Intracellular Production of Brucella L Forms I. Recovery of L Forms from Tissue Culture Cells Infected with Brucella abortus

Osmotically sensitive Brucella in infected normal and immune macrophages

When Brucella suis is grown in tissue cultures of normal guinea pig macrophages, the Brucella multiplies significantly without the induction of osmotically sensitive forms. In immune macrophages in the presence of normal guinea pig serum, there is a reduction in the number of intracellular Brucella and no multiplication is seen over a 72-hr period. After 6 hr of exposure to immune macrophages, however, approximately 50% of the surviving intracellular Brucella are osmotically sensitive, i.e., they will survive and grow only on medium containing 0.2 m sucrose. Brucella grown in immune macrophages, in the presence of rabbit antiserum against whole guinea pig serum, show the presence of osmotically sensitive forms, although at a reduced level compared to the number seen with immune macrophages in normal guinea pig serum.

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.

Penetration and intracellular growth of Brucella abortus in nonphagocytic cells in vitro

In pregnant ruminants, Brucella abortus localizes and replicates within the rough endoplasmic reticulum of trophoblastic epithelial cells. In this study, Vero cells were exposed to B. abortus to investigate its internalization and intracellular growth in nonphagocytic cells. A new double-fluorescence staining procedure to discriminate between extracellular and intracellular bacteria was developed. Studies with the double-fluorescence staining procedure and quantitative bacteriologic culture of disrupted host cells showed that various B. abortus strains replicated within Vero cells, including smooth virulent (strains 2308S and 544), smooth attenuated (strain 19), and rough (strains 45/20 and 2308R) strains. Rough brucellae were more adherent and entered a greater number of Vero cells. Intracellular replication occurred in a larger percentage of cells with smooth virulent (2308S and 544) strains than with smooth attenuated (19) or rough (45/20 and 2308R) strains. Differences in adhesiveness and invasiveness were correlated to hydrophobicity of the organism, as measured by hydrocarbon adherence. Ultrastructurally, intracellular smooth (2308S) and rough (45/20) brucellae were consistently found within cisternae of the rough endoplasmic reticulum and nuclear envelope. The results suggest that transfer to the rough endoplasmic reticulum is the limiting step in the infection of nonphagocytic cells by B. abortus.

Relevance of in vitro antimicrobial susceptibility of Brucella melitensis to relapse rate in human brucellosis

The in vitro susceptibility of Brucella melitensis was examined vis-a-vis the clinical outcome in 75 patients with brucellosis. The initial MICs for Brucella isolates from patients who relapsed and from those who did not were similar. Furthermore, the MICs for isolates from patients whose infections relapsed were no different from those for original isolates. Our results clearly showed that neither initial nor subsequent antibiotic susceptibility plays a role in the likelihood of relapse of patients with brucellosis.

Demonstration of the phenomena of microbial persistence and reversion with bacterial L-forms in human embryonic kidney cells

A series of experiments was undertaken in which human embryonic kidney (HEK) fibroblasts were infected with either relatively stable or stable L-forms of Streptococcus faecalis. The infected cells were maintained by splitting over long periods (1 to 2 months) while samples were withdrawn for culture and electron microscopic studies. Relatively stable S. faecalis L-forms could be cultured from infected cells only during the first week after infection, although L-form-like material was frequently detected at later periods by electron microscopy. HEK cells continued to proliferate and showed no gross histopathology until reversion occurred. At reversion, electron microscopy revealed the presence of intracellular L-forms, transitional variants, and intra- and extracellular bacterial forms. Unlike relatively stable L-forms, stable L-forms were culturable throughout the experimental period. These experiments demonstrate the phenomena of persistence and reversion in vitro. Electron microscopy indicated that the L-forms entered the HEK cells, where they underwent morphological changes. Observations suggested that these altered L-forms (elementary bodies) persisted in the cell until reversion to the parent bacterial form was triggered. Infected cells, when treated with L-form antiserum and stained with fluorescein-conjugated goat anti-rabbit serum, were consistently positive regardless of cultural findings.

Probable L-forms of Nocardia asteroides induced in cultured mouse peritoneal macrophages

Mouse peritoneal macrophages were infected with varying numbers of Nocardia asteroides 10905, and the fate of the ingested organisms was determined by viable plate count (VPC), light microscopy (LM), immunofluorescent microscopy (IM), and electron microscopy (EM). The results obtained with these methods differed. VPC indicated that intracellular Nocardia decreased in numbers during the first 12 days, followed by significant increases after 16 days. LM suggested that N. asteroides 10905 was slowly degraded by macrophages with no subsequent increases observed. In contrast, IM demonstrated large numbers of intracellular Nocardia throughout the experiment. EM studies of infected macrophages failed to demonstrate intact bacteria after 8 days; however, wall-less and spheroplast-like organisms were seen. These results suggested that N. asteroides 10905 was present within the macrophages in an altered form. By using hypertonic culture medium, we were able to isolate, from infected macrophages, organisms which exhibited many of the properties of bacterial L-forms. IM demonstrated these variants to be of nocardial origin. These altered forms also reverted to typical nocardial cells either spontaneously or upon transfer into broth. These findings indicate that N. asteroides 10905 is capable of existing within macrophages in an altered state. Further investigation is in progress to determine whether these altered forms represent L-forms or transitional-phase variants.

