Do maggots have an influence on bacterial growth? A study on the susceptibility of strains of six different bacterial species to maggots of Lucilia sericata and their excretions/secretions

In vitro antibacterial activity and synergetic effect of crude extract of the Wohlfahrtia nuba (Diptera: Sarcophagidae) flesh fly larvae

Multidrug-resistant pathogens have become ubiquitous, and effective treatment alternatives are urgently required. Maggot therapy is a promising agent that is being studied to overcome antibiotic-resistant pathogens. This study evaluated the antibacterial activity of the larvae extract of the Wohlfahrtia nuba (wiedmann) (Diptera: Sarcophagidae) flesh fly on the growth of five pathogenic bacterial species (methicillin-sensitive Staphylococcus aureus [ATCC 29213], methicillin-resistant Staphylococcus aureus [ATCC BAA-1680], Pseudomonas aeruginosa [ATCC 27853], Escherichia coli [ATCC 25922], and Salmonella typhi [ATCC 19430]) in vitro by using different techniques. Resazurin-based turbidimetric assay demonstrated that the W. nuba maggot exosecretion (ES) was potent against all the bacterial species tested, and according to the determined minimum inhibitory concentration (MIC) for each bacterium, gram-negative bacteria were more sensitive than gram-positive bacteria. Additionally, colony-forming unit assay showed that maggot ES was able to inhibit bacterial growth rate for all bacterial species tested, where the highest bacterial reduction was observed with methicillin-sensitive S. aureus (MSSA) followed by S. typhi. Moreover, maggot ES was shown to be concentration-dependent, where 100 μL of ES at 200 mg/mL was bactericidal towards methicillin-resistant S. aureus (MRSA) and P. aeruginosa compared with 100 μL at the MIC of the ES. Moreover, based on the result of agar disc diffusion assay, maggot extract was more efficient against P. aeruginosa and E. coli than the remaining reference strains tested. Furthermore, the combination between regular antibiotics with maggot ES at different concentrations indicated that ES acts synergistically with the tested antibiotics against the five bacterial models.

The devil is in the details: Variable impacts of season, BMI, sampling site temperature, and presence of insects on the post-mortem microbiome

Background

Post-mortem microbial communities are increasingly investigated as proxy evidence for a variety of factors of interest in forensic science. The reported predictive power of the microbial community to determine aspects of the individual's post-mortem history (e.g., the post-mortem interval) varies substantially among published research. This observed variation is partially driven by the local environment or the individual themselves. In the current study, we investigated the impact of BMI, sex, insect activity, season, repeat sampling, decomposition time, and temperature on the microbial community sampled from donated human remains in San Marcos, TX using a high-throughput gene-fragment metabarcoding approach.

Materials and methods

In the current study, we investigated the impact of BMI, sex, insect activity, season, repeat sampling, decomposition time, and temperature on the microbial community sampled from donated human remains in San Marcos, TX using a high-throughput gene-fragment metabarcoding approach.

Results

We found that season, temperature at the sampling site, BMI, and sex had a significant effect on the post-mortem microbiome, the presence of insects has a homogenizing influence on the total bacterial community, and that community consistency from repeat sampling decreases as the decomposition process progresses. Moreover, we demonstrate the importance of temperature at the site of sampling on the abundance of important diagnostic taxa.

Conclusion

The results of this study suggest that while the bacterial community or specific bacterial species may prove to be useful for forensic applications, a clearer understanding of the mechanisms underpinning microbial decomposition will greatly increase the utility of microbial evidence in forensic casework.

Anti-inflammatory and wound healing potential of medicinal maggot excretions/secretions at the ocular surface

PURPOSE

In the skin, Lucilia sericata maggot excretions/secretions (ES) accelerate wound healing and limit inflammation. This study aimed to determine whether ES have similar beneficial effects at the ocular surface.

METHODS

Human corneal epithelial cells (HCEC) were cultured with ES and cell viability was determined by the MTT assay. Additionally, mRNA expression of growth factors, antimicrobial peptides (AMPs) and cytokines was assessed by qPCR. ES ability to modulate TLR-induced IL-6 and IL-8 expression was determined by qPCR and ELISA. ES potential to promote corneal healing was evaluated in vitro by a migration assay in HCEC, and in vivo using a mouse model.

RESULTS

ES did not impair HCEC viability up to 25 μg/ml. Among the factors evaluated, only hBD-2 was upregulated (2.5-fold) by 1.5 μg/ml ES after 6 hrs (P = 0.04). In HCEC, ES reduced Poly I:C-induced IL-6 and IL-8 mRNA (P ≤ 0.001) and protein (P ≤ 0.0001) expression. A similar effect was observed with Flagellin (TLR5 agonist) but it was less robust for FSL-1 (TLR2/6 agonist) and Pam3CSK4 (TLR1/2 agonist). The greatest in vitro migration effect was observed with 6.2 μg/ml ES after 44 hrs where gap area compared to vehicle was 53.3 ± 3.7% vs. 72.6 ± 5.4% (P = 0.001). In the mouse model, the maximum healing effect was present with 1.5 μg/ml ES after 12 hrs with a wound area of 19.0 ± 2.7% vs. 60.1 ± 21.6% (P = 0.003) or 77% reduction of the wound area compared to the negative control.

CONCLUSIONS

ES significantly reduce in vitro TLR-induced production of inflammatory cytokines and promote corneal wound healing.

