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

Abstract

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 ofpili to colony type was examined in various species ofNeisseria. 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 ofboth 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.

Pili of Neisseria meningitidis: effect of media on maintenance of piliation, characteristics of Pili, and colonial morphology

“…These workers also assessed piliation of gonococci in vivo by carbonplatinum-shadowing techniques and found that in purulent exudates the ratio of nonpiliated to piliated gonococci was 18:1 (i.e., 94% of the gonococci lacked pili) and the number of pili per microorganism was low. Thus, piliation of gonococci in vivo differed from the piliation of type 1 or 2 gonococci grown in our own or other laboratories, of which virtually all would have 10 to 30 pili per microorganism (20,26). Evans (10) found no pili upon thin-section electron microscopy of gonococci in specimens from cervical biopsies and concluded that pilii are a laboratory phenomenon confined to growth on artificial media or in organ culture models."…”

“…(pH 7.45). A Formvar-carboncoated grid was inverted and floated successively on the surface of one drop each of the bacterial suspension, 1% glutaraldehyde in 0.1 M cacodylate buffer (pH 7.4), distilled water, and 1% sodium phosphotungstate (pH 6.5) under the conditions previously described (20). The grids were examined with a Phillips 300 electron microscope at 60 kV.…”

“…However, when 10 of the strains from carriers and 15 of the strains from cerebrospinal fluid were subcultured, approximately half of the microorganisms lost pili on the first passage, and a second passage resulted in either the complete loss of detectable pili or a very low frequency of piliation. Thus, despite interest in pili as a potential mechanism of virulence, as well as the finding of McGee et al (20) that the pili of meningococci were morphologically indistinguishable from those of gonococci, the apparent difficulty in maintaining pili on meningococci cultivated in vitro seems to have discouraged investigation of these structures.…”

Distribution of specific DNA sequences among pathogenic and commensal Neisseria species

“…Less is known about meningococcal pili; however, they share morphologic characteristics, antigenicity, and some amino acid sequence homology with gonococcal pili (12,29,32). Pili have also been observed on commensal Neisseria species (24,37), but the function of these pili and their relationship to pili found on pathogenic species are unclear. P.11 is a heat-modifiable outer membrane protein fouhd on gonococci (21,34).…”

“…Each panel was probed with a different DNA probe. ( were then negatively stained with 1% potassium phosphotungstate E~t 1 ri L (pH 7.0) on carbon-coated Formvar grids as described by McGee et al (24). The specimens were examined with a JEOL 100 CX transmission electron microscope at 80 kV.…”