Babies more prone to colonisation by bacteria that bring disease, new study confirms.

Babies born by caesarean section are missing normal bacteria and their guts are colonised instead by bugs found in operating rooms and intensive care units, according to a new British study in the journal Nature.

Worryingly, those hospital bacteria include strains that are antibiotic-resistant.

The finding is the latest in a wave of research on the “gut microbiome”, the trillions of bacteria that call your intestine home and collectively weigh up to two kilograms in adults.

Far from being passive free riders, these gut bugs are increasingly known to have a hand in illnesses from depression to cancer and even autism. Hence the deep interest in cultivating the right class of passenger.

The kinds of bacteria that lurk in your darker recesses depend in part on what the researchers, led by microbiologist Trevor Lawley at the Wellcome Sanger Institute in the UK, call “pioneering microorganisms”.

These first settlers stake an early claim in the race to colonise your gut.

Their ranks are swelled by bacteria bub picks up on its way through the vagina, mingled with more bugs from mum’s poo, which tends to put in a showing at delivery due to pressure from the baby’s head.

But as medicine intrudes on the birth process – global caesarean rates have almost doubled since 2000 – the bugs in the guts of tiny tots are changing, something linked to asthma and allergy in childhood.

Until now, however, understanding how early life shapes our bacterial inheritance has been limited by small studies with limited poo samples.

Read the full story in Cosmos magazine here