Antibiotic Resistance Profiles of Diarrhoeagenic Enterobacterales in Bioko Island, Equatorial Guinea

Abstract

Acute diarrhoeal disease caused by antibiotic-resistant diarrhoeagenic bacteria is a significant global public health issue, particularly in low- and middle-income countries. This study provides the first molecular characterisation of antimicrobial resistance profiles, including the detection of CTX-M-15 and CTX-M-55 extended-spectrum beta-lactamases (ESBLs), among diarrhoeagenic Enterobacterales in Bioko Island, Equatorial Guinea, offering novel epidemiological insights into an understudied region. This study investigated the antibiotic resistance profiles of pathogenic bacteria isolated from diarrhoeal samples on Bioko Island. A total of 153 clinical isolates were collected between 1 February and 30 May 2014, and antimicrobial susceptibility testing was performed at Loeri Comba Polyclinic (Malabo) using the Kirby–Bauer method. The molecular characterisation of β-lactamase-associated genes was performed on different isolates of diarrhoeagenic pathotypes—144 Escherichia coli, 7 Salmonella enterica, and 2 Shigella flexneri—at the National Centre for Microbiology (Majadahonda, Spain). High resistance rates were detected against ampicillin (98%), tetracycline (93.5%), sulfonamides (94.8%), sulfamethoxazole–trimethoprim (88.2%), and cefotaxime (78.8%), while moderate rates of resistance were noted for ciprofloxacin (26.7%), and all isolates remained susceptible to imipenem. Of the isolates, 107 (69.9%) produced either single or multiple β-lactamases. Among these, 73 (68.2%) harbored classical β-lactamases, specifically TEM and OXA-1 types, representing 47.7% of the total sample. Additionally, 34 (31.8%) of the isolates were identified as producers of extended-spectrum β-lactamases (ESBLs), specifically CTX-M enzymes. Sequencing identified CTX-M-15 and CTX-M-55 variants. The predominant ESBL-producing bacteria were enteroaggregative Escherichia coli (56.2%), followed by enteropathogenic and enterotoxigenic E. coli. These findings confirm the circulation of multidrug-resistant diarrhoeagenic Enterobacterales in Equatorial Guinea, raising concerns about limited treatment options due to widespread resistance to multiple antibiotic classes, including third-generation cephalosporins and quinolones. The most important conclusion drawn from this study is that a high percentage of diarrhoeagenic bacteria have an antibiotic resistance and multi-resistance profile, especially to beta-lactams and other groups of antibiotics such as tetracyclines and sulphonamides. There is also a moderate prevalence of isolates carrying ESBLs on Bioko Island, Equatorial Guinea, which could indicate the inappropriate use of antimicrobials.