The prophylactic and therapeutic use of tetracyclines in aquaculture has been shown to contribute to the spread of tetracycline resistance in the environment. In this work, the prevalence of four different tetracycline-resistance genes, tetA, tetC, tetH, and tetM, in sediments from four aquaculture farms and their surroundings in the Baltic Sea was monitored by quantitative polymerase chain reaction (qPCR). The presence of three additional tetracycline-resistance genes (tetE, tetG, and tetW) was studied qualitatively by standard PCR, and the amount of bioavailable tetracyclines and total amounts of tetracycline and oxytetracycline in samples were also measured. None of the farms were using tetracycline at the time of the sampling and one of the farms had stopped all antibiotic use six years prior to the first sampling. Two of the farms were sampled over four successive summers and two were sampled once. Our results showed greater copy numbers of tetA, tetC, tetH, and tetM at the farms compared to pristine sites and demonstrated the presence of tetE, tetG, and tetW genes in the sediments under aquaculture farms at most sampling times. However, no resistance genes were found in samples collected 200 m from any of the farms. None of the samples contained therapeutically active concentrations of tetracyclines at any of the sampling times, suggesting that the increase in the prevalence of tetracycline resistance genes is caused by the persistence of these genes in the absence of selection pressure.

Microbes are easily dispersed from one place to another, and immigrant microbes might contain information about the environments from which they came. We hypothesized that part of the microbial community on a flower's surface is transferred there from insect body surfaces and that this community can provide information to identify potential pollinator insects of that plant. We collected insect samples from the field, and found that an insect individual harbored an average of 12.2 × 105 microbial cells on its surface. A laboratory experiment showed that the microbial community composition on a flower surface changed after contact with an insect, suggesting that microbes are transferred from the insect to the flower. Comparison of the microbial fingerprint approach and direct visual observation under field condition suggested that the microbial community on a flower surface could to some extent indicate the structure of plant–pollinator interactions. In conclusion, species-specific insect microbial communities specific to insect species can be transferred from an insect body to a flower surface, and these microbes can serve as a “fingerprint” of the insect species, especially for large-bodied insects. Dispersal of microbes is a ubiquitous phenomenon that has unexpected and novel applications in many fields and disciplines.

Fluoroquinolone antibiotics (FQs) have been used worldwide for chemotherapy, animal husbandry, and aquaculture, and the occurrence of FQ-resistant (FQs r ) bacteria in natural environments has been reported. Plasmid-mediated transferable quinolone resistance (PMQR) genes are suspected to originate from the chromosomes of water-dwelling bacteria. However, the occurrence of and the potential reservoir of FQs r bacteria and PMQR genes in aquatic environments have not been elucidated. In this study, we detected FQs r bacteria and PMQR genes in aquatic environments in Thailand and Vietnam, and measured FQ contamination. Levels of contamination were greater Thailand (avg. 5130, max 46100 ng L −1 ) than in Vietnam (avg. 235, max 1130 ng L −1 ); however, the occurrence of FQs r bacteria was higher in Vietnam (~15%) than in Thailand (~7.0%), suggesting that contamination by FQs is not directly linked to the development of FQs r bacteria. Diverse taxonomic groups of FQs r -bacteria were identified, and one of the PMQR genes, qnrB, was detected from bacteria of environmental origin, not enteric bacteria. This suggests that the environmental bacteria are a potential reservoir of antibiotic resistance determinants even at un-contaminated sites.