Induction and reversion of the L-form of Neisseria gonorrhoeae

The biology of the gonococcus

Gonorrhea has been known since antiquity. Today, this disease is the most commonly reported infectious disease in the U.S. The natural environment of the etiological agent, Neisseria gonorrhoeae, is man. In this host, the organism usually parasitizes mucosal surfaces populated by columnar epithelial cells. Under certain conditions, the gonococcus may disseminate or spread to adjacent organs. The gonococcus is well adapted to its environment and is a successful parasite. Until recently, gonococci were uniformly sensitive to penicilin. However, a plasmid encoding beta-lactamase has been identified in some isolates. Most strains exhibit specific requirements for various amino acids, vitamins, purines, and pyrimidines. Only glucose, pyruvate, and lactate are utilized as sources of energy. Glucose is dissimilated by a combination of the Entner-Doudoroff and pentose phosphate pathways. A tricarboxylic acid cycle is also present and active under certain conditions. Structurally, the cell envelope of the gonococcus resembles that of a typical Gram-negative bacterium. Gonococci are highly autolytic, especially in older cultures or after depletion of the energy source. Autolysis is not due solely to peptidoglycan hydrolysis, but appears to involve a destabilization of the outer membrane as well. Cell surface components such as pili, lipopolysaccharide, outer membrane proteins, and a capsule are associated with the virulence and pathogenicity of this organism.

Studies on Neisseria gonorrhoeae cultured in liquid medium

Experiments were carried out to determine the minimum amount of inoculum of gonococci that is needed to produce growth in ANM liquid medium. This was found to be less than had previously been thought. Minimum inocula were used to study penicillin sensitivity in liquid medium. This work showed that growth occurred at higher concentrations of penicillin with larger inocula. Evidence was also obtained which suggested that in some circumstances penicillin acts bacteriostatically rather than bacteriocidally. It was also shown that growth of gonococci can be inhibited in liquid medium by the presence of hyperimmune serum, the inhibition being more marked in the presence of fresh complement. This work is continuing in the hope that it may provide a basis for a much-needed serological test for gonorrhoea. This would be especially valuable in chronic assymptomatic infections.

Use of polyvinylpyrrolidone in the testing of staphylococci for sensitivity to methicillin and cephradine

The use of polyvinylpyrrolidone, an inert polymer resembling plasma proteins in its colligative effects, in the testing of micrococcaceae for sensitivity to methicillin and cephradine is described. Generally results are quite comparable with those of conventional methods. The absence of any inhibitory effect of the polymer compared to sodium chloride, and its physiological inertia compared to sucrose, along with its suitability for sterilisation by autoclaving are seen as advantages. It is suggested that the use of this substance may give results which are more applicable to the in vivo situation. This may apply particularly in the case of cephradine.

Postgonococcal urethritis. Relationship to penicillin sensitivity of the gonococcus

Postgonococcal urethritis (PGU) occurred in 69 (21.3%) of 344 men with urethral gonorrhoea. Each case of gonorrhoea was treated with intramuscular procaine penicillin 2.4 megaunits and the penicillin sensitivity was determined. All 69 of the isolates from patients with PGU were fully sensitive to penicillin (IC50 less than 0.08 iu penicillin per ml). Twenty-eight (10.2%) of 275 cases of gonorrhoea which were not followed by PGU were relatively resistant to penicillin. The persistence of gonococcal L-forms is therefore not likely to be a main cause of PGU. An incidental finding was that significantly more of the 69 men who developed PGU had a history of non-specific urethritis compared with the 224 men who fully recovered (P less than 0.01).

Detection and identification of gonococcal L-Forms using a direct immunofluorescence test

A fluorescent antibody test was used to identify L-Forms of N. gonorrhoeae induced in vitro. It was possible to differentiate the Large Bodies of the L-Forms from parent gonococci and the fluorescent reaction remained specific in the presence of tissue culture cells. A possible method to identify L-Forms of gonococci from patients presenting with postgonococcal urethritis is described.

