ROME: Michael Phelps ended the world championships on a golden note Sunday as the United States rounded out the week's world record total at a staggering 43 with a medley relay triumph.

Phelps, whose campaign began with a shock defeat in the 200m freestyle, bounced back to win the 100m and 200m butterfly, and the United States won all three men's relays to give America's superstar a creditable cache of five gold after all.

It was fitting that the meet concluded with the Americans' world record swim of 3min 27.28sec in the 4x100m medley, an improvement on the mark set by the US in winning Olympic gold in Beijing.

After all, world records were what these championships, the fastest swimming competition in history, were all about.

Germany's Britta Steffen broke her third world record of the meet with her triumph in the women's 50m free - a win that saw her match her 50m-100m freestyle double of Beijing.

Liam Tancock of Britain lowered the men's 50m backstroke world record for the second time in as many days and Russia's Yulia Efimova clocked a world record to win the women's 50m breaststroke.

Tunisia's Oussama Mellouli added a world title to his Olympic 1,500m freestyle gold.

His 14:37.28 was the second-fastest ever, but shy of Grant Hackett's world record of 14:34.56 - leaving at least one sacrosanct mark on the books.

Nor did the records fall in the demanding 400m individual medleys.

Hungary's Katinka Hosszu, winner of two bronze medals already, climbed the top step of the podium with a victory in the women's 400m medley, and American Ryan Lochte captured his fourth gold of the championships with a triumph in the men's 400m individual medley.

Lochte capitalized on the absence of Phelps, who opted out of the four-stroke races this season. He broke Phelps's world record in winning the 200m individual medley, and also earned gold on two freestyle relays.

Steffen came out on top in a frantic 50m free final. Her world record of 23.73 beat the previous mark of 23.96 set by Marleen Veldhuis in April.

Sweden's Therese Alshammar was inside the old mark as well, taking silver in 23.88, while Aussie teen Cate Campbell and the Netherland's Veldhuis shared the bronze in 23.99.

At the other end of the distance spectrum, Mellouli kept things close through the first 1,000m, then pulled inexorably away to get the win over Canadian Ryan Cochran and China's Sun Yang.

Cochrane was second, more than four seconds adrift in 14:41.38 and Sun earned bronze in 14:46.84.

Hosszu couldn't challenge the women's 400m medley world record of Australian Stephanie Rice, but she beat the woman herself.

Hosszu won her first gold of the championships to go with two bronzes.

She dueled with Olympic silver medallist Kirsty Coventry throughout, finally overtaking the Zimbabwean for good on the final freestyle leg to win in 4:30.31.

Coventry was second in 4:32.12 and Rice, who set the world record in winning gold in Beijing but has had a chequered build-up to worlds, was third in 4:32.29.

Efimova clocked a record 30.09 to win a 50m breaststroke in which silver medallist Rebecca Soni (30.11) and bronze medallist Sarah Katsoulis (30.16) were both under the previous mark of 30.23 set by Canadian Amanda Reason in July. LINK