Species Identification and Antimicrobial Resistance of Streptococcus spp. Isolated from Nasal Swabs of Wild Boars in Avellino Province, Southern Italy

From an ecological epidemiology perspective, wildlife nasal cavities may serve as critical ecological niches for the maintenance and spread of bacterial pathogens relevant to both animal and human health. This study investigated Streptococcus spp. as the most prevalent genus in the nasal cavities of 82 wild boars (Sus scrofa), sampled across six hunting districts in Avellino Province (Southern Italy), assessing the diversity of the colonizing streptococcal populations and their antimicrobial resistance profiles. The sampled population consisted of 43 males (52%) and 39 females (48%). A total of 173 Gram-positive isolates were recovered, with 74 identified as Streptococcus spp. by MALDI-TOF MS. These isolates originated from 59 positive swabs (72%; 59/82). Streptococcus gallolyticus was the most prevalent species (41%; 30/74), followed by Streptococcus porcinus (27%; 20/74) and Streptococcus suis (19%; 14/74). No statistically significant geographic association was found across sampling districts (p = 0.491), whereas a significant association was found between bacterial species and antimicrobial resistance profiles (χ2 = 16.70, p < 0.001). Specifically, all Streptococcus porcinus isolates (100%; 20/20) exhibited resistance to sulfamethoxazole–trimethoprim and tetracycline, while high tetracycline resistance was also noted in Streptococcus suis (93%; 13/14) and Streptococcus gallolyticus (83%; 25/30). Overall, 69% (51/74) of isolates were classified as MDR and 5% (4/74) as XDR. These findings suggest the potential role of wild boars as reservoirs for antimicrobial-resistant streptococci, emphasizing the need for continuous surveillance under a One Health framework.