What indicates a positive reaction for the beta-lactamase chromogenic cephalosporin method?

A positive reaction for the beta-lactamase chromogenic cephalosporin method is indicated by a color change. This method is specifically designed to detect the presence of beta-lactamase enzymes, which are produced by certain bacteria that confer resistance to beta-lactam antibiotics, such as penicillins and cephalosporins.

In this testing method, a chromogenic substrate is used, which is cleaved by the beta-lactamase enzyme. When the enzyme acts on this substrate, it results in a color change that signifies a positive result. The specific color change depends on the substrate used but is an essential indicator that the beta-lactamase enzyme is present, indicating antibiotic resistance.

The other options, such as gas production, liquid turbidity, or pH change, are not characteristics associated with this particular method of detection. While certain biochemical tests may involve these parameters, they do not apply to the chromogenic cephalosporin method specifically. Hence, the color change serves as the definitive indication of a positive reaction in this context.