<i>Bacillus</i>Endophthalmitis: Roles of Bacterial Toxins and Motility during Infection

Callegan, Michelle C.; Kane, Scott T.; Cochran, Daniel C.; Novosad, Billy D.; Gilmore, Michael S.; Gominet, Myriam; Lereclus, Didier

doi:10.1167/iovs.05-0410

Cited by 67 publications

(74 citation statements)

References 32 publications

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“…In this study, virulence was strongly decreased by both forcefeeding and intrahemocoelic injection. This is the first demonstration of the role of FlhA in the virulence of B. thuringiensis in insects, but a recent study showed an effect on rabbit endophthalmitis (10). Moreover, so far, no other B. thuringiensis factors have been described to play a role by both oral and intrahemocoel inoculation.…”

Section: Discussionmentioning

confidence: 76%

FlhA InfluencesBacillus thuringiensisPlcR-Regulated Gene Transcription, Protein Production, and Virulence

Bouillaut

Ramarao

Buisson

et al. 2005

Appl Environ Microbiol

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Bacillus thuringiensis and Bacillus cereus are closely related. B. thuringiensis is well known for its entomopathogenic properties, principally due to the synthesis of plasmid-encoded crystal toxins. B. cereus appears to be an emerging opportunistic human pathogen. B. thuringiensis and B. cereus produce many putative virulence factors which are positively controlled by the pleiotropic transcriptional regulator PlcR. The inactivation of plcR decreases but does not abolish virulence, indicating that additional factors like flagella may contribute to pathogenicity. Therefore, we further analyzed a mutant (B. thuringiensis 407 Cry ؊ ⌬flhA) previously described as being defective in flagellar apparatus assembly and in motility as well as in the production of hemolysin BL and phospholipases. A large picture of secreted proteins was obtained by twodimensional electrophoresis analysis, which revealed that flagellar proteins are not secreted and that production of several virulence-associated factors is reduced in the flhA mutant. Moreover, we quantified the effect of FlhA on plcA and hblC gene transcription. The results show that the flhA mutation results in a significant reduction of plcA and hblC transcription. These results indicate that the transcription of several PlcR-regulated virulence factors is coordinated with the flagellar apparatus. Consistently, the flhA mutant also shows a strong decrease in cytotoxicity towards HeLa cells and in virulence against Galleria mellonella larvae following oral and intrahemocoelic inoculation. The decrease in virulence may be due to both a lack of flagella and a lower production of secreted factors. Hence, FlhA appears to be an essential virulence factor with a pleiotropic role.Bacillus thuringiensis is a gram-positive, spore-forming species, motile by peritrichous flagella and belonging to the Bacillus cereus group, which also includes Bacillus anthracis and Bacillus cereus sensu stricto. B. thuringiensis is an entomopathogenic bacterium that produces, during the stationary phase, a large variety of Cry toxins that are active against insect larvae (43). B. cereus does not produce the Cry toxins and is an opportunistic human pathogen responsible for gastroenteritis (23) and local infections such as endophthalmitis (7). Although these bacteria infect distinct hosts, they share common pathogenic features. Indeed, the opportunistic properties of B. thuringiensis and B. cereus have been demonstrated in a vertebrate infection model by administering spores to mice via nasal instillation, suggesting that the two species might share common virulence factors (41).B. thuringiensis and B. cereus produce many putative virulence factors that are positively controlled by the pleiotropic regulator PlcR (1,28,34). Expression and activation of the plcR regulon at the onset of the stationary phase is dependent on a quorum-sensing system involving the PapR peptide (44).

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Section: Discussionmentioning

confidence: 76%

FlhA InfluencesBacillus thuringiensisPlcR-Regulated Gene Transcription, Protein Production, and Virulence

Bouillaut

Ramarao

Buisson

et al. 2005

Appl Environ Microbiol

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“…However, it should also be taken into consideration that B. cereus is able to produce additional food spoilage and virulence factors, including phospholipases, proteases, hemolysins, and enterotoxins, which are unambiguously of medical and economical impact (10,35,54). lux gene reporter systems, similar to the one described in this work, might also be useful for monitoring enterotoxin expression and could add important information to the hazard identification of different food systems.…”

Section: Discussionmentioning

confidence: 99%

Identification of the Main Promoter Directing Cereulide Biosynthesis in Emetic Bacillus cereus and Its Application for Real-Time Monitoring of ces Gene Expression in Foods

