Media for Staphylococcus Aureus Detection

Jvo Siegrist

AnalytiX Volume 10 Article 2

ivo.siegrist@sial.com

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.

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 person¹.

Today there are many innovative solutions to detect MRSA. We strongly support 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.

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 flow chart (Figure 2), the table of kits and tests (Table 1), and the table listing media for the differentiation of Staphylococcus aureus (Table 2).

Figure 2. ID flow chart for Staphylococus aureus

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

Table 1 Test for detection and identification of Staphylococcus 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 2 Media for detection and identification of Staphylococcus aureus

Identification Media	Cat. No.	Testing features
Baird Parker Agar Supplements: Egg-Yolk Tellurite Emulsion (75208) or RPF Supplement (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 (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 (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 (plates)	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 (91010)	91015	Detection and enumeration of lipolytic activity
Vogel-Johnson Agar Supplements: Potassium Tellurite 1% (17774)	70195	Checking for ability to reduce tellurite to tellurium and ability to ferment mannitol

References

1. Methicillin-Resistant Staphylococcus Aureus Canadian Centre for Occupational Health and Safety. [Internet].[updated 03 Apr 2018]. Available from: https://www.ccohs.ca/oshanswers/biol_hazards/methicillin

2. 2005. Dr. Alan Johnson, Methicillin resistant Staphylococcus aureus (MRSA) infection. . [Internet]. The Support group for MSRA sufferers and Dependents.