Klebsiella spp. are a genus of Gram-negative, opportunistic bacteria frequently found in the flora of the mucosal membranes of healthy animals and humans, and in the environment. Species of this group can cause serious infections (meningitis, sepsis, bacteraemia, urinary tract infections, liver damage) and possible death in immunocompromised organisms (and even in immunocompetent ones in the case of hypervirulent K. pneumoniae) that are exposed to them. K. pneumoniae is part of the ESKAPE organisms, and so it is important to understand this genus in terms of multidrug-resistant bacteria and as a carrier of antibiotic resistance mechanisms. As it is a durable bacterium, it survives well even in hostile environments, making it possible to colonize all kinds of habitats, even the mucosal flora of wildlife. This systematic review explores the prevalence of Klebsiella spp. bacteria in wild animals, and the possibility of transmission to humans according to the One Health perspective. The isolates found in this review proved to be resistant to betalactams (blaTEM, blaOXA-48…), aminoglycosides (strAB, aadA2…), fosfomycin, tetracyclines, sulphonamides, trimethoprim, phenicols (catB4), and polymyxins (mcr4).

Background/Objectives: Enterobacterales are widely distributed in animals and environmental matrices and represent important reservoirs of antimicrobial resistance within a One Health framework. Gulls are particularly relevant because of their synanthropic behavior and frequent contact with anthropogenic waste, which may facilitate the acquisition and dissemination of resistant bacteria. Therefore, this study aimed to investigate the diversity, genomic backgrounds, and resistance determinants of Enterobacterales recovered from gulls and coastal environments in Portugal. Methods: A total of 265 samples, including seagull feces, saltwater, stagnant water, and sand, were collected from four coastal locations. Enterobacterales isolates were recovered and characterized by whole-genome sequencing, and comparative genomic analyses were performed for selected chromosomal beta-lactamase regions. Results:Enterobacterales were recovered from 41 samples and comprised 11 Klebsiella spp., 11 Leclercia spp., 9 Enterobacter spp., and 3 Citrobacter spp. isolates. Isolates were recovered mainly from seagull feces, followed by sand, and Berlenga Grande and Miramar showed the highest diversity. Klebsiella spp. and Enterobacter spp. concentrated most clinically relevant resistance determinants, including chromosomal bla_SHV-like, bla_OXY-like, and bla_ACT-like genes. By contrast, Leclercia pneumoniae was mainly associated with sand and showed a limited resistome, whereas Citrobacter braakii carried relevant genes such as bla_CMY and qnrB10. Comparative genomic analysis showed conserved chromosomal contexts surrounding bla_SHV-like, bla_OXY-like, and bla_ACT-like regions. Conclusions: These findings indicate that gull-associated fecal contamination may play an important role in the introduction and dissemination of resistant Enterobacterales in coastal ecosystems, with subsequent spread to sand and water. Coastal gulls and beach-associated matrices may therefore act as relevant reservoirs and indicators of antimicrobial resistance circulation at the human–environment interface.