In vitro spheroplast and L-form induction within the pathogenic nocardiae

Nocardiosis from 1888 to 2017

The genus Nocardia is an aerobic bacterium, Gram-positive and catalase positive that is in Nocardiaceae family. This bacterium first described by Edmond Nocard in 1888 and is not in human commensal bacteria. To date, nocardiosis incidence is increasing due to increase population growth rate, increase in patients with immune disorder diseases and immunocompromised patients. We surveyed taxonomic position, isolation methods, phenotypic and molecular identification at the genus and species levels, antibiogram, treatment and epidemiology in the world from 1888 to 2017.

Comparison of the indentation and elasticity of E. coli and its spheroplasts by AFM

Atomic force microscopy (AFM) provides a unique opportunity to study live individual bacteria at the nanometer scale. In addition to providing accurate morphological information, AFM can be exploited to investigate membrane protein localization and molecular interactions on the surface of living cells. A prerequisite for these studies is the development of robust procedures for sample preparation. While such procedures are established for intact bacteria, they are only beginning to emerge for bacterial spheroplasts. Spheroplasts are useful research models for studying mechanosensitive ion channels, membrane transport, lipopolysaccharide translocation, solute uptake, and the effects of antimicrobial agents on membranes. Furthermore, given the similarities between spheroplasts and cell wall-deficient (CWD) forms of pathogenic bacteria, spheroplast research could be relevant in biomedical research. In this paper, a new technique for immobilizing spheroplasts on mica pretreated with aminopropyltriethoxysilane (APTES) and glutaraldehyde is described. Using this mounting technique, the indentation and cell elasticity of glutaraldehyde-fixed and untreated spheroplasts of E. coli in liquid were measured. These values are compared to those of intact E. coli. Untreated spheroplasts were found to be much softer than the intact cells and the silicon nitride cantilevers used in this study.

Tinctorial properties of spherical bodies in broth cultures of Nocardia asteroides GUH-2

In yeast extract-supplemented brain heart infusion (BHI) broth cultures of Nocardia asteroides GUH-2, many spherical bodies (SBs) were frequently seen nearby filamentous cells. They showed no gram-positivity when Gram stain was applied. When acridine orange stain was applied, many of them showed different green fluorescence from bright orange fluorescence of the filamentous nocardiae under ultraviolet light. Their acid-fastness appeared to depend on the presence of paraffin. Using the polymerase chain reaction (PCR) method, 16S rRNA genes were detected in SB-containing broth cultures inoculated with culture filtrates from broth cultures of the strain and identical to that of N. asteroides. These results suggest that SBs are cell wall-defective (CWD) forms which result from the spontaneous mutation of N. asteroides GUH-2.

Bacterial persistence and expression of disease

A considerable body of experimental and clinical evidence supports the concept that difficult-to-culture and dormant bacteria are involved in latency of infection and that these persistent bacteria may be pathogenic. This review includes details on the diverse forms and functions of individual bacteria and attempts to make this information relevant to the care of patients. A series of experimental studies involving host-bacterium interactions illustrates the probability that most bacteria exposed to a deleterious host environment can assume a form quite different from that of a free-living bacterium. A hypothesis is offered for a kind of reproductive cycle of morphologically aberrant bacteria as a means to relate their diverse tissue forms to each other. Data on the basic biology of persistent bacteria are correlated with expression of disease and particularly the mechanisms of both latency and chronicity that typify certain infections. For example, in certain streptococcal and nocardial infections, it has been clearly established that wall-defective forms can be induced in a suitable host. These organisms can survive and persist in a latent state within the host, and they can cause pathologic responses compatible with disease. A series of cases illustrating idiopathic conditions in which cryptic bacteria have been implicated in the expression of disease is presented. These conditions include nephritis, rheumatic fever, aphthous stomatitis, idiopathic hematuria, Crohn's disease, and mycobacterial infections. By utilizing PCR, previously nonculturable bacilli have been identified in patients with Whipple's disease and bacillary angiomatosis. Koch's postulates may have to be redefined in terms of molecular data when dormant and nonculturable bacteria are implicated as causative agents of mysterious diseases.