Maggot Extract Interrupts Bacterial Biofilm Formation and Maturation in Combination with Antibiotics by Reducing the Expression of Virulence Genes

Biofilms are aggregates of bacteria encased in an extracellular polymer matrix that acts as a diffusion barrier protecting the microbial community. Bacterial communication occurs by small signaling molecules called quorum sensing (QS) factors, which are involved in the activation of virulence genes and formation of biofilms. Larvae of the green bottle blowfly Lucilia sericata remove necrotic tissue by mechanical action (debridement) and proteolytic digestion. We produced a freeze-dried storable powder from larval extract and investigated its therapeutic effect on biofilms. Larval extract in concentrations of 6 and 12 mg/mL in combination with 0.5% antibiotics (≙50 U/mL penicillin and 50 μg/mL streptomycin) diminished free-floating (planktonic) Pseudomonas aeruginosa maintenance, while it showed no effect on Staphylococcus aureus and was not toxic to dermal cells. We established an ex vivo human dermal wound model. Larval extract in concentrations of 24 and 75 mg/mL in the presence of antibiotics (0.5%) significantly destroyed the biofilm stability of both P. aeruginosa and S. aureus biofilms. Furthermore, SEM analyses revealed crack and gap formations on P. aeruginosa. biofilm surface and decreased expression of P. aeruginosa biofilm maturation and virulence genes (lasR, rhlR and rhlA) was observed after treatment by larval extract in combination with antibiotics.

Bactericidal Activity of Chrysomya rufifacies and Cochliomyia macellaria (Diptera: Calliphoridae) Larval Excretions-Secretions Against Staphylococcus aureus (Bacillales: Staphylococcaceae)

The inhibitory effect of Chrysomya rufifacies (Macquart) and Cochliomyia macellaria (Fabricius) larval excretions-secretions (ES) on Staphylococcus aureus was determined using a portable colorimetric method without the need for any dedicated spectral instrument. Polystyrene 96 well microplates were used and 100 μl of the bacterial inoculum (5 × 105 CFU/ml) plus 100 μl of the dipteran exosecretions at different concentrations were added to each well. Subsequently, 50 μl of a 1% solution of the triphenyl tetrazolium chloride stain was added to each well to determine the bacterial viability. The color development in each well was measured with the ImageJ software S. aureus was exposed to different concentrations of the ES of both species individually. At a concentration of 800 ppm ES of C. rufifacies or Co. macellaria, bacterial growth was inhibited 97.45 ± 1.70% and 82.21 ± 1.88%, respectively. As expected, exposure to a lower concentration (i.e., 50 ppm) was less inhibitory (C. rufifacies ES, 77.65 ± 4.25% and Co. macellaria ES, 43.54 ± 4.63%). This study demonstrates for the first time the bactericidal activity of C. rufifacies and Co. macellaria ES against S. aureus. This finding is promising as it could result in the identification and synthesis of proteins capable of suppressing pathogen development in wounds. Additionally, the proposed method can simplify the use of expensive laboratory instruments for antimicrobial activity determination.

Advanced drug delivery systems and artificial skin grafts for skin wound healing

Cutaneous injuries, especially chronic wounds, burns, and skin wound infection, require painstakingly long-term treatment with an immense financial burden to healthcare systems worldwide. However, clinical management of chronic wounds remains unsatisfactory in many cases. Various strategies including growth factor and gene delivery as well as cell therapy have been used to enhance the healing of non-healing wounds. Drug delivery systems across the nano, micro, and macroscales can extend half-life, improve bioavailability, optimize pharmacokinetics, and decrease dosing frequency of drugs and genes. Replacement of the damaged skin tissue with substitutes comprising cell-laden scaffold can also restore the barrier and regulatory functions of skin at the wound site. This review covers comprehensively the advanced treatment strategies to improve the quality of wound healing.

Decomposition of biowaste macronutrients, microbes, and chemicals in black soldier fly larval treatment: A review

Processing of biowaste with larvae of the black soldier fly, Hermetia illucens L. (Diptera: Stratiomyidae), is an emerging waste treatment technology. Larvae grown on biowaste can be a relevant raw material for animal feed production and can therefore provide revenues for financially viable waste management systems. In addition, when produced on biowaste, insect-based feeds can be more sustainable than conventional feeds. Among others, the scalability of the technology will depend on the availability of large amounts of biowaste with a high process performance (e.g. bioconversion of organic matter to proteins and lipids) and microbial and chemical product safety. Currently, in contrast to other waste treatment technologies, such as composting or anaerobic digestion, the process performance is variable and the processes driving the decomposition of biowaste macronutrients, inactivation of microbes and fate of chemicals is poorly understood. This review presents the first summary of the most important processes involved in black soldier fly larvae (BSFL) treatment, based on the available knowledge concerning five well-studied fly species. This is a starting point to increase understanding regarding the processes of this technology, with the potential to increase its efficiency and uptake, and support the development of appropriate regulations. Based on this review, formulating different types of biowaste, e.g. to produce a diet with a similar protein content, a balanced amino acid profile and/or pre- and co-treatment of biowaste with beneficial microbes, has the potential to increase process performance. Following harvest, larvae require heat or other treatments for microbial inactivation and safety.

