Stress-induced L-forms of Mycobacterium bovis: a challenge to survivability

This study addressed the ability of Mycobacterium bovis to produce unusual extreme morphologic forms (cell wall-deficient or L-forms) under stress conditions. Models using nutrient starvation and cryogenic stress treatments of Mycobacterium bovis, as well as the filtration technique followed by cultivation in semisolid medium, were used for isolation of L-form variants. Morphological transformations and developmental stages, typical for the bacterial L-cycle were observed by electron microscopy. Of special interest was the formation of giant filaments and common extremely thick membranous structures enveloping the entire L-form population. Following collapse of giant filamentous structures small viable cell elements, mainly granules and coccobacilli, were released and proved able to grow into large bodies or multiply by fission or budding. Derivation of viable filterable forms from L-form cultures and parental strain and their identification as Mycobacterium bovis based on specific IS6110 PCR was noteworthy. We suggest that formation of giant filaments and thick common membranous envelopes, observed under stress conditions, may serve a twofold purpose - protection against an unfavourable environment, and a role in reproduction of Mycobacterium bovis L-forms. The observed L-form conversion phenomenon in Mycobacterium bovis seems to be associated with an adaptive strategy of this pathogen for survival and reproduction in an unfavorable environment.

Unstable Escherichia coli L forms revisited: growth requires peptidoglycan synthesis

Growing bacterial L forms are reputed to lack peptidoglycan, although cell division is normally inseparable from septal peptidoglycan synthesis. To explore which cell division functions L forms use, we established a protocol for quantitatively converting a culture of a wild-type Escherichia coli K-12 strain overnight to a growing L-form-like state by use of the beta-lactam cefsulodin, a specific inhibitor of penicillin-binding proteins (PBPs) 1A and 1B. In rich hypertonic medium containing cefsulodin, all cells are spherical and osmosensitive, like classical L forms. Surprisingly, however, mutant studies showed that colony formation requires d-glutamate, diaminopimelate, and MurA activity, all of which are specific to peptidoglycan synthesis. High-performance liquid chromatography analysis confirmed that these L-form-like cells contain peptidoglycan, with 7% of the normal amount. Moreover, the beta-lactam piperacillin, a specific inhibitor of the cell division protein PBP 3, rapidly blocks the cell division of these L-form-like cells. Similarly, penicillin-induced L-form-like cells, which grow only within the agar layers of rich hypertonic plates, also require d-glutamate, diaminopimelate, and MurA activity. These results strongly suggest that cefsulodin- and penicillin-induced L-form-like cells of E. coli-and possibly all L forms-have residual peptidoglycan synthesis which is essential for their growth, probably being required for cell division.

[Salmonella typhimurium population in water environment under the influence of temperature]

The strategy of the adaptation of S. typhimurium population to water environment under the influence of temperature factor was studied by scanning electron microscopy. Salmonellae were found to adhere to the surface of the Daphnia chitin covering. The study revealed that S. typhimurium population existed in water in the form of covered microcolonies as well as in the form of spheroplast-type cells and small cells in the L-form, joined with bands. The viability of salmonellae in water environment was studied without interaction and following interaction with Daphnia.

Induction of L-form-like cell shape change of Bacillus subtilis under microculture conditions

A remarkable cell shape change was observed in Bacillus subtilis strain 168 under microculture conditions on CI agar medium (Spizizen's minimal medium supplemented with a trace amount of yeast extract and Casamino acids). Cells cultured under a cover glass changed in form from rod-shaped to spherical, large and irregular shapes that closely resembled L-form cells. The cell shape change was observed only with CI medium, not with Spizizen's minimum medium alone or other rich media. The whole-cell protein profile of cells grown under cover glass and cells grown on CI agar plates differed in several respects. Tandem mass analysis of nine gel bands which differed in protein expression between the two conditions showed that proteins related to nitrate respiration and fermentation were expressed in the shape-changed cells grown under cover glass. The cell shape change of CI cultures was repressed when excess KNO3 was added to the medium. Whole-cell protein analysis of the normal rod-shaped cells grown with 0.1% KNO3 and the shape-changed cells grown without KNO3 revealed that the expression of the branched-chain alpha-keto acid dehydrogenase complex (coded by the bfmB gene locus) was elevated in the shape-changed cells. Inactivation of the bfmB locus resulted in the repression of cell shape change, and cells in which bfmB expression was induced by IPTG did show changes in shape. Transmission electron microscopy of ultrathin sections demonstrated that the shape-changed cells had thin walls, and plasmolysis of cells fixed with a solution including 0.1 M sucrose was observed. Clarifying the mechanism of thinning of the cell wall may lead to the development of a new type of cell wall biosynthetic inhibitor.

