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1. Smelly shark, smelly ray: what is infecting you?

   https://doi.org/10.1093/jambio/lxae068  

   Cardoso, Maíra Duarte ; Maciel, Oswaldo Luiz de C. ; de Souza, André Luiz Medeiros ; Roges, Emily Moraes ; Gonçalves, Verônica Dias ; Siciliano, Salvatore ; Rodrigues, Dália dos Prazeres ; Hauser-Davis, Rachel Ann ( March 2024 , Journal of Applied Microbiology)

   Although elasmobranchs are consumed worldwide, bacteriological assessments for this group are still sorely lacking. In this context, this study assessed bacteria of sharks and rays from one of the most important landing ports along the Rio de Janeiro coast.

   Bacteria were isolated from the cloacal swabs of the sampled elasmobranchs. They were cultured, and Vibrio, Aeromonas, and Enterobacterales were isolated and identified. The isolated bacteria were then biochemically identified and antimicrobial susceptibility assays were performed. Antigenic characterizations were performed for Salmonella spp. and Polymerase Chain Reaction (PCR) assays were performed to identify Escherichia coli pathotypes. Several bacteria of interest in the One Health context were detected. The most prevalent Enterobacterales were Morganella morganii and Citrobacter freundii, while Vibrio harveyi and Vibrio fluvialis were the most prevalent among Vibrio spp. and Aeromonas allosacharophila and Aeromonas veronii bv. veronii were the most frequent among Aeromonas spp. Several bacteria also displayed antimicrobial resistance, indicative of Public Health concerns. A total of 10% of Vibrio strains were resistant to trimethoprim-sulfamethoxazole and 40% displayed intermediate resistance to cefoxitin. Salmonella enterica strains displayed intermediate resistance to ciprofloxacin, nalidixic acid and streptomycin. All V. cholerae strains were identified as non-O1/non-O139. The detected E. coli strains did not exhibit pathogenicity genes. This is the first study to perform serology assessments for S. enterica subsp. enterica isolated from elasmobranchs, identifying the zoonotic Typhimurium serovar. Salmonella serology evaluations are, therefore, paramount to identify the importance of elasmobranchs in the epidemiological salmonellosis chain.

   The detection of several pathogenic and antibiotic-resistant bacteria may pose significant Public Health risks in Brazil, due to high elasmobranch consumption rates, indicating the urgent need for further bacteriological assessments in this group.

    

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2. A dose response model for quantifying the infection risk of antibiotic-resistant bacteria

   https://doi.org/10.1038/s41598-019-52947-3  

   Chandrasekaran, Srikiran ; Jiang, Sunny C. ( November 2019 , Scientific Reports)

   Quantifying the human health risk of microbial infection helps inform regulatory policies concerning pathogens, and the associated public health measures. Estimating the infection risk requires knowledge of the probability of a person being infected by a given quantity of pathogens, and this relationship is modeled using pathogen specific dose response models (DRMs). However, risk quantification for antibiotic-resistant bacteria (ARB) has been hindered by the absence of suitable DRMs for ARB. A new approach to DRMs is introduced to capture ARB and antibiotic-susceptible bacteria (ASB) dynamics as a stochastic simple death (SD) process. By bridging SD with data from bench experiments, we demonstrate methods to (1) account for the effect of antibiotic concentrations and horizontal gene transfer on risk; (2) compute total risk for samples containing multiple bacterial types (e.g., ASB, ARB); and (3) predict if illness is treatable with antibiotics. We present a case study of exposure to a mixed population of Gentamicin-susceptible and resistantEscherichia coliand predict the health outcomes for varying Gentamicin concentrations. Thus, this research establishes a new framework to quantify the risk posed by ARB and antibiotics.

    

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3. Dead but Not Forgotten: How Extracellular DNA, Moisture, and Space Modulate the Horizontal Transfer of Extracellular Antibiotic Resistance Genes in Soil

   https://doi.org/10.1128/aem.02280-21  

   Kittredge, Heather A. ; Dougherty, Kevin M. ; Evans, Sarah E. ( April 2022 , Applied and Environmental Microbiology)

   Elkins, Christopher A. (Ed.)