Acid-fastness of Nocardia asteroides GUH-2 cultured in brain heart infusion broth supplemented with paraffin

Nocardia asteroides GUH-2 was not acid-fast when grown in brain heart infusion (BHI) broth. When grown in BHI broth supplemented with paraffin, many filamentous cells showed acid-fastness after treatment with 1% acid-alcohol as the decolorizing agent. When treated with 3% acid-alcohol, filamentous cells were not acid-fast. In addition to the acid-fast filamentous cells of nocardiae, unknown acid-fast spherical bodies were observed in the paraffin-supplemented BHI broth cultures.

Nocardia species: host-parasite relationships

The nocardiae are bacteria belonging to the aerobic actinomycetes. They are an important part of the normal soil microflora worldwide. The type species, Nocardia asteroides, and N. brasiliensis, N. farcinica, N. otitidiscaviarum, N. nova, and N. transvalensis cause a variety of diseases in both normal and immunocompromised humans and animals. The mechanisms of pathogenesis are complex, not fully understood, and include the capacity to evade or neutralize the myriad microbicidal activities of the host. The relative virulence of N. asteroides correlates with the ability to inhibit phagosome-lysosome fusion in phagocytes; to neutralize phagosomal acidification; to detoxify the microbicidal products of oxidative metabolism; to modify phagocyte function; to grow within phagocytic cells; and to attach to, penetrate, and grow within host cells. Both activated macrophages and immunologically specific T lymphocytes constitute the major mechanisms for host resistance to nocardial infection, whereas B lymphocytes and humoral immunity do not appear to be as important in protecting the host. Thus, the nocardiae are facultative intracellular pathogens that can persist within the host, probably in a cryptic form (L-form), for life. Silent invasion of brain cells by some Nocardia strains can induce neurodegeneration in experimental animals; however, the role of nocardiae in neurodegenerative diseases in humans needs to be investigated.

Nocardia species: host-parasite relationships

The nocardiae are bacteria belonging to the aerobic actinomycetes. They are an important part of the normal soil microflora worldwide. The type species, Nocardia asteroides, and N. brasiliensis, N. farcinica, N. otitidiscaviarum, N. nova, and N. transvalensis cause a variety of diseases in both normal and immunocompromised humans and animals. The mechanisms of pathogenesis are complex, not fully understood, and include the capacity to evade or neutralize the myriad microbicidal activities of the host. The relative virulence of N. asteroides correlates with the ability to inhibit phagosome-lysosome fusion in phagocytes; to neutralize phagosomal acidification; to detoxify the microbicidal products of oxidative metabolism; to modify phagocyte function; to grow within phagocytic cells; and to attach to, penetrate, and grow within host cells. Both activated macrophages and immunologically specific T lymphocytes constitute the major mechanisms for host resistance to nocardial infection, whereas B lymphocytes and humoral immunity do not appear to be as important in protecting the host. Thus, the nocardiae are facultative intracellular pathogens that can persist within the host, probably in a cryptic form (L-form), for life. Silent invasion of brain cells by some Nocardia strains can induce neurodegeneration in experimental animals; however, the role of nocardiae in neurodegenerative diseases in humans needs to be investigated.

Nocardia in naturally acquired and experimental infections in animals

There are three commonly recognized species ofNocardiathat cause disease in a large variety of animals including humans. In the United States, pulmonary or systemic nocardiosis in humans caused byN. asteroidesis most frequently diagnosed. It should be noted thatN. brasiliensiscan cause nocardiosis also. In Central and South America mycetomas induced byN. brasiliensisappear to be more prevalent even thoughN. asteroidescan be seen in this type of infection. Sporadic cases of both mycetoma and nocardiosis caused byN. caviaehave been reported. These three species ofNocardiaappear to be present in the soils of most countries; butN. asteroidesis more frequently isolated in the temperate climates whereasN. brasiliensispredominates in the tropical and subtropical regions of the world. No specific geographic distribution has been noted withN. caviae. Infections involving these three species of bacteria are, therefore, worldwide in occurrence. Even though nocardial infections in both humans and animals were recognized as early as 1888, traditionally, they have been considered rare in frequency as compared to many other infectious diseases. This is a perception that probably is not accurate. During the past twenty years, greater diagnostic awareness combined with more intensive medical and veterinary surveillance have resulted in significantly increased recognition of disease caused by these aerobic actinomycetes.

