Spontaneous Autolysis Research Articles

Assessment of changes in the phenotype, intensity of degranulation, death and lysis of neutrophils in <i>ex vivo</i> modeling of <i>Staphylococcal</i> bacteremia

Introduction. At present, it is important to study the interaction of Staphylococcus aureus with human innate immunity cells under conditions of ex vivo bacteremia modeling, but not only in experiments with phagocytes previously isolated from the blood.
 Purpose: comparative assessment of changes in the phenotype, intensity of aurophilic degranulation, death and lysis of neutrophils in whole blood samples from apparently healthy donors following the addition of live and killed microbial cells of S. aureus ATCC 6538 (209-P).
 Materials and methods. Bacteremia was modeled by adding microbes to whole blood (with heparin) at doses ranging from 108 to 101 mc/ml. The bactericidal effect was determined at different time points of blood incubation at 37C (for 6 hours) by the microbiological method. The blood leukocyte immunophenotyping was performed using flow cytometry according to the Lyse/No-Wash protocol to determine the expression of markers of azurophilic degranulation (CD63), early apoptosis (CD95) on the surface of neutrophilic granulocytes (NG) and cell adhesion (CD62L), as well as to assess the surface expression density of the molecular trigger of netosis FcᵧRIIIb (CD16) and tyrosine protein phosphatase (CD45), which is a regulator of FcR-mediated cell signaling during phagocytosis and netosis. The presence of degenerative changes in NG was confirmed by microscopy in the analysis of blood smears stained according to RomanovskyGiemsa.
 Results. Significant differences were revealed in the response of human blood NG to live and killed S. aureus cells according to the studied phenotypic parameters. Only live microbes triggered azurophilic degranulation in NCs and stimulated, starting from 2 h incubation, the appearance of a large number of NG with the CD95+ phenotype in the blood. In addition, live bacteria induced in phagocytes twice as much functional rearrangement in terms of CD45 expression. They induced a rapid decrease in the density of CD16 expression on NG and activated NG lysis in the blood with an intensity depending on the initial microbial concentration. Following 6 h incubation at concentrations of more than 105 mc/ml, flow cytometry detected the presence in the blood of a population of low density neutrophils characteristic of sepsis (Low Density Neutrophils with the CD63+CD16low phenotype), whose cells are prone to spontaneous autolysis (netosis).
 Conclusion. Under the conditions of ex vivo modeling of bacteremia, various strategies of human blood neutrophils in the implementation of the mechanisms of protection of the macroorganism from infection were evaluated, and the prospects of using the obtained information to identify individuals at high risk of developing staphylococcal sepsis were determined.

Assessment of neutrophil degranulation intensity and changes in neutrophil phenotype by FCᵧRIIIB expression level in blood of patients with COVID-19 and convalescents

Introduction. Disease severity in hospitalized COVID-19 patients correlates with the relative content in the blood of a specific low-density neutrophilic granulocyte (NG) population, whose cells are characterized by reduced granularity, high heterogeneity in the expression of FcᵧRIIIb (CD16) and a tendency to spontaneous autolysis (netosis).The aim of the study was to compare the intensity of NG degranulation and the FcᵧRIIIb expression by these cells in blood of patients with COVID-19 and convalescents.Materials and methods. The blood leukocytes of 40 patients diagnosed with COVID-19, 33 convalescents and 20 healthy donors (control) were examined using flow cytometry. To identify NG (CD16+-granulocytes) and to assess the surface expression of the netosis molecular trigger (FcᵧRIIIb), a single-color reagent of labeled monoclonal antibodies CD16-FITC was used. Immunophenotyping of lymphocytes was performed using two four-color reagents. In addition, cell debris content was determined in each Lyse/No-Wash-stained whole blood sample. The presence of neutrophils at the stage of netosis was confirmed by microscopy. Cytokine production was determined on an automatic enzyme immunoassay analyzer.Results. Against the background of characteristic changes in the lymphocyte subpopulation composition and cytokine production, in blood of COVID-19 patients with acute pneumonia, hypoxia and tachycardia a more intense degranulation of NG (2.6 times), higher degree of CD16 expression heterogeneity (1.8 times) and an increased leukocytolysis intensity (1.6 times) were observed compared to convalescents who have undergone severe and moderate forms of the disease. In convalescents, the degree of differences of these indicators compared to control values varied in concordance with the disease severity.Conclusion. The nature of changes in the parameters studied in COVID-19 patients in the acute phase of the disease and during the period of convalescence confirms the possible mechanism of the development of complications due to an imbalance between the activity of elastase released from NG granules and its plasma inhibitor α1 -antitrypsin.