[Identification of L-forms of Mycobacterium tuberculosis complex by polymerase chain reaction (PCR)]

Polymerase chain reaction (PCR) was used to verify the tuberculous origin of L-forms isolated from clinical non-respiratory samples from patients with extrapulmonary tuberculosis. PCR was made by using cultured L-forms obtained from negative and positive cultures. PCR used a total of 60 cultured L-forms different in the morphology of colonies and the rate of growth. The total count of L-forms yielding positive amplification with M. tuberculosis complex-specific primers was 51 (85%). L-form passages were subjected to PCR analysis. A total of 14 third-generation L-forms were examined. They turned out to be positive. Thus, the fact that L-forms isolated from nonrespiratory clinical samples from patients with tuberculosis are most commonly L-forms of M. tuberculosis was genetically substantiated.

Induction, growth and antibiotic production of Streptomyces viridifaciens L-form bacteria

AIMS

To induce, cultivate and investigate the characteristics of L-form bacteria derived from the filamentous actinomycete Streptomyces viridifaciens.

METHODS AND RESULTS

L-forms were induced in a liquid medium supplemented with lysozyme and penicillin. A stable culture which no longer required inducing agents but could still revert, was obtained by the twelfth subculture. The specific growth rate of stable L-forms was faster (0.751) than unstable L-forms (0.361). After the exponential growth phase, the cell diameter continued to increase, as did the percentage of vacuoles. Morphologically, the L-forms appeared as spherical bodies with no signs of differentiation and were sensitive to osmotic stress, indicating removal of the cell wall. The L-forms produced secondary metabolites although much lower levels of antibiotic were assayed in the L-forms compared with the cell walled forms.

CONCLUSION

Stable L-form bacteria were induced from S. viridifaciens and their growth characterized. The L-forms produced secondary metabolites.

SIGNIFICANCE AND IMPACT OF THE STUDY

Stable Streptomyces L-forms were induced and have potential as biocontrol agents.

Introduction of a mini-gene encoding a five-amino acid peptide confers erythromycin resistance on Bacillus subtilis and provides temporary erythromycin protection in Proteus mirabilis

A 15-bp mini-gene was introduced into Bacillus subtilis and into stable protoplast-like L-forms of Proteus mirabilis. This mini-gene encoded the peptide MVLFV and modeled a fragment of Escherichia coli 23S rRNA responsible for E. coli erythromycin (Ery) resistance. Expression of the introduced mini-gene conferred permanent Ery resistance on B. subtilis. In L-forms of P. mirabilis, the Ery-protective effect was maintained in the course of several generations. Herewith, the mechanism of Ery resistance mediated by expression of specific short peptides was shown to exist in evolutionary distant bacteria. Three new plasmids were constructed containing the gene under study transcriptionally fused with the genes encoding glutamylendopeptidase of Bacillus licheniformis or delta-endotoxin of Bacillus thuringiensis. The Ery resistance pentapeptide (E-peptide) mini-gene served as an efficient direct transcriptional reporter and allowed to select bacillar glutamylendopeptidase with improved productivity. The mini-genes encoding E-peptides may be applied as selective markers to transform both Gram-positive and Gram-negative bacteria. The small size of the E-peptide mini-genes makes them attractive selective markers for vector construction.