Sarconesin: Sarconesiopsis magellanica Blowfly Larval Excretions and Secretions With Antibacterial Properties

Larval therapy (LT) is an alternative treatment for healing chronic wounds; its action is based on debridement, the removal of bacteria, and stimulating granulation tissue. The most important mechanism when using LT for combating infection depends on larval excretions and secretions (ES). Larvae are protected against infection by a spectrum of antimicrobial peptides (AMPs); special interest in AMPs has also risen regarding understanding their role in wound healing since they degrade necrotic tissue and kill different bacteria during LT. Sarconesiopsis magellanica (Diptera: Calliphoridae) is a promising medically-important necrophagous fly. This article reports a small AMP being isolated from S. magellanica ES products for the first time; these products were obtained from third-instar larvae taken from a previously-established colony. ES were fractionated by RP-HPLC using C18 columns for the first analysis; the products were then lyophilised and their antimicrobial activity was characterized by incubation with different bacterial strains. These fractions' primary sequences were determined by mass spectrometry and de novo sequencing; five AMPs were obtained, the Sarconesin fraction was characterized and antibacterial activity was tested in different concentrations with minimum inhibitory concentrations starting at 1.2 μM. Potent inhibitory activity was shown against Gram-negative (Escherichia coli D31, E. coli DH5α, Salmonella enterica ATCC 13314, Pseudomonas aeruginosa 27853) and Gram-positive (Staphylococcus aureus ATCC 29213, S. epidermidis ATCC 12228, Micrococcus luteus A270) bacteria. Sarconesin has a significant similarity with Rho-family GTPases which are important in organelle development, cytoskeletal dynamics, cell movement, and wound repair. The data reported here indicated that Sarconesin could be an alternative candidate for use in therapeutics against Gram-negative and Gram-positive bacterial infections. Our study describes one peptide responsible for antibacterial activity when LT is being used. The results shown here support carrying out further experiments aimed at validating S. magellanica AMPs as novel resources for combating antibacterial resistance.

Nonconsumptive Effects of Predatory Chrysomya rufifacies (Diptera: Calliphoridae) Larval Cues on Larval Cochliomyia macellaria (Diptera: Calliphoridae) Growth and Development

Forensic entomologists often rely on development data associated with a given species to estimate when it colonized human or other vertebrate remains. In most instances, these development studies are based on single species reared in isolation in the laboratory. This study examined the impact of excretions and secretions (ES) associated with third-instar Chrysomya rufifacies (Macquart), a predator, on the development of its prey, Cochliomyia macellaria (F.). Not surprisingly, Ch. rufifacies ES did not impact the development of first- or second-instar C. macellaria, which are typically not preyed on by Ch. rufifacies. However, development of third-instar C. macellaria, which do experience predation, was impacted. First, larvae were longer than those in the control (deionized water, dH2O). Filtering the ES and removing the associated bacteria and byproducts >0.2 µm dampened the previous impact observed by the unfiltered ES on third-instar C. macellaria. Second, third-instar C. macellaria treated with unfiltered ES completed pupariation 8 h quicker than the controls. Filtering the ES lessened this effect by 50%. And finally, third-instar C. macellaria treated with filtered or unfiltered Ch. rufifacies ES reached adulthood ∼5 h faster than controls treated with dH2O. In summary, these data have large ramifications for forensic entomology, as multiple species being present on decomposing remains is not uncommon. Understanding the impact of associated ES produced by interspecific cohorts on associated development could lead to more precise estimates of the minimum postmortem interval for forensic investigation of decomposing remains.

First Record of Larval Secretions of Cochliomyia macellaria (Fabricius, 1775) (Diptera: Calliphoridae) Inhibiting the Growth of Staphylococcus aureus and Pseudomonas aeruginosa

Maggot debridement therapy (MDT) consists on the intentional and controlled application of sterilized larvae of the order Diptera on necrotic skin lesions with the purpose of cleaning necrotic tissue and removing pathogenic bacteria. During MDT, a marked antimicrobial activity has been reported in literature specially associated with antibacterial substances from Lucilia sericata (Meigen); however, regarding Cochliomyia macellaria (Fabricius), little is known. This study aimed to evaluate in vitro inhibition of bacterial growth of Pseudomonas aeruginosa and Staphylococcus aureus in contact with excretions and secretions (ES) from C. macellaria larvae. Larval ES were extracted in sterile distilled water and divided in three groups: ES, containing 400 μL of autoclaved ES; ES+BAC, containing 400 μL of autoclaved ES+0.5-μL bacterial inoculum; and CONT-BAC, containing 400 μL of sterile distilled water +0.5 μL of bacterial inoculum. Aliquots of each experimental group were plated by spreading onto Petri dishes. Seedings were made at 0, 1, 2, 4, and 12 h after the extraction of ES. In ES+BAC groups, inhibition of S. aureus was verified between times 1 and 2 h and P. aeruginosa was inhibited between 0 and 4 h. There was no growth observed in any ES group. In the CONT-BAC groups, the number of colonies from time 4 h became countless for S. aureus and decreased for P. aeruginosa. As reported in the literature, we note here that ES have excellent bactericidal activity for both gram-positive and gram-negative bacteria, and this study shows for the first time the action of the bactericidal activity of exosecretions of C. macellaria against S. aureus and P. aeruginosa.

