Identification of Bacillus Strains for Biological Control of Catfish Pathogens

Bacillus strains isolated from soil or channel catfish intestine were screened for their antagonism against Edwardsiella ictaluri and Aeromonas hydrophila, the causative agents of enteric septicemia of catfish (ESC) and motile aeromonad septicaemia (MAS), respectively. Twenty one strains were selected and their antagonistic activity against other aquatic pathogens was also tested. Each of the top 21 strains expressed antagonistic activity against multiple aquatic bacterial pathogens including Edwardsiella tarda, Streptococcus iniae, Yersinia ruckeri, Flavobacterium columnare, and/or the oomycete Saprolegnia ferax. Survival of the 21 Bacillus strains in the intestine of catfish was determined as Bacillus CFU/g of intestinal tissue of catfish after feeding Bacillus spore-supplemented feed for seven days followed by normal feed for three days. Five Bacillus strains that showed good antimicrobial activity and intestinal survival were incorporated into feed in spore form at a dose of 8×10⁷ CFU/g and fed to channel catfish for 14 days before they were challenged by E. ictaluri in replicate. Two Bacillus subtilis strains conferred significant benefit in reducing catfish mortality (P<0.05). A similar challenge experiment conducted in Vietnam with four of the five Bacillus strains also showed protective effects against E. ictaluri in striped catfish. Safety of the four strains exhibiting the strongest biological control in vivo was also investigated in terms of whether the strains contain plasmids or express resistance to clinically important antibiotics. The Bacillus strains identified from this study have good potential to mediate disease control as probiotic feed additives for catfish aquaculture.     

Using mixture design to construct consortia of potential probiotic Bacillus strains to protect gnotobiotic Artemia against pathogenic Vibrio

To evaluate the potential probiotic effect of three Bacillus strains on the survival and growth of an Artemia culture and to obtain the optimal formulation of pure cultures of the bacilli, challenge tests were performed with the pathogenic bacterium Vibrio alginolyticus (S1) using mixture design. According to molecular analyses involving amplified ribosomal DNA restriction analysis (ARDRA), these bacteria corresponded to Bacillus subtilus, Bacillus cereus and Bacillus coagulans. An antimicrobial susceptibility and antagonism assay revealed that these strains were susceptible to most antimicrobial drugs and have an inhibitory effect against tested pathogenic Vibrio. Furthermore, the investigated Bacillus strains were fairly adhesive to polystyrene, with values ranging from 0.10 to 0.32 at 595 nm. Statistical analysis demonstrated that Bacillus strains enhance protection against pathogens, have no impact on survival, but improve the growth of larvae, for which the highest growth rate was obtained when the mixture composition was 32% B. subtilus, 68% B. cereus and no B. coagulans.     

Isolation of Enterococcus faecium NM113, Enterococcus faecium NM213 and Lactobacillus casei NM512 as novel probiotics with immunomodulatory properties

Probiotics, defined as living bacteria that are beneficial for human health, mainly function through their immunomodulatory abilities. Hence, these microorganisms have proven successful for treating diseases resulting from immune deregulation. The aim of this study was to find novel candidates to improve on and complement current probiotic treatment strategies. Of 60 lactic acid bacterial strains that were isolated from fecal samples of healthy, full‐term, breast‐fed infants, three were chosen because of their ability to activate human immune cells. These candidates were then tested with regard to immunomodulatory properties, antimicrobial effects on pathogens, required pharmacological properties and their safety profiles. To identify the immunomodulatory structures of the selected isolates, activation of specific innate immune receptors was studied. The three candidates for probiotic treatment were assigned Enterococcus faecium NM113, Enterococcus faecium NM213 and Lactobacillus casei NM512. Compared with the established allergy‐protective strain Lactococcus lactis G121, these isolates induced release of similar amounts of IL‐12, a potent inducer of T helper 1 cells. In addition, all three neonatal isolates had antimicrobial activity against pathogens. Analysis of pharmacological suitability showed high tolerance of low pH, bile salts and pancreatic enzymes. In terms of safe application in humans, the isolates were sensitive to three antibiotics (chloramphenicol, tetracycline and erythromycin). In addition, the Enterococcus isolates were free from the four major virulence genes (cylA, agg, efaAfs and ccf). Moreover, the isolates strongly activated Toll‐like receptor 2, which suggests lipopeptides as their active immunomodulatory structure. Thus, three novel bacterial strains with great potential as probiotic candidates and promising immunomodulatory properties have here been identified and characterized.     

