Dry-heat destruction of lipopolysaccharide: dry-heat destruction kinetics.

Dry-heat destruction kinetics of lipopolysaccharides from Escherichia coli, Serratia marcescens, and Salmonella typhosa at 170 to 250 degrees C are described. The destruction rate seems to follow the second order and can be linearized by the equation, log y = a + b . -10cx. Because c is the slope, 1/c = D3. Both a and b are constant at a given temperature and are linear functions of temperature. The D(3)170, D(3)190, D(3)210, D(3)230, and D(3)250 values for E. coli lipopolysaccharide are 251, 99.4, 33.3, 12.3, and 4.99 min, respectively, with a z value of 46.4 min. The D values for lipopolysaccharides from S. marcescens and S. typhosa are not significantly different from those from E. coli lipopolysaccharide.     

Cloning and characterization of two Serratia marcescens genes involved in core lipopolysaccharide biosynthesis.

Bacteriocin 28b from Serratia marcescens binds to Escherichia coli outer membrane proteins OmpA and OmpF and to lipopolysaccharide (LPS) core (J. Enfedaque, S. Ferrer, J. F. Guasch, J. Tomás, and M. Requé, Can. J. Microbiol. 42:19-26, 1996). A cosmid-based genomic library of S. marcescens was introduced into E. coli NM554, and clones were screened for bacteriocin 28b resistance phenotype. One clone conferring resistance to bacteriocin 28b and showing an altered LPS core mobility in polyacrylamide gel electrophoresis was found. Southern blot experiments using DNA fragments containing E. coli rfa genes as probes suggested that the recombinant cosmid contained S. marcescens genes involved in LPS core biosynthesis. Subcloning, isolation of subclones and Tn5tac1 insertion mutants, and sequencing allowed identification of two apparently cotranscribed genes. The deduced amino acid sequence from the upstream gene showed 80% amino acid identity to the KdtA protein from E. coli, suggesting that this gene codes for the 3-deoxy-manno-octulosonic acid transferase of S. marcescens. The downstream gene (kdtX) codes for a protein showing 20% amino acid identity to the Haemophilus influenzae kdtB gene product. The S. marcescens KdtX protein is unrelated to the KdtB protein of E. coli K-12. Expression of the kdtX gene from S. marcescens in E. coli confers resistance to bacteriocin 28b.     

Endotoxic lipopolysaccharides stimulate steroidogenesis and adenylate cyclase in adrenal tumor cells.

Lipopolysaccharides (endotoxins) from Escherichia coli, Serratia marcesens and Salmonella typhosa stimulated steroid production in Y-1 adrenal tumor cells in culture with a latent period of 3-4 h. Lipid A, derived from Escherichia coli lipopolysaccharide, also stimulated steroidogenesis. Lipopolysaccharides and lipid A also stimulate adenylate cyclase activity and cause rounding of the cells. In contrast, lipopolysaccharides do not stimulate steroidogenesis in receptor-deficient adrenal tumor cells (OS-3) or Leydig tumor cells (I-10). This tends to rule out contamination by enterotoxin to which these lines respond. Although both hormone and lipopolysaccharide responses are lost in these lines, there was no interaction between these sites as judged by the failure of lipopolysaccharides to block, during their latency, the response to corticotropin in Y-1 cells. The possibility that the lipopolysaccharide effect is one on membrane conformation is discussed.     

The expression of lipopolysaccharide by strains of Shigella dysenteriae, Shigella flexneri and Shigella boydii and their cross-reacting strains of Escherichia coli

Strains of Shigella dysenteriae, Shigella flexneri and Shigella boydii express lipopolysaccharides, that enable the serotyping of strains based on their antigenic structures. Certain strains of S. dysenteriae, S. flexneri and S. boydii are known to share epitopes with strains of Escherichia coli ; however, the lipopolysaccharide profiles of the cross-reacting organisms have not been compared by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) lipopolysaccharides profiling. In the present study, type strains of these bacteria were examined using SDS-PAGE/silver staining to compare their respective lipopolysaccharide profiles. Strains of S. dysenteriae, S. boydii and S. flexneri all expressed long-chain lipopolysaccharide, with distinct profile patterns. The majority of strains of Shigella spp., known to cross-react with strains of E. coli , had lipopolysaccharide profiles quite distinct from the respective strain of E. coli . It was concluded that while cross-reacting strains of Shigella spp. and E. coli may express shared lipopolysaccharide epitopes, their lipopolysaccharide structures are not identical.     