Evaluating Sarconesiopsis magellanica blowfly-derived larval therapy and comparing it to Lucilia sericata-derived therapy in an animal model

Larval therapy is used as alternative treatment for hard-to-heal chronic and infected wounds. Lucilia sericata is the most used blowfly species. However, it has been shown recently that Sarconesiopsis magellanica larval excretions and secretions have potent antibacterial activity; this blowfly belongs to the Calliphoridae family. The present work has dealt with evaluating larval therapy using S. magellanica on wounds induced in diabetic rabbits and its action was compared to the effect induced by L. sericata. Twelve New Zealand White rabbits (Oryctolagus cuniculus) were used; they were divided into 4 groups, the first two being treated with larval therapy derived from both aforementioned necrophagous blowflies, an antibiotic was used in the third and the fourth was used as control. All the animals were wounded on the back and infected with Pseudomonas aeruginosa and Staphylococcus aureus. Samples of the secretion from each animal's infected wound were taken and sown on blood agar. The colony forming units were then counted. The PUSH scale was used for the macroscopic evaluation of the wounds. Bacterial control was encountered 48 h post-treatment in the treatments involving larval therapy and to a lesser extent with the antibiotic. Likewise, wound debridement was quicker and more efficient with larval therapy compared to the antibiotic group; however, wound closing time was 23 days in all treatments. The group treated with S. magellanica larvae had relatively quicker evolution until the proliferation phase and the start of maturation, even though there were no significant differences between both blowfly species evaluated here regarding treatments by the end of the treatment period. The present study has validated the diabetic rabbit model for inducing chronic wounds regarding larval therapy and has likewise confirmed the effectiveness of S. magellanica-derived larval therapy as an alternative for curing and healing wounds.

Selection and Evaluation of Tissue Specific Reference Genes in Lucilia sericata during an Immune Challenge

The larvae of the common green bottle fly Lucilia sericata (Diptera: Calliphoridae) have been used for centuries to promote wound healing, but the molecular basis of their antimicrobial, debridement and healing functions remains largely unknown. The analysis of differential gene expression in specific larval tissues before and after immune challenge could be used to identify key molecular factors, but the most sensitive and reproducible method qRT-PCR requires validated reference genes. We therefore selected 10 candidate reference genes encoding products from different functional classes (18S rRNA, 28S rRNA, actin, β-tubulin, RPS3, RPLP0, EF1α, PKA, GAPDH and GST1). Two widely applied algorithms (GeNorm and Normfinder) were used to analyze reference gene candidates in different larval tissues associated with secretion, digestion, and antimicrobial activity (midgut, hindgut, salivary glands, crop and fat body). The Gram-negative bacterium Pseudomonas aeruginosa was then used to boost the larval immune system and the stability of reference gene expression was tested in comparison to three immune genes (lucimycin, defensin-1 and attacin-2), which target different pathogen classes. We observed no differential expression of the antifungal peptide lucimycin, whereas the representative targeting Gram-positive bacteria (defensin-1) was upregulated in salivary glands, crop, nerve ganglion and reached its maximum in fat body (up to 300-fold). The strongest upregulation in all immune challenged tissues (over 50,000-fold induction in the fat body) was monitored for attacin-2, the representative targeting Gram-negative bacteria. Here we identified and validated a set of reference genes that allows the accurate normalization of gene expression in specific tissues of L. sericata after immune challenge.

A metagenomic assessment of the bacteria associated with Lucilia sericata and Lucilia cuprina (Diptera: Calliphoridae)

Lucilia Robineau-Desvoidy (Diptera: Calliphoridae) is a blow fly genus of forensic, medical, veterinary, and agricultural importance. This genus is also famous because of its beneficial uses in maggot debridement therapy (MDT). Although the genus is of considerable economic importance, our knowledge about microbes associated with these flies and how these bacteria are horizontally and trans-generationally transmitted is limited. In this study, we characterized bacteria associated with different life stages of Lucilia sericata (Meigen) and Lucilia cuprina (Wiedemann) and in the salivary gland of L. sericata by using 16S rDNA 454 pyrosequencing. Bacteria associated with the salivary gland of L. sericata were also characterized using light and transmission electron microscopy (TEM). Results from this study suggest that the majority of bacteria associated with these flies belong to phyla Proteobacteria, Firmicutes, and Bacteroidetes, and most bacteria are maintained intragenerationally, with a considerable degree of turnover from generation to generation. In both species, second-generation eggs exhibited the highest bacterial phylum diversity (20 % genetic distance) than other life stages. The Lucilia sister species shared the majority of their classified genera. Of the shared bacterial genera, Providencia, Ignatzschineria, Lactobacillus, Lactococcus, Vagococcus, Morganella, and Myroides were present at relatively high abundances. Lactobacillus, Proteus, Diaphorobacter, and Morganella were the dominant bacterial genera associated with a survey of the salivary gland of L. sericata. TEM analysis showed a sparse distribution of both Gram-positive and Gram-negative bacteria in the salivary gland of L. sericata. There was more evidence for horizontal transmission of bacteria than there was for trans-generational inheritance. Several pathogenic genera were either amplified or reduced by the larval feeding on decomposing liver as a resource. Overall, this study provides information on bacterial communities associated with different life stages of Lucilia and their horizontal and trans-generational transmission, which may help in the development of better vector-borne disease management and MDT methods.

