Streptomycin Application Has No Detectable Effect on Bacterial Community Structure in Apple Orchard Soil

Abstract

Streptomycin is commonly used to control fire blight disease on apple trees. Although the practice has incited controversy, little is known about its nontarget effects in the environment. We investigated the impact of aerial application of streptomycin on nontarget bacterial communities in soil beneath streptomycin-treated and untreated trees in a commercial apple orchard. Soil samples were collected in two consecutive years at 4 or 10 days before spraying streptomycin and 8 or 9 days after the final spray. Three sources of microbial DNA were profiled using tag-pyrosequencing of 16S rRNA genes: uncultured bacteria from the soil (culture independent) and bacteria cultured on unamended or streptomycin-amended (15 g/ml) media. Multivariate tests for differences in community structure, Shannon diversity, and Pielou's evenness test results showed no evidence of community response to streptomycin. The results indicate that use of streptomycin for disease management has minimal, if any, immediate effect on apple orchard soil bacterial communities. This study contributes to the profile of an agroecosystem in which antibiotic use for disease prevention appears to have minimal consequences for nontarget bacteria.

Tackling antibiotic resistance: the environmental framework

“…At present, it is difficult to ascertain whether antibiotics reaching the environment at low concentrations exert a substantial selective pressure on ARGs or ARB 50,51 . However, there is increasing evidence showing that repeated exposure of the environment to anthropogenically generated ARGs (for example, soil manure) correlate with the emergence and proliferation of ARGs in indigenous microbiota 66,67,73,74 . However, the impact of animal production on the propagation of antibiotic resistance is demonstrated by some zoonotic species of the genera Salmonella, Campylobacter, Listeria, Staphylococcus, Enterococcus and Escherichia, which are known to exhibit high levels of acquired antibiotic resistance 29,[75][76][77][78] .…”

Ecotoxicological assessment of antibiotics: A call for improved consideration of microorganisms

“…Sequencing offers distinct advantages such as the ability to evaluate species richness in much higher detail as even rare community members can be captured leading to a more unbiased evaluation of species richness (Bent and Forney, 2008). Although high-throughput sequencing of 16S rRNA genes is now a mainstream approach in microbial ecology research (Jansson, 2011), it has only recently been applied in ecotoxicological studies on bacterial communities (Table S1; Berg et al, 2012;Ge et al, 2012;Shade et al, 2013). However, estimates of species richness may still be biased and therefore unreliable (Gihring et al, 2012).…”

Long-term antibiotic exposure in soil is associated with changes in microbial community structure and prevalence of class 1 integrons

“…No overall effects on community diversity, evenness or structure were observed. However, rarer taxa belonging to Proteobacteria, Bacteroidetes and Actinobacteria, that were not observed in soil samples from under unsprayed trees, were detected in the post-spray samples with one, a Flavobacterium, consistently observed (Shade et al, 2013).…”

“…Islas-Espinoza et al (2012) observed an increase in species richness as determined by Shannon-Wiener and Margalef indexes in a soil supplemented with sulfamethazine. Shade et al (2013), using a 16S rRNA gene sequencing approach, compared soil bacterial communities under apple trees (Malus domestica) that had undergone spray treatments with streptomycin sulphate. No overall effects on community diversity, evenness or structure were observed.…”