Conservation and transfer of Escherichia coli genetic segments by partial diploid Hfr strains of Salmonella typhosa

Heterozygous, partial diploid hybrids were obtained in a Salmonella typhosa Hfr strain by using it as the recipient in a mating with the Escherichia coli Hfr donor WR2004 (O...proA...leu). Three of these S. typhosa Hfr hybrids were observed to mobilize and transfer the diploid E. coli genes, at high frequencies, to an E. coli recipient. The gradient of transfer frequencies of E. coli markers from these S. typhosa Hfr hybrids was similar to that observed with E. coli Hfr WR2004, from which they were derived. Interrupted matings with one of these S. typhosa Hfr hybrids, designated WR4272, showed the entry times for the proA, thr(-)leu, and argB E. coli diploid markers to be identical to the times obtained for these markers with E. coli Hfr WR2004. Also, the pattern of unselected inheritance of the diploid E. coli markers of S. typhosa Hfr hybrid WR4272 was similar to that observed with the chromosomal markers of E. coli Hfr WR2004. It was concluded that S. typhosa Hfr hybrid WR4272 contains, in addition to its Salmonella genome, a physically continuous E. coli chromosomal segment which is genetically complete from proA to at least the strA locus. The two other S. typhosa Hfr hybrids, on the basis of transmission frequency gradients, appeared to contain a continuous E. coli diploid segment complete from proA through the fuc locus. Other classes of S. typhosa Hfr hybrids, derived from mating with E. coli Hfr WR2010 (O...tna...xyl), were also observed to transfer E. coli genes at high frequency.     

Inefficiency of genetic recombination in hybrids between Escherichia coli and Salmonella typhosa

An Escherichia coli Hfr strain in which three negative chromosomal alleles (leu(-), arg(-), and mtl(-)) were closely linked to three positive alleles (ara(+), rha(+), and xyl(+), respectively) was employed in matings with a Salmonella typhosa recipient. The detected expression of the negative E. coli alleles in S. typhosa hybrids selected for receipt of an associated positive E. coli marker was used to determine the occurrence of haploid S. typhosa recombinants, as distinguished from stable partial diploid hybrids. At the same time, the inheritance patterns and segregation behavior of the positive alleles provided indicators of the occurrence of partial diploid hybrids. Examination of both positive and negative markers inherited by ara(+), rha(+), and xyl(-) selected S. typhosa hybrid classes indicated that relatively short E. coli chromosomal segments (generally about 4 min or less in length) were involved in recombination (haploidy), whereas rather extensive E. coli genetic segments were conserved in the diploid state. S. typhosa hybrids selected for receipt of the ara(+) marker showed a 52% incidence of leu(-) haploidy, which is probably close to being an accurate measure of recombination at the site of the ara(+) allele. S. typhosa hybrids selected for receipt of the rha(+) or xyl(+) markers showed only a 20% incidence of arg(-) or mtl(-) haploidy, respectively, but both of these hybrid classes exhibited a higher incidence of conservation of extensive E. coli diploid segments than did the ara(+) selected class. Remating of haploid S. typhosa hybrids with recombinant xyl(+)mtl(-) or rha(+)arg(-) regions resulted in higher frequencies of hybrid recovery than were observed in the initial matings. However, there was a higher incidence of partial diploidy and a lower incidence of haploidy among the hybrids obtained from these rematings.     

Chromosomal Location of Ribosomal Protein Cistrons Determined by Intergeneric Bacterial Mating

Intergeneric mating between Escherichia coli and Salmonella typhosa was used to locate at least three 30S ribosomal proteins near the streptomycin locus in the region of 54 to 66 min of the E. coli map. This procedure utilizes differences in the electrophoretic patterns of 30S ribosomal protein of the parents. The results show that cistrons for 30S proteins of E. coli can replace those of S. typhosa in the Salmonella genome. Moreover, in a diploid hybrid with a Salmonella endogenote and an E. coli exogenote, both sets of cistrons are expressed.     

