Visits to Tallaght Hospital have been restricted following an outbreak of a deadly, antibiotic-resistant "nightmare bacteria" which can kill up to half of the people it infects.
The hospital yesterday took the step after a number of patients tested positive for Carbapenem Resistant Enterobacteriaceae (CRE).
A statement from the hospital said the infection which can be caused by CRE is "difficult but not impossible" to treat.
According to the Centres for Diseases Control and Prevention in the United States, healthy people do not usually get CRE infections.
They usually happen to patients in hospitals, nursing homes, and other healthcare settings.
"Some CRE bacteria have become resistant to most available antibiotics," according to the website.
"Infections with these germs are very difficult to treat, and can be deadly - one report cites they can contribute to death in up to 50pc of patients who become infected."
It has been called a "nightmare bacteria" by the organisation's director, Dr Tom Frieden.
The first case of CRE in Ireland was reported in 2009.
A Tallaght Hospital spokesperson said restrictions have been put in place with immediate effect and it was unclear when they could be lifted.
One visitor only per patient is permitted during designated visiting hours, which for the adult hospital are from 2pm to 4pm and 6.30pm to 8.30pm.
Children will not be permitted to visit this section of the facility under any circumstances.
However, parents and guardians of paediatric inpatients are allowed to visit as normal as the paediatric unit is not affected.
"Tallaght Hospital is appealing to the public for their support in observing these restrictions and management would like to acknowledge the co-operation of the public in advance," a statement said.
"As always, patients with non-urgent requirements are urged to seek advice from their local GP before presenting to Tallaght Hospital Emergency Department."
Earlier this month it emerged Ireland was over-using so-called 'last defence' antibiotics which increase the risks of superbugs, such as CRE, becoming untreatable.
Figures for antibiotic consumption in 2015 showed Irish hospitals, among facilities in other countries, were high users of drugs like carbapenems which are last-line treatments for serious infections.
These drugs need to be used sparingly to avoid bugs becoming resistant to them.
An eminent economist and epidemiologist, Prof Ramanan Laxminarayan, spoke recently at the O'Brien lecture in UCD where he warned of "potentially catastrophic results" if antibiotic overuse was not curtailed.
The report on antibiotic use in hospitals by the disease watchdog, the Health Protection Surveillance Centre, said our consumption of carbapenems in Ireland has tripled since 2008 and peaked in 2014, with the figure for 2015 unchanged.