TABLE OF CONTENTS
Content Pages
Title page i
Certification ii
Dedication iii
Acknowledgement iv
Table of Contents v
List of Tables ix
List of Plates xi
List of Figures xii
Abstract xiii
INTRODUCTION 1
LITERATURE REVIEW 4
MATERIALS AND METHODS 61
Soil sample collection 61
Isolation of soil actinomycetes 61
Selection of antagonistic strain 61
Taxonomic studies 62
Growth characterization 62
v
Micromorphological characterization of isolates 62
Physiological and biochemical characterization of isolates 63
Melanin production by isolates 63
Carbon utilization by isolates 63
Resistance towards sodium chloride 63
Casein hydrolysis
Gelatin liquifaction 64
Starch hydrolysis 64
Nitrate reduction 65
Primary selection of antibiotic production medium 65
Antibiotic assay 65
Effect of different concentrations of glucose
on antibiotic production by Streptomyces SP-76 66
Effect of different concentrations of soy bean
on antibiotic production by Streptomyces SP-76 66
Effect of surfactants on antibiotic production
by Streptomyces SP-76 67
Effect of growth factors on antibiotic production
by Streptomyces SP-76 67
vi
Effect of pH on antibiotic production by
Streptomyces SP-76 68
Time course of pH and antibiotic production by
Streptomyces SP-76 68
Paper chromatography of the culture filtrate 68
RESULTS 70
Selection of antagonistic strain 70
Taxonomic studies 70
Growth characterization 70
Micromorphological characterization of isolates 87
Physiological and biochemical characterization of isolates 87
Carbon utilization by isolates 87
Primary selection of antibiotic production medium 92
Effect of different concentrations of glucose
on antibiotic production by Streptomyces SP-76 92
Effect of different concentrations of soy bean
on antibiotic production by Streptomyces SP-76 92
Effect of surfactants on antibiotic production
by Streptomyces SP-76 98
Effect of growth factors on antibiotic production
vii
by Streptomyces SP-76 98
Effect of pH on antibiotic production by
Streptomyces SP-76 98
Time course of pH and antibiotic production by
Streptomyces SP-76 104
Paper chromatography of the culture filtrate 104
DISCUSSION AND CONCLUSION 108
DISCUSSION 108
CONCLUSION 113
REFERENCES
114
viii
LIST OF TABLES
Table Title Pages
1a. Antimicrobial Activity of Isolates against Gram
negative organisms 83
1b. Antimicrobial activity of isolates against Gram
positive organisms 84
2. Cultural characteristics of isolates 85
3. Physiological and biochemical property of isolates 90
4. Carbon utilization by isolates 91
5. Primary selection of antibiotic production medium 93
6. Effect of different concentrations of glucose on
antibiotic production by Streptomyces SP-76. 96
7. Effect of different concentrations of soybean on
antibiotic production by Streptomyces SP-76 87
8a. Effect of different concentrations of Tween 80
on antibiotic production by Streptomyces SP-76 99
8b. Effect of different concentrations of oleic acid
on antibiotic production by Streptomyces SP-76 100
8c. Effect of different concentrations of stearic acid
on antibiotic production by Streptomyces SP-76 101
8d. Effect of different concentrations of palmitic acid
on antibiotic production by Streptomyces SP-76 102
9. Effect of growth factors on antibiotic production
by Streptomyces SP-76 103
10. Effect of pH on antibiotic production by Streptomyces
ix
SP-76 103
11. Rf values of the culture filtrate of Streptomyces
SP-76 and different antibiotics. 107
x
LIST OF PLATES
Plate Title Page
1a. Spore chains of isolate MP-75 on starch casein
nitrate agar Incubated at 300C for 14 days. 88
1b. Spore chains of isolate SP-76 on starch casein
nitrate agar incubated at 300C for 14 days 88
1c. Spore chains of isolate QP-100 on starch casein
nitrate agar incubated at 300C for 14 days 89
2. Inhibition of E. coli and Bacillus sp. by the culture
filtrate of isolate MP-75 and SP-76. 95
xi
LIST OF FIGURES
Figure Title Page
1. Time course of pH and antibiotic production by
Streptomyces SP-76 using medium C 105
2. Paper chromatogram of culture filtrate of
Streptomyces SP-76 and some purified antibiotics. 106
xii
ABSTRACT
A total of 106 actinomycetes isolated from the rhizosphere of plants in abbatoir and
refuse dumps in Awka and Onitsha were investigated for the production of
antimicrobial substances. Five of them were found to show antimicrobial activity
against Gram positive and Gram negative bacteria as well as fungi on solid media.