In vitro assessment of probiotic properties of <Emphasis Type="Italic">Bacillus</Emphasis> isolated from naturally fermented congee from Inner Mongolia of China

A total of thirty-three strains of Bacillus were isolated from sixteen samples of naturally fermented congee in Inner Mongolia of China and identified by 16S rDNA sequence analysis. Probiotic properties including acid, bile tolerance and artificial gastrointestinal juice resistance as well as inhibition on pathogenic bacteria were used for screening of Bacillus. After the preliminary selection, four strains including Bacillus licheniformis IMAUB1002, Bacillus subtilis IMAUB1011, Bacillus amyloliquefaciens IMAUB1014 and Bacillus amyloliquefaciens IMAUB1034 showed high tolerance to simulated gastric juice at pH 2.0 for 3 h with survival rate all above 92%. And then through gastrointestinal transit, survival rates of these four strains were above 90%. Furthermore, Bacillus licheniformis IMAUB1002 performed well in tolerance to bile salt (0.6%) and inhibitory activity to five food-borne pathogens among four strains of Bacillus. The results suggested that Bacillus licheniformis IMAUB1002 should be considered as a potential probiotics. Further study will be focused on evaluation of these porbiotics properties in vivo and clarification of its other functional properties so as to use it in functional foods production in future.     

Novel strains of Bacillus,isolated from compost and compost-amended soils,as biological control agents against soil-borne phytopathogenic fungi

A stepwise screening strategy made it possible to identify five new Bacillus spp. strains for biocontrol of Rhizoctonia solani, Sclerotinia minor and Fusarium solani. In vitro and in vivo biocontrol activity and M13-PCR DNA-fingerprinting led to the selection of these valuable biological control agents (BCAs) from a wide collection of over 250 candidates. At the end of this selection, the highest potential antagonists were identified at species level by 16S-rRNA gene sequence analysis, and results assigned them to Bacillus subtilis group as Bacillus amyloliquefaciens- and Bacillus methylotrophicus-related strains. In the current study, spore-forming bacteria provided substantial biocontrol of telluric diseases on cress and other different host plants. The strains named 15S and 09C were effective in disease control on Brassica oleracea/R. solani pathosystem, whereas Sclerotinia drop of lettuce was reduced by treatments with the strains 17S and 08C. Finally, the strains 17S and 12S were equally effective to control potato Fusarium rot. The evident zone of inhibition seen in dual culture plates suggested antibiosis-like antagonisms as the main mechanisms used by these bacterial isolates in interaction with the pathogens. Additionally, the API-ZYM method revealed constitutive activity of certain extracellular enzymes that could be involved in plant fortification. Bacillus strains isolated from compost and compost-amended soils are promising BCAs that have potential for practical application as biofungicides.     

Genome analysis reveals insights of the endophytic <Emphasis Type="Italic">Bacillus toyonensis</Emphasis> BAC3151 as a potentially novel agent for biocontrol of plant pathogens

Diseases caused by phytopathogenic microorganisms account for enormous losses for agribusiness. Although Bacillus species are recognized as being antimicrobial producers and some may provide benefits to plants, the association between Bacillus toyonensis and plants has not been studied. In this study, the whole-genome sequenced endophytic B. toyonensis BAC3151, which has demonstrated antimicrobial activity and quorum sensing inhibition of phytopathogenic bacteria, was investigated for its potential for the production of compounds for biocontrol of plant pathogens. Four whole-genome sequenced B. toyonensis strains shared 3811 protein-coding DNA sequences (CDSs), while strain-specific CDSs, such as biosynthetic gene clusters of antimicrobials, were associated with specific chromosomal regions and mobile genetic elements of the strains. B. toyonensis strains had a higher frequency of putative bacteriocins gene clusters than that of Bacillus species traditionally used for the production of antimicrobials. In addition, gene clusters potentially involved in the production of novel bacteriocins were found in BAC3151, as well as biosynthetic genes of several other compounds, including non-ribosomal peptides, N-acyl homoserine lactonase and chitinases, revealing a genetic repertoire for antimicrobial synthesis greater than that of other Bacillus strains that have demonstrated effective activity against phytopathogens. This study showed for the first time that B. toyonensis has potential to produce various antimicrobials, and the analyses performed indicated that the endophytic strain BAC3151 can be useful for the development of new strategies to control microbial diseases in plants that are responsible for large damages in agricultural crops.     

