Scanning electron microscopic study of virulent and avirulent colonies of Neisseria gonorrhoeae

Subminimum Inhibitory Concentrations Tetracycline Antibiotics Induce Biofilm Formation in Minocycline-Resistant Klebsiella pneumonia by Affecting Bacterial Physical and Chemical Properties and Associated Genes Expression

Biofilm formation of Klebsiella pneumoniae can protect bacteria from antibiotics and is difficult to eradicate. Thus, the influence of subinhibitory concentrations of antibiotics on bacteria is becoming increasingly important. Our study showed that subminimum inhibitory concentrations (sub-MICs) of tetracycline antibiotics can increase biofilm formation in minocycline-resistant Klebsiella pneumoniae clinical strains. However, in the bacterial adhesion and invasion experiments, the adhesion and invasion ability decreased and the survival rate of Galleria mellonella increased. Under sub-MICs of tetracycline antibiotics treatment, abnormal stretching of bacteria was observed by scanning electron microscopy. Treatment with sub-MICs of tetracyclines leads to increased surface hydrophobicity and eDNA content and decreased outer membrane permeability. The expression levels of the fimA, luxS, qseB, and qseC genes decreased, the expression level of mrkA increased, and the expression level of acrA was inconsistent under different tetracycline antibiotics treatments. Together, our results suggested that the increase in Klebsiella pneumoniae biofilm formation caused by sub-MICs of tetracycline antibiotics may occur by affecting bacterial physical and chemical properties and associated genes expression.

Frequency of dividing cells, a new approach to the determination of bacterial growth rates in aquatic environments

Frequency of dividing cells is suggested to be an indirect measure of the mean growth rate of an aquatic bacterial community. Seasonal changes in frequency of dividing cells were found which covariated with the bacterial uptake of C-labeled phytoplankton exudates. Batch and continuous culture growth experiments, using brackish water bacteria in pure and mixed enrichment cultures, were performed to establish a relationship between frequency of dividing cells and growth rate. An improved technique for bacterial direct counts, using fluorescent staining and epifluorescence microscopy, is presented. Based on a 6-month survey in a coastal area of the Baltic Sea, the bacterial production in the photic zone is estimated. Compared to the total primary production in the area, the bacterial population during this period utilized approximately 25% of the amount of carbon originally fixed by the primary producers.

Scanning electron microscopy of Eikenella corrodens colony morphology variants

Eikenella corrodens is a gram-negative, human pathogen which exhibits colony morphology variation. Scanning electron microscopy (SEM) was used to examine large (non-corroding) and small (corroding) colony variants from the type strain (ATCC 23834) and two clinical isolates (strains VA1 and CM1). Large colonies were large, flatter, and appeared relatively featureless compared to small colonies and had even, smooth colony margins. Small colonies were more raised from the medium surface, and often had a central raised region surrounded by flatter border. Cells on the surface of large colonies were more regularly arranged at the colony edge, and end-to-end rows of cells around the colony were seen in some strains. Cells in the center of the upper surface of small colonies were usually randomly arranged. Within cross sections of small colonies, cells were arranged randomly or perpendicular to the medium; in large colonies, cells were random or arranged horizontally. Amorphous, "slime" material was often seen covering groups of cells in large and small variants. An unusual variant, possibly a mutant, which combined features of both colony types was isolated.

Scanning electron microscopy of piliated Neisseria gonorrhoeae processed with hexamethyldisilazane

Piliated Neisseria gonorrhoeae are virulent and attach readily to some human mucosal cells. The study of interactions between piliated Neisseria gonorrhoeae and surface structures of eukaryotic cells in tissue culture requires consistent high resolution imaging in scanning electron microscopy (SEM). The combination of the fixatives glutaraldehyde, osmium, tannic acid, and uranyl acetate improves preservation of pili and other delicate structures. Following the critical point drying (CPD) process, pili bundles remained intact, but charging produced image distortion in most of the specimens. The use of hexamethyldisilazane (HMDS) with air drying substantially reduced charging and image distortion. Less contrast and greater resolution of pili bundles and surface structures of bacteria or tissue culture cells were obtained at magnifications of 10,000 or higher. As an alternative to CPD, HMDS processing of cell culture monolayers was simple and was more efficient when a large number of samples was processed.