[Observations of characteristics of the mechanisms of biological oxidation of cell wall-deficient bacteria]

The L-forms were induced from Staphylococcus aureus, Escherichia coli and Bacillus cereus by beta-lactam antibiotics and then observations on the properties of oxygen requirement, sugar fermentation and sensitive to cyanide of the L-forms were done. The results were shown that the L-forms derived from the obligate aerobe or the facultative anaerobe did not ferment sugars and were highly oxygen-dependent and more sensitive to cyanide than their parent bacteria. The metabolic activities which were same as the parent bacteria of the L-forms would return after the L-forms reverted to the typical bacteria forms. It was possible that the changes of biological oxidation mechanism were due to the deficiency of the cell wall which led to loss of the periplasmic space or the membrane-wall interlayer so that the enzymes for fermentation existed in the space could not be hold.

Cell wall-deficient forms (L-forms) of Listeria monocytogenes in experimentally infected rats

Experimental infections were induced with different bacterial forms of Listeria monocytogenes: parental (S-forms), protoplastic (L-forms) and combined inoculum of both forms by i.p. injection of rats. The parental bacterial forms (S-forms) were isolated up to 7 days after challenge from the peritoneal cavity and the liver, while the L-forms were isolated up to 60 days from the peritoneal cavity. Continuous adhesion of L-forms on the peritoneal macrophage surface was found by scanning-electron microscopy. Erythrocyte and leucocyte count as well as some clinical chemistry parameters were measured during infections. They showed different dynamics in the three experimental groups. Histomorphological changes in the liver (microabscesses and mononuclear cellular granulomas) of infected animals were observed. They were less intensive and appeared later in rats infected with L-forms. The experiments demonstrated that infections caused by parental bacterial forms and by combined inoculum took an acute course, while the infection caused by L-forms could be distinguished as a prolonged and persistent one.

Growth of acid fast L forms from the blood of patients with sarcoidosis

BACKGROUND

Acid fast cell wall deficient forms (CWDF) of bacteria have been grown from blood, bronchial washings, and ocular anterior chamber fluid from patients with sarcoidosis. A monoclonal antibody raised against Mycobacterium tuberculosis whole cell antigen (H37RV) was used to characterise further CWDF grown from the blood of patients with sarcoidosis.

METHODS

Blood from 20 patients with active sarcoidosis and from 20 controls was cultured using methods favourable for the growth of CWDF. Isolates were further characterised by indirect fluorescent antibody analysis using a monoclonal antibody highly reactive with M tuberculosis.

RESULTS

CWDF were grown from the blood of 19 of 20 subjects with sarcoidosis. All isolates stained positively with the monoclonal antibody and with a modified Kinyoun stain. No organisms were grown from the blood of controls.

CONCLUSIONS

These data demonstrate that CWDF can be grown from the blood of nearly all patients with active sarcoidosis. The results confirm that the organisms are mycobacterial in origin and are similar, if not identical, to M tuberculosis. Their role in the pathogenesis of sarcoidosis is unknown.

CCD-monitoring of bioluminescence during the induction of the cell wall-deficient, L-form state of a genetically modified strain of Pseudomonas syringae pv. phaseolicola

Bioluminescence from developing L-form colonies of the plant pathogen, Pseudomonas syringae pv. phaseolicola, was monitored using the enhanced light-detecting capabilities of a charge-coupled device. During L-form induction, the bacteria entered a prolonged period during which the level of light output and hence metabolic activity, was very low. A relatively small number of highly bioluminescent L-form colonies were then observed to develop against a background of non-bioluminescent bacteria. When these colonies were sub-cultured and examined microscopically, typical L-form morphology was observed and continued high bioluminescence was detectable from derived colonies.

Serum inhibits penicillin-induced L-form growth in Staphylococcus aureus: a note of caution on the use of serum in cultivation of bacterial L-forms

Heat-inactivated horse serum inhibited penicillin-induced L-form colony formation in Staphylococcus aureus when included in an osmotically stabilized culture medium. Most, perhaps all, L-form colonies that appeared with low frequencies on the serum-supplemented medium were of the penicillin-independent, stable type. This relationship must be taken into account when use of serum is considered for L-form cultivation.