Rapid and Cost-Effective RNA Extraction of Rat Pancreatic Tissue.

Regardless of the extraction method, optimized RNA extraction of tissues and cell lines are carried out in four stages: 1) homogenization, 2) effective denaturation of proteins from RNA, 3) ribonuclease inactivation, and 4) removal of contamination from DNA, proteins, and carbohydrates. However, it is very laborious to maintain the integrity of RNA when there are high levels of RNase in the tissue. Spontaneous autolysis makes it very difficult to extract RNA from pancreatic tissue without damaging it. Thus, a practical RNA extraction method is needed to maintain the integrity of pancreatic tissues during the extraction process. An experimental and comparative study of existing protocols was carried out by obtaining 20-30 mg of rat pancreatic tissues in less than 2 minutes and extracting the RNA. The results were assessed by electrophoresis. The experiments were carried out three times for generalization of the results. Immersing pancreatic tissue in RNA stabilization reagent at -80 °C for 24 h yielded high integrity RNA, when the RNA extraction reagent was used as the reagent. The results obtained were comparable to the results obtained from commercial kits with spin column bindings.

P879Discharge medication and 1-year outcomes in patients with myocardial infarction and nonobstructive coronary artery disease: a nationwide registry-based study

Abstract Introduction Myocardial infarction with nonobstructive coronary arteries (MINOCA) occurs in 5% to 10% of all patients with myocardial infarction. Although these patients are often treated as if they had obstructive coronary artery disease (OCAD), optimal medical therapy for secondary prevention in MINOCA patients have not been prospectively studied. We hypothesize that the same treatment strategy as for OCAD is unlikely to be beneficial in MINOCA patients due to their heterogeneous nature. Purpose Characterize and assess the impact of discharge medication on 1-year mortality or hospitalization in patients with MINOCA. Methods Retrospective cohort study of consecutive patients with acute myocardial infarction (AMI) recorded in the Portuguese Registry of Acute Coronary Syndromes (ProACS) between 2010 and 1017. All patients who underwent coronary angiography and had no obstructive lesions (defined as <50% diameter stenosis) were included for analysis (n=829, 4.8% of a total of 17213). Patient demographics, clinical characteristics and medication at discharge were analyzed. The association between treatment and outcome was estimated by comparing treated and untreated groups using Cox proportional hazard models. The exposures considered were treatment at discharge with statins, angiotensin-converting enzyme inhibitors/angiotensin receptor blockers (ACEi/ARBs), beta-blockers (BB), aspirin (ASA) or dual antiplatelet therapy (DAPT). The outcomes evaluated were 1-year all-cause mortality and 1-year hospitalization due to cardiovascular disease (CVD) Results 829 patients (54% male, mean age 65±13 years) were included. 67% had hypertension, 20% diabetes mellitus, 45% hyperlipidemia, 66% were overweight, 23% were current smokers, 5.5% had history of heart failure, 4.3% valvular heart disease, 8% cerebrovascular disease and 4.7% chronic kidney disease. The admission diagnosis was most frequently non-ST elevation MI (79.3%) and mean left ventricular ejection fraction (%) was 56±12. 4 patients died during hospitalization (0.5%). At discharge, aspirin was prescribed in 85.7% patients, clopidogrel in 54.8%, ticagrelor in 7.5%, DAPT in 57.7%, ACEi/ARB in 79.2%, beta-blocker in 69% and statins in 90.2%. 1-year mortality and 1-year CVD hospitalization was 3.8% and 9%, respectively. After adjusting for covariates in Cox regression analysis, we found no association between any medication at discharge and 1-year outcomes. Conclusion A high proportion of patients are prescribed antiplatelet therapy, including DAPT. We found no significant 1-year beneficial effect of treatment with statins, ACEi/ARBs, BB, aspirin or DAPT in MINOCA. This may be partially explained by the highly heterogenous population and relative short-term follow-up. In MINOCA patients, treatment should be individualized after an exhaustive diagnostic workup to identify the underlying cause (e.g. CAD with spontaneous autolysis of an intracoronary thrombus, myocarditis or takotsubo syndrome).

