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New discoveries in antibiotic resistance: What is the true sensitivity of Ans strains to drugs?
“The virulence of the Ans strain makes it an ideal candidate for developing a vaccine.”
Toxicity mechanisms and characteristics
For B. anthracis, researchers have identified two specific toxic masses, pXO1 and pXO2. Based on comparative studies, the Ans strain showed greater virulence than other strains. This toxicity mainly comes from these two masses. The pXO2 mass encodes a poly-D-glutamate capsule that resists phagocytosis and enables B. anthracis to evade the host immune system; the pXO1 mass encodes three toxin proteins: edema factor (EF), lethal factor (LF), and ) and protective antigen (PA).
Variation regarding virulence can be explained by the presence or absence of the pXO; for example, isolates lacking pXO1 or pXO2 are considered attenuated and do not cause significant infection. The researchers found that pXO2 contributed significantly to the observed toxicity variation, as mutants that produced more capsules had significantly increased toxicity. Although pathogenic strains have emerged that have removed the pXO1 mass, these bacteria still remain highly pathogenic to mice.
Antibiotic resistance
The Ans strain was found to be susceptible to standard antibiotics against anthrax, consistent with most other Bacillus anthracis strains. This strain is no exception to the susceptibility of post-exposure prophylaxis drugs recommended by the Centers for Disease Control and Prevention (CDC). Ciprofloxacin is the recommended treatment for respiratory anthrax, but studies have shown that the new fluoroquinolone drug gatifloxacin can improve the survival rate of mice susceptible to the Ans strain.
"The Ans strain's sensitivity to antibiotics allows for effective treatment of the infection."
Vaccine development and its challenges
Reduction of toxicity can usually be achieved by removing toxic masses, so these attenuated strains can be used to develop vaccines against B. anthracis. If the pXO1 or pXO2 mass is missing, the strain is unable to produce all virulence factors and is considered to be attenuated. The old Sterne strain-based vaccine is now widely used for animal immunization, but many communities are concerned about the side effects of live spore vaccines, so the development of vaccines based on secreted toxin protein protective antigens (PA) has become a focus.
Currently, the only human anthrax vaccine authorized in the United States is an anthrax immunizer based on protective antigens, but the protective effect against Ans strains is inconsistent in different animal models. In addition, researchers are considering how to inactivate anthrax spores to provide an alternative to vaccines with live spores and protective antigens.
Ans strain tracking study
Using single nucleotide polymorphisms (SNPs) specific to the Ans strain, diagnostic tests can be developed to help track the outbreak. These SNPs can define specific gene groups and are of obvious importance for detecting and typing bacterial pathogens. Six SNPs are known to occur only in the anthracis strain and can effectively distinguish the other 88 Bacillus anthracis strains. The combination of these specific SNPs and real-time PCR can confirm or exclude thousands of samples as Ans strains.
“The stable SNPs allowed researchers to more accurately identify the Ans strain.”
The stability of the Ans strain lies in the low mutation rate of its DNA, making these markers a reliable diagnostic tool. This allows researchers to identify subtle genetic differences and link them to the source sample. This strain-specific SNP-based exploration is not only applicable to anthrax, but can also be extended to the detection of other bioterrorism agents.
As we continue to study the Ans strain, we can't help but wonder: In future public health strategies, can we effectively control the spread and prevention of this deadly pathogen?
