Phenotypic Antibiotic Resistance Patterns of Escherichia coli Isolates from Clinical UTI Samples and Municipal Wastewater in a Grenadian Community

Abstract

Antimicrobial resistance (AMR) is a growing global health threat. This study investigated antibiotic resistance in E. coli isolates from municipal wastewater (86 isolates) and clinical urinary tract infection (UTI) cases (34 isolates) in a Grenadian community, using data from January 2022 to October 2023. Antibiogram data, assessed per WHO guidelines for Critically Important antimicrobials (CIA), showed the highest resistance levels in both clinical and wastewater samples for ampicillin, followed by amoxicillin/clavulanic acid and nalidixic acid, all classified as Critically Important. Similar resistance was observed for sulfamethoxazole-trimethoprim (highly important) in both groups, with nitrofurantoin showing resistance in the important category. According to the WHO AWaRe classification, ampicillin (ACCESS group) had the highest resistance, while nitrofurantoin had the lowest across all samples. The WATCH group antibiotics, cefuroxime and cefoxitin, showed comparable resistance levels, whereas aztreonam from the RESERVE group (tested only in wastewater) was 100% sensitive. Multiple Antibiotic Resistance (MAR) index analysis revealed that 7% of wastewater and 38.2% of clinical samples had MAR values over 0.2, indicating prior antibiotic exposure in clinical isolates. These parallel patterns in wastewater and clinical samples highlight wastewater monitoring as a valuable tool for AMR surveillance, supporting antibiotic stewardship through ongoing environmental and clinical assessment.

Keywords: Escherichia coli; Grenada; antibiotic resistance; clinical isolates; phenotypic analysis; wastewater surveillance.

Figure 1

WHO AWaRe classification.

Figure 2

Susceptibility patterns of E. coli strains to WHO Medically Important Antimicrobials for Human Medicine rom wastewater: (BLUE) Critically Important antimicrobials, (PURPLE) Highly Important, and (Green) Important to human medicine. The WHO CIA list used was as a reference to help formulate and prioritize risk assessment and risk management strategies for containing antimicrobial resistance: (A) Critically Important: Antibiotics that meet both criteria: (1) they are the sole or limited therapeutic option for treating life-threatening infections, and (2) they are used to treat infections caused by bacteria from non-human sources or carry resistance genes originating from non-human sources. (B) Highly Important: Antibiotics that meet only one of the following criteria: (1) they are the sole or limited treatment option for life-threatening infections, or (2) they are used for infections caused by bacteria from non-human sources or with resistance genes from non-human sources. (C) Important: Antimicrobial classes used in humans that do not meet criteria (1) or (2) [41].

Figure 3

Susceptibility pattern of E. coli strains to WHO Medically Important Antimicrobials for Human Medicine from clinical samples: (BLUE) Critically Important antimicrobials, (PURPLE) Highly Important, and (Green) Important to human medicine.

Figure 4

WHO AWaRe ACCESS classification for E. coli isolated from wastewater and clinical urinary tract isolates. The classification is based, in part, on the risk of developing antibiotic resistance and their importance to medicine. The ACCESS category of this classification includes empiric first or second choice for treatment of most common infection and generally available [42].

Figure 5

WHO AWaRe: WATCH classification for E. coli isolated from wastewater and clinical urinary tract isolates. AWaRe classification: The classification is based, in part, on the risk of developing antibiotic resistance and their importance to medicine. WATCH category: Antibiotics that have higher toxicity issues and higher potential to negatively impact AMR. They should only be prescribed for specific infections [42].