Arrangement of pili in colonies of Neisseria gonorrhoeae

The morphology and arrangement of pili in the P++ colony phenotype of Neisseria gonorrhoeae were examined by a variety of electron microscopic techniques. The apparent structure and organization of gonococcal pili varied depending upon the method of specimen preparation. Pili as thin, individual, unbranched structures were demonstrated by negative staining and in sections of epoxy-embedded specimens. Pili forming thick structures which branch, subdivide, and rejoin to form an irregular lattice were demonstrated in specimens processed by the critical-point drying method and by rapid freezing and low temperature sublimination. We propose that in gonococcal colonies of the P++ phenotype, pili exist as individual threadlike structures only on the bacterial surfaces; as the pili leave the bacterial surfaces, they form thick bundles which branch, subdivide, and rejoin to form a supporting framework interconnecting the colony members. This arrangement of pili is usually disrupted by the commonly used method of negative staining and cannot be clearly detected within epoxy-embedded specimens. These data are summarized in a model depicting the organization of pili in the P++ colony phenotype of N. gonorrhoeae.

Effect of iron on surface charge and hydrophobicity of Neisseria gonorrhoeae

The effect of iron concentration during growth on the physicochemical surface properties of the colonial variants of Neisseria gonorrhoeae has been assessed by aqueous two-phase partitioning in a dextran-polyethyleneglycol system containing positively charged trimethylamino-polyethyleneglycol or hydrophobic polyethyleneglycol-palmitate. The complex effects of iron, in combination with other variables known to affect surface charge and hydrophobicity, have provided some clues as to the properties of the gonococcal surface that are important in promoting virulence.

Effect of colony type and pH on surface charge and hydrophobicity of Neisseria gonorrhoeae

The effect of colonial variation and growth at pH 7.2 or pH 6.0 on the surface properties of Neisseria gonorrhoeae was assessed by the use of two-phase partitioning and hydrophobic interaction chromatography. Cells grown at pH 7.2 tended to be both hydrophobic and to possess a slight negative charge. Growth at pH 6.0 appeared to decrease hydrophobicity and to increase the negative surface charge. Possession of a series of outer membrane proteins, termed the colony opacity-associated proteins, did not appear to significantly affect charge or hydrophobicity. Piliated cells tended to have a higher negative charge than nonpiliated variants. They also tended to be less hydrophobic at pH 7.2, but became more hydrophobic at pH 6.0. The implications of these findings are discussed.

Genetic basis for colonial variation in Neisseria gonorrhoeae

When the piliated colony types of Neisseria gonorrhoeae, which predominate in recent isolates, were nonselectively subcultured in vitro, they gave rise to large numbers of nonpiliated, avirulent colonial variants. Evidence is presented to show that most of this variation occurs after active growth has ceased and that the variation is sensitive to the action of deoxyribonuclease. We suggest that this variation is a result of transformation. A second variation in colonial morphology involved differing levels of "colony opacity-associated proteins" in the outer membrane. This variation was also inhibited by the presence of deoxyribonuclease, but the genetic basis for it is not as yet clear.

Healing of experimentally induced burn wounds. A comparative study of the healing of exposed burn wounds and burn wounds covered with adhesive zinc-tape and a scanning electron microscopic study of the microvasculature of wound healing in the rabbit ear

A comparative study of the healing of experimentally induced burn wounds on the inner side of the rabbit ear treated with either adhesive zinc-tape or exposure to the air is presented. During tape treatment, tissue necroses were dissolved, thus exposing the granulation tissue surface. In wounds treated with zinc-tape, fewer and smaller perforations to the opposite side of the ear were found, compared with those in exposed wounds. It is suggested that the frequency of perforations can be used as a simple measure of extension of tissue necroses after burning in relation to different methods of wound treatment. A microangiographic method is also presented for three-dimensional visualization of vascular events during healing using scanning electron microscopy on vascular casts.