Three of the very active isolates designated MP-75, SP -76 and QP-100 were further
investigated in submerged medium in a shake-flask experiment using glucose and soy
bean as carbon and nitrogen sources respectively. Isolates MP-75 and SP-76 were
found to produce antimicrobial substances. The antimicrobial substance produced by
isolates SP-76 showed the highest antimicrobial activity against Escherichia coli,
Pseudomonas aeruginosa, Klebsiella sp, Staphylococcus aureus and Bacillus sp. The
isolates were identified as Streptomyces species based on their characteristic features.
Activity of the antimicrobial substance produced by Streptomyces SP-76 was
maximum when 4% (w/v) glucose and 2% (w/v) soybean were used in the
fermentation process. Influence of surfactants on accumulation of antimicrobial
substance by Streptomyces SP-76 in the fermentation broth showed that Tween 80,
oleic acid, palmitic acid and stearic acid enhanced antimicrobial activity. The effect of
growth promoters on antibiotic production by Streptomyces SP-76 indicated that
peptone, casein and yeast extract stimulated antimicrobial activity against the test
organisms. The effect of varying pH on antibiotic production by Streptomyces SP-76
showed that there was maximum antimicrobial activity at pH 7. In a time course for
antibiotic production, maximum antimicrobial activity was obtained at 120h. Paper
chromatography of the culture filtrate of Streptomyces SP-76 indicated that it contains
more than one antimicrobial substance. From this, it can be seen that the growth and
subsequent production of bioactive metabolites by Streptomyces SP-76 isolated from
the soil
xiii
INTRODUCTION
For centuries, preparations derived from living matter were applied to wounds to
destroy infection. The fact that a microorganism is capable of destroying one another
was not established until the latter half of the 19th century, when Pasteur noted the
antagonistic effect of other bacteria on the anthrax organism and pointed out that this
action might be put to therapeutic use. Meanwhile, the German Chemist, Paul Ehrlich
developed the idea of selective toxicity; that certain chemicals that would be toxic to
some organisms like infectious bacteria, would be harmless to other organisms e.g
humans (Limbird, 2004).
In 1928, Sir Alexander Fleming, a Scottish biologist, observed that Penicillium
notatum, a common mold, had destroyed Staphylococcus bacteria in culture and in
1939, the American microbiologist Rene Dubois demonstrated that a soil bacterium
was capable of decomposing the starchlike capsule of the Pneumococcus bacterium,
without which the Pneumococcus is harmless and does not cause pneumonia.
Dubois then found in the soil a microbe, Bacillus brevis, from which he obtained a
product, tyrothricin, that was highly toxic to a wide range of bacteria (Limbird, 2004).
Tyrothricin, a mixture of the two peptides, gramicidin and tyrocidine, was also found
to be toxic to red blood and reproductive cells in humans but could be used to good
effect when applied as an ointment on body surfaces. Penicillin was finally isolated in
1939, and in 1994 Selman Waksman and Albert Schatz, American microbiologists,
isolated streptomycin and a number of other antibiotics from Streptomyces griseus
(Calderon and Sabundayo, 2007).