Growth and adhesion of Enterococcus faecium L-forms

Comparisons of growth and surface colonisation of Enterococcus faecium L-forms and their cell-walled forms were undertaken to produce information about their ability to form sessile cells. The growth of L-forms in liquid culture was slower than that of the parent. This was reflected in their longer lag phase and slower specific growth rates: 0.16 h-1 for the L-form and 0.81 h-1 for the parent. Although E. faecium L-forms attached to a silastic rubber surface, the attached population density was 10-100-fold less than that of the parent. Confluent biofilms on the silastic surfaces were not observed for either bacterial form. Comparison of the attachment of E. faecium L-form and parent may provide important information on how bacteria overcome host defence mechanisms and antibiotic treatment.

Growth and physiological characteristics of Bacillus subtilis L-forms

The specific growth rate of stable Bacillus subtilis L-forms was slower (mu = 0.127) than the cell-walled form (mu = 0.219) when measured by optical density (O.D.). However, the L-form growth rate increased (mu = 0.288) when determined by viable cell counts. L-forms of B. subtilis appear to enter a phase of rapid cell division, followed by a period of cell enlargement which is associated with an increase in the number of cells with vacuoles and granules. Thus, maximum viable L-form numbers and DNA content were attained at approx. 30h, before maximum protein content was achieved (46h) and before maximum O.D. was observed at 71 h. Measurements showed that L-form cell size increased even after cell division had stopped. O.D. was therefore inaccurate for assessment of L-form growth. L-forms were sensitive to osmotic shock and unlike the cell-walled organisms from which they were derived, were resistant to penicillin, indicating a loss of peptidoglycan. The L-forms were similar to cell-walled forms in that antibiotic(s) and proteases were produced.

Mechanism of the protective immunity against murine typhoid: persistence of Salmonella L forms in the liver after immunization with live-cell vaccines

Live-cell vaccines of Salmonella typhimurium, either a sub-lethal dose of a wild-type (strain LT2) or a high dose of its two-heptose Rd1 mutant (strain SL1004), induced acquired resistance to murine typhoid, which remained 180 days after immunization. Growth of S. typhimurium as a bacillary form ceased between days 30 and 60 of immunization, but L forms of this bacterium colonized the liver (the mean number of L forms in the liver: 600 L-forming units) even at 180 days post-immunization. In contrast, a high inoculum of either a Ra mutant (strain TV148) of strain LT2 or S. schottmülleri 8006 sharing the same O antigenic components with those of S. typhimurium induced only a short-lived protection in proportion to the number of L forms in the liver, and the protective immunity was lost before day 180. However, there was no significant difference in the salmonella-specific T-cell responses among groups of immunized mice on day 180 of immunization. A lethal infection with strain LT2 in mice which had been immunized 75 days previously with living cells of strain SL1004 resulted in a rapid clearance of the challenge inoculum, together with a rapid elevation of anti-S. typhimurium antibody responses. Thus, the present data suggest that the long-lived immunity conferred upon live S. typhimurium vaccines is attributable to the colonization of this bacterium in the liver as L forms and the ability to colonize the liver as L forms is independent of the chain length of salmonella O-antigens.

Formation of vesiculated large bodies of Staphylococcus aureus L-form in a liquid medium

A method is described in which cells of Staphylococcus aureus can be converted to vesiculated large bodies of L-form. When coccal cells were incubated in a liquid growth medium containing D-cycloserine, N-acetylmuramidase and subtilisin, a large number of vesiculated large bodies were formed. Electron microscopy revealed that development of internal vesicles arose after 6 hr of incubation.. When growth inhibitory concentrations of rifampicin, novobiocin, or chloramphenicol were added to the culture at 6 hr of incubation, small-sized nonvesiculated bodies were produced instead of vesiculated forms. The viability of cultures was reduced by rifampicin and novobiocin but not by chloramphenicol.

Induction and cultivation of a stable L-form of Bacillus subtilis

The induction of L-forms of Bacillus subtilis from protoplasts is described. The method involved the frequent subculture of the unstable L-form on a growth medium supplemented with lysozyme and horse serum. A stable culture, which did not revert when lysozyme and horse serum were omitted from the medium, was obtained after 13 subcultures. This culture could be grown on solid and in liquid medium by routine microbiological methods. Long-term storage of these cells was achieved by freeze drying and maintenance in glycerol at -70 degrees C. The cultural adaptability of the L-form is described and discussed with respect to methods of cultivation and growth.