Comparison of spontaneous and antibiotic-induced L-form production in Neisseria gonorrhoeae

The ability of Neisseria gonorrhoeae to grow as L-forms was found to be independent of the presence of an antibiotic inducing agent and colony type.

Effect of antibiotics on L-form induction of Neisseria meningitidis

Conditions have been developed that permit highly efficient conversion in vitro of all serogroups of Neisseria meningitidis to the L-form. During the course of the studies, optimal parameters for cultivation and propogation were determined and compared with those found in studies done by previous workers on meningococci. The plasma expander polyvinylpyrrolidone (PVP) (molecular weight, 40,000) has been incorporated into the medium as an osmotic stabilizer. A method is outlined for removing toxicity (due to impurities in PVP) reported in some earlier studies done in this laboratory. Light and scanning electron microscopy of the L-form inductants and of a stable L-form have shown characteristics distinctive among the strains observed. Finally, the effects of both cell wall and other antibiotics were studied. It was shown that cell wall antibiotics other than the commonly used potassium penicillin G could induce N. meningitidis to the L-form, using the PVP-stabilized medium base. Furthermore, the antibiotics vancomycin, colistin, nystatin, and trimethoprim, used at the concentrations found in commercially prepared Transgrow formulations, did not adversely affect meningococcal L-form induction. The system described herein will hopefully serve as an effective tool, specifically in the study of "aseptic" meningitis and possible meningococcal L-form etiology and, more generally, in evaluating the ability of bacterial L-forms to cause disease.

Type and strain variation in induction of L forms of Neisseria gonorrhoeae

Strains of Neisseria gonorrhoeae were inoculated onto brain heart infusion (Difco) agar supplemented with penicillin and polyvinylpyrrolidone (PVP) as a stabilizer and cultivated in a candle extinction jar. L-form colonies became visible after a few days. They continued to grow and were viable for up to 38 days. The extent of inducibility of L forms of N. gonorrhoeae was examined semiquantitatively. It was found to be constant for each type and strain and to depend only slightly on the amount of penicillin added to the medium. None of the types of one strain produced L-form colonies. In another strain, avirulent types (T3, T4) showed more ability to produce L forms than virulent types (T1, T2) and no L forms were produced by the subtypes of T1 and T2-T1a and T2a. In a third strain, only T4 produced L forms. Electron microscopic studies showed that the L forms consisted of a number of membranous vesicles and a variety of cell types such as those completely lacking cell walls and those with only remnants of cell walls. The results indicate the existence of subtypes of T1 and T2 of gonococci and the intrinsic inducibility of gonococcal types and strains to produce L forms.

L-Phase variants of Agromyces ramosus

Agromyces ramosus, which is a numerically prevalent bacterium in soil, was easily induced into the L-phase by growing it on agar media containing low levels of penicillin or glycine. The L-forms were stable after initial contact with the inducing agent and could not be reverted to the bacterial form by any of the procedures tried. These results are discussed in relation to a possible natural occurrence of L-forms of this bacterium in soil.

Variations in properties of L-forms of Pseudomonas aeruginosa

In a study of the pathogenic potentials of Pseudomonas L-forms, three unstable L-forms were derived by carbenicillin inductionfrom a mouse virulent strain of Pseudomonas aeruginosa, Rosenthal 180. One L-form, induced on a sucrose-stabilized medium, grew more slowly and differed in a number of properties from two other L-forms induced on a medium supported with polyvinylpyrilidone. After adaptation to a common liquid medium, the three L-forms differed with respect to colonial shape on solid medium, growth rate, certain biochemical properties, antibiotic sensitivities and antigenic surface, and virulence for mice. The L-form may revert in vitro to a serotype different from that of the parent culture. The revertant may acquire new antibiotic resistances and sensitivities in the absence of previous exposure to the drugs and enhanced resistance to the L-inducing agent. The three L-forms showed a characteristically lower, but wide, range of virulence than did the parental form. Though death of mice was accompanied by reversion of the L-forms in vivo to the bacterial form, reversion in vivo was not necessary for virulence of L-forms. Modification of residual cell wall antigens accompanied the induction of each L-form as determined by type-specific antisera.