Preparation of Sedimented Wine Yeast Derived Products for Potential Application in Food and Feed Industry

The aim of this study was to obtain preparations of sedimented wine yeast, which is an unutilised waste from the production of fruit wines in Poland. Yeast extracts, cell wall preparations and purified cell wall preparations were obtained as a result of complete yeast cells fractionation using initial phase of spontaneous autolysis and performed with various process promoters, such as NaCl, glucose, ethanol, acetic acid and lactic acid at different concentrations and in different combinations. The influence of applied autolysis promotors on protein recovery from yeast extracts and protein content in cell wall preparations was assessed. As an important property of yeasts cell wall preparation the influence of alkaline isolation and purification with acetic on the β-glucan content in cell wall were determined. The ability of yeast preparations to bind fat and water was also assessed. Sedimented wine yeast was characterised by low sensitivity to the autolysis process, as from 100 g of dry yeast, depending on the autolysis promoter used, 6.6–10.5 g of protein was recovered. The highest β-glucan content—35.0% in dry matter was assayed in purified cell wall preparation of sedimented wine yeast obtained after autolysis with 0.5% NaCl added to the autolysing mixture. The preparation’s water-binding and fat-binding capacities amounted to 304.8 and 82.9% respectively. Further research in applications obtained yeast products from new raw material (sedimented wine yeast) in food and feed industries must be investigated.

Spontaneous large-scale autolysis in Clostridium acetobutylicum contributes to generation of more spores.

Autolysis is a widespread phenomenon in bacteria. In batch fermentation of Clostridium acetobutylicum ATCC 824, there is a spontaneous large-scale autolysis phenomenon with significant decrease of cell density immediately after exponential phase. To unravel the role of autolysis, an autolysin-coding gene, CA_C0554, was disrupted by using ClosTron system to obtain the mutant C. acetobutylicum lyc::int(72). The lower final cell density and faster cell density decrease rate of C. acetobutylicum ATCC 824 than those of C. acetobutylicum lyc::int(72) indicates that CA_C0554 was an important but not the sole autolysin-coding gene responding for the large-scale autolysis. Similar glucose utilization and solvents production but obvious lower cell density of C. acetobutylicum ATCC 824 comparing to C. acetobutylicum lyc::int(72) suggests that lysed C. acetobutylicum ATCC 824 cells were metabolic inactive. On the contrary, the spore density of C. acetobutylicum ATCC 824 is 26.1% higher than that of C. acetobutylicum lyc::int(72) in the final culture broth of batch fermentation. We speculated that spontaneous autolysis of metabolic-inactive cells provided nutrients for the sporulating cells. The present study suggests that one important biological role of spontaneous large-scale autolysis in C. acetobutylicum ATCC 824 batch fermentation is contributing to generation of more spores during sporulation.

Treatment of leptothrix cells with ultrapure water poses a threat to their viability.