Selection of Bacillus species for targeted in situ release of prebiotic galacto-rhamnogalacturonan from potato pulp in piglets

We have previously shown that galacto-rhamnogalacturonan fibers can be enzymatically extracted from potato pulp and that these fibers have potential for exerting a prebiotic effect in piglets. The spore-forming Bacillus species are widely used as probiotics in feed supplements for pigs. In this study, we evaluated the option for further functionalizing Bacillus feed supplements by selecting strains possessing the enzymes required for extraction of the potentially prebiotic fibers. We established that it would require production and secretion of pectin lyase and/or polygalacturonase but no or limited secretion of galactanase and β-galactosidase. By screening a library of 158 Bacillus species isolated from feces and soil, we demonstrated that especially strains of Bacillus amyloliquefaciens, Bacillus subtilis, and Bacillus mojavensis have the necessary enzyme profile and thus the capability to degrade polygalacturonan. Using an in vitro porcine gastrointestinal model system, we revealed that specifically strains of B. mojavensis were able to efficiently release galacto-rhamnogalacturonan from potato pulp under simulated gastrointestinal conditions. The work thus demonstrated the feasibility of producing prebiotic fibers via a feed containing Bacillus spores and potato pulp and identified candidates for future in vivo evaluation in piglets.

     

Isolation and evaluation of autochthonous Bacillus subtilis strains as probiotics for fat snook (Centropomus parallelus Poey, 1860)

The objective of this study was to isolate and select autochthonous strains of Bacillus subtilis from the fat snook, Centropomus parallelus, and examine the viability of the Bacillus bacteria to determine their beneficial effect on gut colonization in reared fish. Twenty strains of Bacillus were isolated and further confirmed as B. subtilis using PCR. Among the 20 strains, two strains (B02 and B03) exhibited an inhibitory performance against five tested pathogens. The Bacillus strains B02 and B03 were added to the fish ration, and after 30 days the number of viable colonies were maintained or increased under the conditions of refrigeration (5°C), freezing (?18°C), or room temperature (30°C). These strains showed a growth rate of 0.18–0.21 h and a doubling time of 3.34–3.9 h. Both strains were tolerant to variations in NaCl, and B03 was also tolerant to bile exposure. The ability to colonize the gastrointestinal tract was also examined in healthy fat snook juveniles fed diets enriched for 30 days with strains B02 and B03. The amount of B. subtilis in the gastrointestinal juvenile tract was significantly higher in fish fed the enriched ration compared to controls. Based on these results, strains B02 and B03 were considered as candidate probiotics for fat snook.     

Segregation pattern of gene expression in cotton leaf curl virus-resistant transgenics

Non-pathogenic soil bacteria living in association with roots of higher plants enhance their adaptive potential and thus could be beneficial for their growth. Here, we present the current status of the use of Bacillus subtilis in biocontrol. Rhizobacteria are found in the rhizosphere. Plant growth promoting rhizobacteria (PGPR) strains, such as Bacillus and Pseudomonas, were isolated by using Nutreint dextrose Agar medium or Potato Dextrose Agar medium. The selection of PGPR strains was done by duel culture methods against the potato pathogens. The interaction of PGPR (Bacillus) with potato seeds or vegetative parts show promising antagonism by virtue of producing siderophore and antibiotics against black scurf and stem canker diseases of potato caused by Rhizoctonia solani, thereby resulting in increase of potato yield. The effectiveness of PGPR strain (Bacillus spp.) in improving the yield of potato in greenhouse conditions and in the field was observed.     

Protection of Oilseed Rape (<Emphasis Type="Italic">Brassica napus</Emphasis>) Toward Fungal Pathogens by Strains of Plant-associated <Emphasis Type="Italic">Bacillus amyloliquefaciens</Emphasis>

In this report, four Bacillus strains were tested for effects on plant fitness and disease protection of oilseed rape (Brassica napus). The strains belonged to newly discovered plant-associated Bacillus amyloliquefaciens and a recently proposed species, Bacillus endophyticus. The fungal pathogens tested represented different infection strategies and included Alternaria brassicae, Botrytis cinerea, Leptosphaeria maculans, and Verticillium longisporum. The B. amyloliquefaciens strains showed no or a weak plant growth promoting activity, whereas the B. endophyticus strain had negative effects on the plant as revealed by phenological analysis. On the other hand, two of the B. amyloliquefaciens strains conferred protection of oilseed rape toward all pathogens tested. In vitro experiments studying the effects of Bacillus exudates on fungal growth showed clear growth inhibition in several but not all cases. The protective effects of Bacillus can therefore, at least in part, be explained by production of antibiotic substances, but other mechanisms must also be involved probably as a result of intricate plant–bacteria interaction. The protective effects observed for certain Bacillus strains make them highly interesting for further studies as biocontrol agents in Brassica cultivation.     