Dommel

Frenzel

Strasser

et al. 2010

Appl Environ Microbiol

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Cereulide, the emetic Bacillus cereus toxin, is synthesized by cereulide synthetase via a nonribosomal peptide synthetase (NRPS) mechanism. Previous studies focused on the identification, structural organization, and biochemical characterization of the ces gene locus encoding cereulide synthetase; however, detailed information about the transcriptional organization of the ces genes was lacking. The present study shows that the ces-PTABCD genes are transcribed as a 23-kb polycistronic transcript, while cesH, encoding a putative hydrolase, is transcribed from its own promoter. Transcription initiation was mapped by primer extension and rapid amplification of cDNA ends (RACE). Deletion analysis of promoter elements revealed a main promoter located upstream of the cesP coding sequence, encoding a 4-phosphopantetheinyl transferase. This promoter drives transcription of cesPTABCD. In addition, intracistronic promoter regions in proximity to the translational start sites of cesB and cesT were identified but were only weakly active under the chosen assay conditions. The identified main promoter was amplified from the emetic reference strain B. cereus F4810/72 and fused to luciferase genes in order to study promoter activity in complex environments and to establish a biomonitoring system to assess cereulide production in different types of foods. ces promoter activity was strongly influenced by the food matrix and varied by 5 orders of magnitude. The amount of cereulide toxin extracted from spiked foods correlated well with the bioluminescence data, thus illustrating the potential of the established reporter system for monitoring of ces gene expression in complex matrices.Bacillus cereus is the causative agent of two types of food poisoning: diarrhea and emesis. The toxicoinfection referred to as diarrheal disease occurs after consumption of B. cereus spores or vegetative cells, most likely due to the action of heat-labile enterotoxins, which are produced by cells multiplying in the small intestine (4,22,30,39). Contrarily, the emetic type of food-borne illness is caused by intoxication with the heat-stable peptide cereulide, which is preformed in foods and elicits vomiting a few hours after ingestion (18,51,58).Regulation of enterotoxin expression of B. cereus has been studied in some detail (e.g., references 16, 29, and 46; for a review, see reference 58), revealing a major role of the pleiotropic transcription regulator PlcR in activation of enterotoxin genes and other virulence factors (1,29,45). Cereulide synthesis in emetic B. cereus, in contrast to synthesis of B. cereus enterotoxins, is not controlled by PlcR but by the Spo0A phosphorelay. The global transition state factor AbrB was identified as one factor repressing cereulide production in early exponential phase (38). Although B. cereus enterotoxins and the emetic toxin cereulide seem to belong to completely different regulatory networks, production of both types of toxins depends substantially on nutritional and environmental factors (3,46,55), and it is expe...

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“…6 For instance, bacterial communication through motion is believed to be an important factor for infections and for bacterial resistance to antibiotics. 7,8,37 Consequently, the development of sensitive force and motion probes, 9 which can match the time and length scales of microorganisms, has been an important element in the study of motile microorganisms.…”

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confidence: 99%

Nanomechanical motion of Escherichia coli adhered to a surface

Lissandrello

İnci

Francom

et al. 2014

Applied Physics Letters

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Nanomechanical motion of bacteria adhered to a chemically functionalized silicon surface is studied by means of a microcantilever. A non-specific binding agent is used to attach Escherichia coli (E. coli) to the surface of a silicon microcantilever. The microcantilever is kept in a liquid medium, and its nanomechanical fluctuations are monitored using an optical displacement transducer. The motion of the bacteria couples efficiently to the microcantilever well below its resonance frequency, causing a measurable increase in the microcantilever fluctuations. In the time domain, the fluctuations exhibit large-amplitude low-frequency oscillations. In corresponding frequencydomain measurements, it is observed that the mechanical energy is focused at low frequencies with a 1/f a -type power law. A basic physical model is used for explaining the observed spectral distribution of the mechanical energy. These results lay the groundwork for understanding the motion of microorganisms adhered to surfaces and for developing micromechanical sensors for bacteria.

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BacillusEndophthalmitis: Roles of Bacterial Toxins and Motility during Infection

Cited by 67 publications

References 32 publications

FlhA InfluencesBacillus thuringiensisPlcR-Regulated Gene Transcription, Protein Production, and Virulence

FlhA InfluencesBacillus thuringiensisPlcR-Regulated Gene Transcription, Protein Production, and Virulence

Identification of the Main Promoter Directing Cereulide Biosynthesis in Emetic Bacillus cereus and Its Application for Real-Time Monitoring of ces Gene Expression in Foods

Nanomechanical motion of Escherichia coli adhered to a surface

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