Phenotypic and genotypic determination of β-lactamase-producing Escherichia coli strains isolated from raw milk and clinical mastitis samples, Mashhad, Iran

Overlooked volcanic effect during transmission of antibiotic resistance genes induced by copper and zinc

Adding heavy metals such as copper and zinc to animal feeds is common practice to promote growth, but meanwhile has side consequence of enhancing spread of antibiotic resistance genes (ARGs) in soil. This presents a global challenge to food security and human health. We in this study investigated the transmission of typical ARGs, i. e. β-lactamase genes (β-RGs), in dairy farm environments where dietary Cu and Zn were present in a wide range of concentration. The β-RGs were demonstrated to be highly prevalent across environmental media, with a relative abundance of 94.55%, dominated by mechanisms of antibiotic deactivation (93.75%) and cellular protection (6.25%). More importantly, we first found the transmission of ARGs to be highly dependent on the overlooked volcanic effect, i. e. low-concentration Cu (12-22 mg/kg) and Zn (45-80 mg/kg) acted as micronutrients necessary for microbial growth but facilitated ARGs transfer, whereas higher-concentration Cu (22-39 mg/kg) and Zn (80-153 mg/kg) became toxic to microbial communities and gene expression patterns. Notably, the specific microbial phyla Proteobacteria (2.28-82.94%), Bacteroidetes (0.02-56.48%) and Actinobacteria (1.62-12.92%) exhibited resistance at low concentration of Cu and Zn, which enhanced the transmission of β-RGs. However, this process was inhibited at higher concentration due to inactivation of microbes by Cu and Zn. The increase in resistance was first observed in class Gammaproteobacteria (2.02-88.51%) and Alphaproteobacteria (0.68-10.1%) with increased Cu and Zn concentration. This resulted in heightened transfer of ARGs by tnpA-07 (80.35%) due to protection of thicker cell membrane by chelation with Cu and Zn. This study not only offers mechanistic insights into the volcanic effect of dietary metals on dissemination of ARGs, but also has important implications for safe management of agricultural settings.

Genetic basis of antibiotic resistance in bovine mastitis and its possible implications for human and ecological health

Bovine mastitis is a mammary gland inflammation that can occur due to infectious pathogens, Staphylococcus aureus and Escherichia coli, which are, respectively, the most prevalent Gram-positive and Gram-negative bacteria associated with this disease. Currently, antibiotic treatment has become more complicated due to the presence of resistant pathogens. This review, therefore, aims to identify the most common resistance genes reported for these strains in the last four years. During the review, it was noted that blaZ, blaSHV, blaTEM, and blaampC are the most reported genes for S. aureus and E. coli, associated with drug inactivation, mainly β-lactamases. They are characterized by generating bacterial resistance to β-lactam antibiotics, the most common treatment in animal and human bacterial treatments (penicillins and cephalosporins, among others). Genes associated with efflux systems were also present in the two strains and included norA, tetA, tetC, and tetK, which generate resistance to macrolide and tetracycline antibiotics. Additionally, the effects of spreading resistance between animals and humans through direct contact (such as consumption of contaminated milk) or indirect contact (through environmental contamination) has been deeply discussed, emphasizing the importance of having adequate sanitation and antibiotic control and administration protocols.

A systematic review and meta-analysis revealed a high-level antibiotic resistance of bovine mastitis Staphylococcus aureus in Iran

Staphylococcus aureus (S. aureus) is a frequent and major etiological agent of bacterial bovine mastitis, leading to high economic losses. This pathogen readily becomes resistant to many antibiotics, resulting in persistent noncurable intramammary infection (IMI) in animals and the development of multidrug-resistant (MDR) strains. The objectives of this study were to evaluate the prevalence of antimicrobial resistance (AMR) of S. aureus strains causing bovine mastitis in Iran according to published data from 2000 to 2021. As there is still a dearth of information on the AMR of S. aureus from Iranian bovine mastitis, the primary focus and subgroup analysis of the present study was performed on Iranian isolates. A systematic review was done according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). Based on the initial search, 1006 article were identified. According to inclusion and exclusion criteria and removing duplications, 55 English articles and 13 Persian articles (a total of 68 articles) were finally analyzed. The highest overall prevalence of resistance was reported against penicillin G (p-estimate = 0.568 for all isolates, and p-estimate = 0.838 for Iranian isolates), followed by ampicillin (p-estimate = 0.554, and p-estimate = 0.670 for all isolates and Iranian isolates, respectively) and amoxicillin (p-estimate = 0.391, and p-estimate = 0.695 for all isolates and Iranian isolates, respectively). Besides, the lowest prevalence of resistant isolates was related to trimethoprim-sulfamethoxazole (p-estimate = 0.108 and 0.118 for all isolates and Iranian isolates, respectively) and gentamycin (p-estimate = 0.163 and 0.190, for all isolates and Iranian isolates, respectively). Our analysis showed that the Iranian isolates were more resistant to all antibiotics than those of all isolates. This difference was significant in the case of penicillin G, ampicillin, and erythromycin at 5%. To the best of our knowledge, except for ampicillin, AMR has increased over time for all the studied antibiotics in Iranian isolates. This increased rate was significant for penicillin G, amoxicillin, and tetracycline (p < 0.1). No differences in AMR were detected regarding the mastitis types (clinical vs. subclinical mastitis) for almost evaluated antibiotics. In conclusion, the prevalence of AMR S. aureus isolated from IMI was high particularly for bovine mastitis used antibiotics like penicillin G and ampicillin. Additionally, according to the increasing rate of AMR S. aureus in recent years in Iran, control strategies should be reinforced to avoid the spread of this pathogen and drug resistance.