Development of a live biotherapeutic throat spray with lactobacilli targeting respiratory viral infections

Respiratory viruses such as influenza viruses, respiratory syncytial virus (RSV), and coronaviruses initiate infection at the mucosal surfaces of the upper respiratory tract (URT), where the resident respiratory microbiome has an important gatekeeper function. In contrast to gut-targeting administration of beneficial bacteria against respiratory viral disease, topical URT administration of probiotics is currently underexplored, especially for the prevention and/or treatment of viral infections. Here, we report the formulation of a throat spray with live lactobacilli exhibiting several in vitro mechanisms of action against respiratory viral infections, including induction of interferon regulatory pathways and direct inhibition of respiratory viruses. Rational selection of Lactobacillaceae strains was based on previously documented beneficial properties, up-scaling and industrial production characteristics, clinical safety parameters, and potential antiviral and immunostimulatory efficacy in the URT demonstrated in this study. Using a three-step selection strategy, three strains were selected and further tested in vitro antiviral assays and in formulations: Lacticaseibacillus casei AMBR2 as a promising endogenous candidate URT probiotic with previously reported barrier-enhancing and anti-pathogenic properties and the two well-studied model strains Lacticaseibacillus rhamnosus GG and Lactiplantibacillus plantarum WCFS1 that display immunomodulatory capacities. The three strains and their combination significantly reduced the cytopathogenic effects of RSV, influenza A/H1N1 and B viruses, and HCoV-229E coronavirus in co-culture models with bacteria, virus, and host cells. Subsequently, these strains were formulated in a throat spray and human monocytes were employed to confirm the formulation process did not reduce the interferon regulatory pathway-inducing capacity. Administration of the throat spray in healthy volunteers revealed that the lactobacilli were capable of temporary colonization of the throat in a metabolically active form. Thus, the developed spray with live lactobacilli will be further explored in the clinic as a potential broad-acting live biotherapeutic strategy against respiratory viral diseases.     

动物用芽孢杆菌微生态制剂中蜡样芽孢杆菌的分离及安全性

【背景】芽孢杆菌是仅次于乳酸菌常用于微生态制剂中的菌种,然而部分芽孢杆菌微生态制剂规范不严,应用存在安全隐患。【目的】调查我国在售动物用芽孢杆菌微生态制剂中蜡样芽孢杆菌携带情况,揭示蜡样芽孢杆菌应用的潜在风险。【方法】对微生态制剂预处理,选择性筛选分离蜡样芽孢杆菌,通过全基因组测序测绘细菌毒素基因谱与耐药基因谱,细胞计数试剂盒-8法测定菌株对细胞的毒性,利用微量肉汤稀释法确定菌株耐药值。【结果】从50份微生态制剂产品中筛选分离得到23株蜡样芽孢杆菌群细菌,它们对氨苄西林、林可霉素和泰妙菌素3种抗生素均耐药,主要毒力基因nhe、hbl、cytK、ces的检出率分别为100%、30%、39%和4%,分离株均有溶血性且39%菌株产生热稳定毒素,不同菌株对非洲绿猴肾细胞呈现出不同程度的毒性。【结论】微生态制剂来源的蜡样芽孢杆菌毒性与耐药性严重,携带毒素基因与耐药基因广泛,多株菌株呈高细胞毒性且产生热稳定毒素。芽孢杆菌微生态制剂存在安全性问题,应加强对蜡样芽孢杆菌的质量安全监管力度,规范微生态制剂的市场秩序,杜绝安全隐患。     

Investigation of antibacterial activity of Bacillus spp. isolated from the feces of Giant Panda and characterization of their antimicrobial gene distributions

Bacillus group is a prevalent community of Giant Panda’s intestinal flora, and plays a significant role in the field of biological control of pathogens. To understand the diversity of Bacillus group from the Giant Panda intestine and their functions in maintaining the balance of the intestinal microflora of Giant Panda, this study isolated a significant number of strains of Bacillus spp. from the feces of Giant Panda, compared the inhibitory effects of these strains on three common enteric pathogens, investigated the distributions of six universal antimicrobial genes (ituA, hag, tasA, sfp, spaS and mrsA) found within the Bacillus group by PCR, and analyzed the characterization of antimicrobial gene distributions in these strains using statistical methods. The results suggest that 34 strains of Bacillus spp. were isolated which has not previously been detected at such a scale, these Bacillus strains could be classified into five categories as well as an external strain by 16S rRNA; Most of Bacillus strains are able to inhibit enteric pathogens, and the antimicrobial abilities may be correlated to their categories of 16S rRNA; The detection rates of six common antimicrobial genes are between 20.58 %(7/34) and 79.41 %(27/34), and genes distribute in three clusters in these strains. We found that the antimicrobial abilities of Bacillus strains can be one of the mechanisms by which Giant Panda maintains its intestinal microflora balance, and may be correlated to their phylogeny.     

