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These studies indicate that the acidimetric test was less sensitive than the chromogenic cephalosporin substrates and that nitrocefin and S1 could be used to screen for beta - lactamase production in these tested species .
 beta - lactamase
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
 beta - lactamase