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reactions for some staphylococci and anaerobic species may take up to 60 minutes to develop. For the rapid detection of β-lactamase enzymes in Some strains of Staphylococcus aureus produce isolated colonies of Neisseria gonorrhoeae, small amounts of the β-lactamase enzyme unless Moraxella catarrhalis, Staphylococcus spp., enzyme production is induced by growth in a medium Haemophilus influenzae and anaerobic bacteria. containing sub-inhibitory concentrations of a β-lactam Contents
A positive result should be interpreted as resistance Nitrocefin is a chromogenic cephalosporin which has to penicillin or cephalosporin activity. Susceptibility been found to be effective in detecting all known β- should be confirmed by standard growth-dependent lactamase enzymes4-7. β-lactamase enzymes susceptibility testing methods. Negative results imply hydrolyse the amide bond in the β-lactam ring of Nitrocefin resulting in a distinctive colour change from Discs should be stored in the freezer at below -10ºC
Nitrocefin discs are intended for use in the rapid on receipt in the containers provided. Allow to testing of isolated colonies of Neisseria equilibrate to room temperature before opening then gonorrhoeae8, Moraxella catarrhalis9, Staphylococcus return to freezer storage immediately after use.
spp.10, Haemophilus influenzae3,11 and anaerobic bacteria, notably Bacteroides spp.12. The Nitrocefin Limitations of Use
test is of little use for closely related taxonomic Resistance to β-lactam antibiotics has been rarely groups of organisms e.g. members of the family reported in the specified organisms without the Enterobacteriaceae7. This is because organisms production of β-lactamases13. Nitrocefin Discs within a taxonomic group or even a single strain may should be used only as a rapid supplemental test and produce a diversity of β-lactamase enzymes with should not replace conventional susceptibility testing. References
Directions
Abraham EP, Chain E. Nature 1940; 146: 837.
1. Place the required number of Nitrocefin discs into McCarthy LR. Clin Microbiol Newsl. 1980; 2: 1-3.
a clean empty Petri dish or onto a microscope Thornsberry C, Gavan TL, Gerlach EH. In: Cummitech. Sherris JC, editor. Washington DC: American Society for Microbiology, 1977; 1-2. O’Callaghan CH, Morris A, Kirby S, Shingler AH. Antimicrob 2. Discs may be moistened with one drop of Agents and Chemother. 1972; 1: 283-288.
Citri M, Pollock MR. Adv in Enzymol. 1966; 28: 237-323.
Richmond MH, Sykes RB. In: Advances in Microbial Physiology. Rose AH, Tempest DW, editors. London and 3. Using a sterile loop or applicator stick remove New York: Academic Press, 1973; 9: 31-88.
several well-isolated and similar colonies and Sykes RB, Matthew M. J Antimicrob Chemother. 1976; 2:
Ashford WA, Golash RG, Hemming VG. Lancet. 1976; ii:
Malmvall BE, Brorsson JE, Johnsson J. J Antimicrob Chemother. 1977; 3: 374-375.
Alternatively: moisten the disc with one drop of deionised water, then holding the disc in forceps wipe J Infect Dis. 1970; 122: 544-546.
Skinner A, Wise R. J Clin Pathol. 1977; 30: 1030-1037.
Olsson B, Dornbush K, Nord CE. Med Microbiol Immunol.
1977; 163: 183-194.
Interpretation of Results
A positive reaction will show as a yellow to red colour change on the area where the culture was applied. Note: - the colour change does not normally develop over the whole of the disc. A negative result will show no colour change on the disc. For most bacterial strains a positive results will develop within 5 minutes. However, positive

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