China
Africa
Explore chapters and articles related to this topic
Bacteria
Published in Julius P. Kreier, Infection, Resistance, and Immunity, 2022
The clinical signs of diphtheria are a result of toxin production by lysogenic strains of Cornyebacterium diphtheriae. A lysogenic strain is one which has been infected with a temperate bacteriophage mu, that carries the genetic code for production of diphtheria toxin. Mu integrates with the host bacterium DNA. Only phage-infected lysogenic strains of the bacterium produce toxin and cause diphtheria. The organism is not very invasive and usually only causes a localized infection of the mucosal membranes of the upper respiratory tract; it is from this site that the toxin diffuses and causes damage. The toxin produced is capable of killing most eukaryotic cells. Antibodies to the toxin neutralize it and prevent the disease even though infection may be present and the host becomes a carrier of the organisms. Immunization with inactivated diphtheria toxin effectively prevents the disease.
Genetics and Biosynthesis of Lipopolysaccharide O-Antigens
Published in Helmut Brade, Steven M. Opal, Stefanie N. Vogel, David C. Morrison, Endotoxin in Health and Disease, 2020
Wendy J. Keenleyside, Chris Whitfield
Although there has been much speculation regarding the role of lateral gene transfer in the generation of antigenic diversity, one area about which there is very little information is the mechanism of DNA transfer. Logically, DNA sequences could be mobilized either through plasmid transfer, transduction by bacteriophage, or by DNA transformation with free DNA. Integration into the recipient cluster could then be mediated by homologous recombination or possibly transposition. The relative involvement of each of these processes is unknown. As previously discussed, lysogenic phage conversion is one source of O-PS diversity, however the phage-encoded changes characterized to date all map outside of the O-PS biosynthesis gene cluster. As discussed above, plasmids are known to be involved to varying extents in O-PS expression, but lateral transfer has only been shown for the O:54 antigen of S. enterica serovar borreze (131). The ColE1-type plasmid carrying the O:54 biosynthesis gene cluster can be mobilized to confer O:54 serospecificity on recipient strains. However, while the various members of the O:54 serogroup are heterogeneous in terms of their endogenous chromosomal O polysaccharide biosynthesis clusters (44,132), the unique structure of the O:54 antigen compared to other Salmonella (or indeed enteric) O antigens (44) and the absence of associated IS or IS-like elements suggest that this plasmid is not a likely source of homologous recombination with chromosomal O-PS biosynthesis sequences.
Introduction to virus structure, classification, replication, and hosts
Published in Avindra Nath, Joseph R. Berger, Clinical Neurovirology, 2020
Philippe Simon, Kevin M. Coombs
Some viruses will bypass the replicative cycle and instead will make use of an alternative pathway termed the lysogenic cycle. Among the herpesviruses, this is generally known as latency, but lysogeny refers to the general phenomenon, originally described for some bacterial viruses. In the lysogenic cycle, the viral DNA will undergo some alteration that results in the viral replicative cycle being arrested. In some cases (e.g., the bacterial virus lambda), the viral DNA integrates into the host cell chromosome. This effectively puts the viral replicative cycle “on hold,” because no progeny virions will be produced. Once integrated, the viral DNA can persist there indefinitely; each daughter cell will contain one or more copies of the viral DNA, because the incorporated DNA is replicated along with the cell’s DNA. As part of the host DNA, the viral DNA can remain silent, can serve to express a low copy number of genes, or can be induced to complete the replicative cycle. Exactly how induction is carried out in the host remains poorly understood, but stress, sunlight, other infections, and certain chemicals can function as inducers. The herpesviruses arrest their replicative cycles and enter latency by a different mechanism. In this case, the viral DNA circularizes and persists in the host cell’s nucleus, being passed to daughter cells, and may eventually be induced.
Bacteriophages for ESKAPE: role in pathogenicity and measures of control
Published in Expert Review of Anti-infective Therapy, 2021
Amrita Patil, Rajashri Banerji, Poonam Kanojiya, Santosh Koratkar, Sunil Saroj
Bacteriophages are viruses, which specifically infect bacterial cells and are one of the most abundant organisms in the environment (total population of ~1030–1032). Bacteriophage possesses tremendous diversity in morphology and genomic content enclosed in its capsid. The basal plate of the bacteriophage consists of tail fibers required for the initial attachment to the host cells. The bacteriophage genetic material is introduced to the host cell via the sheath region, often surrounded by sheath proteins [13]. Inside the host bacterial cell, bacteriophage undergoes either lytic (virulent) or lysogenic (non-virulent) life cycle. The bacteriophage is dependent on the host machinery for the synthesis of bacteriophage particles, assisted by early proteins synthesized during the lytic cycle. The genetic material is then packaged into the capsid constructing a new daughter bacteriophage that eventually bursts into the surrounding after lysis of the host bacterial cell. However, during the lysogenic cycle, rather than undergoing lysis, bacteriophage persists in the host in a dormant state. Bacteriophages and hosts in the lysogenic cycle are known as prophage and lysogen, respectively [14]. Based on the environmental cues, such as changes in pH, nutrients, temperature, and exposure to foreign DNA, hydrogen peroxide, antibiotics, or other agents causing DNA damage prophage enter into a lytic cycle and lead to lysis of the host cell [15] (Figure 1).
Merits of the ‘good’ viruses: the potential of virus-based therapeutics
Published in Expert Opinion on Biological Therapy, 2021
Qianyu Zhang, Wen Wu, Jinqiang Zhang, Xuefeng Xia
Phages play important roles in bacterial pathogenicity and evolution [10]. They can be categorized into obligate lytic (virulent) phages and lysogenic (temperate) phages. As for the anti-bacterial applications, lytic phages are more suitable than lysogenic phages as they are more similar to antibiotic drugs which induce rapid bacterial death [11]. Besides, the lysogenic conversion induced by lysogenic phages might lead to harmful consequences such as endowing bacteria with pathogenic traits or even antibiotic resistance [11]. In early years phages were investigated to manage conditions like typhoid fever, colitis, peritonitis, skin infections, surgical infections, septicemia, urinary tract infections, and otolaryngology infections [12]. However, data collected from early clinical studies lacked standardization such as blinding and the inclusion of appropriate control groups. The interest in phage therapy against bacterial infection was rekindled after Smith & Huggins devised pioneering studies against antibiotic-resistant bacterial strains in human and multiple animal models of septicemia and meningitis in the 1980s. There have been case reports on the antibacterial therapy using bacteriophages in recent years, and clinical trials have been carried out as well [13].
Local drug delivery in the urinary tract: current challenges and opportunities
Published in Journal of Drug Targeting, 2018
Rahul Mittal, Debbie R. Pan, James M. Parrish, Eric H. Huang, Yao Yang, Amit P. Patel, Arul K. Malhotra, Jeenu Mittal, Sanjay Chhibber, Kusum Harjai
Bacteriophages are viruses that selectively infect bacteria. Though capable of both lytic and lysogenic activity in their hosts, bacteriophages with minimal potential for lysogenic conversion are most suitable for therapeutic use, as lysogenic activity carries the risk of inducing expression of bacterial toxins [55]. The bacteriophage lytic cycle involves docking to specific bacterial surface receptors at their tail ends, injecting genetic material into the host cell, and inducing the expression of genes that help replicate their genome alongside genes that interrupt host systems and induce host cell lysis (Figure 3). Theoretically, if bacteriophages are able to reduce bacterial burden in an infection, host immune defences have a much greater chance of eradicating the remaining organisms [56].