Anaerobic bacteraemia - identification of Bacteroides and Phocaeicola in blood samples. Challenges in antimicrobial susceptibility testing

The objective of this retrospective, single-centre, observational study was to determine the prevalence of Gram-negative anaerobic bacteria, specifically Bacteroides, and Phocaeicola in blood samples taken from patients with bacteremia, to describe the antibiotic susceptibility profiles of these clinical isolates, and to investigate the presence of resistance genes. Bacteroides fragilis was the most frequently isolated from blood samples, accounting for 64 % of cases. Antibiotic susceptibility testing revealed different patterns of resistance to antimicrobial agents. Almost all (96 %) strains carried genes associated with resistance to β-lactam antibiotics, in a mechanism related to enzyme production. Phenotypic susceptibility to amoxicillin with clavulanic acid and ticarcillin was observed in 92 % and 72 % of the isolates, respectively. All the strains were susceptible to metronidazole, and the nim  gene was not detected. The erm genes were detected in 24 % of the strains, all of which were phenotypically resistant to clindamycin.