Behavior of coliphage lambda in hybrids between Escherichia coli and Salmonella

Salmonella typhosa hybrids able to adsorb lambda were obtained by mating S. typhosa recipients with Escherichia coli K-12 donors. After adsorption of wild-type lambda to these S. typhosa hybrids, no plaques or infective centers could be detected. E. coli K-12 gal(+) genes carried by the defective phage lambdadg were transduced to S. typhosa hybrids with HFT lysates derived from E. coli heterogenotes. The lysogenic state which resulted in the S. typhosa hybrids after gal(+) transduction differed from that of E. coli. Ability to produce lambda, initially present, was permanently segregated by transductants of the S. typhosa hybrid. S. typhosa lysogens did not lyse upon treatment for phage induction with mitomycin C, ultraviolet light, or heat in the case of thermoinducible lambda. A further difference in the behavior of lambda in Salmonella hybrids was the absence of zygotic induction of the prophage when transferred from E. coli K-12 donors to S. typhosa. A new lambda mutant class, capable of forming plaques on S. typhosa hybrids refractory to wild-type lambda, was isolated at low frequency by plating lambda on S. typhosa hybrid WR4254. Such mutants have been designated as lambdasx, and a mutant allele of lambdasx was located between the P and Q genes of the lambda chromosome. Plaques were formed also on the S. typhosa hybrid host with a series of lambda(i21) hybrid phages which contain the N gene of phage 21. The significance of these results in terms of Salmonella species as hosts for lambda is discussed.     

Comparison of the aspartate transcarbamoylases from Serratia marcescens and Escherichia coli

The aspartate transcarbamoylases (ATCase, EC 2.1.3.2) of Escherichia coli and Serratia marcescens have similar dodecameric enzyme structures (2(c3):3(r2] but differ in both regulatory and catalytic characteristics. The catalytic cistrons (pyrB) of the ATCases from E. coli and S. marcescens encode polypeptides of 311 and 306 amino acids, respectively; there is a 76% identity between the DNA sequences and an overall amino acid homology of 88% (38 differences). The regulatory cistrons (pyrI) of these ATCases encode polypeptides of 153 and 154 amino acids, respectively, and there is a 75% identity between the DNA sequences and an overall amino acid homology of 77% (36 differences). In both species, the two genes are arranged as a bicistronic operon, with pyrB promoter proximal. A comparison of the deduced amino acid sequences reveals that the active site and the allosteric binding sites, as well as most of the intrasubunit interactions and intersubunit associations, are conserved in the E. coli and the S. marcescens enzymes; however, there are specific differences which undoubtedly contribute to the catalytic and regulatory differences between the enzymes of the two species. These differences include residues that have been implicated in the T-R transition, c1:r1 interface interactions, and the CTP binding site. A hybrid ATCase assembled in vivo with catalytic subunits from E. coli and regulatory subunits from S. marcescens has a 6 mM requirement for aspartate at half-maximal saturation, similar to the 5.5 mM aspartate requirement of the native E. coli holoenzyme at half-maximal saturation. However, the heterotropic response of this hybrid enzyme is characteristic of the heterotropic response of the native S. marcescens holoenzyme: ATP activation and CTP activation. Activation by both allosteric effectors indicates that the heterotropic response of this hybrid holoenzyme (Cec:Rsm) is determined by the associated S. marcescens regulatory subunits.     

Synthesis of a Klebsiella pneumoniae O-antigen heteropolysaccharide (O12) requires an ABC 2 transporter

A recombinant clone encoding enzymes for Klebsiella pneumoniae O12-antigen lipopolysaccharide (LPS) was found when we screened for serum resistance of a cosmid-based genomic library of K. pneumoniae KT776 (O12:K80) introduced into Escherichia coli DH5alpha. A total of eight open reading frames (ORFs) (wb(O12) gene cluster) were necessary to produce K. pneumoniae O12-antigen LPS in E. coli K-12. A complete analysis of the K. pneumoniae wb(O12) cluster revealed an interesting coincidence with the wb(O4) cluster of Serratia marcescens from ORF5 to ORF8 (or WbbL to WbbA). This prompted us to generate mutants of K. pneumoniae strain KT776 (O12) and to study complementation between the two enterobacterial wb clusters using mutants of S. marcescens N28b (O4) obtained previously. Both wb gene clusters are examples of ABC 2 transporter-dependent pathways for O-antigen heteropolysaccharides. The wzm-wzt genes and the wbbA or wbbB genes were not interchangeable between the two gene clusters despite their high level of similarity. However, introduction of three cognate genes (wzm-wzt-wbbA or wzm-wzt-wbbB) into mutants unable to produce O antigen allowed production of the specific O antigen. The K. pneumoniae O12 WbbL protein performs the same function as WbbL from S. marcescens O4 in either the S. marcescens O4 or E. coli K-12 genetic background.     