[The electron microscopic study of bacterial development in colonies. The heteromorphous growth of bacteria during the natural development of a population]

In this work data on the morphological features of the heteromorphous growth of bacteria in the process of the natural development of their population are presented. The authors believe that the heteromorphous growth of cells is inherent in the normal cycle of the development of bacteria in the population and that this process is reversible. It has certain regularities, common for different bacteria, in the variability of morphological manifestations and can be regarded as one of the stages of the natural L-transformation of bacteria.

L-form-like colonies of Staphylococcus aureus induced by an extracellular lytic enzyme from Pseudomonas aeruginosa

An extracellular enzyme produced by Pseudomonas aeruginosa had a lytic effect on lyophilized Staphylococcus aureus cells. It was purified from the culture supernatant by ammonium sulfate fractionation followed by column chromatography with P cellulose and Sephadex G-50. The molecular weight of the enzyme was estimated to be 19,000 +/- 1,750 with sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The pI of the enzyme was estimated to be 8.5 with isoelectric focusing. The enzyme was inactive in 4% NaC1-40 mM sodium phosphate buffer or at pH values lower than 6.0 or higher than 11.0; however, it was not affected by 1 M sucrose or 0.25% heat-denatured horse serum. The action of the enzyme on cultures of S. aureus resulted in the presence of many cells lacking cell walls. In addition, when cultivation was carried out on osmotically stabilized solid media, these cell wall-deficient cell developed in L-form colonies.

Morphologic study of Staphylococcus aureus L-form, reverting, and intermediate colonies in situ

Staphylococcus aureus strains of bovine origin were induced to L-form by exposure to 100 U of penicillin in brain heart infusion broth supplemented with 5% NaCl, 5% sucrose, and 10% horse serum. L-forms were cultured on similarly supplemented brain heart infusion agar containing no antibiotic. Light and electron microscopic examination of plastic-embedded L-form colonies revealed a variety of morphologic types. The primary site of growth appeared to be the core area below the agar surface, consisting mainly of pleomorphic budding forms. At the surface, these forms gave rise to large spherules with a gradation from smaller to larger spherules toward the periphery of the colony. Some colonies progressed to reverting forms with the growth of bacterial cells containing cell wall. In addition to L-forms, intermediate colony forms were observed that lacked typical L-form morphology and progressed rapidly to the parent cell form on subculture to bovine blood agar. Description of these forms will be used in the search for similar morphologic types in vivo during antibiotic treatment of chronic S. aureus bovine mastitis.

[Development of protoplasts of Streptomycetes on media favoring the regeneration and formation of L-forms]

The protoplasts of three Streptomyces species and their regenerative ability were studied using light microscopy. When Streptomyces lividans and S. erythraeus protoplasts are cultivated on regeneration media, their regeneration is not synchronous during the first day; some protoplasts revert to yield the mycelial form and also L-forms of these cultures are produced. If the protoplasts are transferred to a medium inducing L-forms, they grow and multiply for a long time with the production of L-form colonies. This process is maintained if S. lividans L-form cells are passaged on the medium inducing L-forms, but the protoplasts revert to yield the mycelial form on the regeneration medium.

Isolation of Staphylococcus aureus L forms from experimentally induced bovine mastitis