Taxonomic Composition and Biological Activity of Microorganisms Associated with a Marine Ascidian Halocynthia aurantium

The taxonomy and biological activity of 176 heterotrophic microorganisms associated with the ascidian Halocynthia aurantiumfrom the coastal waters of Peter the Great Bay (Sea of Japan) were studied. In the microbial community, bacteria of the genera Pseudoalteromonas(38% of all strains studied) and Bacillus(25%) prevailed and showed high biological activity. Bacteria of Pseudoalteromonaswere capable of extracellular hydrolases production and exhibited high antibiotic and antimicrobial properties. Five Pseudoalteromonasstrains were capable of restriction enzyme production. A significant proportion of the pseudoalteromonads inhibited growth ofProteus vulgarisand Candida albicans(81 and 84%, respectively). Spore-forming bacteria of Bacilluswere capable of chitin hydrolysis and extracellular inducible RNAses production (23%). They were active against Staphylococcus aureusand Bacillus subtilis(39 and 23%, respectively). Bacillus pumilusstrain KMM 1364 showed hemolytic activity and antagonistic properties against S. aureusand was found to produce surface active glycolipids and surfactinlike cyclic depsipeptides.     

Diversity and antagonistic potential of Bacillus spp. associated to the rhizosphere of tomato for the management of Rhizoctonia solani

Bacillus spp. has emerged as the most effective alternative to synthetic chemical fungicides. To get a better insight in the antagonistic potential of Bacillus strains, rhizospheric soil samples of healthy tomato plants from Indo-gangetic plain regions of India were analysed. A total of 108 Bacillus strains were obtained from preliminary screening. Potent strains identified on the basis of in vitro antagonistic and biochemical assays were subjected to diversity analysis using 16S-rDNA, BOX and ERIC-PCR. Furthermore, the four best performing antagonistic Bacillus strains under in vitro plant growth promotion and antagonistic assay were selected for pot experiment. In field study, Bacillus amyloliquefaciens MB101 and Bacillus subtilis MB14 showed drastic reduction in disease index by 55.7 and 41.74% with significant elevation in fruit yield up to 220 and 184 qha^–1, respectively. The present study was successful in selecting effective Bacillus strains by performing phenotypic and genotypic characterisation of Bacillus strains that can be used as an integral component of integrated disease management of tomato root rot and damping-off.     

Real-time PCR investigation on the expression of sboA and ituD genes in Bacillus spp

Aims: To investigate the expression of sboA and ituD genes among strains of Bacillus spp. at different pH and temperature. Methods and Results: Different Bacillus strains from the Amazon basin and Bacillus subtilis ATCC 19659 were investigated for the production of subtilosin A and iturin A by qRT‐PCR, analysing sboA and ituD gene expression under different culture conditions. Amazonian strains presented a general gene expression level lower than B. subtilis ATCC 19659 for sboA. In contrast, when analysing the expression of ituD gene, the strains from the Amazon, particularly P40 and P45B, exhibited higher levels of expression. Changes in pH (6 and 8) and temperature (37 and 42°C) caused a decrease in sboA expression, but increased ituD expression among strains from Amazonian environment. Conclusions: Temperature and pH have an important influence on the expression of genes sboA (subtilosin A) and ituD (iturin A) among Bacillus spp. The strains P40 and P45B can be useful for the production of antimicrobial peptide iturin A. Significance and Impact of the Study: Monitoring the expression of essential biosynthetic genes by qRT‐PCR is a valuable tool for optimization of the production of antimicrobial peptides.     