1
Discovery of new antibiotics produced by Streptomyces still continues. Today, due to
the increasing resistance of pathogenic bacteria to our current arsenal of antibiotics, a
great need exist for the isolation and discovery of new antibiotics and other drug
agents (Jarroff, 1994; Rice, 2003; Wenzel, 2004). Fifty years ago, it was easy to
discover new antibiotics by simply screening the fermentation broths of
actinomycetes and fungi. Today, it is much more challenging, but there are much
better tools to address this problem. Discovering new antibiotics, pharmacophores is a
long-term endeavor that requires deft orchestration and support of many innovative
sciences (Cuatrecasas, 2006). There are three approaches that can be used to improve
our chances of finding new antibiotic substances: new test methods, new organisms,
and variation of culture conditions. None of these three options guarantees success
alone and the chances are best if the three are combined. There is need for long-term
basic microbiological research, which should cover the following areas: methods of
isolating and cultivating microorganisms that have not yet been accessed or only with
great difficulty, studies on the transportation of antibiotics into the bacterial cell,
comparative biochemistry of prokaryotes and eukaryotes, mode of action of
antibiotics and pathogenicity factors. In addition to search for new antibiotics, longterm strategies to prevent the development and spreading of resistant bacteria must be
developed (Fiedler and Zanher, 1995). Therefore, it is time to define natural product
discovery from actinomycetes and other microbes as a major priority for medical
sciences and to engage the most creative scientists in academia (Cuatrecasas, 2006) in
close collaboration with biotechnology and pharmaceutical companies, which would
elevate the science to a new level of achievement so as to be commensurate with past
successes and present demonstrated potential.
2
In this study, effort has been made:
– To isolate Streptomyces from the soil, capable of producing antimicrobial
substances
– To study the cultural conditions necessary for antibiotic production.
– To determine the time taken for the optimum production of antimicrobial
substance.
– To determine the type of antimicrobial substance(s) present in the culture
filtrate.
3
LITERATURE REVIEW
Antibiotics can be defined as agents produced by microorganisms, which can kill or
hinder the growth of other microorganisms. They are produced as secondary
metabolites (Bibb, 2005). Antibiotics usually are products of bacteria and fungi,
though synthetic antibiotics exist.
In terms of monetary value, antibiotics are currently the most important products of
microbial biotechnology, apart from such “traditional” products as alcoholic
beverages and cheese. Worldwide antibiotic production was estimated at a value of
about 8 billion dollars in 1981 and has doubled since that time. Antibiotics are used
extensively in human and veterinary medicine, as well as in agriculture, for the
purpose of preventing (prophylaxis) or treating microbial infections. They are also
used to promote the growth of animals (Gaskins et al., 2002). In some countries, they
are used at low doses in animal feeds and are considered to improve the quality of the
product, with a lower percentage of fat and higher protein content (Cromwell, 2002).
Peptide antibiotics are quite diverse, amphipathic, either non-ribosomally synthesized
(e.g. bacitracins, polymyxins and gramicidins) or ribosomally synthesized (Bdefensins, magainins and thionicins) (Gu et al., 2006). Bacteria and fungi use nonribosomal peptide synthetases to produce broad structural and biologically-active
peptides (Sorensen et al., 1996). Naturally occurring antimicrobial peptides are
widely distributed among evolutionary divergent organisms including mammals,
amphibians, insects, plants and bacteria, and play a significant role in innate immunity
(Zasloff, 1992; Boman, 1995). The mechanism of antimicrobial peptides is elucidated
4
through actions like membrane channel and pore formation, which allows passage of
ions and other solutes, inhibition of protein synthesis, DNA damage and interference
with cell wall synthesis (Lehrer et al., 1985; Agawa et al., 1991; Gera and
Lichenstein, 1991; Debano and Gordee, 1994; Bechinger, 1997; Hancock, 1997;
Lehrer et al., 1998; De Lucca and Walsh, 2000; Selitrennikoff, 2001; Brown and
Hancock, 2006).
Most of the antibiotics in use today are derivatives of natural products of
actinomycetes and fungi (Butler and Buss, 2006; Newman and Crag, 2007). Medical
chemistry has played a key role in modifying core natural products to optimize the
pharmacological properties while minimizing toxicity. Recent studies on various
Streptomyces species have shown that many regulatory factors are involved in
creating a complex network, which then influences the morphological differentiation
and production of secondary metabolites. Such regulatory cascade are consistent with
the need of Streptomyces spp. to interact with a variety of environmental changes
(Bibb, 1996). If the regulatory mechanism of anabolic biosynthesis can be wholly
understood and tightly controlled, this could be a starting point for replacing
mutagenesis by UV irradiation or mutagen treatment and the consecutive screening of
high-producer strains for improving the productivity of anabolic biosynthesis.