Bacterial L forms were isolated from milk samples of dairy cattle infected experimentally with Staphylococcus aureus. Initially, bacterial L forms were induced in vitro from 12 of 44 S. aureus strains isolated from bovine mastitis. Cows were experimentally infected in two experiments with strains shown in vitro to be easily inducible to L form and with S. aureus Newbould 305. Each quarter of the mammary gland was infected with either 10(3) or 10(6) CFU of the test strains. Treatment was initiated with 100,000 U of penicillin G per quarter at the first signs of clinical mastitis. Milk samples were collected daily and cultured on bovine blood agar and PPLO agar (Difco Laboratories, Detroit, Mich.) with 10% horse serum and 5% NaCl. Staphylococcal L forms were isolated from milk samples collected from infected glands in both experiments after antibiotic therapy. Glands with the highest concentrations of leukocytes and bacteria were most likely to yield L forms in milk samples after treatment was initiated. Cows harboring L forms typically yielded parental organisms after cessation of antibiotic therapy. No detectable changes occurred in antibiotic susceptibilities, coagulase production, or biochemical activities in strains induced to L form followed by reversion to the parental form. These results demonstrated that L forms can occur during treatment of bovine mastitis and that L forms may be one explanation for the poor response of staphylococcal bovine mastitis to antibiotic therapy.

[Comparative biological characteristics of the L-form of Streptococcus group A and B]

The comparative study of the biological and serological properties of the L-forms of streptococci, groups A and B, has been made. Their morphological similarity on the level of light microscopy has been demonstrated. The use of ring precipitation, gel diffusion, passive hemagglutination, aggregate hemagglutination, as well as the immunoferritin technique, has made it possible to establish the presence of specific antigens in the L-forms of streptococci, groups A and B. Serological cross reactions are negligible. The future development of a diagnosticum for the specific indication of these antigens is proposed. The fact of the presence of specific antigens in the L-forms of streptococci in comparison with the initial streptococcal strains has been confirmed.

Effect of the composition of reversion medium on change of Staphylococcus aureus lysostaphin protoplasts to coccal forms and L-forms

The experimental conditions under which protoplasts of Staphylococcus aureus strain MS353 (pCp) are converted to the coccal or L-form were investigated. Protoplasts prepared by treating coccal MS353 (pCp) strain with Lysostaphin formed various types of colonies (coccal form, L-form and mixed types) in about 50% yield when they were plated on reversion (R) medium consisting of 2% brain heart infusion, 0.5M sodium succinate, 0.01% bovine serum albumin, 20 mM MgCl2 and 0.6% agar. The L-form type colonies with a typical fried-egg appearance that developed on the R medium at an early stage gradually reverted to the coccal form through a mixed type stage in which a high density area first appeared in the periphery of the colony and then spread throughout the colony. The use of modified R medium without MgCl2 or R medium in which 0.5M sodium succinate as an osmotic stabilizer was replaced by 7.5% NaCl resulted in marked delay in the appearance of reverted cells. R medium without bovine serum albumin yielded atypical L-form type colonies, which contained masses of coccal cells with very irregular margins. On the other hand, R medium without MgCl2 but with penicillin G supported development of L-form type colonies at high rate (13-15%) from the inoculated protoplasts.

Studies of colicin action on wall-less stable L-forms of Escherichia coli. II. Growth inhibition of complete and wall-less (L-form) cells of Escherichia coli by basic colicin types

The inhibitive activity of colicins of 16 types (produced by 22 colicinogenic strains) on rods and protoplast-like stable L-form cells of the strains Escherichia coli B, W1655 F+ and W1655 F- was compared. The results of 58 combinations tested fall into four groups (with three subgroups): both cell forms are sensitive: a) both cell forms are about equally sensitive, b) rods are distinctly more sensitive than L-form cells, c) L-form cells are distinctly more sensitive than rods; only rods are sensitive, L-form cells are not sensitive; only L-form cells are sensitive, rods are not sensitive; neither cell form is sensitive. Group la represents simple sensitivity; both cell wall and cytoplasmic membrane receptors are present and functioning. Groups 1b and 2 represent sensitivity, substantially or completely mediated by cell wall receptors. Groups 1c and 3 represent partial or complete "pseudoresistance" or "pseudotolerance"; cell wall receptors are absent or non-lethal, but cytoplasmic membrane ones are present and mediate the lethal effect. Group 4 represents both true resistance and true tolerance.

