Predictive statistical models for monitoring antimicrobial resistance spread in the environment using Apis mellifera (L. 1758) colonies.

The rise of antimicrobial resistance (AMR) is one of the most relevant problems for human and animal health. According to One Health Approach, it is important to regulate the use of antimicrobials and monitor the spread of AMR in the environment as well. Apis mellifera (L. 1758) colonies were used as bioindicators thanks to their physical and behavioural characteristics. During their foraging flights, bees can intercept small particles, including atmospheric particulate matter, etc., and also microorganisms. To date, the antimicrobial surveillance network is limited to the sanitary level but lacks into environmental context. This study aimed to evaluate the use of A. mellifera colonies distributed throughout the Emilia-Romagna region (Italy) as indicators of environmental antimicrobial-resistant bacteria. This was performed by creating a statistical predictive model that establishes correlations between environmental characteristics and the likelihood of isolating specific bacterial genera and antimicrobial-resistant strains. A total of 608 strains were isolated and tested for susceptibility to 19 different antimicrobials. Aztreonam-resistant strains were significantly related to environments with sanitary structures, agricultural areas and wetlands, while urban areas present a higher probability of trimethoprim/sulfamethoxazole-resistant strains isolation. Concerning genera, environments with sanitary structures and wetlands are significantly related to the genera Proteus spp., while the Escherichia spp. strains can be probably isolated in industrial environments. The obtained models showed maximum values of Models Accuracy and robustness (R2) of 55 % and 24 %, respectively. The results indicate the efficacy of utilizing A. mellifera colonies as valuable bioindicators for estimating the prevalence of AMR in environmentally disseminated bacteria. This survey can be considered a good basis for the development of further studies focused on monitoring both sanitary and animal pathology, creating a specific network in the environments of interest.

Phenotypic and genotypic antimicrobial resistance patterns in honey bee (Apis mellifera L.) bacterial symbionts.

Antimicrobial resistance (AMR) is a major global public health problem. Nevertheless, the knowledge of the factors driving the spread of resistance among environmental microorganisms is limited, and few studies have been performed worldwide. Honey bees (Apis mellifera L.) have long been considered bioindicators of environmental pollution and more recently also of AMR. In this study, 53 bacterial strains isolated from the body surface of honey bees at three ontogenetic stages, collected from ten different geographic locations, were tested for their phenotypic and genotypic resistance to eight classes of the most widely used antimicrobials in human and veterinary medicine. Results showed that 83% of the strains were resistant to at least one antimicrobial and 62% were multidrug-resistant bacteria, with a prevalence of resistance to nalidixic acid, cefotaxime, and aztreonam. A high percentage of isolates harbouring at least one antimicrobial gene was also observed (85%). The gene encoding resistance to colistin mcr-1 was the most abundant, followed by those for tetracycline tetM and tetC. Geographical features influenced the distribution of these traits more than bacterial species or bee stage, supporting the use of honey bee colonies and their associated bacteria as indicators to monitor environmental resistance. This approach can improve the scientific understanding of this global threat by increasing data collection capacity.

Using honey bee colonies to monitor phenotypic and genotypic resistance to colistin.

Colistin is a polymyxin antimicrobic mainly used to treat infection caused by multi-drug resistant Gram-negative bacteria. Mechanisms of colistin resistance are linked to the mobile colistin resistance (mcr) genes, which are transferable within mobile plasmids. Currently, there is limited research on the environmental dissemination of these genes. The behavioural and morphological characteristics of Apis mellifera L. make honey bees effective environmental bioindicators for assessing the prevalence of antimicrobial-resistant bacteria. This study aims to evaluate the colistin phenotypic and genotypic resistance in environmental Gram-negative bacteria isolated from foraging honey bees, across a network of 33 colonies distributed across the Emilia-Romagna region in Italy. Phenotypic resistances were determined through a microdilution assay using the minimum inhibitory concentration (MIC) with dilutions ranging from 0.5 µg/ml to 256 µg/ml. Strains with MIC values gather than 2 µg/ml were classified as resistant. Also, the identification of the nine mcr genes was carried out using two separate multiplex PCR assays. The study found that 68.5% of isolates were resistant and the genus with the higher resistance rates observed in Enterobacter spp. (84.5%). At least one mcr gene was found in 137 strains (53.3%). The most detected gene was mcr5 (35.3%), which was the most frequently detected gene in the seven provinces, while the least observed was mcr4 (4.8%), detected only in two provinces. These results suggested the feasibility of detecting specific colistin resistance genes in environmentally spread bacteria and understanding their distribution at the environmental level, despite their restricted clinical use. In a One-Health approach, this capability enables valuable environmental monitoring, considering the significant role of colistin in the context of public health.

Antibiotic Resistance in Enterococci and Enterobacteriaceae from Laboratory-Reared Fresh Mealworm Larvae (Tenebrio molitor L.) and Their Frass.

The occurrence of antibiotic-resistant bacteria in foodstuff involves a human health risk. Edible insects are a precious resource; however, their consumption raises food safety issues. In this study, the occurrence of antibiotic resistant bacteria in laboratory-reared fresh mealworm larvae (Tenebrio molitor L.) and frass was assessed. Antibiotics were not used during the rearing. Enterobacteriaceae and enterococci were isolated from 17 larvae and eight frass samples. In total, 62 and 69 isolates presumed to belong to Enterobacteriaceae and Enterococcus spp., respectively, were obtained and tested for antibiotic susceptibility via disk diffusion. Based on the results, isolates were grouped, and representative resistant isolates were identified at species level through 16S rRNA gene sequencing. For enterococci resistance, percentages higher than 15% were observed for vancomycin and quinupristin-dalfopristin, whereas Enterobacteriaceae resistance higher than 25% was found against cefoxitin, ampicillin, and amoxicillin-clavulanic acid. Based on the species identification, the observed resistances seemed to be intrinsic both for enterococci and Enterobacteriaceae, except for some ß-lactams resistance in Shigella boydii (cefoxitin and aztreonam). These could be due to transferable genetic elements. This study suggests the need for further investigations to clarify the role of edible insects in the spreading of antibiotic resistance determinants through the food chain.