The absorbance due to antibody is then the total absorbance minus the optical density due to the antigen added at equivalence. That is total absorbance at equivalence is 0. 68; the absorbance due to antibody is this total absorbance minus the absorbance due to antigen. Therefore 0. 68 – 0. 068 = 0. 612 The mass of antibody is then calculated using the knowledge that 1 mg/mL solution of antibody equates to an absorbance.
Thus an absorbance of 0. 612 gives the concentration of antibody at equivalence point to be 0.44 mg/mL. Considering the original antibody was present in 0. 5 mL and was diluted 1 in 2, the antibody present in the original antiserum sample was: 0. 88 mg/mL. Darwin’s evolutionary hypothesis dictates the survival of the fittest. Accordingly, bacteria that overcome the onslaught of antibiotics (which can destroy them) and still replicate, provide a survival advantage for future generations of the same bacteria. However, from the human viewpoint, this genetic resistance to antibiotic treatment can be detrimental.
Not only can ineffectiveness of antibiotics lead to exacerbation of an infection within an individual that may have been overcome, but can lead to the spread of an infection within a population that could have been contained. There is an economic consequence of this resistance as additional treatments, hospitalisation and lost labour hours cost money. More importantly, in the worst cases, unchecked infections of this type can lead to death. A very real example of this situation is multi-antibiotic resistance present in a strain of Staphylococcus aureus.
This multi-resistance arose in stages1; penicillin resistant S. Aureus were first described within a few years of penicillin being introduced in clinical practice. To combat this resistance, a semi-synthetic penicillin, methicillin, was used. Within a year however, a penicillin and methicillin resistant Staphylococcus aureus (MRSA) strain was described. Subsequently, vanomycin has been used in the fight against MRSA but recently vanomycin resistant S. Aureus (VRSA) have also been identified. Unlike MRSA, VRSA is not so widespread.
Aureus is capable of causing a wide range of infections including skin and wound infections and bacteraemia, thus, untreatable MRSA infections pose a particular risk to the more immuno-compromised, such as critically ill patients. 1 Unfortunately, we humans have contributed ourselves in making antibiotic resistance into a health risk. Overuse of antibiotics in the past sixty years have led to the emergence of antibiotic resistant infectious strains of various bacteria. This occurs because the death of susceptible bacteria confers a favourable selection pressure, and the resistant bacteria become the dominant species.
This phenomenon is aided by two factors: first, the rapid bacterial proliferation rate of twenty minutes and second, the horizontal transmission of genetic elements such as transposons, integrons and plasmids which propagate antibiotic resistance within and among bacterial species. 2 The overuse of antibiotics is due to a number of factors, and both doctors and patients are guilty of indiscriminate use. Doctors may over-prescribe, sometimes for illnesses such as the common cold that cannot actually be treated by any known antibiotic.
Patients on the other hand, make unnecessary requests for antibiotics, or purchase them over-the-counter in countries where this is possible, and often fail to complete a necessary antibiotic course3. Another factor that contributes to a high background selection pressure for bacterial resistance is the use of antibacterial soaps and cleaning products in the home. The routine use of antibiotics in animal husbandry, not for their anti-bacterial action but rather for their accelerated growth properties is proposed to select for antibiotic-resistant bacteria that cause diseases in humans.
However, whilst there is undoubtedly a risk from eating undercooked and contaminated meat, the risk of antibiotic-resistant bacteria of animal origin causing serious human diseases has been evaluated to be minimal. 4 Having understood the pitfalls of indiscriminate antibiotic use, there is a need to monitor the usage. Surveillance systems are in place to evaluate the degree of resistance present in different populations, but this practice needs to be more extensive and the data gathered used to implement a better antibiotic strategy that can slow down the progress of resistant bacteria.
Other general preventative measures include the re-education of patients/households on the dangers of antibiotic over/misuse and of healthcare personnel in improving hygiene in hospitals (where MRSA infections are usually found) to prevent the spread of infections. Interestingly, extension of antibiotic patent rights has also been proposed as a possible solution. This would prevent flooding of the antibiotic market by cheaper antibiotics, increasing availability once patent rights expire. 6 To allow for more rational use of antibiotics there is a need to reduce, tailor and cycle antibiotics.
When the selection pressure is reduced, resistant strains can be replaced by susceptible ones. There is evidence of this occurring in European livestock after antibiotic use in animal husbandry was discontinued. 7 From a drug-development perspective, increased knowledge of bacterial physiology and evolution are providing novel mechanisms for antibiotic action. This knowledge has to be exploited better in order to design more specific antibiotics. Targets for new antibiotics include the fundamental fatty acid biosynthesis metabolic pathway8 and inhibition of resistance-gene vectors, such as plasmids, to inhibit horizontal transfer.
Whilst there are many mechanisms to target, the pace of new antibiotic development is slow, thus pharmaceutical companies need to invest more in this area. Of course, whether old or new antibiotics are used, the lessons of the past have to be utilised to allow for a more sensible utilisation of antibiotics. In general, this encompasses tailoring antibiotic use to specific bacteria/infections at doses that are in agreement with its pharmacology data. Only with the correct implementation of antibiotics and a multi-faceted approach can we avoid widespread resistance and prevent repeating past mistakes.
Bibliography
Hardy KJ, Hawkey PM et al. “Methicillin resistant Staphylococcus Aureus in the critically ill” 2004 British Journal of Anaesthesia. 92:121-30 Baron S, “Bacterial Resistance” Medical Microbiology 4th Ed. www. ncbi. nlm. nih. gov/books/bv. fcgi? rid=mmed. section . 698 www. keepantibioticsworking. com Phillips I, Casewell M et al. “Does the use of antibiotics in food animals pose a risk to human health? A critical review of published data. ” 2004 Journal of Antimicrobial Chemotherapy 53:28-52 Critchley IA and Karlowsky JA “Optimal use of antibiotic resistance surveillance systems” 2004 Clinical Microbiology and Infection 10:502-11