarily in compromised individuals. Staphylococcal infections were treated using penicillin, but over the years this pathogen developed resistance to penicillin by building penicillinase. Methicillin was the next drug of choice as it is not cleaved by the penicillinase. While methicillin is very eff ective in treating most Staphylococcus infections, some strains have developed resistance to methicillin by production of penicillin-binding protein, and can no longer be killed by this antibiotic. These resistant bacteria are called Methicillin Resistant Staphylococcus aureus (MRSA) [1]. Patients with breaks in their skin due to wounds, indwelling catheters or burns are at high risk of developing MRSA infection [2]. Spread of MRSA infections can be controlled to a great extent by maintaining personal hygiene after interaction with an MRSA-infected person [1].

Today there are many innovative solutions to detect MRSA. Sigma-Aldrich® strongly supports the microbiologist with a selective chromogenic HiCrome MeReSa Agar for detection of MRSA from clinical isolates and other samples. The proprietary chromogenic mixture incorporated in the medium is specifi cally cleaved by S. aureus to give bluish-green colonies on this medium and can be clearly diff erentiated from other species. The medium is made selective for MRSA by the addition of methicillin.


Figure 1. S. aureus

Foods that are frequently associated with staphylococcal food poisoning include meat and egg products, milk and dairy products, and various other products that may contain these food ingredients. Processes in the food industry that are kept at slightly elevated temperatures must guard against staphylococcal food poisoning, one of the leading causes of gastroenteritis. The food poisoning is due to the presence of staphylococcal enterotoxins produced by Staphylococcus aureus in the food.

Staphylococci are facultative anaerobes Gram-positive bacteria that grow by aerobic respiration or by fermentation that yields principally lactic acid. The bacteria are catalase-positive and oxidase-negative. S. aureus produce diverse enzymes such as staphylokinase (coagulase), proteases, phopshatase, a lipase, a deoxyribonuclease (DNase) and a fatty acid modifying enzyme (FAME). The majority of clinical isolates of S. aureus express special surface polysaccharide and protein A. Diff erentiation and identifi cation of S. aureus can be made based on these biochemical characteristics. More details may be found in the ID fl ow chart (Figure 2), the table of Fluka’s kits and tests (Table 1), and the table listing Fluka’s media for the differentiation of Staphylococcus aureus (Table 2).


Figure 2 ID flow chart for Staphylococus aureus

Figure 2 ID flow chart for Staphylococus aureus


Table 1 and Table 2 specify characteristics which Fluka®’s kits and tests utilise for the identification of S. aureus.


Kit or Test Cat. No. Testing features
Catalase Test (Hydrogen peroxide 3%) 88597 Testing of catalase production
Coagulase Test (Slide) 75832 Detection of coagulase
Coagulase Test (Tubes) 74226
Oxidase Reagent acc. Gaby-Hadley A +
Oxidase Reagent acc. Gaby-Hadley B
07345
07817
Checking presence of Oxidase
Oxidase Reagent acc. Gordon-McLeod 18502
Oxidase Strips 40560
Oxidase Test 70439
Staphylo Monotec test kit Plus 50448 Coagulase and protein A can be detected in one step (increased sensitivity and specificity compared to the previous Staphylo Monotec test kit, resulting in increased detection of MRSA)

Table 1 Test for detection and identification of Staphylococcus aureus


Identification Media Cat. No. Testing features
Baird Parker Agar
Supplements: Egg-Yolk Tellurite Emulsion (Fluka 75208) or
RPF Supplement (Fluka 05939)
11705 Detection of lipolytic and proteolytic activity, ability to reduce tellurite to metallic tellurium (EN-ISO 6888-1: 1999); with RPF Supplement the coagulase activity and the ability to reduce tellurite is detected (EN-ISO 6888-2:2000)
Blood Agar
Supplement: defibrinated blood
70133 Detection of β-hemolysis
Blood Agar No. 2
Supplement: defibrinated blood
B1676 "
Bromo Thymol Blue (B.T.B.) Lactose Agar B3676 Differentiated by their ability to grow at a high pH and in the presence of bromo thymol blue (golden yellow colonies)
CLED Agar 55420 Detection of lactose fermentation
Deoxyribonuclease Test Agar 30787
70136
Detection of deoxyribonuclease activity
DNase Test Agar with Toluidine Blue D2560 "
Giolitti Cantoni Broth 48905 Ability to reduce tellurite to tellurium and selective conditions
HiCrome™ Aureus Agar Base
Supplement: Egg-Yolk Tellurite Emulsion (Fluka 75208)
05662 Testing for ability to reduce tellurite to metallic tellurium and detection of lipase and protease by chromogenic substrate; brown-black colonies
HiCrome™ MeReSa Agar Base
Supplement: MRSA Selective Supplement (Fluka 51387)
90923 Detection by chromogenic substrate mixture specifically cleaved by S. aureus; selective to MRSA; MRSA give bluish-green colonies
China Blue Lactose Agar 22520 Detection of lactose fermentation
Mannitol Salt Agar 63567
09166(plattes)
Detection of mannitol fermentation in high sodium chloride concentration
Nutrient Gelatin 70151 Detection of gelatin-liquefying (proteolytic enzymes)
Phenolphthalein Phosphate Agar 68879 Phosphatase detection; pink-red colonies
Spirit Blue Agar
Supplement: Lipase Substrate (see data sheet)
S4306 Detection and enumeration of lipolytic activity
Staphylococcus Agar 70193 Detection of salt tolerance, pigmentation, D-mannitol utilisation and gelatin liquefaction
Tributyrin Agar
Supplement: Neutral Tributyrin (Fluka 91010)
91015 Detection and enumeration of lipolytic activity
Vogel-Johnson Agar
Supplements: Potassium Tellurite 1% (Fluka 17774)
70195 Checking for ability to reduce tellurite to tellurium and ability to ferment mannitol

Table 2 Media for detection and identification of Staphylococcus aureus

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Materials

     

References

  1. Methicillin Resistant Staphylococcus aureus Copyright © 1997–2005 Canadian Centre for Occupational Health and Safety, Sept 19th (2005).
  2. Dr. Alan Johnson, methicillin resistant Staphylococcus aureus (MRSA) infection. The Support group for MSRA sufferers and Dependents, Aug 1st (2005).

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