[Ultrastructure of the unbalanced growth forms of Salmonellae obtained by the action of various factors]

The unbalanced growth forms (UGF), also known as heteromorphous or pleomorphous forms, of salmonellae were obtained under the action of penicillin, homologous antiserum in combination with complement and lysozyme, as well as ultraviolet radiation. The effect of these factors was studied after their momentaneous action and in successive passages. The viability of UGF was determined in terms of colony-forming units. The appearance of UGF was induced by penicillin, a complex of immune substances and ultraviolet radiation, yet the action of two latter factors irreparably damaged most of the cells. The formation of UGF, showing stability in prolonged passages and capable of transformation into L-forms, occurred only under the influence of penicillin. Elementary bodies appeared in UGF, both capable and incapable of transformation into L-forms after successive passages. In the viable part of the UGF population obtained under the action of all the above factors damages in the peptidoglycan layer of the cell wall and, partly, in the cytoplasmic membrane, as well as disturbances in the process of cell division, linked with these cell elements, were observed.

[Ultrastructure of Salmonella typhimurium forms with unbalanced growth induced by lithium chloride]

The action of 1.0 and 1.5 M LiCl on S. typhimurium induces the appearance of unbalanced growth forms capable of growing and multiplication, when subcultured in a medium with this preparation. In this culture the prevalence of cells differing in their structure from the initial Salmonella cells and from stable L-form cultures is observed. Cells characteristic of the initial culture and cells resembling the L-forms occur in lesser numbers. LiCl seems to affect peptidoglycan and the cytoplasmic membrane, which brings about disturbances in the permeability of the surface structures of the cell.

Elimination of mycoplasma contamination from mammalian cell cultures by the bibenzimidazole derivative Hoechst 33258

Cell cultures contaminated with mycoplasma or bacterial L-forms were treated with 8 micrograms/ml of Hoechst 33258. No microorganisms could be detected by fluorescence microscopy after two rounds of treatment.

[Attempts of ultrastructural and biochemical characterisation of cell wall deficient "Brucella" (L forms) (author's transl)]

In previous studies the in vivo conversion of Brucella suis to L-form state was put in evidence. The L forms isolated from mouse spleen had original structural aspects in common: the absence of the cell wall layer and the extracellular multilayer "membranous" structures. The biological characterization of these L forms and the preliminary identification of specific chemical markers of the bacterial envelope is reported in the present study, performed with the stable L forms well-growing in the liquid media. The electron microscopy confirmed the absence of cell wall and the presence of numerous dense multilayer membranous structures in the L forms cultivated for a long time on appropriate media. This aspect was changed in the L forms adapted to growth on the ordinary medium for brucella: numerous small dense bodies limited by unit membrane were observed. The chemical analysis of stable L forms showed the absence of diaminopimelic acid, confirming the lack of peptidoglycan. The result of chemical determination in L forms of the Na-2-keto-3-deoxyoctonate was negative. However, biological assays suggested that outer membrane components such as LPS and receptors for the bacteriophage Weybridge remained in the L forms, albeit in reduced amount as compared to parental brucella.

Growth characteristics and ultrastructure of protoplast type L-forms from streptomycetes

L-form colonies from S. hygroscopicus, S. griseus and S. levoris were isolated after incubation of lysozyme protoplasts on an osmotically stabilized complex agar medium. Unstable and stable L-forms grow on solid and in liquid media. L-form colonies are 5-10 times smaller than normal colonies and show a typical morphology for each species. In ultrathin sections L-form cells are characterized by nucleoid areas with typical core-like structures, by a ribosome-rich cytoplasm with different inclusion bodies, and by a cytoplasmic membrane. Because there are no cell wall structures L-forms of the three Streptomyces species belong to the protoplast type. Analysis of cell size and cell shape shows a variation in diameter and a cell propagation by regular and irregular division- and budding-like processes. Many L-form cells contain more than two chromosomes. The results are discussed with regard to the cellular organisation of streptomycetes and the nature of the stable L-form.