Sarconesiopsis magellanica (Diptera: Calliphoridae) excretions and secretions have potent antibacterial activity

The most important mechanism for combating infection using larval therapy depends on larval excretions and secretions (ES). The present work was aimed at evaluating Sarconesiopsis magellanica (Diptera: Calliphoridae) ES antibacterial activity in six bacterial strains (three Gram-positive and three Gram-negative) and comparing this to the effect of Lucilia sericata-derived ES. Antibacterial activity at 50μg/mL minimum inhibitory concentration (MIC) was observed for Staphylococcus epidermidis ATCC-12228 and Staphylococcus aureus ATCC-29213 strains, when the turbidimetry test involving S. magellanica ES was used; the rest of the bacterial strains (Staphylococcus aureus ATCC-6538, Pseudomonas aeruginosa ATCC-10145, Pseudomonas aeruginosa ATCC-9027 and Pseudomonas aeruginosa ATCC-27853) were inhibited at a 100μg/mL MIC. Twice the amount was required to inhibit the aforementioned bacteria with L. sericata-derived ES using this same technique; a similar trend was observed when the agar diffusion method was used instead. Furthermore, when the previously established MIC for each bacterial strain was used, their colonies became reduced following 1-6h incubation with S. magellanica derived ES, whilst the reduction occurred from 2 to 6hours with those from L. sericata. Although the MIC for each strain obtained with ciprofloxacin was lower than those established when using either blowfly derived-ES, the gradual reduction of the colonies occurred at a longer incubation time (6h or more). The results showed that S. magellanica ES antibacterial activity was more potent and effective, compared to that of L. sericata-derived ES.

Sterilization of Chrysomya putoria (Insecta: Diptera: Calliphoridae) eggs for use in biotherapy

Large-scale, quality-controlled laboratory production of fly larvae is needed for biotherapy. The objective of this study was to assess the action of glutaraldehyde on the sterilization of Chrysomya putoria eggs by applying pharmaceutical sterility tests. Egg masses with 0.600 g were divided into three parts of 0.200 g, the eggs were separated using sterile distilled water, and the suspensions obtained were mixed with activated 2% glutaraldehyde solution. After 15-min contact, the suspensions were filtered through Whatman filter paper, and the glutaraldehyde residue obtained in the filtrate was neutralized by rinsing with Tryptone Soy Broth. The treated eggs were placed aseptically on Petri dishes containing gauze moistened with sterile saline solution. About 10% of the sterilized mass was transferred to test tubes containing Tryptone Soy Broth and Fluid Thioglycollate Broth. The tubes were incubated, respectively, at 22.5 and 35.0°C for 14 d to verify egg mass sterility. The plates containing the rest of the eggs (90%) were sealed with plastic film and kept in a climatized chamber at 30°C/d, 28°C per night, 60 ± 10% relative humidity, and under a 12-h light period to assess insect viability and survival. Each experiment was carried out in triplicate using a biological class II safety cabinet. No change in color or turgidity was observed with the agent tested, proving the sterility of the product and that there was no trace of contamination. Forty larvae (in three replications) in the periods of 12, 24, and 48 h after sterilization, when transferred to diet, produced larvae, pupae, and total viability similar to the control (larvae without sterilization). However, for the 72-h treatment, larvae and total viability were significantly lower than for the other treatments. There was no significant difference for the pupal stage. The product tested was shown to be efficacious for use as a sterilizer of C. putoria eggs for all the parameters assessed.

Proteolytic activity regarding Sarconesiopsis magellanica (Diptera: Calliphoridae) larval excretions and secretions

Sarconesiopsis magellanica (Diptera: Calliphoridae) is a medically important necrophagous fly which is used for establishing the post-mortem interval. Diptera maggots release proteolytic enzymes contained in larval excretion and secretion (ES) products playing a key role in digestion. Special interest in proteolytic enzymes has also been aroused regarding understanding their role in wound healing since they degrade necrotic tissue during larval therapy. This study was thus aimed at identifying and characterising S. magellanica proteolytic enzyme ES products for the first time. These products were obtained from first-, second- and third-instar larvae taken from a previously-established colony. ES proteins were separated by SDS-PAGE and their proteolytic activity was characterised by zymograms and inhibition assays involving BAPNA (Nα-benzoyl-dl-Arg-p-nitroanilide) and SAPNA substrates, using synthetic inhibitors. The protein profile ranged from ∼69kDa to ∼23kDa; several of them coincided with the Lucilia sericata ES protein profile. Serine-protease hydrolysis activity (measured by zymogram) was confirmed when a ∼25kDa band disappeared upon ES incubation with PMSF inhibitor at pH 7.8. Analysis of larval ES proteolytic activity on BAPNA and SAPNA substrates (determined by using TLCK and TPCK specific inhibitors) suggested a greater amount of trypsin-like protease. These results support the need for further experiments aimed at validating S. magellanica use in larval therapy.

Antibacterial potency of housefly larvae extract from sewage sludge through bioconversion

Use of the fly to convert sewage sludge into nutrient-rich soil conditioner and amendment is an attractive approach for sludge bioconversion. During this process, fecal coliforms, an indicating pathogen, in sludge were reduced to 5.3 x 10(2) most probable number/g dry solid from initial 3.32 x 10(6) MPN/g dry solid. It was also found that the extract of larvae grown in sludge during bioconversion have an observable inhibitory effect against bacteria compared to larvae grown in wheat bran as measured by minimum bacterial concentration tests. In vitro antimicrobial assay tests over time also showed that the extract had strong inhibitory efficiencies of ca. 99% against Bacillus cereus, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Serratia marcescens, while the efficiency was 69% and 57% against Bacillus subtilis and Klebsiella pneumoniae, respectively. The observed pathogenic bacterial cell membrane damage was found to be responsible for the phenomenon mentioned above, with nuclear acids leaching out quickly and alkaline phosphatase increasing in the outer membrane, followed by an increase of beta-galactosidase in the inner membrane. Clearly, housefly larvae extract from sewage sludge through bioconversion possesses antibacterial potency against pathogenic bacteria.

