Failure of intravitreal dexamethasone to diminish inflammation or retinal toxicity in an experimental model of Bacillus cereus endophthalmitis.

PURPOSE: To determine whether the usual clinical dose of intravitreal dexamethasone can attenuate intraocular inflammation and retinal necrosis in a rabbit model of fulminant Bacillus cereus endophthalmitis induced by crude exotoxins. METHODS: Thirty-six eyes from pigmented mongrel rabbits received intravitreal injections of varying concentrations of crude B. cereus exotoxins with or without concomitant injections of 400 microg of dexamethasone sodium phosphate (0.1% solution). After ophthalmoscopic examination at 4 or 18 hr postinjection, the animals were killed and histopathologic findings graded. RESULTS: Intraocular inflammation and retinal necrosis scores in eyes receiving both exotoxins and dexamethasone did not differ significantly from eyes receiving exotoxins alone for any exotoxin dose at 4 or 18 hr. The severity of retinal necrosis increased with toxin dose and was nearly maximal after 4 hr. Intraocular inflammation also generally increased with dose, but continued to increase until 18 hr. CONCLUSIONS: Standard clinical doses of intravitreal dexamethasone do not appear to attenuate the intraocular inflammatory or tissue response to secreted B. cereus exotoxins. Other treatment modalities including vitrectomy, to decrease exotoxin load, and exotoxin inhibitors may be necessary for the effective treatment of B. cereus endophthalmitis.

Swarming behavior of and hemolysin BL secretion by Bacillus cereus.

An association between swarming and hemolysin BL secretion was observed in a collection of 42 Bacillus cereus isolates (P=0.029). The highest levels of toxin were detected in swarmers along with swarm cell differentiation (P=0.021), suggesting that swarming B. cereus strains may have a higher virulence potential than nonswarming strains.

Forensic application of microbiological culture analysis to identify mail intentionally contaminated with Bacillus anthracis spores.

The discovery of a letter intentionally filled with dried Bacillus anthracis spores in the office of a United States senator prompted the collection and quarantine of all mail in congressional buildings. This mail was subsequently searched for additional intentionally contaminated letters. A microbiological sampling strategy was used to locate heavy contamination within the 642 separate plastic bags containing the mail. Swab sampling identified 20 bags for manual and visual examination. Air sampling within the 20 bags indicated that one bag was orders of magnitude more contaminated than all the others. This bag contained a letter addressed to Senator Patrick Leahy that had been loaded with dried B. anthracis spores. Microbiological sampling of compartmentalized batches of mail proved to be efficient and relatively safe. Efficiency was increased by inoculating culture media in the hot zone rather than transferring swab samples to a laboratory for inoculation. All mail sampling was complete within 4 days with minimal contamination of the sampling environment or personnel. However, physically handling the intentionally contaminated letter proved to be exceptionally hazardous, as did sorting of cross-contaminated mail, which resulted in generation of hazardous aerosol and extensive contamination of protective clothing. Nearly 8 x 10(6) CFU was removed from the most highly cross-contaminated piece of mail found. Tracking data indicated that this and other heavily contaminated envelopes had been processed through the same mail sorting equipment as, and within 1 s of, two intentionally contaminated letters.

Cooperative, synergistic and antagonistic haemolytic interactions between haemolysin BL, phosphatidylcholine phospholipase C and sphingomyelinase from Bacillus cereus.

Haemolysis of erythrocytes from different species (sheep, bovine, swine and human), caused by various combinations of phosphatidylcholine (PC)-preferring phospholipase C (PC-PLC), sphingomyelinase (SMase) and the three-component, pore-forming toxin haemolysin BL (HBL) from Bacillus cereus was analysed. The lytic potency of HBL did not correlate with phospholipid (PL) content, but lysis by the individual or combined enzymes did. SMase alone lysed ruminant erythrocytes, which contain 46-53% sphingomyelin (SM). The cooperative action of PC-PLC and SMase was needed to lyse swine and human erythrocytes (22-31% PC and 28-25% SM). SMase synergistically enhanced haemolysis caused by HBL for all erythrocytes tested, which all contained >25% SM. PC-PLC enhanced HBL haemolysis only in cells containing significant amounts of PC (swine, 22% PC; human, 31% PC). Unexpectedly, PC-PLC inhibited HBL lysis of sheep erythrocytes (<2% PC) and enhanced the discontinuous haemolysis pattern that is characteristic of HBL in sheep blood agar. Inhibition and pattern enhancement was abolished by washing PC-PLC-treated erythrocytes or by adding EDTA, suggesting that enzymic alteration of the membrane is not involved, but that zinc in the active site is required, perhaps to facilitate binding. These observations highlight the potential for cooperative and synergistic interactions among virulence factors in B. cereus infections and dependence of these effects on tissue composition.

Tripartite haemolysin BL: isolation and characterization of two distinct homologous sets of components from a single Bacillus cereus isolate.

