Pseudomonas aeruginosa variants obtained from veterinary clinical samples reveal a role for cyclic di-GMP in biofilm formation and colony morphology

Hypermutability bypasses genetic constraints in SCV phenotypic switching in Pseudomonas aeruginosa biofilms

Biofilms are critical in the persistence of Pseudomonas aeruginosa infections, particularly in cystic fibrosis patients. This study explores the adaptive mechanisms behind the phenotypic switching between Small Colony Variants (SCVs) and revertant states in P. aeruginosa biofilms, emphasizing hypermutability due to Mismatch Repair System (MRS) deficiencies. Through experimental evolution and whole-genome sequencing, we show that both wild-type and mutator strains undergo parallel evolution by accumulating compensatory mutations in factors regulating intracellular c-di-GMP levels, particularly in the Wsp and Yfi systems. While wild-type strains face genetic constraints, mutator strains bypass these by accessing alternative genetic pathways regulating c-di-GMP and biofilm formation. This increased genetic accessibility, driven by higher mutation rates and specific mutational biases, supports sustained cycles of SCV conversion and reversion. Our findings underscore the crucial role of hypermutability in P. aeruginosa adaptation, with significant implications for managing persistent infections in clinical settings.

Does Every Strain of Pseudomonas aeruginosa Attack the Same? Results of a Study of the Prevalence of Virulence Factors of Strains Obtained from Different Animal Species in Northeastern Poland

BACKGROUND

Pseudomonas aeruginosa is a pathogen that causes infections in animals and humans, with veterinary implications including ear infections in dogs, respiratory diseases in cats, and mastitis in ruminants. In humans, it causes severe hospital-acquired infections, particularly in immunosuppressed patients. This study aimed to identify and assess the prevalence of specific virulence factors in Pseudomonas aeruginosa isolates.

METHODS

We analyzed 98 Pseudomonas aeruginosa isolates from various animal samples (dogs, cats, ruminants, fowl) from northeastern Poland in 2019-2022 for virulence-related genes (toxA, exoU, exoT, exoS, lasB, plcN, plcH, pldA, aprA, gacA, algD, pelA, endA, and oprF) by PCR and assessed biofilm formation at 48 and 72 h. Genomic diversity was assessed by ERIC-PCR.

RESULTS

The obtained results showed that all strains harbored the pelA gene (100%), while the lowest prevalence was found for pldA (24%) and exoU (36%). Regardless of the animal species, strong biofilm forming ability was prevalent among the strains after both 48 h (75%) and 72 h (74%). We obtained as many as 87 different genotyping profiles, where the dominant one was profile ERIC-48, observed in four strains.

CONCLUSIONS

No correlation was found between presence or absence of determined genes and the nature of infection. Similarly, no correlation was found between biofilm-forming genes and biofilm strength. The high genetic diversity indicates challenges for effective prevention, emphasizing the need for ongoing monitoring and research.

Pseudomonas spp. in Canine Otitis Externa

Canine otitis externa (OE) is a commonly diagnosed condition seen in veterinary practice worldwide. In this review, we discuss the mechanisms of the disease, with a particular focus on the biological characteristics of Pseudomonas aeruginosa and the impact that antibiotic resistance has on successful recovery from OE. We also consider potential alternatives to antimicrobial chemotherapy for the treatment of recalcitrant infections. P. aeruginosa is not a typical constituent of the canine ear microbiota, but is frequently isolated from cases of chronic OE, and the nature of this pathogen often makes treatment difficult. Biofilm formation is identified in 40-95% of P. aeruginosa from cases of OE and intrinsic and acquired antibiotic resistance, especially resistance to clinically important antibiotics, highlights the need for alternative treatments. The role of other virulence factors in OE remains relatively unexplored and further work is needed. The studies described in this work highlight several potential alternative treatments, including the use of bacteriophages. This review provides a summary of the aetiology of OE with particular reference to the dysbiosis that leads to colonisation by P. aeruginosa and highlights the need for novel treatments for the future management of P. aeruginosa otitis.

Antimicrobial resistance and genotyping of Pseudomonas aeruginosa isolated from the ear canals of dogs in Japan

The strong bond between dogs and their owners creates a close association that could result in the transfer of antibiotic-resistant bacteria from canines to humans, potentially leading to the spread of antimicrobial resistance genes. Pseudomonas aeruginosa, a common causative agent of persistent ear infections in dogs, is often resistant to multiple antibiotics. Assessing the antimicrobial resistance profile and genotype of P. aeruginosa is crucial for the appropriate use of veterinary pharmaceuticals. However, in recent years, few studies have been conducted on this bacterium in Japan. We determined the antimicrobial resistance profile and genotype of P. aeruginosa isolated from the ear canal of dogs in Japan in 2020. Analysis of antimicrobial resistance using disk diffusion tests indicated a high frequency of resistance to most antimicrobial agents. Particularly, 29 isolates from the ear canals of the 29 affected dogs (100%) were resistant to cefovecin, cefpodoxime, and florfenicol; however, they were susceptible to cefepime and piperacillin/tazobactam. Only 3.4, 10.3, and 10.3% of the isolates were resistant to ceftazidime, tobramycin, and gentamicin, respectively. Furthermore, upon analyzing the population structure using multilocus sequence typing, a considerably large clonal complex was not observed in the tested isolates. Three isolates, namely ST3881, ST1646, and ST532, were clonally related to the clinically isolated sequence types in Japan (such as ST1831, ST1413, ST1812, and ST1849), which is indicative of dog-to-human transmission. Considering the variation in antibiotic resistance compared to that reported by previous studies and the potential risk of dog-to-human transmission, we believe that the survey for antimicrobial resistance profile and population structure should be continued regularly. However, the prevalence of multidrug-resistant P. aeruginosa in dogs in Japan is not a crisis.

