Monitor has warned four foundation trusts it will intervene if they fail to improve performance on MRSA. Doncaster and Bassetlaw Hospitals, Calderdale and Huddersfield, Lancashire Teaching Hospitals and Poole Hospital were told they had breached their terms of authorisation.

Last week Monitor informed all four they would get a red rating for governance for the last quarter. The regulator will step in if they fail to make progress over the next three months. The move follows meetings with seven foundation trusts that failed to hit national MRSA targets.

Monitor executive chair Bill Moyes said three - Southend University Hospital, Royal Bournemouth and Christchurch Hospitals and Northumbria Healthcare - had shown they were "doing absolutely everything they could". But he said the others had not persuaded Monitor this was the case.

Doncaster and Bassetlaw director of nursing Hilary Bond said the trust would "continue to make every effort to eradicate MRSA and meet the demanding national targets".

Lancashire Teaching Hospitals nursing director Sue Reed said the trust had made huge strides in reducing MRSA but the target was tough.

Poole Hospital foundation trust said it had a "robust action plan" in place, while Calderdale and Huddersfield said its plan had "started to show further improvements".

Northumbria Healthcare - one of the seven trusts that avoided censure - said it screened all adult admissions, worked with community colleagues to identify high-risk patients and had weekly management meetings on infection control.