Gut Colonization and Antibiotic-Associated Diarrhea by Clostridium innocuum in Children and Adults

To the Editor—A recent study by Cherny et al [1] described the association between Clostridium innocuum and antibiotic-associated diarrhea (AAD). Clostridium innocuum was isolated more frequently from asymptomatic controls than in participants with AAD (38% vs 50%) [1]. By genomic analysis, the authors also reported no strain difference for C. innocuum isolates between the 2 groups [1]. Furthermore, Clostridioides difficile was found to commonly co-exist with C. innocuum [1]. Despite the intriguing findings, the study still raised several issues that remain uncertain. First, the colonization rate in gastrointestinal (GI) tract of healthy populations remains unknown [2–4]. To discern the rate at different age groups, we conducted a cross-sectional molecular screening study. In brief, C. innocuum–specific polymerase chain reaction (PCR; forward, 5′-GGGGGATAATTATGGATCAC-3′; reverse, 5′-GTCGCTGCTCTTTGTGG-3′) was applied to screen the presence of C. innocuum in stool samples [5]. We also utilized quantitative PCR to determine the bacterial load in each stool sample. The stool samples tested were collected in an ongoing study of microbiota database construction for healthy subjects at different age ranges (IRB201801262B0). We randomly picked up fecal samples from the storage for PCR and quantitative PCR (qPCR) experiments. The results showed that C. innocuum could be detected in stool samples from different age groups at a high rate (Figure 1A). It could be detected in infants as early as 2 ∼ 6 months old; the colonization rate then increased rapidly to 60% at 1 year of age and reached to a peak of approximately 75% at the age group of 1–2 years. The colonization remained relatively high and stable, around 50% to 70%, in an adult population. The cycle threshold (Ct) value of qPCR from different age groups revealed a significantly lower Ct value in infants aged 6 months to 2 years, while it remained stable in age groups older than 2 years (Figure 1B). According to our results and the findings of Cherny et al, the carriage rate of C. innocuum in the gut is high in children and adults, without a specific age preference. The bacterial load appeared to be lower in the infants.