Evidence-based topical management of chronic wounds according to the T.I.M.E. principle

The number of patients suffering from chronic wound healing disorders in Germany alone is estimated to be 2.5-4 million. Therapy related expenses reach 5-8 billion Euros annually. This number is partially caused by costly dressing changes due to non-standardized approaches and the application of non-evidence-based topical wound therapies. The purpose of this paper is to elucidate a straightforward principle for the management of chronic wounds, and to review the available evidence for the particular therapy options. The T.I.M.E.-principle (Tissue management, Inflammation and infection control, Moisture balance, Epithelial [edge] advancement) was chosen as a systematic strategy for wound bed preparation. Literature was retrieved from the PubMed and Cochrane Library databases and subjected to selective analysis. Topical wound management should be carried out according to a standardized principle and should further be synchronized to the phases of wound healing. Despite the broad implementation of these products in clinical practice, often no benefit exists in the rate of healing, when evaluated in meta-analyses or systematic reviews. This insufficient evidence is additionally limited by varying study designs. In case of non-superiority, the results suggest to prefer relatively inexpensive wound dressings over expensive alternatives. Arbitrary endpoints to prove the effectiveness of wound dressings, contribute to the random use of such therapies. Defining rational endpoints for future studies as well as the deployment of structured therapy strategies will be essential for the economical and evidence-based management of chronic wounds.

Complement activation and inhibition in wound healing

Complement activation is needed to restore tissue injury; however, inappropriate activation of complement, as seen in chronic wounds can cause cell death and enhance inflammation, thus contributing to further injury and impaired wound healing. Therefore, attenuation of complement activation by specific inhibitors is considered as an innovative wound care strategy. Currently, the effects of several complement inhibitors, for example, the C3 inhibitor compstatin and several C1 and C5 inhibitors, are under investigation in patients with complement-mediated diseases. Although (pre)clinical research into the effects of these complement inhibitors on wound healing is limited, available data indicate that reduction of complement activation can improve wound healing. Moreover, medicine may take advantage of safe and effective agents that are produced by various microorganisms, symbionts, for example, medicinal maggots, and plants to attenuate complement activation. To conclude, for the development of new wound care strategies, (pre)clinical studies into the roles of complement and the effects of application of complement inhibitors in wound healing are required.

Excretions/secretions from bacteria-pretreated maggot are more effective against Pseudomonas aeruginosa biofilms

BACKGROUND

Sterile larvae--maggots of the green bottle blowfly Lucilia sericata are employed as a treatment tool for various types of chronic wounds. Previous studies reported that excretions/secretions (ES) of the sterile larvae could prevent and remove the biofilms of various species of bacteria. In the present study we assessed the effect of ES from the larvae pretreated with Pseudomonas aeruginosa on the bacteria biofilms.

METHODS AND FINDINGS

We investigated the effects of ES from the maggot pretreated with P. aeruginosa on the biofilms using microtitre plate assays and on bactericidal effect using the colony-forming unit (CFU) assay. The results showed that only 30 µg of the ES from the pretreated maggots could prevent and degrade the biofilm of P. aeruginosa. However, the CFU count of P. aeruginosa was not decrease when compared to the ES from non pretreated maggots in this study condition. It is suggested that the ES from the pretreated maggot was more effective against biofilm of P. aeruginosa than sterile maggot ES.

CONCLUSIONS

Our results showed that the maggot ES, especially the bacteria-pretreated larva ES may provide a new insight into the treatment tool of the bacterial biofilms.

Maggot excretions affect the human complement system

The complement system plays an important role in the activation of the inflammatory response to injury, although inappropriate complement activation (CA) can lead to severe tissue damage. Maggot therapy is successfully used to treat infected wounds. In this study, we hypothesized that maggot excretions/secretions influence CA in order to modulate the host's inflammatory response. Therefore, the effect of maggot excretions on CA was investigated in preoperatively and postoperatively obtained sera from patients. Our results show that maggot excretions reduce CA in healthy and postoperatively immune-activated human sera up to 99.9%, via all pathways. Maggot excretions do not specifically initiate or inhibit CA, but break down complement proteins C3 and C4 in a cation-independent manner and this effect proves to be temperature tolerant. This study indicates a CA-reducing substrate that is already successfully used in clinical practice and may explain part of the improved wound healing caused by maggot therapy. Furthermore, the complement activation-reducing substance present in maggot excretions could provide a novel treatment modality for several diseases, resulting from an (over)active complement system.

Biocompatibility of antimicrobials to maggot debridement therapy: medical maggots Lucilia sericata (Diptera: Calliphoridae) exhibit tolerance to clinical maximum doses of antimicrobials

The larvae of calliphorid flies are used to debride wounds of patients with severe tissue destruction, often concurrently with antimicrobials. The current study evaluates the effects of ceftazidime, tobramycin, amikacin, gentamicin, polymyxin B, doxycycline, paromomycin, amphotericin B, sodium stibogluconate, and miltefosine at 1, 10, and 100 x the Maximum Clinical Concentration (mg/kg/d) in raw liver assays. Effects on larvae were small and depended on dose and antimicrobial formulation, with hours in assay (24 or 48 h) having a significant effect on larval survival. Sodium stibgluconate had the strongest effect on maggot survival (80.0% at 48 h). These results suggest that the antimicrobials tested here may be used simultaneously with maggot debridement therapy, and may actually increase the effectiveness of maggot debridement therapy in certain applications where >1 x Maximum Clinical Concentration is indicated, such as topical creams for cutaneous leishmaniasis.

