Galleria mellonella larvae exhibit a weight-dependent lethal median dose when infected with methicillin-resistant Staphylococcus aureus

Exploring the virulence potential of Staphylococcus aureus CC121 and CC152 lineages related to paediatric community-acquired bacteraemia in Manhiça, Mozambique

Staphylococcus aureus is a frequent agent of bacteraemia. This bacterium has a variety of virulence traits that allow the establishment and maintenance of infection. This study explored the virulence profile of S. aureus strains causing paediatric bacteraemia (SAB) in Manhiça district, Mozambique. We analysed 336 S. aureus strains isolated from blood cultures of children younger than 5 years admitted to the Manhiça District Hospital between 2001 and 2019, previously characterized for antibiotic susceptibility and clonality. The strains virulence potential was evaluated by PCR detection of the Panton-Valentine leucocidin (PVL) encoding genes, lukS-PV/lukF-PV, assessment of the capacity for biofilm formation and pathogenicity assays in Galleria mellonella. The overall carriage of PVL-encoding genes was over 40%, although reaching ~ 70 to 100% in the last years (2014 to 2019), potentially linked to the emergence of CC152 lineage. Strong biofilm production was a frequent trait of CC152 strains. Representative CC152 and CC121 strains showed higher virulence potential in the G. mellonella model when compared to reference strains, with variations within and between CCs. Our results highlight the importance of monitoring the emergent CC152-MSSA-PVL+ and other lineages, as they display important virulence traits that may negatively impact the management of SAB paediatric patients in Manhiça district, Mozambique.

Environment-host-parasite interactions in mass-reared insects

The mass production of insects is rapidly expanding globally, supporting multiple industrial needs. However, parasite infections in insect mass-production systems can lower productivity and can lead to devastating losses. High rearing densities and artificial environmental conditions in mass-rearing facilities affect the insect hosts as well as their parasites. Environmental conditions such as temperature, gases, light, vibration, and ionizing radiation can affect productivity in insect mass-production facilities by altering insect development and susceptibility to parasites. This review explores the recent literature on environment-host-parasite interactions with a specific focus on mass-reared insect species. Understanding these complex interactions offers opportunities to optimise environmental conditions for the prevention of infectious diseases in mass-reared insects.

Galleria mellonella-A Model for the Study of aPDT-Prospects and Drawbacks

Galleria mellonella is a promising in vivo model insect used for microbiological, medical, and pharmacological research. It provides a platform for testing the biocompatibility of various compounds and the kinetics of survival after an infection followed by subsequent treatment, and for the evaluation of various parameters during treatment, including the host-pathogen interaction. There are some similarities in the development of pathologies with mammals. However, a limitation is the lack of adaptive immune response. Antimicrobial photodynamic therapy (aPDT) is an alternative approach for combating microbial infections, including biofilm-associated ones. aPDT is effective against Gram-positive and Gram-negative bacteria, viruses, fungi, and parasites, regardless of whether they are resistant to conventional treatment. The main idea of this comprehensive review was to collect information on the use of G. mellonella in aPDT. It provides a collection of references published in the last 10 years from this area of research, complemented by some practical experiences of the authors of this review. Additionally, the review summarizes in brief information on the G. mellonella model, its advantages and methods used in the processing of material from these larvae, as well as basic knowledge of the principles of aPDT.

Wssv susceptibility in the early life stages of penaeus vannamei shows relationship with bodyweight

White Spot Syndrome Virus (WSSV) continues to cause considerable loss to shrimp farmers globally with frequent outbreaks even in specific pathogen free Peneaus vannamei. Our studies showed that the bodyweight (BW) of PL has a bearing on their susceptibility to the virus. To test this hypothesis, PL of the same age group and family were grouped according to BW (10-20, 30-40, and 50-60 mg) and challenged through immersion route with two viral doses (10⁶ and 10⁷ virus copies/L of water). It was observed that the PL became susceptible to WSSV at ≥50 mg BW. In the 50-60 mg PL group, the higher challenge dose shows a sharp mortality curve with 100% mortality at 10 days post immersion, while the lower dose shows a steady increase in cumulative mortality that reaches 100% on the 13^th day post immersion. The study also brings out that an in vivo viral load of approximately 3.5 to 4.5×10⁷WSSV copies/100 ng shrimp DNA results in mortality. This is the first report on the relationship between BW and WSSV susceptibility in shrimp PL. Also reported here is a quantitative assessment of WSSV infection in P. vannamei PL and an optimized challenge protocol.

Antibiofilm Activities of Borneol-Citral-Loaded Pickering Emulsions against Pseudomonas aeruginosa and Staphylococcus aureus in Physiologically Relevant Chronic Infection Models