Evolution of cyclic di-GMP signalling on a short and long term time scale

Diversifying radiation of domain families within specific lineages of life indicates the importance of their functionality for the organisms. The foundation for the diversifying radiation of the cyclic di-GMP signalling network that occurred within the bacterial kingdom is most likely based in the outmost adaptability, flexibility and plasticity of the system. Integrative sensing of multiple diverse extra- and intracellular signals is made possible by the N-terminal sensory domains of the modular cyclic di-GMP turnover proteins, mutations in the protein scaffolds and subsequent signal reception by diverse receptors, which eventually rewires opposite host-associated as well as environmental life styles including parallel regulated target outputs. Natural, laboratory and microcosm derived microbial variants often with an altered multicellular biofilm behaviour as reading output demonstrated single amino acid substitutions to substantially alter catalytic activity including substrate specificity. Truncations and domain swapping of cyclic di-GMP signalling genes and horizontal gene transfer suggest rewiring of the network. Presence of cyclic di-GMP signalling genes on horizontally transferable elements in particular observed in extreme acidophilic bacteria indicates that cyclic di-GMP signalling and biofilm components are under selective pressure in these types of environments. On a short and long term evolutionary scale, within a species and in families within bacterial orders, respectively, the cyclic di-GMP signalling network can also rapidly disappear. To investigate variability of the cyclic di-GMP signalling system on various levels will give clues about evolutionary forces and discover novel physiological and metabolic pathways affected by this intriguing second messenger signalling system.

Antibiotic Resistant Pseudomonas Spp. Spoilers in Fresh Dairy Products: An Underestimated Risk and the Control Strategies

Microbial multidrug resistance (MDR) is a growing threat to public health mostly because it makes the fight against microorganisms that cause lethal infections ever less effective. Thus, the surveillance on MDR microorganisms has recently been strengthened, taking into account the control of antibiotic abuse as well as the mechanisms underlying the transfer of antibiotic genes (ARGs) among microbiota naturally occurring in the environment. Indeed, ARGs are not only confined to pathogenic bacteria, whose diffusion in the clinical field has aroused serious concerns, but are widespread in saprophytic bacterial communities such as those dominating the food industry. In particular, fresh dairy products can be considered a reservoir of Pseudomonas spp. resistome, potentially transmittable to consumers. Milk and fresh dairy cheeses products represent one of a few "hubs" where commensal or opportunistic pseudomonads frequently cohabit together with food microbiota and hazard pathogens even across their manufacturing processes. Pseudomonas spp., widely studied for food spoilage effects, are instead underestimated for their possible impact on human health. Recent evidences have highlighted that non-pathogenic pseudomonads strains (P. fluorescens, P. putida) are associated with some human diseases, but are still poorly considered in comparison to the pathogen P. aeruginosa. In addition, the presence of ARGs, that can be acquired and transmitted by horizontal genetic transfer, further increases their risk and the need to be deeper investigated. Therefore, this review, starting from the general aspects related to the physiological traits of these spoilage microorganisms from fresh dairy products, aims to shed light on the resistome of cheese-related pseudomonads and their genomic background, current methods and advances in the prediction tools for MDR detection based on genomic sequences, possible implications for human health, and the affordable strategies to counteract MDR spread.

Biofilm production of Pseudomonas spp. isolates from canine otitis in three different enrichment broths

BACKGROUND

Pseudomonas spp. are commonly isolated from dogs with clinical otitis and have been shown to produce biofilm. There is a paucity of studies demonstrating biofilm growth in veterinary medicine.

HYPOTHESIS/OBJECTIVES

To compare biofilm production of Pseudomonas spp. isolated from dogs with otitis using three different enrichment broths at two different time points. Speciation was performed.

ANIMALS

One hundred isolates from 98 dogs with clinical otitis were assessed for biofilm production.

METHODS AND MATERIALS

One hundred isolates were assessed for biofilm production using a microtitre plate assay. Biofilm production in Luria-Bertani Broth (LBB), Mueller-Hinton Broth (MHB) and Tryptic Soy Broth (TSB) were assessed after 18 and 24 h of incubation.

RESULTS

At 18 h, biofilm production was demonstrated in 87% of LBB, 91% of TSB and 93% of MHB grown isolates. By 24 h, this was 92% of LBB, 96% of TSB and 99% of MHB isolates. Biofilm production was significantly increased after 24 h incubation compared to 18 h. A significant difference was noted in biofilm production between LBB and MHB (P = 0.0349), but not between LBB and TSB (P = 0.3727) or MHB and TSB (P = 0.3687) at 24 h incubation. Two isolates were speciated as P. fluorescens and 98 as P. aeruginosa.

CONCLUSION AND CLINICAL IMPORTANCE

Not all enrichment broths were equivalent to one another and 24 h incubation was superior to 18 h. Biofilm production was high in this population of Pseudomonas spp. isolates.