Structural studies of glucorhamnans isolated from the lipopolysaccharides of reference strains for Serratia marcescens serogroups O4 and O7, and of an O14 strain

Partially acetylated glucorhamnans have been isolated from the lipopolysaccharides of three strains of Serratia marcescens. The polymer from the reference strain (C.D.C. 864-57) for serogroup O4 has the disaccharide repeating-unit shown below, in which acetylation at position 2 of the rhamnosyl residue is approximately 90% complete. Similar glucorhamnans from the reference strain (C.D.C. 843-57) for serogroup O7 and from a pigmented strain (NM) of serogroup O14 differ only in the configuration of the L-rhamnopyranosyl residue (beta) and the extent of O-acetylation (O7, almost stoichiometric; NM, 80-90%). Glucorhamnans of the second type have been isolated previously from the lipopolysaccharides of other strains of S. marcescens, including the reference strain for serogroup O6 and another pigmented O14 strain (N.C.T.C. 1377). In all cases, the lipopolysaccharide extracts also contained acidic glycans, but the glucorhamnans are believed to constitute the integral side-chains. (Formula: see text).     

Dry-heat destruction of lipopolysaccharide: design and construction of dry-heat destruction apparatus.

A dry-heat oven with automatic, multiple-sample introduction and withdrawal has been constructed to achieve instantaneous heating and cooling of samples. The oven temperature fluctuation at set points of 170 to 250 degrees C was +/- 0.1 degrees C, with temperature variation between the replicate samples of +/- 0.2 degrees C. Correction required for a sample come-up time was minimal, i.e., less than 0.25 min of the dry-heat destruction time.     

Evidence for unique DNA repair activity encoded by a cloned Serratia marcescens gene: suppression of Escherichia coli mutations that reduce repair of alkylated DNA.

A recombinant plasmid containing a Serratia marcescens DNA repair gene has been analyzed biochemically and genetically in Escherichia coli mutants deficient for repair of alkylated DNA. The cloned gene suppressed sensitivity to methyl methanesulfonate of an E. coli strain deficient in 3-methyladenine DNA glycosylases I and II (i.e., E. coli tag alkA) and two different E. coli recA mutants. Attempts to suppress the methyl methanesulfonate sensitivity of the E. coli recA mutant by using the cloned E. coli tag and alkA genes were not successful. Southern blot analysis did not reveal any homology between the S. marcescens gene and various known E. coli DNA repair genes. Biochemical analysis with the S. marcescens gene showed that the encoded DNA repair protein liberated 3-methyladenine from alkylated DNA, indicating that the DNA repair molecular is an S. marcescens 3-methyladenine DNA glycosylase. The ability to suppress both types of E. coli DNA repair mutations, however, suggests that the S. marcescens gene is a unique bacterial DNA repair gene.     

Isolation of Circular Deoxyribonucleic Acid from Salmonella typhosa Hybrids Obtained from Matings with Escherichia coli Hfr Donors

Heterozygous, partial diploid Salmonella typhosa hybrids obtained from matings with Escherichia coli K-12 Hfr strains were observed to contain supercoiled, circular deoxyribonucleic acid (DNA) when examined by the dye-buoyant density method. Examination of one such S. typhosa hybrid after its loss, by segregation, of the inherited E. coli genetic markers revealed a concurrent loss of its supercoiled circular DNA. Subsequent remating of this segregant with various E. coli Hfr strains resulted in the reappearance of the circular DNA. Molecular weight determinations of circular DNA molecules isolated from a number of S. typhosa partial diploid hybrids were made by sucrose density gradient ultracentrifugation and electron microscopy. These studies revealed a range of molecular sizes among the various hybrids examined, but each hybrid exhibited only a single characteristic size for its contained circular DNA. The range of size is consistent with the presence in each hybrid of a different length of E. coli chromosome. It was concluded that the E. coli Hfr genetic segments transferred to these S. typhosa hybrids were conserved, in the diploid state, in the form of supercoiled, circular DNA molecules.     