Unfortunately, however the molecular processes regulating the events leading to
differentiation and simultaneous anabolic biosynthesis are still poorly understood,
despite the discovery of numerous useful insights into Streptomyces genetics (Hwang
et al., 2002).
5
GOALS OF ANTIBIOTIC RESEARCH
The study and development of antibiotics certainly share some of the same aims as
other areas of biotechnology. For example, it is always desirable to try to improve the
yield of an antibiotic fermentation and subsequent processing steps. Indeed, in the
early stage of the development of penicillin, the crucial achievement was to obtain the
compound in amounts sufficient for therapeutic use. Also, for antibiotics that are put
mainly to veterinary or agricultural uses, reducing cost through improved yields is of
paramount importance. However, much of the research on the antibiotics for human
use has a very different focus. When trying to develop a cure for a life-threatening
infection, the cost of treatment is not the most important factor (Glazer and Nikaido,
2001).
A very large fraction of antibiotic research is directed towards the development of
new agents. They are needed because of the many micro-organisms including most
fungi and viruses, for which we do not yet possess truly effective and safe antibiotic
agents. Some bacteria, such as Pseudomonas aeruginosa, also are intrinsically
resistant to most antibiotics (Kirst and Sides, 1989).
An even more complex problem is the emergence of resistant strains among the
organisms that were sensitive to antibiotics before the drugs became widely used.
This phenomenon tends to limit the useful life of any new antibiotic, requiring the
pharmaceutical industry to come up with new compounds continually. The need is
especially acute because of the following unfortunate situation. In any modern
hospital, huge amounts of antibiotics are used in the treatment as well as the
prevention of infectious diseases. As a result, the hospital environment becomes
highly enriched for bacteria that are resistant to those antibiotics. At the same time,
6
the immune and other defence mechanisms of the body are not functioning well in
many hospitalized-patients, who are thus especially vulnerable to hospital acquired
(nosocomial) infection by these resistant bacteria (Glazer and Nikaido, 2001).
HISTORY OF ANTIBIOTICS
Many cures for infectious diseases prior to the beginning of the twentieth century
were based on medicinal folklore. Cures for infection in ancient Chinese medicine
using plants with antibiotic– like properties began to be described over 2,500 years
ago (Lindbland, 2008). Many other ancient cultures, including the ancient-Egyptians,
ancient-Greeks and Madeira Arabs already use molds and plants to treat infections
(Forrest, 1982; Wain- Wright, 1989). Cinchona bark was a widely effective plant for
treatment of malaria in the 17th Century, the disease caused by protozoan parasites of
the genus Plasmodium (Lee, 2002). Scientific endeavors to understand the science
behind what caused these diseases, the development of synthetic antibiotic
chemotherapy, the isolation of the natural antibiotics marked milestones in antibiotic
development (Foster and Raoult, 1974).
Originally known as antibiosis, which means ‘against life’, the term was introduced
by the French bacteriologist Vuilleum as a descriptive name of the phenomenon
exhibited by these drugs (Calderon and Sabundayo, 2007). Antibiosis was first
described in 1877 in bacteria when Louis Pasteur and Robert Koch observed that an
airborne bacillus could inhibit the growth of Bacillus anthracis (Landberg, 1949).
These drugs were later renamed antibiotics by Selman Waksman,an American
microbiologist in 1942 (Waksman, 1947; Calderon and Sabundayo, 2007).
7
Synthetic antibiotic chemotherapy as a science and the story of antibiotic
development began in Germany with Paul Ehrlich, a German medical scientist in the
late 1880s. He noted that certain dyes would bind to and colour human, animal or
bacterial cells, while others did not. He then extended the idea that it might be
possible to make certain dyes or chemicals that would act as a magic bullet or
selective drug that would bind to and kill bacteria while not harming the human host.
