# Molecular Characterization of Carbapenem and Colistin Resistance in Isolates Causing Urinary Tract Infections at an Outpatient Setting of a Tertiary Care Hospital

## TL;DR

This study found carbapenem and colistin resistance in outpatient urinary tract infections, highlighting the need for early detection of antibiotic resistance genes.

## Contribution

The study provides new data on carbapenem and colistin resistance in outpatient settings, where such data is scarce.

## Key findings

- 5.97% of isolates were carbapenem-resistant, with blaNDM being the most common gene detected.
- Colistin resistance in carbapenem-resistant isolates was 11%, similar to previous studies at the same hospital.
- Some isolates co-expressed multiple carbapenemase genes, indicating complex resistance patterns.

## Abstract

Background

Increasing resistance to higher-end antibiotics like carbapenems and colistin is a great cause of concern. There is a paucity of data on the detection of carbapenem and colistin in outpatient settings. This study was to determine the prevalence of carbapenem-resistant Enterobacterales (CRE) and colistin resistance in CRE at the outpatient setting of a tertiary care institute of North India.

Methods

A prospective study was conducted from January to December 2020. A total of 6,829 non-repetitive urine samples were cultured on cysteine lactose electrolyte-deficient (CLED) agar. Identification was done by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), and antimicrobial susceptibility testing followed Clinical and Laboratory Standards Institute (CLSI) 2020, using Kirby-Bauer and Vitek 2 (BioMérieux, Marcy-l'Étoile, France). Carbapenem-resistant isolates were screened for carbapenemase genes (blaNDM, blaKPC, blaOXA, blaOXA-48). Colistin resistance was confirmed by broth microdilution.

Results

A total of 669/6829 (9.79%) urine specimens yielded significant growth, mostly in females (54.1%), less than in other studies probably due to fewer samples received because of the COVID-19 pandemic. The majority (50.82%) of patients belonged to the early adult group (15-45 years). Most organisms were Enterobacteriaceae (509/669, 76.08%). The most common organism isolated was E. coli (56.5%) followed by K. pneumoniae (18.2%). 5.97% (40/669) isolates were carbapenem-resistant. 6.87% (35/509) of Enterobacteriaceae were carbapenem-resistant, which is less than in other studies possibly due to samples from outpatient settings. The following carbapenemase genes were detected: blaNDM (18/35), blaKPC (2/35), blaOXA (11/35) and blaOXA-48 (5/35). Some isolates had co-existence of more than two carbapenemase genes. Colistin resistance in CRE was 11% which is like other studies conducted in the same tertiary centre. Comparison of resistance patterns of other antibiotics in CRE and carbapenem-sensitive Enterobacterales (CSE) group shows that fosfomycin, ticarcillin-clavulanate and tetracycline had higher sensitivity in the CRE group.

Conclusion

The presence of these genes in outpatient settings is worrisome. Both blaNDM and blaOXA-48 resulted in higher minimum inhibitory concentrations (MICs) against carbapenems. Co-presence of NDM with OXA-48-producing E. coli in urine culture. Colistin resistance in an outpatient setting is alarming. Early detection of these resistance-determinant genes by molecular methods is essential in limiting the spread of infection due to these organisms.