The export of the DNA replication inhibitor Microcin B17 provides immunity for the host cell.

Microcin B17 (MccB17) is a peptide antibiotic which inhibits DNA replication in Enterobacteriaceae. Microcin-producing strains are immune to the action of the microcin. Physical and genetic studies showed that immunity is mediated by three genes: mcbE, mcbF and mcbG. We sequenced these genes and identified polypeptide products for mcbF and mcbG. By studying the contribution of each gene to the expression of immunity we found that immunity is determined by two different mechanisms. One of these, encoded by mcbE and mcbF, is also involved in the production of extracellular MccB17. To reconcile these observations we propose that McbE and McbF serve as a 'pump' for the export of active MccB17 from the cytoplasm. This model is supported by the predicted properties of the McbE and McbF proteins, which are thought to be, respectively, an integral membrane protein and an ATP-binding protein with homology to other transport proteins.

Cloning and mapping of the genetic determinants for microcin C7 production and immunity.

Microcin C7, a peptide antibiotic inhibitor of protein synthesis, is produced by Escherichia coli K-12 strains that carry the 43-kilobase low-copy-number plasmid pMccC7. Microcin C7 production and immunity determinants of this plasmid have been cloned into the vectors pBR322 and pACYC184. The resulting plasmids overproduce microcin C7 and express immunity against the microcin. Mcc- and Mcc- Imm- mutants have been isolated on recombinant plasmids by inserting transposable elements. Physical and phenotypic characterization of these mutants shows that a DNA region of 5 kilobases is required to produce microcin C7, and that two small regions located inside the producing region are also required to express immunity. Analysis of plasmids carrying mcc-lacZ gene fusions indicates that all microcin DNA is transcribed in the same direction. The results suggest that a structure like a polycistronic operon is responsible for microcin C7 production and immunity.

Lysis of Streptococcus sanguis by an extracellular enzyme from the bacterium Streptococcus mutans from human dental plaque.

The ability of crude extracellular enzyme produced by the oral bacterium Streptococcus mutans AL7-1 to lyse living cells of Streptococcus sanguis ATCC 10556, 10557 and 10558 was examined. This enzyme showed lytic activity of living cells and cell walls of only Strep. sanguis ATCC 10558 strain and severed at random the long chains of this strain of living cells. Early log phase cells of this strain were more sensitive to this lytic enzyme than were late-log phase cells. In view of these results, the relationship between this lytic enzyme from Strep. mutans and a decrease in the number of serotype III strains of Strep. sanguis in dental plaque is discussed.

Colonization of the subgingival area by Bacteroides gingivalis.

The initial event in colonization of the subgingival area by B. gingivalis is its attachment to host cells and Gram-positive bacteria in pre-formed plaque. The level of B. gingivalis is partly governed by products of other plaque bacteria, especially by sanguicin. Once B. gingivalis resides in its nidus and starts to proliferate, expulsion of pre-existing residents may occur, especially of attached Gram-positive bacteria, through the inhibitory action of the B. gingivalis product, hematin. The bacteriocin produced by black-pigmented Bacteroides also seems to play an important role in their establishment. Melaninogenicus possessed strong inhibitory activity against Actinomyces species. This was not completely confirmed with fresh isolates of B. gingivalis from advanced periodontitis patients. Various factors other than inhibitory substances produced by B. gingivalis and related bacteria can also affect the colonization of this species. Since the crevice area is influenced by gingival fluid, the nature of specific antibody and the other affecting components should be considered collectively with the interaction between new predominant colonizers and other pre-existing residents.

Pyocin R1 inhibits active transport in Pseudomonas aeruginosa and depolarizes membrane potential.

Pyocin R1, a bacteriocin of Pseudomonas aeruginosa, inhibited active transport of proline in the presence of high concentrations of malate and magnesium salt. Pyocin R1 did not affect the respiration of sensitive cells nor induce cell lysis, but it caused a decrease in the intracellular ATP level. In addition, a passive inflow of [14C]thiocyanate anion, a probe of membrane potential, was induced by pyocin R1, showing a depolarization of the cytoplasmic membrane. It is considered that membrane depolarization is a primary action of pyocin R1.

Biological properties of a plaque-inducing agent obtained from Acholeplasma oculi.

A plaque-forming agent arose spontaneously during cloning of Acholeplasma oculi 19L. The agent produced plaques on A. oculi 19L and A. oculi-i, but not on A. laidlawii, A. modicum, or wild isolates of A. oculi. The agent required horse serum for plaque formation as well as for adsorption to the indicator lawn; however, it was extremely sensitive to an inhibitor in some horse sera. The agent retained infectivity after passage through a 50 nm filter and was heat-, Nonidet P-40-, and chloroform-labile, but relatively ether-stable. It was not determined whether the agent is a virus or a bacteriocin-like substance.

Bacterial interference in streptococcal tonsillitis.

On the basis of the presented results and those published by other investigators it can be stated that in the throat (i) bacterial interference is a multifaceted phenomenon; (ii) bacterial interference not only varies individually but also fluctuates in the individual by time and the epidemiological situation; (iii) bacterial interference among the microbes in the normal flora apparently helps the individual to combat the invading microorganisms; (iv) bacteriocins, if present, in the invading bacteria represent an important virulence factor; (v) bacterial interference as a factor of the host resistance to infection can be influenced negatively by antibiotic therapy; (vi) bacterial interference can act synergistically with antibiotics given in optimal doses saving the normal flora.

Establishment and localization of mixtures of Streptococcus mutans serotypes in the oral cavity of the rat.

The colonization of S. mutans serotypes on different tooth surfaces of the rat was investigated. Fissures appeared to be the main habitat. In the presence of a serotype c strain, S. mutans serotype d could only be established when sucrose-containing diets were supplied. However, the serotype c strain was always present in higher proportions. The production of a bacteriocin for which the serotype d strain was sensitive appeared to be responsible for the observed predominance of the serotype c strain.