Objectives: To study the epidemiology of antibiotic resistance among circulating invasive isolates of non-beta-hemolytic streptococci (NBHS) in France.
Materials: A total of 522 NBHS were sent to the French National Reference Center for Streptococci between March and April 2021. Antibiotic susceptibility by disk diffusion was carried out and minimum inhibitory concentrations (MIC) of penicillin G (PEN), amoxicillin (AMX), cefotaxime (CTX) and ceftriaxone (CRO) were measured by broth microdilution and E-test according to EUCAST recommendations. Genetic determinants of resistance to macrolides, lincosamides, synergistins (MLS) and tetracycline (TET) were detected by PCR.
Results: The isolates distribution in the different NBHS groups was as follows: milleri (n=172, 33%), mitis (n=148, 28%), sanguinis (n=81, 16%), bovis (n=77, 15%), salivarius (n=39, 8%) and mutans (n=5, 1%). Isolates were mainly from bacteraemia without focus (n=241, 46%), intra-abdominal infections (n=95, 18%) and endocarditis (n=58, 11%). All strains were susceptible to glycopeptides and had low level gentamicin resistance. All strains of the bovis, milleri and mutans groups were susceptible to β-lactams. MICs showing non-susceptibility to PEN, AMX, CTX or CRO were found in 31% of mitis, 28% of salivarius isolates and 52% of sanguinis. Notably, 41% (41/99) of intermediate or resistant isolates were categorized susceptible to β-lactams according to PEN disk diffusion testing. Resistance to MLS and TET was found in 216 (41%) and 158 (30%) strains respectively. Cross-resistance between MLS and TET was found in 121 strains (23%) of which 22 (4%) had intermediate susceptibility or resistance to β-lactams.
Conclusions: Surveillance of antibiotic resistance in streptococci remains essential, particularly to monitor the possible emergence of multi-resistant clones.