Nalidixic acid does not inhibit bacterial transformation

Phage-Antibiotic Combination Treatments: Antagonistic Impacts of Antibiotics on the Pharmacodynamics of Phage Therapy?

Bacteria can evolve resistance to antibiotics. Even without changing genetically, bacteria also can display tolerance to antibiotic treatments. Many antibiotics are also broadly acting, as can result in excessive modifications of body microbiomes. Particularly for antibiotics of last resort or in treating extremely ill patients, antibiotics furthermore can display excessive toxicities. Antibiotics nevertheless remain the standard of care for bacterial infections, and rightly so given their long track records of both antibacterial efficacy and infrequency of severe side effects. Antibiotics do not successfully cure all treated bacterial infections, however, thereby providing a utility to alternative antibacterial approaches. One such approach is the use of bacteriophages, the viruses of bacteria. This nearly 100-year-old bactericidal, anti-infection technology can be effective against antibiotic-resistant or -tolerant bacteria, including bacterial biofilms and persister cells. Ideally phages could be used in combination with standard antibiotics while retaining their anti-bacterial pharmacodynamic activity, this despite antibiotics interfering with aspects of bacterial metabolism that are also required for full phage infection activity. Here I examine the literature of pre-clinical phage-antibiotic combination treatments, with emphasis on antibiotic-susceptible bacterial targets. I review evidence of antibiotic interference with phage infection activity along with its converse: phage antibacterial functioning despite antibiotic presence.

SPP1 DNA replicative forms: growth of phage SPP1 in Bacillus subtilis mutants temperature-sensitive in DNA synthesis

The development of bacteriophages SPP1 and phi 29 has been studied in several B. sutilis mutants defective in host DNA replication, under non permissive conditions. Several gene products, involved in the synthesis of host DNA, are required for phi 29 replication, while SPP1 seems to require only the host DNA polymerase III. In addition both phages are unable to grow in a dna A mutant (ribonucleotide reductase). Taking advantage of the fact that SPP1 DNA is actively replicated in several dna mutants at non-permissive temperature, we have studied the structure of the replicative intermediates of this phage in the absence of interfering host DNA synthesis. Fast sedimenting forms of SPP1 DNA can be isolated from phage infected cells and evidence of covalently joined concatemers has been obtained, suggesting the presence of terminally repeated sequences.

Metabolic requirements for entry of DNA in Branhamella catarrhalis

Although requirements for transformation in Branhamella catarrhalis are quite complex, DNA synthesis does not appear to be one of these needs, as indicated by the inability of nalidixic acid to interefere with transformation. Exogenous sources of energy, such as cAMP and cGMP also failed to enhance frequency, suggesting cells may actively engage in energy production to achieve uptake of DNA, or lack a transport mechanism for these compounds.

Effect of deoxyribonucleic acid replication inhibitors on bacterial recombination

Two inhibitors of replicative deoxyribonucleic acid (DNA) synthesis, nalidixic acid (NAL) and 6-(p-hydroxyphenylazo)-uracil (HPUra), showed different effects on genetic recombination and DNA repair in Bacillus subtilis. Previous work (Pedrini et al., 1972) showed that NAL does not interfere with the transformation process of B. subtilis. The results reported in this work demonstrated that the drug was also without effect on the transfection by SPP1 or SPO-1 phage DNA (a process that requires a recombination event). The drug was also ineffective on the host cell reactivation of ultraviolet-irradiated SPP1 phage, as well as on transfection with ultraviolet-irradiated DNA of the same phage. HPUra instead markedly reduced the transformation process, as well as transfection, by SPO-1 DNA, but it did not affect the host cell reactivation of SPO-1 phage. In conclusion, whereas the NAL target seems to be specific for replicative DNA synthesis, the HPUra target (i.e., the DNA polymerase III of B. subtilis) seems to be involved also in recombination, but not in the excision repair process. The mutations conferring NAL and HPUra resistance used in this work were mapped by PBS-1 transduction.

Effect of nalidixic acid on PBS2 bacteriophage infection of Bacillus subtilis

Infection of Bacillus subtilis by PBS2 phage, whose DNA contains uracil instead of thymine, is relatively unaffected by low concentrations of nalidixic acid which severely inhibit B. subtilis DNA synthesis. High concentrations of nalidixic acid do inhibit PBS2 DNA synthesis, but more severely reduce the burst size of PBS2 infections. Hydroxyurea blocks PBS2 DNA synthesis, preventing progeny phage production.