The genus Leptothrix, a type of Fe/Mn-oxidizing bacteria, is characterized by its formation of an extracellular and microtubular sheath. Although almost all sheaths harvested from natural aquatic environments are hollow, a few chained bacterial cells are occasionally seen within some sheaths of young stage. We previously reported that sheaths of Leptothrix sp. strain OUMS1 cultured in artificial media became hollow with aging due to spontaneous autolysis within the sheaths. In this study, we investigated environmental conditions that lead the OUMS1 cells to die. Treatment of the cells with ultrapure water or acidic buffers (pH 6.0) caused autolysis of the cells. Under these conditions, the plasma membrane and cytoplasm of cells were drastically damaged, resulting in leakage of intracellular electrolytes and relaxation of genomic DNA. The autolysis was suppressed by the presence of Ca2+. The hydrolysis of peptidoglycan by the lysozyme treatment similarly caused autolysis of the cells and was suppressed also by the presence of Ca2+. However, it remains unclear whether the acidic pH-dependent autolysis is attributable to damage of peptidoglycan. It was observed that L. discophora strain SP-6 cells also underwent autolysis when suspended in ultrapure water; it is however, uncertain whether this phenomenon is common among other members of the genus Leptothrix.

Discrete and overlapping functions of peptidoglycan synthases in growth, cell division and virulence of Listeria monocytogenes.

Upon ingestion of contaminated food, Listeria monocytogenes can cause serious infections in humans that are normally treated with β-lactam antibiotics. These target Listeria's five high molecular weight penicillin-binding proteins (HMW PBPs), which are required for peptidoglycan biosynthesis. The two bi-functional class A HMW PBPs PBP A1 and PBP A2 have transglycosylase and transpeptidase domains catalyzing glycan chain polymerization and peptide cross-linking, respectively, whereas the three class B HMW PBPs B1, B2 and B3 are monofunctional transpeptidases. The precise roles of these PBPs in the cell cycle are unknown. Here we show that green fluorescent protein (GFP)-PBP fusions localized either at the septum, the lateral wall or both, suggesting distinct and overlapping functions. Genetic data confirmed this view: PBP A1 and PBP A2 could not be inactivated simultaneously, and a conditional double mutant strain is largely inducer dependent. PBP B1 is required for rod-shape and PBP B2 for cross-wall biosynthesis and viability, whereas PBP B3 is dispensable for growth and cell division. PBP B1 depletion dramatically increased β-lactam susceptibilities and stimulated spontaneous autolysis but had no effect on peptidoglycan cross-linkage. Our in vitro virulence assays indicated that the complete set of all HMW PBPs is required for maximal virulence.

Characterization of an Enterococcus faecium small-colony variant isolated from blood culture

Small-colony variants (SCVs) of bacteria are slow-growing subpopulations which can cause latent or recurrent infections due to better intracellular survival compared to their wild-type counterparts. Atypical colony morphology and altered biochemical profile may lead to failure in identification of SCV strains. We here report for the first time the isolation of an Enterococcus faecium SCV phenotype. The case of a 65-year-old woman with acute myeloid leukaemia who developed symptoms of sepsis during induction chemotherapy is presented. E. faecium with normal and SCV phenotype was isolated from blood cultures. At the same time urine culture was positive with E. faecium suggesting that bacteraemia originated from the urinary tract. The SCV phenotype was characterized by atypical growth behaviour. Electron microscopic analyses revealed perturbation of the separation of daughter cells and the accumulation of cell wall material. Accordingly, the SCV variant showed a dysfunction or lack of spontaneous autolysis whereas the normal phenotype did not. In contrast to conventional identification systems based on biochemical characteristics, the E. faecium SCV was precisely identified by MALDI-TOF MS analysis implemented in our laboratory. Hence, the increasing use of MALDI-TOF MS analysis for the identification of bacteria might be an appropriate tool for the detection of SCV variants, the diagnosis of which is of importance for the clinical outcome and the antibiotic treatment.

A single step purification for autolytic zinc proteinases.

