Gram negative bacteria related urinary tract infections: spectrum of antimicrobial resistance over 9 years in a University tertiary referral Hospital.

Objective: Overuse of antibiotics has led to an increase in antimicrobial resistance (AMR) worldwide, with a negative impact on the healthcare system and the patients. In this context, our study aims to assess the current AMR patterns of urinary tract infections (UTIs) associated to Gram-negative bacteria. Thus, we provide useful information for doctors dealing with prophylactic and therapeutic empiric therapies.

Materials and methods: We retrospectively analysed more than 650,000 urine cultures collected in the Microbiology Department of a referral University Hospital of Southern England from January 2014 to December 2022.

Results: AMR spectra for 164,059 Gram-negative associated (UTIs) were analysed. The lowest percentage of resistance was found for Amikacin (2.30%), Gentamicin (5.89%) and Co-Amoxiclav (10.49%). Over a 9-year time, there was no significant change in resistance to Amikacin (2.04% in 2014 compared to 2.18% in 2022; p = 0.602) and to Fosfomycin (11.50% in 2014 versus 16.65% in 2022; p = 0.577). Overall, the trend of AMR significantly rose for Cefalexin (17.96-18.42%; p < 0.0001), Co-amoxiclav (9.46-12.69%; p < 0.0001), Nitrofurantoin (10.20-14.18%; p < 0.0001) and Piperacillin/Tazobactam (14.52-18.96%; p < 0.0001). Gram-negative resistance spectrum towards Ciprofloxacin (11.83-9.01%; p < 0.0001), Gentamicin (6.29-5.26%; p < 0.0001), Pivmecillinam (26.88-11.02%; p < 0.0001), Trimethoprim (36.72-29.23%; p < 0.0001) and Ampicillin/Amoxicillin (65.20-57.99%; p < 0.0001) significantly decreased.

Conclusion: Despite the application of national and international guidelines for prophylaxis and treatment of UTIs, the spectrum of resistance for the most common antibiotics is still changing. Clinicians in primary and secondary care must keep that in mind when prescribing antibiotics for suspected UTI and sepsis associated with Gram-negative infections Up-to-date therapeutic strategies can help implement treatment of UTI, reducing selection of multi-resistant pathogens and providing more accurate care for patients. Future studies will be required to help clinicians and keep the guidelines updated.