For example, Salmonella typhimurium is sensitive to Ceftriaxone, but resistant to Cefotaxime.
Therapeutically: resistance to one of the extended-spectrum cephalosporins (ceftazidime, cefotaxime, or ceftriaxone), when mediated by an ESBL, means therapeutic resistance to all, even when sensitivity test results may indicate otherwise.
Answer specific to your question: Usually if an isolate is resistant to cefotaxime it is also resistant to ceftriaxone.
Though it is possible for an isolate to be CTX-M ESBL producing, turning susceptible to ceftazidime (may be to ceftriaxione too) but resistant to cefotaxime (word CTX is derived from cefotaximase).
One more answer justifying varying susceptibility pattern to same generation of cephalosporins:
More than 100 different sequence variants of SHV and TEM genes with various levels of activity against ceftazidime, cefotaxime, and ceftriaxone have so far been demonstrated. However the most commonly encountered ones are TEM-3, which confers broad resistance to ceftazidime, cefotaxime, and ceftriaxone, and TEM-10, which confers high-level resistance to ceftazidime and appears to be sensitive in vitro to cefotaxime and ceftriaxone. Most ESBLs found in the United Kingdom are derived from the TEM and SHV genes.
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