Giolitti-Cantoni Broth (Double Concentration) ISO

Description

The growth of staphylococci is promoted by pyruvate, glycine and above all by a high concentration of mannitol. Addition of Polysorbate 80 is necessary for the successful recovery of Staphylococcus aureus (Chopin et al., 1985). Accompanying flora are inhibited by lithium chloride and potassium tellurite.

Anaerobic growth conditions increase the selectivity of the medium. Generally, growth of staphylococci can be recognized by a blackening or black precipitates in the culture medium due to reduction of tellurite to metallic tellurium.

Technique

Refer to the standard protocol for specific products (Food and animal feeding stuffs EN-ISO 6888-3:2003; Milk and milk based products ISO 5944:2001 and FIL-IDF 60:2001). As a general technique the following is suggested:

Use food macerates or a 10-fold serial dilution and inoculate 1 mL in single strength medium. To lower the detection limit, 10 mL of the test sample (liquid products) or the first dilution (other products) may be inoculated in double strength medium. MPN procedures need at least three tubes for at least three dilution steps. If no anaerobic jar is available, overlay with a layer of sterilized vaseline or vaspar. Incubate anaerobically for 24-48 hours at 37 °C.

After 24 hours, subculture any tubes showing blackening or black precipitate by streaking onto Baird-Parker Agar. Incubate the remainder of the tubes for a further 24 hours and subculture all tubes showing growth (irrespective of blackening) to Baird-Parker Agar.

When determining the bacterial count by the MPN method, all tubes showing growth are considered as presumptive positive for staphylococci and they are confirmed only if they produce a positive result in the coagulase test.

Physical/chemical control

Microbiological control

Inoculate: practical range 100 ± 20 CFU; min. 50 CFU (productivity) / 10⁴-10⁶ (selectivity).

Dilute to normal concentration.

Aerobiosis. Incubation at 37 ± 1 °C, reading after 24/44 ± 4 h.

Microbiological control according to ISO 11133:2014.

Sterility control

Incubation 48 hours at 30-35 °C and 48 hours at 20-25 °C: NO GROWTH.

Check at 7 days after incubation in same conditions.

• CHOPIN, A. et al. (1985) ICMSF Methods Studies XV. Comparison of four media and methods for enumerating Staphylococcus aureus in powdered milk. J. Food Protect. 48:21-27.
• EN-ISO 6888-3 Standard (2003) Microbiology of food and animal feeding stuffs. Horizontal method for the enumeration of coagulase positive staphylococci (Staphylococcus aureus and other species). Part 3: Detection and MPN technique for low numbers.
• EN-ISO 6888-3/AC Standard (2005) Microbiology of food and animal feeding stuffs. Horizontal method for the enumeration of coagulase positive staphylococci (Staphylococcus aureus and other species). Part 3: Detection and MPN technique for low numbers.
• FIL-IDF (2001) Milk and milk based Products. Detection of coagulase-positive staphylococci. MPN technique. Standard 60:2001. Brussels.
• GIOLITTI, G. A. CANTONI, C. (1966) A medium for the isolation of staphylococci from foodstuffs. J. Appl. Bact. 29, 395-398.
• HARRIGAN, WF. & McCANCE, M.E. (1976) Laboratory Methods in Food and Dairy Microbiology. Academic Press. London.
• ISO 5944 Standard (2001) Milk and milk based Products. Detection of coagulase-positive staphylococci. MPN technique.
• ISO 11133:2014/Amd 1:2018. Microbiology of food, animal feed and water. Preparation, production, storage and performance testing of culture media.