A man who told U.S. authorities he had sexual contact with as many 300 people since being diagnosed with HIV pleaded not guilty to infecting another man with the virus, and prosecutors said more charges are expected.

David Mangum entered the plea Thursday after being charged with recklessly infecting another with HIV, which in Missouri — where penalties for such crimes are among the nation's harshest — carries a maximum sentence of life in prison. His attorney didn't return messages seeking comment.

Court documents allege that the 36-year-old told detectives that he had unprotected sex with as many as 300 partners since being diagnosed a decade ago with HIV, the virus that causes AIDS.

Many of his trysts stemmed from Craigslist ads, he told investigators, and he would meet up with men at parks, truck stops and other remote locations. Police believe many were truckers or others passing through the region, and because Mangum had little information about many of the men, investigators are concerned about finding potential victims, police detective Cory Mills said.

So authorities turned to the media, and since then more potential victims have come forward, prosecutor Russell Oliver said. Oliver wouldn't say how many people, but he said more charges were expected.

Local health clinics are reporting a recent surge in people seeking HIV tests.

Magnum is jailed on $250,000 cash-only bond. A preliminary hearing is set for Sept. 26.

Missouri is among 37 states that make it a crime to knowingly transmit HIV to others.