Susceptibility Profiles of Anaerobes Isolated from Deep-Seated and Sterile Site Clinical Samples: Implications for...

To determine the resistance rates of anaerobic bacteria to metronidazole and amoxicillin/clavulanate and to assess the susceptibility of metronidazole-resistant isolates to meropenem.

A laboratory-based observational study. Place and Duration of the Study: Department of Microbiology, Chughtai Institute of Pathology, Lahore, Pakistan, from July 2023 to June 2025.

Anaerobic bacteria isolated from various clinical specimens were identified, and antimicrobial susceptibility testing was performed using MIC Test Strip®. Minimum inhibitory concentrations were interpreted according to the Clinical Laboratory Standards Institute (CLSI M100, 33rd edition) guidelines. Isolates resistant to metronidazole were further tested for susceptibility to meropenem. Descriptive statistics were used to calculate the frequencies and percentages of anaerobic isolates and antimicrobial susceptibility patterns.

A total of 251 anaerobes were recovered from 243 clinical samples, mainly from deep-seated pus and sterile body fluids. B. fragilis (n = 103) was the most common isolate, followed by Peptostreptococcus anaerobius and Prevotella bivia. More than half (53%) of the isolates were from polymicrobial infections. Resistance to amoxicillin-clavulanate and metronidazole was observed in 24.7% and 42.7% of isolates, respectively. Among metronidazole-resistant isolates, 91.7% remained susceptible to meropenem, with resistance detected in three B. fragilis isolates, suggesting emerging multidrug resistance.

There is a notable increase in resistance among anaerobic bacteria against metronidazole and amoxicillin/clavulanate. Although meropenem remains largely effective, the emergence of resistant isolates is concerning and underscores the need for stringent antimicrobial stewardship.

Anaerobic bacteria, Drug resistance, Metronidazole, Meropenem, Amoxicillin-clavulanate.