* U.S. approval for MRSA treatment ceftobiprole delayed

* FDA says needs further site audits, other data

* New U.S. application planned within the year

* Basilea stock down 27 pct

ZURICH, Nov 26 (Reuters) - U.S. regulators have delayed a decision on approval of an antibiotic from Johnson & Johnson (JNJ.N) and Basilea (BSLN.S), saying they need further audits of clinical sites, the two companies said on Wednesday.

Ceftobiprole, a broad-based spectrum antibiotic to treat deadly superbug MRSA, is Basilea's lead product and the news hit the Swiss biotech shares, which plummeted 27 percent to 110.00 Swiss francs by 0848 GMT.

"At current it is difficult to gauge the extent of the impact on the approvability of ceftobiprole by the FDA," Piper Jaffray analyst Richard Parkes said.

A delay of six months or more seems inevitable, but the precedent of Theravance's (THRX.O:) telavancin -- an antibiotic whose approval was delayed due to what appear to be similar reasons -- is encouraging, Parkes said.

In a so-called complete response letter on the drug's approval application, for complicated skin and skin structure infections, the Food and Drug Administration (FDA) said it was unable to review the clinical data submitted until issues of data integrity had been resolved, the companies said.

"The FDA has indicated that they cannot approve the NDA (new drug application) for ceftobiprole at this time," J&J said in a statement. "They have asked J&J to conduct additional audit work of clinical investigator sites and to address specific questions related to site monitoring."

Ceftobiprole is approved in Canada and Switzerland and has been recommended for approval in the European Union.

However, it has hit delays in the United States. The FDA had already issued an approvable letter for the antibiotic in March, indicating that further assessment of clinical data was needed.

A new application in the United States is planned within a year and European authorities have had no problems with the drug, Basilea Chief Executive Anthony Man told reporters.

The emergence of hospital superbugs such as MRSA, which are resistant to existing medicines, has increased the need for alternative treatments and re-focused attention on antibiotics.

"The agency has requested information on J&J's clinical quality assurance programmes and also asked for a new audit plan that also addresses deficiencies in contract research organisation monitoring," Basilea added. "We are deeply disappointed with the further delay in the review."