An L-form of Staphylococcus aureus adapted to a brain heart infusion medium without osmotic stabilizers

An L-form derived from halotolerant Staphylococcus aureus Tasaki was adapted to growth in a brain heart infusion medium without any supplemental osmotically protective solutes (360 mOsm/kg). This L-form had no chemically detectable peptidoglycan residues on its surface. Electron microscopic observations confirmed morphologically the absence of the structures and also of other osmotically protective polymers within or exterior to the cytoplasmic membrane. The osmotic stability and susceptibility to bacitracin, D-cycloserine, and vancomycin of the L-form adapted to growth in 360 mOsm osmotically unprotective medium was higher than that of the L-form grown in 1,950 mOsm supplemented with 4.5% NaCl. The adapted L-form tended to be more sensitive to almost all of the antibiotics examined, other than the inhibitors for cell wall-synthesis, than the original L-form strain requiring osmotic protection for growth. Chemical analysis of the membrane of the adapted L-form indicated 16.3% total lipids and 20.6% proteins by dry weight of the membrane, and it contained larger amounts of lipid phosphorus (20.0 microgram/mg).

Isolation of L-forms from the spleens of Brucella suis-infected, penicillin-treated mice

Previous attempts to obtain in vitro wall-deficient stable L-forms of various strains of Brucella have failed because the obtained spheroplasts revert quickly to bacterial form. Here, we report the isolation of L-forms from mice infected with a B. suis strain type 1 and treated with penicillin. In defined experimental conditions, L-type microcolonies associated with tissue debris were observed in primary spleen cultures, even on antibiotic free media. After several transfers on penicillin-containing medium. typical, tissue-free L colonies were obtained. At first, when cultivated on antibiotic-free medium, these colonies reverted to the bacterial form (identified as B suis, biotype 1). Later, after approximately fifteen transfers on penicillin-supplemented medium, they no longer reverted even after several subcultures on antibiotic-free medium. The L-forms' ultrastructural features included many giant empty bodies, considerable variation in size, shape and density of the wall-deficient cells, and many multilayered membranes. The stabilized L-forms were propagated in vitro and inoculated into mice, and then recovered from their spleens as tissue associated L-microcolonies. An occasional in vivo revertant was identified as B. suis, biotype 1. These data provide one possible explanation for earlier failures to detect the presence of atypical bacteria in clinical or experimental Brucella infections.

Quantitation of bacillus subtilis L-form growth parameters in batch culture

Several methods were used to monitor the growth of a stable L-form in batch culture. The end of the exponential growth phase was determined with greatest accuracy by the amounts of deoxyribonucleic acid per milliliter of culture. Optical density and viable count data were not as reliable because the L-forms began to lyse at the end of exponential growth. Lysis was detected visually, by phase-contrast observations of wet mounts, and by release of ultraviolet-absorbing material into culture supernatant fluids.

Isolation of a stable cell wall-defective form of Neisseria gonorrhoeae from a case of untreated gonococcal urethritis

A cell wall-defective form of Neisseria gonorrhoeae from an exudate of an untreated patient with gonococcal urethritis was isolated on medium containing 7% polyvinylpyrrolidone. Initial attempts to grow the organism by standard microbiological methods had failed. This isolate was incapable of reversion to a normal gonococcus even after numerous subcultures and appeared to be a stable cell wall-defective form.

Isolation of staphylococcal L-phase variants from the blood and egg yolks of normal chickens

The use of special microbiological media and modified techniques has resulted in the stimulation of growth and development of bacterial L forms in samples of blood and egg yolk free from mature bacteria and derived from normal healthy chickens. After prolonged cultivation the majority of these L form cultures reverted to staphylococci.

Induction of L-phase variants of Nocardia caviae within intact murine lungs

The data presented show that cells of Nocardia caviae 112 were converted to cell wall-deficient microbial variants within the intact murine lung after intranasal administration. At the time that these L-phase variants were recovered in large numbers from the lung, there was a correspondingly enhanced inflammation leading to alveolar consolidation and animal death. During the peak of this response (at 1 week after infection), normal nocardial cells were neither isolated from nor seen within the lung. It is suggested that the conversion of these normal nocardial cells to their L-phase variant leads to this extensive pulmonary damage. Furthermore, the L-phase organisms appear to play an active role in this pathological effect since introduction of similar amounts of killed nocardial cells into the lungs of the mice failed to produce a similar response.