Phytochemicals are promising antibacterials for the development of novel antibiofilm drugs, but their antibiofilm activity in physiologically relevant model systems is poorly characterized. As the host microenvironment can interfere with the activity of the phytochemicals, mimicking the complex environment found in biofilm associated infections is essential to predict the clinical potential of novel phytochemical-based antimicrobials. In the present study, we examined the antibiofilm activity of borneol, citral, and combinations of both as well as their Pickering emulsions against Staphylococcus aureus and Pseudomonas aeruginosa in an in vivo-like synthetic cystic fibrosis medium (SCFM2) model, an in vitro wound model (consisting of an artificial dermis and blood components at physiological levels), and an in vivo Galleria mellonella model. The Pickering emulsions demonstrated an enhanced biofilm inhibitory activity compared to both citral and the borneol/citral combination, reducing the minimum biofilm inhibitory concentration (MBIC) values up to 2 to 4 times against P. aeruginosa PAO1 and 2 to 8 times against S. aureus P8-AE1 in SCMF2. In addition, citral, the combination borneol/citral, and their Pickering emulsions can completely eliminate the established biofilm of S. aureus P8-AE1. The effectiveness of Pickering emulsions was also demonstrated in the wound model with a reduction of up to 4.8 log units in biofilm formation by S. aureus Mu50. Furthermore, citral and Pickering emulsions exhibited a significant degree of protection against S. aureus infection in the G. mellonella model. The present findings reveal the potential of citral- or borneol/citral-based Pickering emulsions as a type of alternative antibiofilm candidate to control pathogenicity in chronic infection. IMPORTANCE There is clearly an urgent need for novel formulations with antimicrobial and antibiofilm activity, but while there are plenty of studies investigating them using simple in vitro systems, there is a lack of studies in which (combinations of) phytochemicals are evaluated in relevant models that closely resemble the in vivo situation. Here, we examined the antibiofilm activity of borneol, citral, and their combination as well as Pickering emulsions (stabilized by solid particles) of these compounds. Activity was tested against Staphylococcus aureus and Pseudomonas aeruginosa in in vitro models mimicking cystic fibrosis sputum and wounds as well as in an in vivo Galleria mellonella model. The Pickering emulsions showed drastically increased antibiofilm activity compared to that of the compounds as such in both in vitro models and protected G. mellonella larvae from S. aureus-induced killing. Our data show that Pickering emulsions from phytochemicals are potentially useful for treating specific biofilm-related chronic infections.

Hospital sink traps as a potential source of the emerging multidrug-resistant pathogen Cupriavidus pauculus: characterization and draft genome sequence of strain MF1

Introduction.Cupriavidus pauculus is historically found in soil and water but has more recently been reported to cause human infection and death. Hospital sink traps can serve as a niche for bacterial persistence and a platform for horizontal gene transfer, with evidence of dissemination of pathogens in hospital plumbing systems driving nosocomial infection.

Gap Statement. This paper presents the first C. pauculus strain isolated from a hospital sink trap. There are only six genome assemblies available on NCBI for C. pauculus; two of these are PacBio/Illumina hybrids. This paper presents the first ONT/Illumina hybrid assembly, with five contigs. The other assemblies available consist of 37, 38, 111 and 227 contigs. This paper also presents data on biofilm formation and lethal dose in Galleria mellonella; there is little published information describing these aspects of virulence.

Aim. The aims were to identify the isolate found in a hospital sink trap, characterize its genome, and assess whether it could pose a risk to human health.

Methodology. The genome was sequenced, and a hybrid assembly of short and long reads produced. Antimicrobial susceptibility was determined by the broth microdilution method. Virulence was assessed by measuring in vitro biofilm formation compared to Pseudomonas aeruginosa and in vivo lethality in Galleria mellonella larvae.

Results. The isolate was confirmed to be a strain of C. pauculus, with a 6.8 Mb genome consisting of 6468 coding sequences and an overall G+C content of 63.9 mol%. The genome was found to contain 12 antibiotic resistance genes, 8 virulence factor genes and 33 metal resistance genes. The isolate can be categorized as resistant to meropenem, amoxicillin, amikacin, gentamicin and colistin, but susceptible to cefotaxime, cefepime, imipenem and ciprofloxacin. Clear biofilm formation was seen in all conditions over 72 h and exceeded that of P. aeruginosa when measured at 37 °C in R2A broth. Lethality in G. mellonella larvae over 48 h was relatively low.

Conclusion. The appearance of a multidrug-resistant strain of C. pauculus in a known pathogen reservoir within a clinical setting should be considered concerning. Further work should be completed to compare biofilm formation and in vivo virulence between clinical and environmental strains, to determine how easily environmental strains may establish human infection. Infection control teams and clinicians should be aware of the emerging nature of this pathogen and further work is needed to minimize the impact of contaminated hospital plumbing systems on patient outcomes.

Nutraceutical intervention protects against bacterial and chemical-induced gastrotoxicity in a non-mammalian model, Galleria mellonella

Preparations of the fungus Cordyceps sinensis and bovine colostrum are considered nutraceuticals due to their anti-inflammatory, repair and gut alimentation properties in mammalian models. To reduce the reliance on rodents in routine experimentation, we gauged the capacity of nutraceuticals to alleviate gastric damage in an insect surrogate, Galleria mellonella. Larvae were reared on standard or supplemented diets - 10% (w/w) colostrum, 10% (w/w) C. sinensis, or 5% + 5% each - prior to receiving an oral dose of the NSAID indomethacin (30 mg/kg) or challenged with the bacterial pathogen Campylobacter jejuni (1-3 x10⁶) via two inoculation routes. Insects reared on a cordyceps-supplemented diet proved most resistant to indomethacin-induced gut leakiness, and displayed stable health indices after C. jejuni challenge (~77% survival). Insects reared on a colostrum-supplemented diet also showed recalcitrance in the gut, but were more sensitive to C. jejuni when injected directly into the body cavity (50% survival). The nutraceutical blend yielded improved health outcomes when compared to the standard diet, but was not as effective as either nutraceutical alone. Our findings represent clear evidence that insects were more resistant to known chemical and microbial agitators when reared on nutraceutical-supplemented diets - toxicological endpoints that are shared with vertebrate studies.