We describe a novel single-step method for the purification of stromelysin-1 catalytic domain (SCD) via immobilized metal affinity chromatography under denaturing conditions that inhibit proteolytic activity followed by on-column refolding and spontaneous autolysis of the fusion peptide to yield pure, active stromelysin-1 catalytic domain. The methodology provides a general approach for the rapid purification of large quantities of zinc proteinases.

A Novel Mechanism of Autolysis in Helicobacter pylori: Possible Involvement of Peptidergic Substances

Helicobacter pylori survival in a hostile acidic environment is known to be caused by its production of urease, which is not released by known secretion pathways. It has been proposed that H. pylori cells undergo spontaneous autolysis during cultivation and that urease becomes surface-associated only concomitant with bacterial autolysis. The aim of this study was to elucidate mechanisms by which H. pylori cells undergo autolysis during cultivation. Autolysis of H. pylori KZ109 cells was estimated by measuring the turbidity of the culture, by detection of cytoplasmic protein release into the culture supernatant and by scanning electron microscopic observation of H. pylori cells during cultivation. An autolysis-inducing factor (AIF) was partially purified from the culture supernatant by a partition method using ethyl acetate. Bacterial turbidity of KZ109 cells was drastically decreased after late-log phase accompanying release of urease and HspB into the extracellular space. Concomitantly, cell lytic activity was detected in the culture supernatant. Scanning electron microscopic observation suggested that partially purified AIF induced cell lysis. It was also shown that the AIF is different from other autolytic enzymes or substances so far reported. This study demonstrated the presence of the peptidergic autolytic substances in the culture supernatant of H. pylori KZ109 cells. The results of this study should be useful for further studies aimed at elucidation of the strategy of survival of H. pylori in the gastric environment and elucidation of the mechanisms of pathogenesis induced by H. pylori.

Capsular Expression inStreptococcus pneumoniaeNegatively Affects Spontaneous and Antibiotic‐Induced Lysis and Contributes to Antibiotic Tolerance

Penicillin and vancomycin induce a lytic response in Streptococcus pneumoniae that requires the N-acetylmuramyl-l-alanine amidase LytA. We show that clinical isolates of pneumococci of capsular serotypes 1, 4, 6B, and 23F were generally less lytic to penicillin than pneumococci of serotypes 14 and 3. In addition, most 9V isolates were less lytic to vancomycin, compared with isolates of other serotypes. Parent-mutant pairs expressing and not expressing capsular serotypes 2, 4, and 9V were compared for antibiotic-induced lysis. The nonencapsulated variants were considerably more lytic after beta-lactam and/or vancomycin treatment, and antibiotic tolerance was seen only in the context of capsule expression. Conversion from a nonlytic to a lytic phenotype, after loss of capsule expression, required an intact lytA autolysin gene. Exogenous addition of purified LytA gave a lower lytic response in capsulated strains, compared with that in nonencapsulated mutants. Spontaneous autolysis in stationary phase also was negatively affected by capsule expression in an autolysin-dependent manner. Long-term starvation in the stationary phase of the vancomycin- and penicillin-tolerant isolate I95 yielded nonencapsulated mutants that had lost antibiotic tolerance and were lytic to penicillin and vancomycin. The 9V capsular locus of I95 and one of these stationary phase-selected mutants were completely sequenced. The only difference found was a 1-bp frameshift deletion in the cps9vE gene of the lytic mutant, encoding a uridine diphosphate-glucosyl-1-phosphate transferase. Two additional independently isolated lytic mutants of I95 from the stationary phase also contained mutations in the same region of cps9vE, which identified it as a mutational hot spot. This report demonstrates that capsular polysaccharides negatively influence the lytic process and contribute to antibiotic tolerance in clinical isolates of pneumococci.

The AbcA transporter of Staphylococcus aureus affects cell autolysis.

