Adaptive Growth ……………………………………………………………………9 The increasing fitness of MRSA bacteria

ossification - the process of replacing cartilage with bone - takes place at an almost normal rate. Additionally, in cases where the cell density drops below a certain level, it was found that the compensatory proliferation that occurred in the remaining chondrocytes happened to an extent proportional to the number of affected chondrocytes. Therefore, it is thought that the spared chondrocytes are responding not to the cell density, but to stress signals released by the affected chondrocytes. The systemic response involved the stunting of the growth of the right limb. This correlates with levels of placental insulin-like growth factor (IGF) signalling, revealing that communication was taking place between the bone and the placenta. Insulin-like growth factor (IGF) is a group of hormones which controls the effects of growth hormone (GH) in our body. They are called insulin-like due to their similarity to insulin in their structure, and growth-factor refers to any protein that can stimulate cell proliferation. There are two proposed mechanisms for how the communication between the injured bone and placenta takes place. The first is that locally produced stress signals are released into circulation and impair the functions of placental cells. In particular, if a subpopulation of natural killer cells in the placenta which are known to promote placental function and foetal growth are impaired, this could explain the reduction in growth. The second mechanism is a sizemonitoring system which detects impaired long-bone growth and causes system growth reduction. However, there is still little evidence for such a mechanism.

This new type of catch-up growth, which takes place during insult to tissue, is known as adaptive growth. Although it is still a relatively new field, further research could aid our understanding of human growth disorders and have applications in treating such disorders.

-Sara

The increasing fitness of MRSA bacteria and the growth of new strains

MRSA bacteria is a common bacterium that is resistant to many antibiotics. It is most known as the ‘superbug’, and the use of different antibiotics has led to mutations in genes, which has given rise to the growth of different strains. Antibiotic resistance is becoming an increasingly important issue, and this essay will explore the fitness of different strains and potential solutions to reduce resistant bacteria.

Methicillin is an antibiotic which works by inhibiting penicillin-binding proteins which synthesise peptidoglycan, a polymer that forms the cell walls of bacteria. Staphylococcus aureus has become resistant to methicillin through expressing foreign penicillin-binding proteins (PBP) and can replicate the production of PBP’S. S. aureus also shows susceptibility to gentamicin, an example of an aminoglycoside antibiotic that is used as prophylaxis. In 1992, a new strain of MRSA emerged in France, and the incidence of this strain, with a new phenotype, has increased steadily. Instead of just looking at the evolution and growth of these strains from a molecular point of view, there has been a shift to looking at the ‘physiological characteristics’, which has led to the discoveries of

maximal growth rate and generation times. The study has shown that the GSMRSA-A1 strain has a much faster growth rate than of the GR-MRSA, so it has increased fitness. Although both strains were inoculated at equal amounts at the beginning of the study, the GS-MRSA-A1 strain accounted for 88-97% of the population 8 hours later. The difference in growth rate has led to the GS-MRSA-A1 strain being a predominant issue and will eventually replace the old MRSA strain. For researchers, it is even more difficult to treat these bacteria as they have found ways to mutate and adapt to their environment. Consequently, the increase in the prevalence of this strain has led to reduced consumption of gentamicin antibiotics.

A possible solution can be to find agents that are able to reduce resistance to an existing antibiotic. Research has shown that there are other proteins in cell wall synthesis, so these are possible targets and antibiotics can be made to inhibit the production of these proteins. Compounds can also be formed to regulate methicillin resistance. In some cases, the only antimicrobial therapy available is the glycopeptide antibiotic, vancomycin, mainly used to treat infection in the intestines.

India, an LIC, does not have the money to spend on advancing medical facilities. This means that diagnoses are uncertain and often, MRSA infections are unrecognised thus the primary antibiotic that is prescribed is important. In many areas in Kolkata, the antibiotic that is normally prescribed is linezolid. Although, it is more costly, the uncertainty surrounding the type of infection the patients have, leads to precautions being taken immediately. A recent study showed that linezolid is a better option than vancomycin, as the rate of success was significantly higher and people who received this antibiotic stayed a shorter duration in hospital and had reduced intravenous therapy. Therefore, these are two possible antibiotics that can be used as opposed to methicillin.

Quorum sensing is the process in which bacteria become pathogenic. Each bacterium sends out a chemical whilst also interpreting the other chemicals released by the bacteria surrounding them, so they can tell whether they can fight against the immune system now. Disruption of this process will treat the infection and natural selection is avoided as no selective pressures are applied to cause resistant bacteria to remain. However, this has not been fully investigated in humans but only seen to work in animals. The mechanics could be a potential site of exploration and eventually, solutions can be devised to disrupt quorum sensing. In conclusion, the growth of other strains, which are almost ‘cloned’ versions of the original MRSA, but have slight mutations that increase their fitness, is leading to increasing pressure to discover new antibiotics to treat infections. The discovery of other proteins in the cell walls of the bacteria