Age-related frequency of penicillin resistance of oral Veillonella

Veillonella spp. are early colonizing inhabitants in the mouth. As part of studies on penicillin resistance among oral indigenous anaerobic microbiota in childhood, the aim of the present longitudinal study was to examine the emergence of resistant strains in Veillonella populations. Altogether 305 Veillonella isolates from saliva of 49 healthy infants followed from 2 to 24 months of age were examined for their in vitro susceptibility to penicillin G and, further, 20 penicillin-resistant isolates representing 5 MIC categories to ampicillin, amoxicillin, amoxicillin/clavulanate, cefoxitin, and β-lactamase production. In infants positive for oral Veillonella, the recovery rate of penicillin-resistant (MIC ≥2 μg/ml) strains increased with age up to 68%, however, most infants simultaneously harbored penicillin-susceptible strains. During the follow-up, the MIC 50 increased from 0.5 μg/ml to 2 μg/ml. In addition to penicillin G, 8/20 strains also showed reduced susceptibility to ampicillin and/or amoxicillin but none produced β-lactamase. Our study suggests other mechanisms than enzymatic degradation of β-lactam ring for resistance of oral Veillonella to penicillin.