After much experimentation, screening hundreds of dyes against various organisms,
he discovered a medicinally useful drug, the man-made antibiotic Salvarsan (Limbird
2004; Calderon and Sabundayo, 2007; Bosch and Rosich, 2008). However, the
adverse side-effect profile of Salvarsan, coupled with the later discovery of the
antibiotic penicillin, superseded its use as an antibiotic. The work of Ehrlich, which
marked the birth of the antibiotic revolution, was followed by the discovery of
prontosil by Domagk in 1932 (Bosh and Rosich, 2008). Prontosil, the first
commercially available antibacterial antibiotic was developed by a research team led
by Gerhard Domagk, at the Bayer laboratories of the IG Farben conglomerate in
Germany. Prontosil had a relatively broad effect against Gram-positive cocci but not
against enterobacteria. The discovery and development of this first sulfonamide drug
opened the era of antibiotics.
The discovery of natural antibiotics produced by microorganisms stemmed from
earlier work on the observation of antibiosis between micro-organisms. Pasteur
observed that “if we could intervene in the antagonism observed between some
bacteria, it would offer “perhaps the greatest hopes for therapeutics” (Kingston,
2008). Bacterial antagonism of Penicillium sp. as first described in England by John
Tyndall in 1875 (Kingston, 2008). However, his work went by without much notice
8
from the scientific community until Alexander Fleming’s discovery of Penicillin in
1928. Even then the therapeutic potential of Penicillin was not pursued. More than ten
years later, Ernst Chain and Howard Florey became interested in Fleming’s work, and
came up with the purified form of Penicillin. The purified antibiotic displayed
antibacterial activity against a wide range of bacteria. It also had low toxicity and
could be taken without causing adverse effect. Furthermore, its activity was not
inhibited by biological constituents such as pus, unlike the synthetic antibiotic. No
one had discovered a compound equaling this activity previous to this. The discovery
of penicillin led to renewed interest in the search for antibiotic compounds with
similar capabilities. Because of their discovery of penicillin, Ernst Chain, Howard
Florey and Alexander Fleming shared the 1945 Nobel prize in medicine. In 1939,
Rene Dubois isolated gramicidin, one of the first commercially manufactured
antibiotics in use during world war ll, which proved highly effective in treating
wounds and ulcers (van Epps, 2006). Florey credited Dubois for reviving his research
in penicillin (van Epps, 2006).
ANTIMICROBIAL PHARMACODYNAMICS.
The assessment of the activity of an antibiotic is crucial to the successful outcome of
antimicrobial therapy. Non-microbiological factors such as host defense mechanisms,
the location of an infection, the underlying disease as well as the intrinsic
pharmacokinetics and pharmacodynamics affect the properties of an antibiotic
(Pankey and Sabath, 2004). Fundamentally, antibiotics are classified as either having
lethal or bactericidal action against bacteria or are bacteriostatic, preventing bacterial
growth. The bactericidal activity of antibiotics may be growth phase dependent and in
most but not all cases the action of many bactericidal antibiotics requires ongoing cell
9
activity and cell division for the drugs killing activity (Mascio et al., 2007). These
classifications are based on laboratory behaviour; in practice, both of these are
capable of ending a bacterial infection (Pelczar et al., 1999; Pankey and Sabath,
2004). ‘In vitro’ characterization of the action of antibiotics to evaluate activity
measure the minimum inhibitory concentration and minimum bactericidal
concentration of an antimicrobial and are excellent indicators of antimicrobial potency
(Weigand et al., 2008). However, in clinical practice, these measurements alone are
insufficient to predict clinical outcome. By combining the pharmacokinetic profile of
an antibiotic with the antimicrobial activity, several pharmacological parameters
appear to be significant markers of drug efficacy (Spanu et al., 2004). The activity of
antibiotics may be concentration-dependent and their characteristic antimicrobial
activity increases with progressively higher antibiotic concentrations (Rhee and
Gardiner, 2004). They may also be time-dependent, where their antimicrobial activity
does not increase with increasing antibiotic concentrations; however, it is critical that
a minimum inhibitory serum concentration is maintained for a certain length of time
(Rhee and Gardiner, 2004). A laboratory evaluation of the killing kinetics of the
antibiotic using killing curves is useful to determine the time-or concentrationdependence of antimicrobial activity (Pankey and Sabath, 2004).