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.

Cell wall modification resulting from in vitro induction of L-phase variants of Nocardia asteroides

The chemical composition of the cell walls of several L-form revertants derived from Nocardia asteroides 10905 was determined at different stages of growth. It was observed that each L-form revertant had a cell well that differed from that of the parental strain when grown under identical conditions. In some strains the peptidolipid and mycolic acid components were affected the most, whereas in other strains the fatty acid, sugar, and mycolic acid moieties were altered. Shifts in mycolic acid size were prominent, whereas the basic peptidoglycan structure appeared to be affected the least. Both the method used to induce the L-form of N. asteroides 10905 and the length of time these organisms were maintained in the wall-less state affected the degree of cell wall modification during the reversion process. Thus, removal of the cell wall appeared to potentiate and select for mutational alterations within the cell envelope of N. asteroides, and these changes resulted in altered cellular and colonial morphology.

Variations in properties of Nocardia asteroides resulting from growth in the cell wall-deficient state

Several revertants possessing a cell wall were obtained from L-forms of Nocardia asteroides 10905. These L-form revertants differed from the parent in respect to colonial and cellular morphology, pigmentation, metabolic, capacities, cell wall structure, and mycolic acid composition. These data suggest a possible mechanism for the taxonomic heterogeneity and phenotypic diversity observed among N. asteroides strains.

Role of L-forms of Nocardia caviae in the development of chronic mycetomas in normal and immunodeficient murine models

Single-cell suspensions of Nocardia caviae 112 were injected into normal, athymic, and asplenic mice by several different routes. The 50% lethal dose values, kill curve characteristics, histological and electron microscopic properties, organ clearance patterns, and induction of L-forms during the acute and chronic phase of disease were determined in groups of mice for up to 2 years after infection. From these data we concluded the following. (i) Athymic and asplenic animals were significantly more susceptible to N. caviae than their littermate controls regardless of inoculation route. (ii) All mice were most susceptible to lethal infection after intranasal administration and least affected when the organisms were injected into the peritoneal cavity. (iii) Chronic, progressive disease leading to the formation of mycetomas occurred only in mice injected intravenously. (iv) T-cell-deficient animals were impaired in the development of typical mycetomas. (v) L-forms of N. caviae were induced within immunocompetent hosts, whereas the cell wall-less state of the bacteria was not observed in the immunodeficient animals. (vi) Two colony types of the cell wall-deficient state were isolated from infected animals. (vii) These cell wall-deficient organisms were intimately involved in the pathogenesis of disease and bacterial persistence within the host. Finally (viii), with this strain of Nocardia, cell wall-deficient organisms played a major role in the development of the characteristic bacterial granule formed within the mycetomatous lesions 6 months to 1 year after intravenous inoculation.

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.

An ultrastructural comparison of the cell envelopes of selected strains of Nocardia asteroides and Nocardia brasiliensis

Growth curves were determined for three strains each of Nocardia asteroides and Nocardia brasiliensis. Two strains of N. brasiliensis and one strain of N. asteroides had longer lag periods of growth than the remaining three strains. All strains had generation times of approximately 5.5 hours. The ultrastructure of the cell envelope of each Nocardia strain in early stationary phase growth was also examined. All the strains had typical trilaminar cell walls and cell membranes. The thickness of the cell wall layers, especially the inner peptidoglycan layer, varied from strain to strain. The inner layer of two strains of N. brasiliensis and one strain of N. asteroides was 12 nm or more in thickness, while that of the remaining three strains was 7 nm thick. These observed differences in growth patterns and/or thickness of the cell wall layers could be correlated to the varying degrees of virulence as well as the divergent pathologies exhibited by these organisms.