Characterization and evaluation of two Bacillus strains,SS-12.6 and SS-13.1, as potential agents for the control of phytopathogenic bacteria and fungi

Two strains of Bacillus sp., SS-12.6 and SS-13.1, showed very strong antibacterial and antifungal activity against phytopathogens. The PCR analysis showed that both strains have the genes for biosynthesis of iturin, bacillomycin and surfactin. Kinetics of production of antimicrobial substances in these strains showed that synthesis started at the beginning of exponential phase of growth. Maximum of activity was slowly reached at the beginning of stationary growth phase and was maintained until the end of observed period. Ethyl acetate extracts of cell-free supernatants of both strains were particularly active against several postharvest fungal pathogens, in vitro and in vivo, in the experiment with apple fruits. Mass spectrometry analysis of ethyl acetate extract of the supernatant of strain SS-12.6 confirmed the presence of antimicrobial lipopeptide surfactin.     

Resistance to infection and activation of the monocyto-macrophage system caused byBacillus firmus and its fractions

Crude lipids isolated fromBacillus firmus, but not from other bacilli, were previously found to induce significant resistance againstListeria monocytogenes infection in mice. In this study, formaldehyde-and heat-killed bacterins of eightBacillus species and some cellular fractions ofB. firmus were prepared and tested for further immunomodulatory activities. Crude lipids, their aqueous extract, LTA, Protodyne and Pex-residue preparations exhibited a strong anti-infection activity, whereas Pextract, P40 and all bacterins tested had no effect. Formaldehyde-killed bacterins, live bacteria and the P40 preparation of bothB. firmus strains, as well as bacterins of bothB. subtilis strains, induced pronounced splenomegaly in mice. Peptidoglycan and Pex-residue induced significant depression of cytochrome P-450 in mouse liver microsomes after application of 0.1 mg per mouse. Optimal conditions for obtaining a bacterial suspension exhibiting these immunomodulatory properties were elaborated.     

Action of antimicrobial substances produced by different oil reservoir Bacillus strains against biofilm formation

Microbial colonization of petroleum industry systems takes place through the formation of biofilms, and can result in biodeterioration of the metal surfaces. In a previous study, two oil reservoir Bacillus strains (Bacillus licheniformis T6-5 and Bacillus firmus H₂O-1) were shown to produce antimicrobial substances (AMS) active against different Bacillus strains and a consortium of sulfate-reducing bacteria (SRB) on solid medium. However, neither their ability to form biofilms nor the effect of the AMS on biofilm formation was adequately addressed. Therefore, here, we report that three Bacillus strains (Bacillus pumilus LF4—used as an indicator strain, B. licheniformis T6-5, and B. firmus H₂O-1), and an oil reservoir SRB consortium (T6lab) were grown as biofilms on glass surfaces. The AMS produced by strains T6-5 and H₂O-1 prevented the formation of B. pumilus LF4 biofilm and also eliminated pre-established LF4 biofilm. In addition, the presence of AMS produced by H₂O-1 reduced the viability and attachment of the SRB consortium biofilm by an order of magnitude. Our results suggest that the AMS produced by Bacillus strains T6-5 and H₂O-1 may have a potential for pipeline-cleaning technologies to inhibit biofilm formation and consequently reduce biocorrosion.     

Absence of in vitro innate immunomodulation by insect‐derived short proline‐rich antimicrobial peptides points to direct antibacterial action in vivo

Some antimicrobial peptides (AMPs) have been described to exert immunomodulatory effects, which may contribute to their in vivo antibacterial activity. Very recently, we could show that novel oncocin and apidaecin derivatives are potently antibacterially active in vivo. Therefore, we studied oncocin and apidaecin derivatives for their effects on murine dendritic cells (DC) and macrophages and compared them with well‐known immunomodulatory activities of murine cathelicidin‐related antimicrobial peptide (CRAMP). To characterize the immunomodulatory activity of the peptides on key cells of the innate immune system, we stimulated murine DC and macrophages with the oncocin and apidaecin derivatives alone, or in combination with lipopolysaccharide (LPS). We analyzed the secretion of pro‐inflammatory cytokines, the expression of surface activation markers, and the chemotactic activity of the AMPs. In contrast to LPS, none of the oncocin and apidaecin derivatives alone has an influence on cytokine or surface marker expression by DC and macrophages. Furthermore, the tested oncocin and apidaecin derivatives do not modulate the immune response after LPS stimulation, whereas CRAMP shows a reduction of the LPS‐mediated immune response as expected. All peptides tested are not chemotactic for DC. Together, lack of in vitro immunomodulatory effects by oncocin and apidaecin derivatives on key cells of the innate murine immune system suggests that their potent in vivo antibacterial activity relies on a direct antibacterial effect. This will simplify further pharmaceutical investigation and development of insect peptides as therapeutic compounds against bacterial infections. Copyright © 2012 European Peptide Society and John Wiley & Sons, Ltd.