Articles by Editor,Elen Johnston

Science

Stomach churning video reveals the amount of bacteria lurking on your left over pizza

READ MORE: Scientists make major blood pressure breakthrough By ELEN JOHNSTON, HEALTH REPORTER Published: 19:30 GMT, 10 November 2025 | Updated: 19:30 GMT, 10 November 2025 A microbiologist has revealed the surprising amount of bacteria which can be growing on leftover takeaway pizza—and it might make you think twice about what you have for dinner. In a recent video, which has garnered over 13,000 views, Nicholas Aicher, a Chicago-based senior quality control analyst, tested the amount of bacterial growth on a pizza shortly after purchase and a day after. The clip posted to his TikTok page, @howdirtyis which has nearly 500,000 followers began with him unveiling the large half-cheese, half-pepperoni takeaway pizza and using a swab to get a sample from each side. Then the following morning, he swabbed slices leftover from the night before, to transfer samples onto petri dishes which he labelled and stored in an incubator. After a certain time period, which Mr Aicher doesn't specify, he went back to check on them and discovered the fresh cheese slice was 'spotless'. But the sample taken from the fresh pepperoni slice appeared to have significant bacterial growth. He then checked the older slices, and found that the cheese slice had 'a lil bit of yuck', which visible bacterial growth in the petri dish. However, surprisingly, the older slice of pepperoni actually had less bacteria than the fresh piece, something he couldn't explain. A microbiologist has revealed the disgusting amount of bacteria on takeaway pizza On the experiment, Mr Aicher said: 'I thought it would be fun for people to know all the little nastiness that we don't think about every day.' But despite the stomach-churning results, his followers were not deterred from ordering takeaway pizza. In the comment section, one user wrote: 'I'm still eating it.' Another wrote: 'A pepperoni is super salty and that's why pepperoni can exist right out on the shelf at the grocery store. Bacteria don't like salt.' Meanwhile, a third wrote: 'Sooo the grease from the pepperoni is what's making bacteria grow? Cause how? And I'm still eating day old pizza out of the box idc.' Previously the microbiologist tested the 'five second rule' to see if it really is safe to eat something that has dropped on the floor as long as it's been picked up within five seconds. In the older clip, which has been viewed over a million times, he monitored bacterial growth on food that had been on the floor for various time periods. This included within one second, dive seconds, 10 seconds, 20 seconds, 30 seconds and one minute. Mr Aicher bizarrely discovered the day old peperoni pizza was cleaner than the fresh one Rather than swabbing food, this time he placed a petri dish for each on the floor for the respective lengths of time. Microbiologist puts five second rule to the test to find out just how dirty dropped food really is After again an unspecified time period, he inspected them and found they all had some amount of bacteria growth on them. While showing white bacteria growths on the one-second petri dish, he said: 'Looks like even zero seconds is too long.' Meanwhile, the five-second petri dish appeared to have roughly the same as the first one - debunking the myth dropped food is safe if picked up within five seconds. Moving on, he showed the sample he put on the floor for 10 seconds has 'a bit more' growth, while those placed for 20 and 30 seconds have noticeably more bacteria. However, the sample placed on the floor for one minute appeared to have a similar amount of bacteria to the five-second sample. After the experiment, his verdict on the rule was that whether the food has been on the flood for five or 60 seconds, 'it'll be nasty'. Share or comment on this article: Stomach churning video reveals the amount of bacteria lurking on your left over pizza Add comment