Antimicrobial resistance and phylogenetic relatedness of extended-spectrum ß-lactamase (ESBL)-producing Escherichia coli in peridomestic rats (Rattus norvegicus and Rattus tanezumi) linked to city areas and animal farms in Hong Kong.

Extended-spectrum ß-lactamase-producing Escherichia (E.) coli (ESBL-EC) in the clinical setting have emerged as a major threat to public and animal health. Wildlife, including Rattus spp. may serve as reservoirs and spreaders of ESBL-EC in the environment. Peridomestic rats are well adapted to living in proximity to humans and animals in a variety of urban and agricultural environments and may serve as sentinels to identify variations of ESBL-EC within their different habitats. In this study, a set of 221 rats (Rattus norvegicus, R. tanezumi, R. andamanensis, and Niviventer huang) consisting of 104 rats from city areas, 44 from chicken farms, 52 from pig farms, and 21 from stables of horse-riding schools were screened for ESBL-EC. Overall, a total of 134 ESBL-EC were isolated from the caecal samples of 130 (59%) rats. The predominant blaESBL genes were blaCTX-M-14, blaCTX-M-15, blaCTX-M-55, and blaCTX-M-65. Phylogenetic analysis revealed a total of 62 sequence types (STs) and 17 SNP clusters. E. coli ST10 and ST155 were common to ESBL-EC from city areas and chicken farms, and ST44 were found among ESBL-EC from city areas and pig farms. Extra-intestinal pathogenic E. coli (ExPEC) ST69, ST131 and ST1193 were found exclusively among rats from city areas, and avian pathogenic E. coli (APEC) ST177 was restricted to ESBL-EC originating from chicken farms. Phylogenetic analysis showed that the populations of rodent ESBL-EC from city areas, chicken farms and pig farms were genetically different, suggesting a certain degree of partitioning between the human and animal locations. This study contributes to current understanding of ESBL-EC occurring in rats in ecologically diverse locations.

Beyond body size: consistent decrease of traits within orthopteran assemblages with elevation.

Morphological traits provide the interface between species and their environment. For example, body size affects the fitness of individuals in various ways. Yet especially for ectotherms, the applicability of general rules of interspecific clines of body size and even more so of other morphological traits is still under debate. Here we tested relationships between elevation (as a proxy for temperature) and productivity with four ecologically relevant morphological traits of orthopteran assemblages that are related to fecundity (body size), dispersal (wing length), jumping ability (hind femur length), and predator detection (eye size). We measured traits of 160 orthopteran species that were sampled along an extensive environmental gradient at Mt. Kilimanjaro (Tanzania), spanning elevations from 790 to 4,410 m above sea level (a.s.l.) with different levels of plant productivity. For traits other than body size, we calculated the residuals from a regression on body length to estimate the variation of traits irrespective of body size. Bayesian analyses revealed that mean body size of assemblages, as well as the means of relative wing length, hind femur length, and eye size, decreased with increasing elevation. Body size and relative eye size also decreased with increasing productivity. Both phylogenetic relationships, as well as species-specific adaptations, contributed to these patterns. Our results suggest that orthopteran assemblages had higher fecundity and better dispersal and escape abilities, as well as better predator detection at higher temperatures (low elevations) than at low temperatures (high elevations). Large body sizes might be advantageous in habitats with low productivity because of a reduced risk of starvation. Likewise, large eye size might be advantageous because of the ability to detect predators in habitats with low vegetation cover, where hiding possibilities are scarce. Our study highlights that changes in temperature and productivity not only lead to interspecific changes in body size but are also related to independent changes of other morphological traits that influence the ecological fit of organisms in their environment.