Bacteriophages are of two types: lytic and lysogenic bacteriophages. Lytic phages are virulent, causing lysis of bacterial cells, allowing lytic phage progeny to be released into the environment. Due to their lytic properties specific to bacteria, they are supposed to be used as alternative therapeutics against multi-drug resistant bacteria. On the other hand, lysogenic phages are the viruses that integrate their whole genome into bacterial chromosome and maintain their DNA replications along with bacterial genome within bacterial cells. These bacteriophages contribute to bacterial pathogenesis either by delivering their toxin producing genes into bacterial DNA or by transducing bacterial DNA from one bacteria to another. In this context, ten bacteriophages that cause conversion of non-virulent bacteria into virulent and thereby cause disease in the human body, have been discussed along with their associated genes, bacterial hosts and bacterial diseases.
- Lysogenic bacteriophage CTXΦ.
Lysogenic bacteriophage CTXΦ, a filamentous bacteriophage converts non-virulent Vibrio cholera strain into a highly virulent strain. The phage integrates its toxin gene (ctxAB) within the genome of non-virulent strains that do not have the toxin gene. Thus the cholera toxin of newly virulent strains causes severe food poisoning.
- β-coryneform bacteriophage
β-coryneform bacteriophage passing its gene (tox) to the genome of Corynebacterium diptheriae, produces diphtheria toxin. This toxin mainly causes diphtheria, an upper respiratory tract infection, characterized by fever and sore throat. It also travels through the bloodstream and causes harm to heart and other organs.
- Shiga toxin-containing lysogenic bacteriophage H-19B
Lysogenic bacteriophages H-19B causes the production of Shiga toxins by incorporating its gene (stx1, stx2) into the genome Enterohemorrhagic E. coli (EHEC). This toxin causes hemorrhagic colitis or infantile diarrhea. It also causes fever, severe dehydration, abdominal pain and hemolytic–uremic syndrome (HUS).
- MAV1 phage
MAV1 phage produces Vir protein by integrating its gene (vir gene) with the genome of Mycoplasma arthritidis and converts it into a virulent strain. The phage genome contains virulence factors contributing to polyarthritis in different organs. One of the several virulence factors is superantigen MAM which is strongly associated with MAV1 phage-encoded virulence.
- SM1 phage
It incorporates its genes into Streptococcus mitis, a causative agent of infective endocarditis. SM1 Phage contains two genes (pnlA and pblB), which encodes for two surface coat proteins. These proteins help the bacteria bind to human platelet; a crucial step for the pathogenesis of infective endocarditis.
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- Salmonella enterica phages
Several types of temperate phages lysogenized with Salmonella enterica are involved in human disease. The phages SopEphi (sopE gene), GIFSY-2(sodC-I gene), and Fels-1(nanH gene) produce Type III effector, Superoxide dismutase, and Neuraminidase respectively. These toxins are involved in the invasion of epithelial cells, survival in macrophages and release of sialic acid from gangliosides thus cause intestinal infection.
- NA, phi13, phiPVL phages
NA, phi13, phiPVL phages produce enterotoxin, staphylokinase and leukocidin respectively by integrating their gene (sel, sak and pvl) within the genome of S. aureus. Several diseases are caused by these toxins; food poisoning, skin infection, and life-threatening toxic shock. Enterotoxin causes vomiting and diarrhea. Other two toxins such as Leukocidin and staphylokinase causes lysis of white blood cells and fibrinolysin respectively.
- Pasteurels multocida phage
Pasteurels multocida toxin, a phage-encoded exotoxin that can rapidly cause severe inflammation and swelling at the site of the bite. The phage of this bacteria is unknown. They contain toxin gene (toxA), which is incorporated into Pasteurels multocida to produce Pasteurels multocida toxin (PMT). This toxin is also responsible for the nasal turbinate bone associated with porcine atrophic rhinitis.
- Phage c1
Phage c1 lysogenized with Clostridium botulinium, carries c1 gene that encodes for neurotoxin. This toxin irreversibly binds to the neuron, causing botulism. Botulism is characterized by paralysis, vision and speaking problem, life-threatening swallowing and breathing difficulties and even death due to respiratory failure.
- T12 and H4489A phage
Conversion of non-toxigenic strains of S. pyogenes to toxigenic strain is mediated by bacteriophages. Approximately 90% of this bacteria contains phage gene within their genome and many of them contain several prophage genomes (polylysogenic). T12 phage containing speA gene, encodes for toxin type A (streptococcal pyrogenic exotoxin). This toxin causes streptococcal toxic shock syndrome and scarlet fever. Another Phage “H4489A” of S. pyogenes carrying gene hylP, encodes for hyaluronidase enzyme. This enzyme catalyzes the degradation of hyaluronic acid, an important substance of connective tissue. Thus it helps pathogens to spread throughout the tissue.