Nature of Lactose-fermenting Salmonella Strains Obtained from Clinical Sources

Six of seven lactose-fermenting (lac(+)) Salmonella strains obtained from clinical sources were found to be capable of transferring the lac(+) property by conjugation to Salmonella typhosa WR4204. All of the six S. typhosa strains which received the lac(+) property transferred it in turn to S. typhimurium WR5000 at the high frequencies typical of extrachromosomal F-merogenotes. These six lac elements were also transmissible from S. typhosa WR4204 to Proteus mirabilis and to some strains of Escherichia coli K-12; moreover, they were capable of promoting low frequency transfer of chromosomal genes from S. typhimurium WR5000 to S. typhosa WR4204. One of these lac elements was shown also to be capable of promoting low frequency chromosome transfer in E. coli K-12. E. coli K-12 strains harboring these lac elements exhibited sensitivity to the male specific phage R-17. Sensitivity to R-17 was not detected in Salmonella strains containing the elements. Examination of the lac elements in P. mirabilis by cesium chloride density gradient centrifugation showed that each element had a guanine plus cytosine content of 50%. The sizes of the elements varied from 0.8 to 3% of the total Proteus deoxyribonucleic acid. The amount of beta-galactosidase produced by induced and uninduced cultures of S. typhimurium WR5000 and S. typhosa WR4204 containing the lac elements was lower than that produced by these strains with the F-lac episome. The heat sensitivity of beta-galactosidase produced by the lac elements in their original Salmonella hosts indicated that the enzyme made by these strains differs from E. coli beta-galactosidase.     

A gene (wbbL) from Serratia marcescens N28b (O4) complements the rfb-50 mutation of Escherichia coli K-12 derivatives.

A cosmid-based genomic library of Serratia marcescens N28b was introduced into Escherichia coli DH5alpha, and clones were screened for serum resistance. One clone was found resistant to serum, to bacteriocin 28b, and to bacteriophages TuIa and TuIb. This clone also showed O antigen in its lipopolysaccharide. Subcloning and sequencing experiments showed that a 2,124-bp DNA fragment containing the rmlD and wbbL genes was responsible for the observed phenotypes. On the basis of amino acid similarity, we suggest that the 288-residue RmlD protein is a dTDP-L-rhamnose synthase. Plasmid pJT102, containing only the wbbL gene, was able to induce O16-antigen production and serum resistance in E. coli DH5alpha. These results suggest that the 282-residue WbbL protein is a rhamnosyltransferase able to complement the rJb-50 mutation in E. coli K-12 derivatives, despite the low level of amino acid identity between WbbL and the E. coli rhamnosyltransferase (24.80%). S. marcescens N28b rmlD and wbbL mutants were constructed by mobilization of suicide plasmids containing a portion of rmlD or wbbL. These insertion mutants were unable to produce O antigen; since strain N28b produces O4 antigen, these results suggest that both genes are involved in O4-antigen biosynthesis.     

The tonB gene of Serratia marcescens: sequence, activity and partial complementation of Escherichia coli tonB mutants

The TonB protein plays a key role in the energy-coupled transport of iron siderophores, of vitamin B12, and of colicins of the B-group across the outer membrane of Escherichia coli. In order to obtain more data about which of its particular amino acid sequences are necessary for TonB function, we have cloned and sequenced the tonB gene of Serratia marcescens. The nucleotide sequence predicts an amino acid sequence of 247 residues (Mr 27,389), which is unusually proline-rich and contains the tandem sequences (Glu-Pro)5 and (Lys-Pro)5. In contrast to the TonB proteins of E. coli and Salmonella typhimurium, translation of the S. marcescens TonB protein starts at the first methionine residue of the open reading frame, which is the only amino acid removed during TonB maturation and export. Only the N-terminal sequence is hydrophobic, suggesting its involvement in anchoring the TonB protein to the cytoplasmic membrane. The S. marcescens tonB gene complemented an E. coli tonB mutant with regard to uptake of iron siderophores, and sensitivity to phages T1 and phi 80, and to colicins B and M. However, an E. coli tonB mutant transformed with the S. marcescens tonB gene remained resistant to colicins Ia and Ib, to colicin B derivatives carrying the amino acid replacements Val/Ala and Val/Gly at position 20 in the TonB box, and they exhibited a tenfold lower activity with colicin D. In addition, the S. marcescens TonB protein did not restore T1 sensitivity of an E. coli exbB tolQ double mutant, as has been found for the overexpressed E. coli TonB protein, indicating a lower activity of the S. marcescens TonB protein. Although the S. marcescens TonB protein was less prone to proteolytic degradation, it was stabilized in E. coli by the ExbBD proteins. In E. coli, TonB activity of S. marcescens depended either on the ExbBD or the TolQR activities.     