   ABSTRACT Antibiotic-resistant bacteria and the spread of antibiotic resistance genes (ARGs) pose a serious risk to human and veterinary health. While many studies focus on the movement of live antibiotic-resistant bacteria to the environment, it is unclear whether extracellular ARGs (eARGs) from dead cells can transfer to live bacteria to facilitate the evolution of antibiotic resistance in nature. Here, we use eARGs from dead, antibiotic-resistant Pseudomonas stutzeri cells to track the movement of eARGs to live P. stutzeri cells via natural transformation, a mechanism of horizontal gene transfer involving the genomic integration of eARGs. In sterile, antibiotic-free agricultural soil, we manipulated the eARG concentration, soil moisture, and proximity to eARGs. We found that transformation occurred in soils inoculated with just 0.25 μg of eDNA g −1 soil, indicating that even low concentrations of soil eDNA can facilitate transformation (previous estimates suggested ∼2 to 40 μg eDNA g −1 soil). When eDNA was increased to 5 μg g −1 soil, there was a 5-fold increase in the number of antibiotic-resistant P. stutzeri cells. We found that eARGs were transformed under soil moistures typical of terrestrial systems (5 to 30% gravimetric water content) but inhibited at very high soil moistures (>30%). Overall, this work demonstrates that dead bacteria and their eARGs are an overlooked path to antibiotic resistance. More generally, the spread of eARGs in antibiotic-free soil suggests that transformation allows genetic variants to establish in the absence of antibiotic selection and that the soil environment plays a critical role in regulating transformation. IMPORTANCE Bacterial death can release eARGs into the environment. Agricultural soils can contain upwards of 10 9 ARGs g −1 soil, which may facilitate the movement of eARGs from dead to live bacteria through a mechanism of horizontal gene transfer called natural transformation. Here, we track the spread of eARGs from dead, antibiotic-resistant Pseudomonas stutzeri cells to live antibiotic-susceptible P. stutzeri cells in sterile agricultural soil. Transformation increased with the abundance of eARGs and occurred in soils ranging from 5 to 40% gravimetric soil moisture but was lowest in wet soils (>30%). Transformants appeared in soil after 24 h and persisted for up to 15 days even when eDNA concentrations were only a fraction of those found in field soils. Overall, our results show that natural transformation allows eARGs to spread and persist in antibiotic-free soils and that the biological activity of eDNA after bacterial death makes environmental eARGs a public health concern. 

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4. Genomic and in vitro pharmacodynamic analysis of rifampicin resistance in multidrug‐resistant canine Staphylococcus pseudintermedius isolates

   https://doi.org/10.1111/vde.12959  

   Hicks, Karly ; Tan, Yongjun ; Cao, Wenqi ; Hathcock, Terri ; Boothe, Dawn ; Kennis, Robert ; Zhang, Dapeng ; Wang, Xu ; White, Amelia ( April 2021 , Veterinary Dermatology)

   Antimicrobial resistance is a growing concern in canineStaphylococcus pseudintermediusdermatitis. Treatment with rifampicin (RFP) is considered only in meticillin‐resistant and multidrug‐resistantS. pseudintermedius(MDR‐MRSP).

   To determine an optimal RFP dosing for MDR‐MRSP treatment without induction of RFP resistance and identify causal mutations for antimicrobial resistance.

   Time–kill assays were performed in a control isolate and three MDR‐MRSP isolates at six clinically relevant concentrations [32 to 1,024 × MIC (the minimum inhibitory concentration)]. Whole‐genome resequencing and bioinformatic analysis were performed in the resistant strains developed in this assay.

   The genomic analysis identified nine antimicrobial resistance genes (ARGs) in MDR‐MRSP isolates, which are responsible for resistance to seven classes of antibiotics. RFP activity against all four isolates was consistent with a time‐dependent and bacteriostatic response. RFP resistance was observed in six of the 28 time–kill assays, including concentrations 64 × MIC in MDR‐MRSP1 isolates at 24 h, 32 × MIC in MDR‐MRSP2 at 48 h, 32 × MIC in MDR‐MRSP3 at 48 h and 256 × MIC in MDR‐MRSP3 at 24 h. Genome‐wide mutation analyses in these RFP‐resistant strains discovered the causal mutations in the coding region of therpoBgene.

   A study has shown that 6 mg/kg per os results in plasma concentrations of 600–1,000 × MIC ofS. pseudintermedius. Based on our data, this dose should achieve the minimum MIC (×512) to prevent RFP resistance development; therefore, we recommend a minimum daily dose of 6 mg/kg for MDR‐MRSP pyoderma treatment when limited antibiotic options are available.

    

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5. Inhalable Antibiotic Resistome from Wastewater Treatment Plants to Urban Areas: Bacterial Hosts, Dissemination Risks, and Source Contributions

   https://doi.org/10.1021/acs.est.1c07023  

   Xie, Jiawen ; Jin, Ling ; Wu, Dong ; Pruden, Amy ; Li, Xiangdong ( January 2022 , Environmental Science & Technology)

   Antibiotic resistance genes (ARGs) are commonly detected in the atmosphere, but questions remain regarding their sources and relative contributions, bacterial hosts, and corresponding human health risks. Here, we conducted a qPCR- and metagenomics-based investigation of inhalable fine particulate matter (PM2.5) at a large wastewater treatment plant (WWTP) and in the ambient air of Hong Kong, together with an in-depth analysis of published data of other potential sources in the area. PM2.5 was observed with increasing enrichment of total ARGs along the coastal–urban–WWTP gradient and clinically relevant ARGs commonly identified in urban and WWTP sites, illustrating anthropogenic impacts on the atmospheric accumulation of ARGs. With certain kinds of putative antibiotic-resistant pathogens detected in urban and WWTP PM2.5, a comparable proportion of ARGs that co-occurred with MGEs was found between the atmosphere and WWTP matrices. Despite similar emission rates of bacteria and ARGs within each WWTP matrix, about 11–13% of the bacteria and >57% of the relevant ARGs in urban and WWTP PM2.5 were attributable to WWTPs. Our study highlights the importance of WWTPs in disseminating bacteria and ARGs to the ambient air from a quantitative perspective and, thus, the need to control potential sources of inhalation exposure to protect the health of urban populations. 

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