Induction of L-variants in human diploid cells infected by group A streptococci

Human diploid cells in culture, infected with a balanced amount of living group A streptococci, were able to survive the infection and could be divided and propagated normally thereafter. The streptococci were rapidly phagocytized by the tissue culture cells. At the beginning, they kept their typical appearance, as well as their ability to fix dyes and group-specific immunoglobulins. After 1 to 2 days, the number of detectable streptococci decreased and they underwent important morphological changes. After some subsequent divisions of the cell line, streptococci persisted in cells only as large, isolated, swollen cocci, and no longer grew on suitable media. After six to eight divisions, a noticeable percentage of the tissue culture cells were very similar in appearance to the same cell line experimentally infected with "stable" L-variants. Cultures on L-phase media of supernatant fraction and cells, made 24 to 48 hr after inoculation, showed typical L-colonies. These grew well on media without antibiotics, as well as on media containing penicillin or vancomycin. They could be propagated on media with penicillin for months and were able to revert to group A streptococci after several subcultures on antibiotic-free media. Controls of uninoculated tissue culture cells never showed the presence of any microorganism. Group A streptococci inoculated into Eagle's basal medium, which was used for the tissue cultures, did not grow and never gave rise to L-colonies, even though the medium contained penicillin. Previous data suggest a biochemical explanation for this conversion, which otherwise is an occasional phenomenon.

Electron microscopy of tissue culture cells infected with Brucella abortus

Thin sections of hamster kidney tissue cultures were examined by electron microscopy over a 7-day period after infection with Brucella abortus 3183. Numerous bacteria and structures resembling L-forms were present both intracellularly and extracellularly after the first 24 hr of infection. Most intracellular microorganisms were enclosed by a cytoplasmic membrane, but in a few instances no limiting membrane was detected. After 4 to 7 days, fewer microorganisms were present, and most normal-appearing bacteria were intracellular, particularly in antibiotic-treated cultures. Structures typical of Brucella L-forms were extracellular at the latter time intervals. Several structures were observed in cells from infected cultures whose relationship to the infecting organisms is not known. These consisted of various membranous structures within cytoplasmic vacuoles, myelin-like structures surrounding occasional intracellular organisms, and small bodies present within vacuoles and extracellularly. The latter structures observed throughout the experimental period appeared to occur more frequently as the duration of the infection increased.

Ultrastructure of Brucella abortus L-forms induced by penicillin in a liquid and in a semisolid medium

Brucella abortus L-forms were induced by 5.0 or 10.0 mug of penicillin/ml in a broth medium containing 0.3 m sucrose, and in a semisolid medium containing 10% calf serum and 20.0, 40.0, or 60.0 mug of penicillin/ml. After 96 hr of incubation, L-forms of various sizes and shapes were observed. Basic structures of the L-forms were similar whether induced in liquid or semisolid medium. L-forms had two "unit" membranes, each consisting of two outer dense layers separated by a lucent layer. A few large, irregularly shaped organisms in penicillin-treated broth cultures had additional surface material and were referred to as "transitional" forms. In contrast with L-forms, the bacterial cells were fairly uniform in size and shape, were smaller, and had a more complex cell wall structure. Small bodies limited by a "unit" membrane were present within and around numerous L-forms from liquid and semisolid medium cultures. Other internal membranous structures were also seen in some L-forms. Most Brucella L-forms described in this paper reverted to bacteria in the absence of penicillin and were structurally characteristic of unstable L-forms.

Serum-mediated immune cellular responses to Brucella melitensis. I. Role of a macrophage-stimulating factor in promoting ingestion of Brucella by streptomycin-protected cells

Injection of rabbits with living Brucella melitensis Rev I induced the appearance of a macrophage-stimulating-factor (MSF) in the sera of these animals. MSF was involved in ingestion of bacilli, hastening the formation of protected loci as measured by the addition of lethal amounts of dihydrostreptomycin. When sufficient time had been allowed for effective ingestion, streptomycin had little effect. This in turn allowed for multiplication of bacilli intracellularly in the presence of 5 to 250 mug of drug per ml. MSF mediated more effective ingestion by both immune and normal macrophages. Under such conditions, there was little, if any, intracellular growth restriction by macrophages from immune animals. The activity appeared within the first 5 days after injection with 10(9) organisms and was present for several months. Three weeks after injection, the activity of serum was partially heat-labile. All activity was removed by absorption with heat-killed or living Rev I cells, suggesting that a specific globulin is concerned.

Intracellular production of Brucella L forms . II. Induction and survival of Brucella abortus L forms in tissue culture

Hatten, Betty A. (The University of Texas Southwestern Medical School, Dallas), and S. Edward Sulkin. Intracellular production of Brucella L forms. II. Induction and survival of Brucella abortus L forms in tissue culture. J. Bacteriol. 91:14-20. 1966.-Intracellular survival of altered brucellae, possibly L forms, was not greatly affected by penicillin or streptomycin in concentrations ranging from 5.0 to 40 mug/ml, but a combination of these two antibiotics (2.5 to 20 mug/ml each) reduced the number of positive L-form cultures. Tetracycline (2.0 mug/ml) decreased the number of positive L-form cultures at about the same rate as combinations of the higher concentrations of penicillin and streptomycin. Various concentrations of tetracycline (0.1 to 2.0 mug/ml) with 5.0 mug/ml of penicillin or streptomycin significantly reduced the number of positive L-form cultures. L forms were recovered for several days after elimination of bacteria from the cultures by all of the antibiotics tested. L-form production was not dependent upon the presence of antibiotics in the culture medium, but they were recovered in greater numbers when bacteria were still present in the hamster kidney cells. Addition of thallium acetate to infected cells (at varying intervals of time after infection) to control bacterial growth and conversion to the L phase during cellular disintegration decreased the number of positive L-form cultures obtained over a 10-day period. Comparison of the antibiotic sensitivity of bacteria recovered from infected tissue culture cells with the stock strain of Brucella abortus indicated that some resistance to penicillin and tetracycline had developed. A marked resistance to streptomycin was observed in those bacteria recovered from cells maintained in the presence of this antibiotic.