SIDE EFFECTS
Although antibiotics are generally considered safe and well tolerated, they have been
associated with a wide range of adverse effects (Slama et al., 2005). Side effects are
many, varied and can be very serious depending on the antibiotics used and the
microbial organisms targeted. The safety profiles of newer medications may not be as
well established as those that have been in use for many years (Slama et al., 2005).
10
Adverse effects can range from fever and nausea to major allergic reactions including
photodermatitis. One of the more common side effects is diarrhea, sometimes caused
by the anaerobic bacterium, Clostridium difficille, which results from one antibiotic
disrupting the normal balance of the intestinal flora. Such overgrowth of pathogenic
bacteria may be alleviated by ingesting probiotics during a course of antibiotics. An
antibiotic-induced disruption of the population of the bacteria normally present as
constituents of the normal vaginal flora may also occur, and may lead to overgrowth
of yeast species of the genus Candida in the vulvo-vaginal area (Pirotta and Garland,
2006). Other side effects can result from interaction with other drugs such as elevated
risk of tendon damage from administration of a quinolone antibiotic with a systematic
corticosteroid.
ANTIBIOTIC RESISTANCE
Emerging antibiotic resistance has created a major public health dilemma,
compounded by a dearth of new antibiotic options. Increasing rates of bacterial
resistance among common pathogens are threatening the effectiveness of even the
most potent antibiotics. The introduction of new antibiotics has not kept pace with the
increasing rate of resistance, leaving clinicians with fewer treatment options.
The emergence of antibiotic resistance is an evolutionary process that is based on
selection for organisms that have enhanced ability to survive doses of antibiotics that
would have previously been lethal (Cowen, 2008). Antibiotics like penicillin and
erythromycin which used to be one-time miracle cures are now less effective because
bacteria have become more resistant. Antibiotics themselves act as a selective
pressure which allows the growth of resistant bacteria within a population and inhibits
11
susceptible bacteria (Levy, 1994). Antibiotic selection of pre-existing antibiotic
resistant mutants within bacterial populations was demonstrated in 1943 by the LuriaDelbruck experiment (Luria and Delbruck, 1943). Survival of bacteria often results
from an inheritable resistance (Witte, 2004). Any antibiotic resistance may impose a
biological cost and the spread of antibiotic resistant bacteria may be hampered by the
reduced fitness associated with the resistance, which proves disadvantageous for
survival of the bacteria when antibiotic is not present. Additional mutations, however,
may compensate for the fitness cost and aids the survival of these bacteria (Anderson,
2006).
The underlying molecular mechanisms leading to antibiotic resistance can vary.
Intrinsic resistance may naturally occur as a result of the bacteria’s genetic makeup
(Alekshun and Levy, 2007). The bacterial chromosome may fail to encode a protein
which the antibiotic targets. Acquired resistance results to a mutation in the bacterial
chromosome or the acquisition of extra-chromosomal DNA (Alekshun and Levy,
2007).
Antibiotic–producing bacteria have evolved resistance mechanisms which have been
shown to be similar to and may have been transferred to antibiotic resistant strains
(Marshall et al., 1998; Nikaido, 2009). The spread of antibiotic resistance
mechanisms occur through vertical transmission of inherited mutations from previous
generations and genetic recombination of DNA by horizontal genetic exchange
(Witte, 2004). Antibiotic resistance exchanged between different bacteria by
plasmids that carry genes which encode antibiotic resistance, may result in coresistance to multiple antibiotics (Witte, 2004; Baker-Austin et al., 2006). These
12
plasmids can carry different genes with diverse resistance mechanisms to unrelated
antibiotics but because they are located on the same plasmid, multiple antibiotic
resistance to more than one antibiotic is transferred. (Baker-Austin et al., 2006).