Cuticular and internal n-alkane composition of Lucilia sericata larvae, pupae, male and female imagines: application of HPLC-LLSD and GC/MS-SIM

The composition of cuticular and internal n-alkanes in Lucilia sericata larvae, pupae, and male and female imagines were studied. The cuticular and internal lipid extracts were separated by HPLC-LLSD, after which the hydrocarbon fraction was identified by GC/MS in selected ion monitoring (SIM) and total ion current (TIC) modes. The cuticular lipids of the larvae contained seven n-alkanes from C23 to C31. The major n-alkane in L. sericata larvae was C29 (42.1%). The total cuticular n-alkane content in the cuticular lipids was 31.46 μg g-1 of the insect body. The internal lipids of L. sericata larvae contained five n-alkanes ranged from C25 to C31. The most abundant compound was C27 (61.71 μg g-1 of the insect body). Eighteen n-alkanes from C14 to C31 were identified in the cuticular lipids of the pupae. The most abundant n-alkanes ranged from C25 to C31; those with odd-numbered carbon chains were particularly abundant, the major one being C29:0 (59.5%). Traces of eight cuticular n-alkanes were present. The internal lipids of L. sericata pupae contained five n-alkanes, ranging from C25 to C31. The cuticular lipids of female imagines contained 17 n-alkanes from C12 to C30. Among the cuticular n-alkanes of females, C27 (47.5%) was the most abundant compound. Four n-alkanes, with only odd-numbered carbon chains, were identified in the internal lipids of females. The lipids from both sexes of L. sericata had similar n-alkane profiles. The cuticular lipids of adult males contained 16 n-alkanes ranging from C13 to C31. C27 (47.9%) was the most abundant cuticular n-alkanes in males. The same n-alkanes only with odd-numbered carbon chains and in smaller quantities of C27 (0.1%) were also identified in the internal lipids of males. The highest amounts of total cuticular n-alkanes were detected in males and females of L. sericata (330.4 and 158.93 μg g-1 of the insect body, respectively). The quantities of total cuticular alcohols in larvae and pupae were smaller (31.46 μg g-1 and 42.08 μg g-1, respectively). The internal n-alkane contents of larvae, pupae, and male and female imagines were significantly higher than the cuticular n-alkane contents (153.53, 99.60, 360.06 and 838.76 μg g-1 of the insect body, respectively).

A de novo transcriptome assembly of Lucilia sericata (Diptera: Calliphoridae) with predicted alternative splices, single nucleotide polymorphisms and transcript expression estimates

The blow fly Lucilia sericata (Diptera: Calliphoridae) (Meigen) is a nonmodel organism with no reference genome that is associated with numerous areas of research spanning the ecological, evolutionary, medical, veterinary and forensic sciences. To facilitate scientific discovery in this species, the transcriptome was assembled from more than six billion bases of Illumina and twenty-one million bases of 454 sequence derived from embryonic, larval, pupal, adult and larval salivary gland libraries. The assembly was carried out in a manner that enabled identification of putative single nucleotide polymorphisms (SNPs) and alternative splices, and that provided expression estimates for various life history stages and for salivary tissue. The assembled transcriptome was also used to identify transcribed transposable elements in L. sericata. The results of this study will enable blow fly biologists, dipterists and comparative genomicists to more rapidly develop and test molecular and genetic hypotheses, especially those regarding blow fly development and salivary gland biology.

Induction of antibacterial activity in larvae of the blowfly Lucilia sericata by an infected environment

Maggot debridement therapy (MDT) is a method for the treatment of intractable, infected and necrotic wounds. In MDT, sterile larvae of Lucilia sericata Meigen (Diptera: Calliphoridae) are applied to infected wounds, where they exert antibacterial effects. Once the larvae are placed in the wound, they are no longer germ-free. This study analysed the influence of infected environments on larval antibacterial activities. Sterile larvae were mixed in a test tube containing a bacterial suspension of Staphylococcus aureus or Pseudomonas aeruginosa, transferred to liver puree agar, and incubated at 25 °C for set periods. To collect the larval extracts, the incubated larvae were transferred to a test tube containing phosphate buffered saline (PBS), cut into multiple pieces with scissors, and centrifuged. The supernatant was used to test antibacterial activities. The results showed that infected larvae had better antibacterial capacities than sterile larvae. Antibacterial activities were induced by pretreatment with a single bacterial species, S. aureus or P. aeruginosa, within 24 h and 12 h, respectively, and disappeared after 36 h. The activities were effective against S. aureus, but not against P. aeruginosa. This natural infection model is very similar to the clinical wound context in MDT and will be a powerful tool with which to study the antibacterial activities of L. sericata larvae in MDT.

Maggot excretions inhibit biofilm formation on biomaterials

BACKGROUND

Biofilm-associated infections in trauma surgery are difficult to treat with conventional therapies. Therefore, it is important to develop new treatment modalities. Maggots in captured bags, which are permeable for larval excretions/secretions, aid in healing severe, infected wounds, suspect for biofilm formation. Therefore we presumed maggot excretions/secretions would reduce biofilm formation.

QUESTIONS/PURPOSES

We studied biofilm formation of Staphylococcus aureus, Staphylococcus epidermidis, Klebsiella oxytoca, Enterococcus faecalis, and Enterobacter cloacae on polyethylene, titanium, and stainless steel. We compared the quantities of biofilm formation between the bacterial species on the various biomaterials and the quantity of biofilm formation after various incubation times. Maggot excretions/secretions were added to existing biofilms to examine their effect.