Haemolysin BL (HBL), a three-component enterotoxic/necrotizing/vascular permeability toxin, is a likely virulence factor of Bacillus cereus diarrhoeal food poisoning and necrotic infections. This paper describes the isolation of two distinct homologous sets of all three HBL components from a single B. cereus isolate, MGBC 145. The proteins of one set (designated HBL, consisting of B, L(1) and L(2)), were about 87-100% identical in N-terminal amino acid sequences to their respective prototype components from strain F837/76, and the proteins of the homologous set (HBL(a), consisting of B(a), L(1a) and L(2a)) were all about 62-65% identical. Only the latter homologues differed immunochemically and physicochemically from the prototypes. HBL and HBL(a) exhibited similar haemolytic and vascular permeability potencies, and the homologues could be interchanged freely. There were no notable differences in activity between the L component homologues. However, components B and B(a) were significantly different. Both were secreted as monomers, but unlike B, B(a) was isolated as a relatively inactive complex that could be reactivated with urea. When B(a) was substituted for B in gel-diffusion assays the distinct discontinuous haemolysis pattern typical of the presence of B did not occur. In suspension assays, excess B inhibited the haemolysis of B-primed cells by L(1) (as previously described), but not that of B(a)-primed cells. Excess B(a) had the opposite effect and enhanced lysis of B(a)-primed cells, but not that of B-primed cells. These differences reveal details about how the toxin components interact on target cell membranes. The authors' observations indicate that HBL represents a new family of multicomponent toxins that was generated by a process of gene and operon duplication that occurred either intracellularly or by horizontal transfer, and raise the possibility of the existence of other related toxins in the genetically diverse B. cereus taxonomic group.

Swarming motility in Bacillus cereus and characterization of a fliY mutant impaired in swarm cell differentiation.

This report describes a new behavioural response of Bacillus cereus that consists of a surface-induced differentiation of elongated and hyperflagellated swarm cells exhibiting the ability to move collectively across the surface of the medium. The discovery of swarming motility in B. cereus paralleled the isolation of a spontaneous non-swarming mutant that was found to carry a deletion of fliY, the homologue of which, in Bacillus subtilis, encodes an essential component of the flagellar motor-switch complex. However, in contrast to B. subtilis, the fliY mutant of B. cereus was flagellated and motile, thus suggesting a different role for FliY in this organism. The B. cereus mutant was completely deficient in chemotaxis and in the secretion of the L2 component of the tripartite pore-forming necrotizing toxin, haemolysin BL, which was produced exclusively by the wild-type strain during swarm-cell differentiation. All the defects in the fliY mutant of B. cereus could be complemented by a plasmid harbouring the B. cereus fliY gene. These results demonstrate that the activity of fliY is required for swarming and chemotaxis in B. cereus, and suggest that swarm-cell differentiation is coupled with virulence in this organism.

Requirement of flhA for swarming differentiation, flagellin export, and secretion of virulence-associated proteins in Bacillus thuringiensis.

Bacillus thuringiensis is being used worldwide as a biopesticide, although increasing evidence suggests that it is emerging as an opportunistic human pathogen. While phospholipases, hemolysins, and enterotoxins are claimed to be responsible for B. thuringiensis virulence, there is no direct evidence to indicate that the flagellum-driven motility plays a role in parasite-host interactions. This report describes the characterization of a mini-Tn10 mutant of B. thuringiensis that is defective in flagellum filament assembly and in swimming and swarming motility as well as in the production of hemolysin BL and phosphatidylcholine-preferring phospholipase C. The mutant strain was determined to carry the transposon insertion in flhA, a flagellar class II gene encoding a protein of the flagellar type III export apparatus. Interestingly, the flhA mutant of B. thuringiensis synthesized flagellin but was impaired in flagellin export. Moreover, a protein similar to the anti-sigma factor FlgM that acts in regulating flagellar class III gene transcription was not detectable in B. thuringiensis, thus suggesting that the flagellar gene expression hierarchy of B. thuringiensis differs from that described for Bacillus subtilis. The flhA mutant of B. thuringiensis was also defective in the secretion of hemolysin BL and phosphatidylcholine-preferring phospholipase C, although both of these virulence factors were synthesized by the mutant. Since complementation of the mutant with a plasmid harboring the flhA gene restored swimming and swarming motility as well as secretion of toxins, the overall results indicate that motility and virulence in B. thuringiensis may be coordinately regulated by flhA, which appears to play a crucial role in the export of flagellar as well as nonflagellar proteins.

Fluorescent amplified fragment length polymorphism analysis of Bacillus anthracis, Bacillus cereus, and Bacillus thuringiensis isolates.

DNA from over 300 Bacillus thuringiensis, Bacillus cereus, and Bacillus anthracis isolates was analyzed by fluorescent amplified fragment length polymorphism (AFLP). B. thuringiensis and B. cereus isolates were from diverse sources and locations, including soil, clinical isolates and food products causing diarrheal and emetic outbreaks, and type strains from the American Type Culture Collection, and over 200 B. thuringiensis isolates representing 36 serovars or subspecies were from the U.S. Department of Agriculture collection. Twenty-four diverse B. anthracis isolates were also included. Phylogenetic analysis of AFLP data revealed extensive diversity within B. thuringiensis and B. cereus compared to the monomorphic nature of B. anthracis. All of the B. anthracis strains were more closely related to each other than to any other Bacillus isolate, while B. cereus and B. thuringiensis strains populated the entire tree. Ten distinct branches were defined, with many branches containing both B. cereus and B. thuringiensis isolates. A single branch contained all the B. anthracis isolates plus an unusual B. thuringiensis isolate that is pathogenic in mice. In contrast, B. thuringiensis subsp. kurstaki (ATCC 33679) and other isolates used to prepare insecticides mapped distal to the B. anthracis isolates. The interspersion of B. cereus and B. thuringiensis isolates within the phylogenetic tree suggests that phenotypic traits used to distinguish between these two species do not reflect the genomic content of the different isolates and that horizontal gene transfer plays an important role in establishing the phenotype of each of these microbes. B. thuringiensis isolates of a particular subspecies tended to cluster together.