Increased production of penicillin-binding protein PBP 4 is known to increase peptidoglycan cross-linking and contributes to methicillin resistance in Staphylococcus aureus. The pbp4 gene shares a 400-nucleotide intercistronic region with the divergently transcribed abcA gene, encoding an ATP-binding cassette transporter of unknown function. Our study revealed that methicillin stimulated abcA transcription but had no effects on pbp4 transcription. Analysis of abcA expression in mutants defective for global regulators showed that abcA is under the control of agr. Insertional inactivation of abcA by an erythromycin resistance determinant did not influence pbp4 transcription, nor did it alter resistance to methicillin and other cell wall-directed antibiotics. However, abcA mutants showed spontaneous partial lysis on plates containing subinhibitory concentrations of methicillin due to increased spontaneous autolysis. Since the autolytic zymograms of cell extracts were identical in mutants and parental strains, we postulate an indirect role of AbcA in control of autolytic activities and in protection of the cells against methicillin.

Formation of resting forms of arthrobacter globiformis in autolyzing cell suspensions

Under conditions of spontaneous or induced autolysis of thick cell suspensions, Arthrobacter globiformis strains produced cells exhibiting features typical of resting microbial forms. The number of viable resting cells was greater under conditions of induced rather than spontaneous autolysis. The thermoresistance of the resting cells of A. globiformis strains isolated from 2- to 3 million-year-old permafrost was higher than that of the collection A. globiformis strain.

Surface localization of Helicobacter pylori urease and a heat shock protein homolog requires bacterial autolysis

Helicobacter pylori is a gram-negative bacterium which causes chronic gastritis and is associated with peptic ulcer disease, gastric carcinoma, and gastric lymphoma. The bacterium is characterized by potent urease activity, thought to be located on the outer membrane, which is essential for survival at low pH. The purpose of the present study was to investigate mechanisms whereby urease and HspB, a GroEL homolog, become surface associated in vitro. Urease, HspB, and catalase were located almost exclusively within the cytoplasm in fresh log-phase cultures assessed by cryo- immunoelectron microscopy. In contrast, significant amounts of surface-associated antigen were observed in older or subcultured preparations concomitantly with the appearance of significant amounts of extracellular antigen, amorphous debris, and membrane fragments. By use of a variety of biochemical methods, a significant fraction of urease and HspB was associated with the outer membrane in subcultured preparations of H. pylori. Taken together, these results strongly suggest that H. pylori cells undergo spontaneous autolysis during culture and that urease and HspB become surface associated only concomitant with bacterial autolysis. By comparing enzyme sensitivity to flurofamide (a potent, poorly diffusible urease inhibitor) in whole cells with that in deliberately lysed cells, we show that both extracellular and intracellular urease molecules are active enzymatically. Autolysis of H. pylori is an important phenomenon to recognize since it likely exerts significant effects on the behavior of H. pylori. Furthermore, the surface properties of H. pylori must be unique in promoting adsorption of cytoplasmic proteins.

Autolysis of 57 strains of dairy propionibacteria

Dairy propionibacteria contribute to proteolysis and lipolysis of the curd in Swiss-type cheese technology by the release of intracellular enzymes. Autolysis of 57 strains of dairy propionibacteria has been compared in 0.1 molli potassium phosphate buffer (pH 6.2 ) and the rate and extent of autoIysis appeared to be strain-dependent. Two distinct clusters were observed: cluster A containing 8 strains highly prone to Iysis and cluster B containing ail the other strains. Genomic fingerprinting of the 8 strains constituting c1uster A revealed 7 distinct profiles. Growth of 4 of these 7 strains showed a spontaneous autolysis in the growth medium just after the maximal growth, without any stationary phase.

A Simple Purification Method of Squeezed Krill for Obtaining High Levels of Hydrolytic Enzymes

The raw material originating from freshly caught Antarctic krill (E. superba) was processed by centrifugation and then immediately frozen. This squeezed fluid adjusted to pH 7 was subjected to spontaneous autolysis by storing at different temperatures (20-45 degrees C) and times (10-48 h). The autolyzed material resulted in 3 distinct phases after high speed centrifugation. The intermediate phase (water-phase) was collected and concentrated by membrane filtration. The high-molecular-weight substances (greater than 10,000 Daltons) were further purified by ion-exchange chromatography and eluted by a salt gradient. In this matter a bulk enzymatic material from krill can be efficiently obtained for further purification of different hydrolytic enzymes (peptide hydrolases/carbohydrases).