Alternatively, cross-resistance to other antibiotics within the bacteria results when the
same resistance mechanism responsible for resistance to more than one antibiotic is
selected for (Baker-Austin et al., 2006).
CAUSES AND RISK FACTORS
The first rule of antibiotics is try not to use them, and the second rule is try not to use
too many of them (Marino, 2007). Inappropriate antibiotic treatment and overuse of
antibiotics have been a contributing factor to the emergence of resistant bacteria. The
problem is further exacerbated by self-prescribing of antibiotics by individuals
without the guidelines of a qualified clinician and the non-therapeutic use of
antibiotics as growth promoters in agriculture (Larson, 2007).
Antibiotics are frequently prescribed for indications in which their use is not
warranted, an incorrect or sub-optimal antibiotic is prescribed or in some cases for
infections likely to resolve without treatment (Slama et al., 2005).
Teaching hospitals and centers that treat critically ill patients are particularly
vulnerable to high rates of bacterial resistance. Risk factors associated with increased
resistance among patients in the intensive care unit (ICU) include long hospital stay,
advanced age, use of invasive devices, immuno suppression, lack of hospital
personnel, adherence to infection-control principles and previous antibiotic use (Fish
and Ohlinger, 2006). Repeated courses of antimicrobial therapy are common in
13
acutely ill, febrile patients, who frequently have endotracheal tubes, urinary catheters
and central venous catheters (Fish and Ohlinger, 2006). In combination with host
factors, indwelling devices are routes for transmission and colonization of resistant
infections (Davis, 2006). However, two principal drivers of resistance appear to be
inadequate: empirical antibiotic therapy and prolonged antibiotic use (Fish and
Ohlinger, 2006).
Lengthy and inappropriate antimicrobial therapy allows microbes to mutate into new
forms that help them survive antibiotics and quickly become new, dominant strains
(Kallel et al., 2006). In prolonged courses, even effective antibiotics may permit the
development of much drug resistance pathogens. In one study, pediatric patients were
treated for various respiratory tract infections with either a standard 10-day course of
amoxicillin or high-dose, short-course amoxicillin therapy. At the end of 28 days, the
high-dose, short-course therapy group had lower rates of penicillin-resistant
Streptococcus pneumoniae and lower risk of resistance to
trimethoprin/sulfamethoxazole (Schraq et al., 2001). The study demonstrated that:
bacterial mutants become dominant if pathogens are exposed to an antimicrobial
agent for a long period and resistance genes travel together, spreading via conjugation
or bacteriophages. These newly emergent resistant strains prey on the weakest
patients, leaving hospitals with more severely ill patients, higher health care costs and
rising mortality rates (Kallel et al., 2006).
What can be done to slow the relentless progression of resistant pathogens? While the
search for new antibiotic options continues, strategies can be employed to slow the
development of resistance to the current armamentarium. For example, we must avoid
14
under dosing, which is a common yet often unrecognized factor associated with
treatment failure and bacterial resistance (Fish and Ohlinger, 2006). An
understanding of pharmacokinetic and pharmacodynamic principles can optimize
antibiotic use, such as by increasing the time above the minimum inhibitory
concentration and by maximizing the peak level or area under the contraction curve
(Craig, 1998).
Resistant containment depends on very early empirical and aggressive treatment for
potentially resistant pathogens, followed by de-escalation and narrowing of the
antimicrobial spectrum after identifying the pathogen. Empirical diagnosis of
infection seems unlikely. De-escalation is a crucial infection management technique
and an effective strategy that balances the need to provide early adequate antibiotic
therapy to high-risk patients and the objective of avoiding antibiotic overuse (Kollef,
2001).
