First isolation of viable Bartonella spp. from wild rodents and rodent fleas in Chile reveals circulation of a putative novel Bartonella specie

In the hidden world of microscopic life, a family of bacteria called Bartonella has long been known to live inside the blood of mammals. These tiny organisms are specialists; they have evolved to settle quietly within the red blood cells and the lining of blood vessels of their hosts, often without causing any immediate sickness. While many species of Bartonella are harmless to the animals they inhabit, some have the ability to jump from animals to people, causing fevers, heart inflammation, and other serious illnesses. Because these bacteria rely on blood-sucking insects like fleas to move from one animal to another, scientists have spent years trying to understand which wild animals carry them and which insects act as the bridges for transmission. This knowledge is vital for public health, as it helps predict where dangerous infections might emerge.

In a quiet, conserved area of Chile known as Laguna Verde, a team of researchers set out to answer a specific question: what live Bartonella bacteria are actually circulating among the wild rodents and their fleas in this region? While previous studies in Chile had found traces of bacterial DNA in these animals, no one had ever successfully grown the living bacteria from them in a laboratory. Without a living sample, scientists cannot fully study the organism's biology or confirm exactly what species it is. The team captured wild rats and native rodents, collected their blood, and carefully gathered the fleas living on them. They then placed these samples into a special nutrient-rich environment designed to encourage the slow growth of these fastidious bacteria, incubating them for up to two months to see if any colonies would appear.

The effort yielded a clear result: the researchers successfully grew living Bartonella bacteria from the blood of four different rodents and from a single flea. The rodents included two black rats, a native species known as the olive grass mouse, and a long-tailed pygmy rice rat. The flea that tested positive belonged to a genus called Neotyphloceras, which was found on one of the native grass mice. By analyzing the genetic code of these newly grown bacteria, the team discovered they were dealing with two distinct groups. The bacteria found in the two black rats and the olive grass mouse were an exact genetic match to a known species called Bartonella coopersplainsensis, which had previously been identified in rats in Australia and Nepal. This confirmed that this specific bacterium is present and active in Chilean rodent populations.

The second group of bacteria was far more intriguing. The living bacteria isolated from the long-tailed pygmy rice rat and the Neotyphloceras flea did not match any known species perfectly. Instead, their genetic sequences were so similar to an uncharacterized strain previously detected only as DNA in Chilean flea samples that the researchers propose this represents a new, previously unknown species of Bartonella. This finding is significant because it is the first time living bacteria of this type have been recovered from a naturally infected flea in Chile. It suggests that the Neotyphloceras flea is not just a passive carrier but a likely vector capable of transmitting this potential new species among native rodents.

The study also highlighted the complexity of how these bacteria move through nature. While the researchers found evidence of two different Bartonella types, the overall diversity was lower than what has been seen in other parts of the world. This may be because the specific mix of rodents and fleas in this particular Chilean relict area supports only a limited number of bacterial strains. The researchers noted that the area they studied is a biologically preserved zone with little human disturbance, which might explain why the infection rates were lower than in more crowded or urban environments where human activity often increases contact between animals and insects.

Perhaps the most important outcome of this work is the creation of a library of living bacteria. Before this study, scientists in Chile could only detect the genetic fingerprints of these organisms, which is like seeing a shadow without knowing the shape of the object casting it. Now, with viable cultures in hand, researchers can perform detailed genomic and taxonomic studies to formally describe and name these bacteria. This step is essential for understanding the true nature of the potential new species and assessing whether it poses a risk to human health. By isolating these organisms directly from the wild, the team has provided the first concrete evidence of a living, circulating Bartonella species in Chilean rodents and their fleas, opening the door to a deeper understanding of the microscopic world that shares our environment.