A turbidimetric and electron microscopic study of the effects of several parameters on the lysis of Streptococcus faecalis by lysozyme.

The lytic effect of lysozyme on Streptococcus faecalis ATCC 9790 was studied by spectrophotometry and electron microscopy and it was found to be highly dependent on the ionic strength of the suspending media and on the ratio lysozyme to bacterial cell mass. When 7.2 X 10(8) bacteria/mL are exposed to 0.4 mg/mL of lysozyme in media with low ionic strength, the enzyme is bound in great amounts, as deduced from protein determinations and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS--PAGE); the binding prevents bacteriolysis in spite of the removal of the cell wall. Extensive lysis of S. faecalis could be obtained by reducing the ratio of lysozyme to bacterial cell mass. Stabilization of S. faecalis by lysozyme was also observed when exponential phase cells incubated under conditions that promote spontaneous autolysis (incubation in 0.05 M tris(hydroxymethyl)aminomethane buffer, pH 8.0, ionic strength = 0.01675) do not lyse and do not leak material which absorbs at 260 nm when lysozyme was present at the highest concentration.

Escherichia coli mutants with an altered sensitivity to cecropin D.

Cecropins are a family of small, basic antibacterial polypeptides which can be isolated from pupae of immunized Lepidoptera. They are active against both gram-negative and gram-positive bacteria. We studied a mutant of Escherichia coli, strain SB1004, which is more sensitive to cecropin D than is the parental strain. The mutant was selected as resistant to a host range mutant of a Serratia marcescens phage. When the protein composition of the outer membrane was examined, strain SB1004 and some other phage-resistant mutants were found to be deficient in the OmpC protein. It was concluded that the OmpC protein is the receptor of the phage. Strain SB1004 was found to differ from other ompC mutants in being especially sensitive to hydrophobic antibiotics and to cecropin D. Furthermore, strain SB1004 has a tendency for spontaneous autolysis. A genetic analysis showed the mutations in strain SB1004 and a suppressor mutant to map in the ompC region. The activity of cecropin D against different strains of E. coli was specifically enhanced when divalent cations were absent. No such effect was found with cecropins A and B, which are less hydrophobic than the D form.

Bacteriolytic Action of Fluoride Ions

Bacillus subtilis, Neisseria subflava, and LYT coccus were found to undergo massive lysis after growth in media containing 0.01 to 10 mM NaF. When cells of these organisms were transferred from late-exponential-phase cultures to 0.02 M sodium phosphate buffer plus 0.1 M KCl, they underwent spontaneous autolysis. Cells grown in media with fluoride were more liable to autolysis, and walls isolated from them also showed enhanced autolytic sensitivity, even though added fluoride did not directly stimulate autolysins. Sporadic or partial lysis occurred in populations of Streptococcus sanguis and Streptococcus mutans BHT or LM-7 after growth in fluoridated media. Most bacteria that were tested did not undergo fluoride-induced lysis. However, cells of all test bacteria were found to have reduced amounts of peptidoglycan per unit of cell weight when grown in the presence of fluoride. Incorporation of labeled lysine or glucosamine into peptidoglycan (Park-Hancock residue) was stimulated, instead of inhibited, by fluoride. However, fluoride also stimulated the loss of radioactivity from Park-Hancock residues of cells that had previously incorporated labeled lysine or glucosamine. Thus, fluoride appeared to enhance peptidoglycan turnover, and this turnover reduced the peptidoglycan contents of all bacteria tested, but induced lysis in only those bacteria that normally have highly active autolytic systems.