Other strategies include avoiding prolonged antibiotic use, prescribing drugs that have
more than one mechanism of action or target, combining agents (where appropriate)
to improve killing and decreasing the duration of therapy (Peterson, 2005; Fish and
Ohlinger, 2006). Patients with ventilator-associated pneumonia (VAP) who received
antimicrobial treatment for 8 days had no greater mortality or recurrent infections than
did those who received 15 days of antibiotics. They did, however, have more
antibiotic free-days (Chastre et al., 2003). Finally, adherence to infection control
principles by hospital personnel, which will often require further training and
education, will create an improved best-practice environment for infection control.
Only a continued commitment to these challenges and vigilance with respect to the
15
use of antibiotics will allow advancement to the next era – one of renewed successes
against infectious diseases.
In addition to the above mentioned strategies, the first generation of drugs that might
treat infectious diseases without incurring the cost of resistance is being developed.
For example, Balaban (1998) described an agent that inhibits density-dependent
expression of virulence factors, while Maurelli (1998) expressed hope in the
production of enterotoxin inhibitors. Vaccines against virulence determinants are
becoming serious possibilities (Li, 1997). These drugs differ from their predecessor
by neutralizing or penalizing the pathogen rather than genetically killing the microbe.
New technologies are promising to identify new generation drug targets and more
rapidly assess the efficacy of new–generation drugs. High-throughput geneexpression analysis (Lennon, 2000), such as DNA micro arrays, would rapidly
diagnose the effects of drugs that do not kill microorganisms but that alter the
expression of virulence genes. Furthermore, genomic and protein function analysis are
producing targets to inhibit and to manipulate pathogens (Schmid, 1998; Loferer,
2000).
Several correlated reductions in resistance rates and drug use (Seppala, 1997) can be
seen as anecdotal evidence that resistance will reduce with the ‘wise’ application of
old drug, or the introduction of new drugs that act in a similar manner to current drugs
(Heinemann, 1999).
Phage therapy: This is an approach that has been extensively researched and utilized
as a therapeutic agent for over 60 years, especially in the Soviet Union. It is an
16
alternative that might help with the problem of resistance. Phage therapy was widely
used in the United States until the discovery of antibiotics, in the early 1940’s.
Bacteriophages or phages’ are viruses that invade bacterial cells and in the case of
lytic phages, disrupt bacterial metabolism and cause the bacterium to lyse. Phage
therapy is the therapeutic use of lytic bacteriophages to treat pathogenic bacterial
infections (Chanishvili et al., 2001; Mulczyk and Gorski, 2003; Jikia et al., 2005).
Bacteriophage is an important alternative to antibiotics in the current era of multidrug
resistant pathogens. A review of studies that dealt with the therapeutic use of phages
from 1966-1996 and few latest ongoing phage therapy projects via internet, showed
that phages were used topically, orally or systemically in Polish and Soviet-studies.
The success rate found in these studies was 80-95% with few gastrointestinal or
allergic side effects. British studies also demonstrated efficiency of phages against
Escherichia coli, Acinetobacter spp., Pseudomonas spp. and Staphylococus aureus.
Phage therapy may prove as an important alternative to antibiotics for treating
multidrug-resistant pathogens (Mathur et al., 2003).
DISCLAIMER: All project works, files and documents posted on this website, eProjectTopics.com are the property/copyright of their respective owners. They are for research reference/guidance purposes only and some of the works may be crowd-sourced. Please don’t submit someone’s work as your own to avoid plagiarism and its consequences. Use it as a reference/citation/guidance purpose only and not copy the work word for word (verbatim). The paper should be used as a guide or framework for your own paper. The contents of this paper should be able to help you in generating new ideas and thoughts for your own study. eProjectTopics.com is a repository of research works where works are uploaded for research guidance. Our aim of providing this work is to help you eradicate the stress of going from one school library to another in search of research materials. This is a legal service because all tertiary institutions permit their students to read previous works, projects, books, articles, journals or papers while developing their own works. This is where the need for literature review comes in. “What a good artist understands is that nothing comes from nowhere. The paid subscription on eProjectTopics.com is a means by which the website is maintained to support Open Education. If you see your work posted here by any means, and you want it to be removed/credited, please contact us with the web address link to the work. We will reply to and honour every request. Please notice it may take up to 24 – 48 hours to process your request.
