The aim of this study is to evaluate the risk factors for colonisation by multidrug resistant (MDR) K. pneumoniae in a critical care unit and the relationship between colonisation and the antibiotic pressure exerted by the antimicrobial treatments received by patients. A prospective observational was designed. Patients admitted for more than 48 h to an intensive care unit were included. Samples for surveillance cultures were obtained from all the patients upon admission and once a week. The association between risk factors and colonisation by MDR K. pneumoniae was determined by logistic regression. A Cox regression model was used to evaluate the effect of the use of antimicrobials on the colonisation rate. An ARMIA model was used to investigate the association between the incidence of colonisation by MDR strains and the global consumption of antimicrobials in the unit. One thousand seven hundred twenty-five patients were included, from which 308 (17.9%) were positive for MDR K. pneumoniae. In the multivariate analysis, hospitalisation for longer than 7 days together with respiratory infection and administration of any antibiotic was associated with increased MR K. pneumoniae colonisation. Patients who received antibiotics for more than 48 h were colonised earlier than patients who did not receive antibiotic treatment [HR: 2.16 (95%CI:1.55–3.03)]. The ARIMA model found a significant association between the monthly colonisation rate for MR K. pneumoniae and the consumption of cephalosporins and carbapenems in the previous month. Individual antibiotic administration and the global antibiotic pressure of cephalosporins and carbapenems are associated to an increased colonisation by MDR K. pneumoniae strains.

Background/Objectives: Escherichia coli is one of the most problematic bacterial species in hospital and community settings and a leading cause of resistant infections worldwide. This reinforces the need of new antibacterial tools like phage therapy. This study aimed to isolate and characterise lytic bacteriophages (phages) targeting clinical E. coli strains with different resistance profiles and to assess their potential for future therapeutic development. Methods: Environmental and clinical samples were used to isolate lytic phages active against clinical E. coli strains, and to evaluate their potential for future therapeutic applications. A phage collection was tested against E. coli strains from human bloodstream infections to determine their bacteriolytic activity, host range and specificity. Two phages were selected for further phenotypic and genomic characterisation. Their infectivity and antibacterial activity were evaluated under growth medium- and filtered human urine-related conditions and across different temperature and pH ranges. Results: Both phages demonstrated consistent antimicrobial activity against susceptible clinical strains, exhibiting a narrow host range and specificity. They retained infectivity under growth medium- and filtered human urine-related conditions, significantly reducing bacterial populations, and maintaining lytic activity across a range of temperatures and pH values. Genomic characterisation confirmed their lytic nature and supported their safety. Taxonomic analysis revealed that one phage was classified as a new podovirus-morphotype species within the genus Xuquatrovirus. The other displayed characteristics consistent with a novel genus, showing myovirus morphology. Conclusions: Environmental reservoirs represent a source of lytic phages active against clinically relevant E. coli strains. The new coliphages provide a basis for future development of phage-based strategies against multidrug-resistant E. coli strains.