Scanning electron microscopy of palatal mucosa maintained in organ culture: a method for three-dimensional visualization of cell morphology

A scanning electron microscopic (SEM) study of palatal mucosa maintained in organ culture (50% O2-Eagle's MEM w/o serum) from 12 to 360 hours is presented. The morphological changes occurring in the explants during culture are illustrated and the findings are compared with those observed using transmission electron microscopy and light microscopy. The results confirm that cellular fine structure in epithelium and connective tissue is more easily visualized when SEM is employed following in vitro maintenance of explants as opposed to examination of fresh uncultured biopsies. The in vitro system used would appear to be applicable to studies designed to investigate the effect of various substances on cell proliferation and cell interactions.

Relationship of pili to colonial morphology among pathogenic and nonpathogenic species of Neisseria

Growth in colonies with type 1 morphology and the presence of pili are characteristics that have been associated with virulence of gonococci for humans. To determine whether the presence of pili per se might be responsible for colony type 1 morphology, the relationship of pili to colony type was examined in various species of Neisseria. Short pili (175 to 210 nm in length) were seen only on nonpathogenic neisseria, whereas long pili (up to 4,300 nm) were seen on organisms of both nonpathogenic and pathogenic species. Although long pili, similar to those found on organisms from high-domed, type 1 colonies of gonococci, were observed on organisms from high-domed, type 1 colonies of nonpathogenic Neisseria species, they were also observed on low-convex, type 4 colonies of meningococci and nonpathogenic neisseria. Among meningococci there was no difference in the morphology of colonies consisting of organisms with many long pili and colonies consisting of organisms that completely lacked pili. Thus, there was no consistent relationship of pili to colonial morphology. Unless the pili of N. gonorrhoeae are unique among Neisseria species in their influence on colonial morphology, it is likely that factors other than pili determine colony type 1 morphology of gonococci. Whether these same factors, either alone or in conjunction with pili, are also responsible for gonococcal virulence warrants further investigation.

Growth pattern and cell division in Neisseria gonorrhoeae

The gram-negative coccus Neisseria gonorrhoeae was found to grow regularly in at least two dimensions. Growth proceeded at a linear rate sequentially in each dimension. Growth in the second dimension (former width) was initiated slightly before the pole-division plane distance equalled the cell width. Penicillin treatment localized presumptive growth zones to the existing septum region. It was suggested that new growth zones were always formed perpendicular to the longitudinal axis created in the incipient daughter cells of a dividing coccus. Neither penicillin nor nalidixic acid induced filaments of N. gonorrhoeae. Such structures could nevertheless be formed in the rod-shaped species Neisseria elongata. N. gonorrhoeae divides by septation; however, complete septal structures with separated cytoplasms were rather infrequent. It is proposed that N. gonorrhoeae be regarded as a short rod which always extends parallel to the actual longitudinal axis and which never undergoes a rod-sphere-rod transition.

Autolysis of Neisseria gonorrhoeae. Relation between mechanical stability and viability

The relationship between the mechanical stability and the viability of N. gonorrhoeae (Type 4) in suspension was investigated. A correlation between viability and optical density recordings was often found. However, in spite of increased mechanical stability in solutions with low pH (5-2) or containing Cu++ or sucrose (10 per cent.), these environments were toxic to the gonococci. A viability preserving effect by Mg++ (4 mM), Ca++ (4 mM), spermine (0-5 mM), polyvinylpyrrolidone (10 per cent.), and low temperature (4 degrees C) was demonstrated. The possibility of improving transport media for gonococci is discussed.