METHODS

Comb-like models of the biomaterials, made to fit in a 96-well microtiter plate, were incubated with bacterial suspension. The formed biofilms were stained in crystal violet, which was eluted in ethanol. The optical density (at 595 nm) of the eluate was determined to quantify biofilm formation. Maggot excretions/secretions were pipetted in different concentrations to (nonstained) 7-day-old biofilms, incubated 24 hours, and finally measured.

RESULTS

The strongest biofilms were formed by S. aureus and S. epidermidis on polyethylene and the weakest on titanium. The highest quantity of biofilm formation was reached within 7 days for both bacteria. The presence of excretions/secretions reduced biofilm formation on all biomaterials. A maximum of 92% of biofilm reduction was measured.

CONCLUSIONS

Our observations suggest maggot excretions/secretions decrease biofilm formation and could provide a new treatment for biofilm formation on infected biomaterials.

[Biosurgical débridement using Lucilia sericata-maggots - an update]

During the last years an increasing number of patients suffering from therapy refractory chronic wounds which are frequently infected by multi-resistant bacteria - e.g. methicillin-resistant Staphylococcus aureus - have led to an increasing interest in the treatment using larvae or maggots of the blow fly species Lucilia sericata. Maggots are responsible for necrectomy and they have antimicrobial activity in particular against grampositive bacteria like a disinfectant of the wound. It is concluded that maggots debridement therapy (MDT) using larvae of the species Lucilia sericata in non-healing chronic ulcers of the lower legs successfully leads to cleaning, debridement, reduced bacterial load, and improved wound granulation. A review is given on the clinical use of maggots, their mechanism of action and clinical efficacy for wound healing.

The antibacterial potency of the medicinal maggot, Lucilia sericata (Meigen): variation in laboratory evaluation

Research to quantify the potency of larval excretion/secretion from Lucilia sericata using liquid culture assays has produced contradictory results. In this study, viable counting was used to investigate the effectiveness of excretion/secretion against three marker bacterial species (Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli) and the effects of varying growing conditions in assays. Results demonstrate that factors such as number of larvae, species of bacteria and addition of nutrient influence its antibacterial potency. Therefore a standardised method should be employed for liquid culture assays when investigating the antibacterial activity of larval excretion/secretion from L. sericata.

A novel approach to the antimicrobial activity of maggot debridement therapy

Objectives

Commercially produced sterile green bottle fly Lucilia sericata maggots are successfully employed by practitioners worldwide to clean a multitude of chronic necrotic wounds and reduce wound bacterial burdens during maggot debridement therapy (MDT). Secretions from the maggots exhibit antimicrobial activity along with other activities beneficial for wound healing. With the rise of multidrug-resistant bacteria, new approaches to identifying the active compounds responsible for the antimicrobial activity within this treatment are imperative. Therefore, the aim of this study was to use a novel approach to investigate the output of secreted proteins from the maggots under conditions mimicking clinical treatments.

Methods

cDNA libraries constructed from microdissected salivary glands and whole maggots, respectively, were treated with transposon-assisted signal trapping (TAST), a technique selecting for the identification of secreted proteins. Several putative secreted components of insect immunity were identified, including a defensin named lucifensin, which was produced recombinantly as a Trx-fusion protein in Escherichia coli, purified using immobilized metal affinity chromatography and reverse-phase HPLC, and tested in vitro against Gram-positive and Gram-negative bacterial strains.

Results

Lucifensin was active against Staphylococcus carnosus, Streptococcus pyogenes and Streptococcus pneumoniae (MIC 2 mg/L), as well as Staphylococcus aureus (MIC 16 mg/L). The peptide did not show antimicrobial activity towards Gram-negative bacteria. The MIC of lucifensin for the methicillin-resistant S. aureus and glycopeptide-intermediate S. aureus isolates tested ranged from 8 to >128 mg/L.

Conclusions

The TAST results did not reveal any highly secreted compounds with putative antimicrobial activity, implying an alternative antimicrobial activity of MDT. Lucifensin showed antimicrobial activities comparable to other defensins and could have potential as a future drug candidate scaffold, for redesign for other applications besides the topical treatment of infected wounds.

Quorum-sensing-regulated virulence factors in Pseudomonas aeruginosa are toxic to Lucilia sericata maggots

Maggot debridement therapy (MDT) is widely used for debridement of chronic infected wounds; however, for wounds harbouring specific bacteria limited effect or failure of the treatment has been described. Here we studied the survival of Lucilia sericata maggots encountering Pseudomonas aeruginosa PAO1 in a simple assay with emphasis on the quorum-sensing (QS)-regulated virulence. The maggots were challenged with GFP-tagged P. aeruginosa wild-type (WT) PAO1 and a GFP-tagged P. aeruginosa ΔlasRrhlR (ΔRR) QS-deficient mutant in different concentrations. Maggots were killed in the presence of WT PAO1 whereas the challenge with the QS mutant showed a survival reduction of ∼25 % compared to negative controls. Furthermore, bacterial intake by the maggots was lower in the presence of WT PAO1 compared to the PAO1 ΔRR mutant. Maggot excretions/secretions (ES) were assayed for the presence of QS inhibitors; only high doses of ES showed inhibition of QS in P. aeruginosa. Thus P. aeruginosa was shown to be toxic to L. sericata maggots. This, coupled to the preferential feeding by the maggots and reduced ingestion of P. aeruginosa, could explain MDT failure in wounds colonized by P. aeruginosa. Wounds heavily colonized with P. aeruginosa should be a counterindication for MDT unless used in combination with a pre-treatment with other topical therapeutics targeting P. aeruginosa.