What’s Our Focus?

----Intestinal Staphylococcus aureus Colonization

Staphylococcus aureus is a major human pathogen that contributes to a variety of lethal diseases, causing a large burden of morbidity and mortality worldwide. Due to its great infectivity and the abuse of antibiotics, many strains have developed resistance to an array of antibiotics, in particular, Methicillin-Resistant Staphylococcus aureus (MRSA), which already becomes an acute clinical problem.
Despite the well-established risk factor of its colonization in human nose, gastrointestinal colonization by Staphylococcus aureus is still ill-defined. The average reported detection rate of intestinal carriage is 20% for normal strains and 9% for MRSA. The high risk population is suggested to be infants, hospitalized patients with inflammatory bowel disease (IBD), patients with a history of MRSA colonization or infection, and those with poor immune system status.
Apart from severe diarrhea, fever and dehydration, it is suggested recently that transient or persistent intestinal S. aureus colonization may cause pseudomembranous colitis, induce specific systemic immune responses and even alter the overall structure of the human colonic microbiota and microbial metabolic profiles. Although it has not been thoroughly studied yet, we believe that the potential clinical impacts cannot be underestimated.

What’s Our Aim and Why?

Based on our concerns on the following:

1. The lack of clinical experience when dealing with this rare symptom caused by Staphylococcus aureus colonization ;
2. The difficulties to prevent and fully eliminate intestinal S. aureus colonization;
3. Abuse of antibiotics and its side effects.

Aim to:

1. Design a novel therapy to combat with, and even prevent the intestinal S. aureus colonization within a short time after infection, thus reducing the use of antibiotics and restraining the development and transmission of MRSA.
2. Introduce a new concept medicine that is safe, effective, and has the potential to be industrialized and put into the drug market (which needs approval of China's State Food and Drug Administration).

How We Make it Happen?

--Probiotic Therapy

We genetically engineered Lactococcus lactis to become our drug carrier (“Grenadier Guards”), which will become active when arriving at the human intestine after ingestion.
Engineered with a copy of the quorum sensing system from S. aureus, the L. lactis cells will quickly sense the presence of the pathogen that is above a certain threshold density and they have the mobility to move near the S. aureus colony. Simultaneously, the synthesis of antimicrobial peptides (“Grenades”) will begin. Tandem repeating are applied here to control the synthesis of the arsenal, different types of AMPs, and allow them to reach a relatively high level. After AMPs accumulation, the L. lactis will go through an endolytic process to release the synthesized peptides to attack the biofilm of S. aureus. All of these processes should proceed within a short time, so when combined with their large quantity and proper anti-diarrhea drugs, the symptom is likely to be reduced and even eliminated.

Why using probiotic as a carrier?

1. Lactic acid bacteria (LAB) are one of the potential vehicles for drug delivery in the gastrointestinal tract. They are bile-resistant and have the ability to survive passage through the GI tract. More importantly, many of them are generally recognized as safe (GRAS) for human and animal consumption. So here we aim to use L. lactis as the carrier, being one of the most amenable expression cell factories for heterologous protein secretion.
2. Research has shown that certain lactic acid bacteria, mainly commercial probiotics, e.g. Lactococcus lactis, are able to reduce adhesion and viability of adherent S. aureus.
3. As a commercial probiotic, genetically-engineered L. lactis has the potential to be widely applied to dairy products, which makes the market even broader.
4. The production of antimicrobial peptides in Lactococcus lactis can be controlled the inducer – nisin. This greatly reduces the wasted AMPs to contaminate the environment as the traditional manufacturing of medicine.

Why choosing antimicrobial peptides?

1. AMPs play a direct antimicrobial and mediator function and provide the initial host defense mechanism against invading pathogens, and they are found to have potential to overcome bacterial resistance.
2. AMPs can enhance the activities of antibiotics and modulate the innate immune response.
3. Many antimicrobial peptides are membrane-active in prokaryotes, they seem to have a lesser ability to disrupt membranes composed of eukaryotic components owing to the absence of negatively charged lipids on the surface.
4. Although bacteria have diverse mechanisms for resistance to AMPs, it is encouraging to notice that the general lipid bilayer structure of bacterial membranes makes it hard to develop a complete resistance against AMPs. Also, the resistance against AMPs reported to date is not as strong as those against antibiotics and it only covers a limited number of AMPs.

Why producing antimicrobial peptides in a synthetic biological way?

1. Natural peptides are limited by their potential lability to proteases, creating potentially unfavorable pharmacokinetics. In particular, chymotrypsin-like enzymes attack antimicrobial peptides at basic residues.
2. Peptides tend to be very expensive drugs to be manufactured by solid-phase chemical synthesis.

How to reduce further drug resistance?

1. The antimicrobial peptides can only be release in the presence of the inducer – nisin, and wouldn’t be activated in the environment out of human body.
2. Engineer L. lactis to produce many kinds of different-functioned antimicrobial peptides together to realize a "cocktail" effect inspired by the cocktail therapy in HIV treatment, in which different drug classes target different parts of HIV virus to impede the HIV replication and cell infection. In other words, there will be a higher genetic barrier for Staphylococcus aureus to gain resistance under the function of a cocktail of different types of AMPs.

What is the drug delivery method?

Enteric coated tablet: Protect the engineered probiotics from partial degradation in the acidic environment of the stomach, and release the drugs when it reaches the intestine.

What Are the Impacts?

1. Clinical

Combined with anti-diarrhoea drug, our probiotic bacteria can quickly detect and eliminate the adherent S. aureus, thus reliving the patients from the suffering.

2. Daily life

By applying the engineered probiotics into the dairy products, the public can get easily access to the drugs, which may results in a prevention of potential S. aureus adherence.