Emergence of metronidazole and clindamycin resistance among anaerobic Bacteroides fragilis group - A study from South India

• Author Details:   
• Sandra Jacob
• Supriya Gachinmath ^*

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Background: Bacteroides fragilis is the most common pathogenic group among anaerobic pathogens, primarily causing infections such as deep visceral abscesses, brain abscesses, diabetic foot ulcers, etc. Recent studies have shown increasing resistance among these bacteria to common antibiotics like metronidazole and clindamycin, which are used for empirical treatment.

Aim and Objective: The study aimed to analyze and identify the common pathogenic species of the Bacteroides fragilis group isolated from clinical samples and to determine the drug resistance for clindamycin and metronidazole.

Materials and Methods: A total of 51 Bacteroides fragilis group isolates were obtained from samples received for anaerobic culture from January 2021 to December 2023.The samples were inoculated onto anaerobic blood agar and other essential media. Identification was done using MALDI-TOF MS. Antibiotic susceptibility was performed using E-strip method and interpreted according to CLSI 2023 breakpoints for clindamycin and metronidazole.

Results: Bacteroides fragilis was found to be the most prevalent among the Bacteroides fragilis group isolates, followed by B.ovatus. The cultures showed a high incidence of polymicrobial growth (80%, n=41), with Prevotella species (n=6) being the most frequent obligate anaerobe grown along with Bacteroides fragilis group, while Escherichia coli (n=15) was the most common facultative anaerobe. 11 out of 51 isolates showed resistance to metronidazole (21%), while 2 isolates were intermediate (3.9%) and the rest were sensitive. 23 out of 51 isolates (45%) were resistant to clindamycin, 1 was intermediate (1.9%), and 27 isolates were sensitive to clindamycin.

Conclusion: This study reiterates that Bacteroides fragilis subspp fragilis is the most common Bacteroides fragilis group and is known to cause various anaerobic infection. There is an emergence of drug resistance among them towards commonly used antibiotics like metronidazole and clindamycin.