Antimicrobial use in food animals may contribute to antimicrobial resistance in bacteria of animals and humans. Commensal bacteria of animal intestine may serve as a reservoir of resistance-genes. To understand the dynamics of plasmid-mediated resistance to cephalosporin ceftiofur in enteric commensals of cattle, we developed a deterministic mathematical model of the dynamics of ceftiofur-sensitive and resistant commensal enteric Escherichia coli (E. coli) in the absence of and during parenteral therapy with ceftiofur. The most common treatment scenarios including those using a sustained-release drug formulation were simulated; the model outputs were in agreement with the available experimental data. The model indicated that a low but stable fraction of resistant enteric E. coli could persist in the absence of immediate ceftiofur pressure, being sustained by horizontal and vertical transfers of plasmids carrying resistance-genes, and ingestion of resistant E. coli. During parenteral therapy with ceftiofur, resistant enteric E. coli expanded in absolute number and relative frequency. This expansion was most influenced by parameters of antimicrobial action of ceftiofur against E. coli. After treatment (>5 weeks from start of therapy) the fraction of ceftiofur-resistant cells among enteric E. coli, similar to that in the absence of treatment, was most influenced by the parameters of ecology of enteric E. coli, such as the frequency of transfer of plasmids carrying resistance-genes, the rate of replacement of enteric E. coli by ingested E. coli, and the frequency of ceftiofur resistance in the latter.

Objective Recent outbreaks of Clostridium difficile infection (CDI) have been difficult to control, and data indicate the importance of different sources of transmission may have changed. Our objectives were to evaluate the contributions of asymptomatic and symptomatic C. difficile carriers to new colonizations and to determine the most important epidemiological factors influencing C. difficile transmission. Design Retrospective cohort Setting and Patients All patients admitted to medical wards at a large tertiary care hospital in the US from Jan 1 to Dec 31, 2008. Methods Data from six medical wards and published literature were used to develop a compartmental model of C. difficile transmission. Patients could be in one of five transition states in the model: resistant to colonization (R), susceptible to colonization (S), asymptomatically colonized without protection against CDI (C−), asymptomatically colonized with protection against CDI (C+), and patients with CDI (D). Results The contributions of C−, C+ and D patients to new colonizations were similar. The simulated basic reproduction number ranged from .55 to 1.99, with median 1.04. These values suggest that transmission within the ward alone from patients with CDI cannot sustain new C. difficile colonizations, and therefore, the admission of colonized patients plays an important role in sustaining transmission in the ward. The epidemiological parameters that ranked as the most influential were the proportion of admitted C− and the transmission coefficient for asymptomatic carriers. Conclusion Our study underscores the need to further evaluate the role of asymptomatically colonized patients in C. difficile transmission in the healthcare setting.

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b Animal-associated bacterial communities are infected by bacteriophages, although the dynamics of these infections are poorly understood. Transduction by bacteriophages may contribute to transfer of antimicrobial resistance genes, but the relative importance of transduction among other gene transfer mechanisms is unknown. We therefore developed a candidate deterministic mathematical model of the infection dynamics of enteric coliphages in commensal Escherichia coli in the large intestine of cattle. We assumed the phages were associated with the intestine and were predominantly temperate. Model simulations demonstrated how, given the bacterial ecology and infection dynamics, most (>90%) commensal enteric E. coli bacteria may become lysogens of enteric coliphages during intestinal transit. Using the model and the most liberal assumptions about transduction efficiency and resistance gene frequency, we approximated the upper numerical limits ("worst-case scenario") of gene transfer through specialized and generalized transduction in E. coli by enteric coliphages when the transduced genetic segment is picked at random. The estimates were consistent with a relatively small contribution of transduction to lateral gene spread; for example, generalized transduction delivered the chromosomal resistance gene to up to 8 E. coli bacteria/hour within the population of 1.47 ؋ 10 8 E. coli bacteria/liter luminal contents. In comparison, the plasmidic bla CMY-2 gene carried by ϳ2% of enteric E. coli was transferred by conjugation at a rate at least 1.4 ؋ 10 3 times greater than our generalized transduction estimate. The estimated numbers of transductants varied nonlinearly depending on the ecology of bacteria available for phages to infect, that is, on the assumed rates of turnover and replication of enteric E. coli.

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Blocking immune checkpoint pathways with an antibody or small interfering RNA (siRNA) has become a promising method to reactivate antitumor responses for cancer treatment. However, both blockade strategies achieve only temporary inhibition of these immune checkpoints. Herein, a photoswitched CRISPR/Cas9 system for genomic disruption of the PD‐L1 gene is developed to achieve permanent blockade of the PD‐1/PD‐L1 pathway; this system is constructed by using a photoactivated self‐degradable polyethyleneimine derivative and the plasmid pX330/sgPD‐L1 (expression of the Cas9 protein and single‐guide RNA targeting PD‐L1). Under light irradiation, this photoswitched CRISPR/Cas9 system efficiently genetically disrupts the PD‐L1 gene in not only bulk cancer cells but also cancer stem‐like cells. As a result, the photoswitched CRISPR/Cas9 system significantly increases the infiltration of CD8+ T cells into tumor tissue, leading to effective activation of a T cell‐mediated antitumor response against cancer cells and cancer stem‐like cells. This study provides an alternative strategy to block the PD‐1/PD‐L1 pathway for efficacious immune checkpoint therapy.