Structural and physicochemical requirements of endotoxins for the activation of arachidonic acid metabolism in mouse peritoneal macrophages in vitro

Lipopolysaccharides of different wild-type and mutant gram-negative bacteria, as well as synthetic and bacterial free lipid A, were studied for their ability to activate arachidonic acid metabolism in mouse peritoneal macrophages in vitro. It was found that lipopolysaccharides of deep-rough mutants of Salmonella minnesota and Escherichia coli (Re to Rc chemotypes) stimulated macrophages to release significant amounts of leukotriene C4 (LTC4) and prostaglandin E2 (PGE2). Lipopolysaccharides of wild-type strains (S. abortus equi, S. friedenau) only induced PGE2 and not LTC4 formation. Unexpectedly, free bacterial and synthetic E. coli lipid A were only weak inducers of LTC4 and PGE2 production. Deacylated Re-mutant lipopolysaccharide preparations were inactive. However, co-incubation of macrophages with both deacylated lipopolysaccharide and lipid A lead to the release of significant amounts of LTC4 and PGE2, similar to those obtained with Re-mutant lipopolysaccharide. The significance of the lipid A portion of lipopolysaccharide for the induction of LTC4 was indicated by demonstrating that peritoneal macrophages of endotoxin-low-responder mice or of mice rendered tolerant to endotoxin did not respond with the release of arachidonic acid metabolites on stimulation with Re-mutant lipopolysaccharide and that polymyxin B prevented the Re-lipopolysaccharide-induced LTC4 and PGE2 release. Physical measurements showed that the phase-transition temperatures of both free lipid A and S-form lipopolysaccharide were above 37 degrees C while those of R-mutant lipopolysaccharides were significantly lower (30-35 degrees C). Thus, with the materials investigated, an inverse relationship between the phase-transition temperature and the capacity to elicit LTC4 production was revealed.     

Accelerated Adsorption of Bacteriophage T5 to Escherichia coli F, Resulting from Reversible Tail Fiber-Lipopolysaccharide Binding

A dual specificity for phage T5 adsorption to Escherichia coli cells is shown. The tail fiber-containing phages T5(+) and mutant hd-3 adsorbed rapidly to E. coli F (1.2 x 10(-9) ml min(-1)), whereas the adsorption rate of the tail fiber-less mutants hd-1, hd-2, and hd-4 was low (7 x 10(-11) ml min(-1)). The differences in adsorption rates were due to the particular lipopolysaccharide structure of E. coli F. Phage T4-resistant mutants of E. coli F with an altered lipopolysaccharide structure exhibited similar low adsorption for all phage strains with and without tail fibers. The same held true for E. coli K-12 and B which also differ from E. coli F in their lipopolysaccharide structures. Only the tail fiber-containing phages reversibly bound to isolated lipopolysaccharides of E. coli F. Infection by all phage strains strictly depended on the tonA-coded protein in the outer membrane of E. coli. We assume that the reversible preadsorption by the tail fibers to lipopolysaccharide accelerates infection which occurs via the highly specific irreversible binding of the phage tail to the tonA-coded protein receptor. The difference between rapid and slow adsorption was also revealed by the competition between ferrichrome and T5 for binding to their common tonA-coded receptor in tonB strains of E. coli. Whereas binding of T5(+) to E. coli K-12 and of the tail-fiber-less mutant hd-2 to E. coli F and K-12 was inhibited 50% by about 0.01 muM ferrichrome, adsorption of T5 to E. coli F was inhibited only 40% by even 1,000-fold higher ferrichrome concentrations.     

Dry-heat destruction of lipopolysaccharide: mathematical approach to process evaluation.

A mathematical model was developed to estimate the number of logarithmic cycles (LDec) of lipopolysaccharide concentration destroyed by a dry-heat sterilization process. The LDec values calculated from the mathematical model agreed well with those obtained from the destruction of lipopolysaccharide by a dry-heat treatment. A discussion of how the mathematical model may be used to evaluate a dry-heat sterilization cycle is presented. This mathematical model and the dry-heat destruction curves indicated existence of a maximum LDec value at each temperature. The implications of this finding are discussed.