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Simple Summary: Lactococcus petauri has been described for the first time in 2017 in a sugar glider. A few years later, it has emerged as important pathogen for fish and more recently it has been reported also in terrestrial mammals and humans. A lot of these cases were misdiagnosed as Lactococcus garvieae infection due to the limitation of the available common standard diagnostic techniques used which were unable to discriminate between these two species and relatively high similarity of the two pathogens at genetic and phenotypic levels. Till today, there are only two reported cases of lactococcosis in dogs with no previous cases were reported from Italy. This report is the first description of L. petauri infection in two domestics dog cases from Italy. The results of the current report provide an update on the host tropism, and additional knowledge on virulence factors and antimicrobial resistance of L. petauri. Lactococcus garvieae has been considered for a long time the only causal agent of lactococcosis. In recent years, different papers reported the involvement of other two bacterial species: Lactococcus petauri and Lactococcus formosensis. A different host tropism has been described for these species where L. garvieae and L. petauri are predominant species in fish and humans' infections, while L. formosensis in bovine. L. garvieae has been reported as rare infectious agent in dog. This paper represents the first isolation of L. petauri in two domesticated dog cases from urine and skin samples, respectively. The recovered L. petauri has been identified using PCR and sequencing based on Internal Transcribe Spacer (ITS) and phylogenetic analysis showed that it belongs to the L. petauri cluster with a 100% of identity with sequences previously reported from fish isolates while there were differences with L. petauri isolated from urinary tract infection from humans. L. petauri in human infection has been considered not necessarily deriving from the ingestion of contaminated food but rather as an opportunistic pathogen colonization intestinal tract. Differences among virulotypes have been reported for humans and dogs, and a comparison was also made between the virulotyping of L. petauri and L. garvieae in dogs. The antimicrobial pattern showed susceptibility for the election treatment molecules. These data contribute to our understanding of the host trophism of this species which was misclassified for long time and provide new data on its virulence factors and antimicrobial resistance. [ABSTRACT FROM AUTHOR]

Methicillin-resistant Staphylococcus pseudintermedius (MRSP) constitutes an emerging health problem for companion animals in veterinary medicine. Therefore, discovery of novel antimicrobial agents for treatment of Staphylococcus-associated canine infections is urgently needed to reduce use of human antibiotics in veterinary medicine. In the present work, we characterized the antimicrobial activity of the peptoid D2 against S. pseudintermedius and Pseudomonas aeruginosa, which is another common integumentary pathogen in dogs. Furthermore, we performed a structure–activity relationship study of D2, which included 19 peptide/peptoid analogs. Our best compound D2D, an all d-peptide analogue, showed potent minimum inhibitory concentrations (MICs) against canine S. pseudintermedius (2–4 µg/mL) and P. aeruginosa (4 µg/mL) isolates as well as other selected dog pathogens (2–16 µg/mL). Time–kill assays demonstrated that D2D was able to inhibit MRSP in 30 min at 1× MIC, significantly faster than D2. Our results suggest that at high concentrations D2D is rapidly lysing the bacterial membrane while D2 is inhibiting macromolecular synthesis. We probed the mechanism of action at sub-MIC concentrations of D2, D2D, the l-peptide analog and its retro analog by a macromolecular biosynthesis assay and fluorescence spectroscopy. Our data suggest that at sub-MIC concentrations D2D is membrane inactive and primarily works by cell wall inhibition, while the other compounds mainly act on the bacterial membrane.

Methicillin-resistant Staphylococcus pseudintermedius (MRSP) constitutes an emerging health problem for companion animals in veterinary medicine. Therefore, discovery of novel antimicrobial agents for treatment of Staphylococcus-associated canine infections is urgently needed to reduce use of human antibiotics in veterinary medicine. In the present work, we characterized the antimicrobial activity of the peptoid D2 against S. pseudintermedius and Pseudomonas aeruginosa, which is another common integumentary pathogen in dogs. Furthermore, we performed a structure–activity relationship study of D2, which included 19 peptide/peptoid analogs. Our best compound D2D, an all d-peptide analogue, showed potent minimum inhibitory concentrations (MICs) against canine S. pseudintermedius (2–4 µg/mL) and P. aeruginosa (4 µg/mL) isolates as well as other selected dog pathogens (2–16 µg/mL). Time–kill assays demonstrated that D2D was able to inhibit MRSP in 30 min at 1× MIC, significantly faster than D2. Our results suggest that at high concentrations D2D is rapidly lysing the bacterial membrane while D2 is inhibiting macromolecular synthesis. We probed the mechanism of action at sub-MIC concentrations of D2, D2D, the l-peptide analog and its retro analog by a macromolecular biosynthesis assay and fluorescence spectroscopy. Our data suggest that at sub-MIC concentrations D2D is membrane inactive and primarily works by cell wall inhibition, while the other compounds mainly act on the bacterial membrane. [ABSTRACT FROM AUTHOR]