Antibacterial activity of silver nanoparticles against Escherichia coli and methicillin-resistant Staphylococcus pseudintermedius is affected by incorporation into carriers for sustained release.

OBJECTIVE: To establish the lowest effective dose of commercially available nanoparticulate silver (AgNP) for antibacterial activity against Escherichia coli (E coli) and methicillin-resistant Staphylococcus pseudintermedius (MRSP), in vitro, and to establish the effect of incorporating AgNP into carriers for sustained release on this antibacterial activity. SAMPLES: Silver nanoparticle dispersion (0.02 mg/mL) composed of citrate-stabilized, spherical, 10 nm diameter nanoparticles in aqueous buffer. PROCEDURES: E coli and MRSP were treated with 0.01 mg/mL AgNP. The highest concentration of bacteria where growth was inhibited by AgNP was selected for treatment with 0.01 mg/mL AgNP incorporated 3 carriers for sustained release: calcium sulfate hemihydrate (CSH) beads, poloxamer 407 gel, and gelatin sponge, respectively. The antibacterial activity of AgNP and AgNP incorporated into carriers for sustained release was compared with a mixed linear effects model. RESULTS: AgNP inhibited bacterial growth at a concentration of 101 for MRSP and 103 for E coli. For MRSP, the treatment group was associated with bacterial growth (P < .001) while the concentration of bacteria and time were not (P = .292 and P = .289, respectively). For E coli, the treatment group and concentration of bacteria were associated with bacterial growth (P < .001 and = .029, respectively) while time was not (P = .095). Poloxamer 407 gel exerted standalone antibacterial activity against both species of bacteria; sponge and CSH beads did not. CLINICAL RELEVANCE: AgNP has antibacterial activity against E coli and MRSP, which can be reduced when incorporated into carriers for sustained release. Poloxamer 407 gel alone and combined with AgNP exerts antibacterial activity against E coli and MRSP.

Approaches Used to Construct Antibiograms for Dogs in a Veterinary Teaching Hospital in the United States.

Non-judicious antimicrobial use (AMU) is a major driver of antimicrobial resistance (AMR). In human hospitals, cumulative antibiograms are often used by clinicians to evaluate local susceptibility rates and to select the most appropriate empiric therapy with the aim of minimizing inappropriate AMU. However, the use of cumulative antibiograms to guide empiric antimicrobial therapy in veterinary hospitals in the United States is limited, and there are no specific guidelines or standardized methods available for the construction of antibiograms in veterinary clinical settings. The objective of this methods article is to describe the approaches that were used to construct antibiograms from clinical samples collected from dogs seen at a veterinary teaching hospital. Laboratory data for 563 dogs for the period from 1 January 2015 to 31 December 2015 was utilized. We used the Clinical and Laboratory Standards Institute (CLSI) guidelines for use in the construction of the antibiograms in human healthcare settings as the basis for the veterinary antibiograms. One general antibiogram and antibiograms stratified by hospital section, the anatomic region of sample collection/by sample type, were created and the challenges encountered in preparing these antibiograms were highlighted. The approaches described could be useful in guiding veterinary antibiogram development for empiric therapy.

Recovery of Salmonella bacterial isolates from pooled fecal samples from horses.

BACKGROUND: It is important to determine if a horse is shedding Salmonella spp., but a complete culture series can be cost prohibitive. OBJECTIVES: Determine the optimal pooling technique to maintain high sensitivity of Salmonella spp. culture using spiked samples, and then demonstrate the efficacy of this protocol on clinical submissions. HYPOTHESIS: Pooled fecal samples are as sensitive as 5 individual cultures for the detection of Salmonella shedding. ANIMALS: A single Salmonella-negative horse from the university herd, and 19 hospitalized horses. METHODS: Salmonella-free fecal samples were spiked with different amounts of Salmonella spp. (102 , 103 , 104 , and 105 colony forming units [cfu]) and homogenized to evaluate pooled samples. Five individual fecal samples were collected from 19 hospitalized horses. Ten-gram aliquots of each individual sample were combined to make a pooled sample. Both individual and pooled samples were cultured for Salmonella spp. The identity of bacterial isolates was confirmed by matrix-assisted laser desorption-ionization time of flight mass spectrometry. RESULTS: A 102  cfu concentration of Salmonella spp. could be recovered from a spiked Salmonella-free fecal sample. Homogenization protocols indicated that the addition of 20 mL of broth to the pooled sample improved recovery, whereas homogenization time did not. Of the 19 horses tested, 5 were positive for Salmonella. In all instances, Salmonella spp. were recovered from the fecal pool as well as individual samples. CONCLUSIONS AND CLINICAL IMPORTANCE: Pooling of 5 fecal samples for Salmonella culture is a sensitive and cost-effective diagnostic approach to detect horses that are shedding the organism.

Genomics accurately predicts antimicrobial resistance in Staphylococcus pseudintermedius collected as part of Vet-LIRN resistance monitoring.

Whole-genome sequencing (WGS) has changed our understanding of bacterial pathogens, aiding outbreak investigations and advancing our knowledge of their genetic features. However, there has been limited use of genomics to understand antimicrobial resistance of veterinary pathogens, which would help identify emerging resistance mechanisms and track their spread. The objectives of this study were to evaluate the correlation between resistance genotypes and phenotypes for Staphylococcus pseudintermedius, a major pathogen of companion animals, by comparing broth microdilution antimicrobial susceptibility testing and WGS. From 2017-2019, we conducted antimicrobial susceptibility testing and WGS on S. pseudintermedius isolates collected from dogs in the United States as a part of the Veterinary Laboratory Investigation and Response Network (Vet-LIRN) antimicrobial resistance monitoring program. Across thirteen antimicrobials in nine classes, resistance genotypes correlated with clinical resistance phenotypes 98.4 % of the time among a collection of 592 isolates. Our findings represent isolates from diverse lineages based on phylogenetic analyses, and these strong correlations are comparable to those from studies of several human pathogens such as Staphylococcus aureus and Salmonella enterica. We uncovered some important findings, including that 32.3 % of isolates had the mecA gene, which correlated with oxacillin resistance 97.0 % of the time. We also identified a novel rpoB mutation likely encoding rifampin resistance. These results show the value in using WGS to assess antimicrobial resistance in veterinary pathogens and to reveal putative new mechanisms of resistance.