Persistence of antibiotic-resistant and -sensitive Proteus mirabilis strains in the digestive tract of the housefly (Musca domestica) and green bottle flies (Calliphoridae)
Synanthropic flies have been implicated in the rapid
dissemination of antibiotic-resistant bacteria and resistance
determinants in the biosphere. These flies stably harbor a
considerable number of bacteria that exhibit resistance to
various antibiotics, but the mechanisms underlying this phenomenon
remain unclear. In this study, we investigated the
persistence of antibiotic-resistant bacteria in the digestive tract
of houseflies and green bottle flies, using Proteus mirabilis as
a model microorganism. One resistant strain carried the bla-
TEM and aphA1 genes, and another carried a plasmid containing
qnrD gene. Quantitative PCR and 454 pyrosequencing
were used to monitor the relative abundance of the Proteus
strains, as well as potential changes in the overall structure of
the whole bacterial community incurred by the artificial induction
of Proteus cultures. Both antibiotic-resistant and -
sensitive P. mirabilis strains persisted in the fly digestive tract
for at least 3 days, and there was no significant difference in
the relative abundance of resistant and sensitive strains despite
the lower growth rate of resistant strains when cultured
in vitro. Therefore, conditions in the fly digestive tract may
allow resistant strains to survive the competition with sensitive
strains in the absence of antibiotic selective pressure. The
composition of the fly-associated bacterial community
changed over time, but the contribution of the artificially
introduced P. mirabilis strains to these changes was not clear.
In order to explain these changes, it will be necessary to obtain
more information about bacterial interspecies antagonism in
the fly digestive tract.
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