Screening Of Bacteria Isolated From Earthworm Cast For Antibacterial Activities

TEST ORGANISMS

Test organisms are single-celled organism such as algae, fish algae or bacteria that can be used in bioassays. These are organisms that are used to indicate the presence and amount of a compound that is a sample. The organisms used is sensitive to the compound for which the test is to be conducted. With the wide varieties of test and also organisms, the test organism used for a particular test needs to be specific for the task, and must provide a result that is readily apparent (Haynes & Millar, 1998). They are involved in a bioassay that has its effects or result to be typically the death or the deteriorated health of these test organisms. Test organisms can vary from animals to plants and microorganisms depending on the type of sample assayed either soil, air or liquid samples.

Microorganisms like bacteria can be used as test organisms, this has been in practice for decades. For example; the use of bacteria to detect and determine the amount of antibiotics or the use of bacteria that has been designed to fluoresce (to emit light). If the bacteria are harmed by a toxic compound in the test sample, then they fail to fluoresce. The test organisms used in this study includes:

Staphylococcus aureus

Staphylococcus aureus is a Gram-positive, round-shaped bacterium that is a member of the Firmicutes, and it is a usual member of the microbiota of the body, frequently found in the upper respiratory tract and on the skin. It is often positive for catalase and nitrate reduction and is a facultative anaerobe that can grow without the need for oxygen (Masalha et al., 2001). Although S. aureus usually acts as a commensal of the human microbiota it can also become an opportunistic pathogen, being a common cause of skin infections including abscesses, respiratory infections such as sinusitis, and food poisoning.

Pathogenic strains often promote infections by producing virulence factors such as potent protein toxins, and the expression of a cell-surface protein that binds and inactivates antibodies. The emergence of antibiotic-resistant strains of S. aureus such as methicillin-resistant S. aureus (MRSA) is a worldwide problem in clinical medicine. Despite much research and development, no vaccine for S. aureus has been approved. It is still one of the five most common causes of hospital-acquired infections and is often the cause of wound infections following surgery. Each year, around 500,000 patients in hospitals of the United States contract a staphylococcal infection, chiefly by S. aureus (Bowersox, 1999).

Pseudomonas Aeruginosa

Pseudomonas aeruginosa is a common encapsulated, Gram-negative, rod-shaped bacterium that can cause disease in plants and animals, including humans. A species of considerable medical importance, P. aeruginosa is a multidrug resistant pathogen recognized for its ubiquity, its intrinsically advanced antibiotic resistance mechanisms, and its association with serious illnesses hospital-acquired infections such as ventilator-associated pneumonia and various sepsis syndromes.

The organism is considered opportunistic insofar as serious infection often occurs during existing diseases or conditions, most notably cystic fibrosis and traumatic burns. It generally affects the immunocompromised but can also infect the immunocompetent as in hot tub folliculitis. Treatment of P. aeruginosa infections can be difficult due to its natural resistance to antibiotics. When more advanced antibiotic drug regimens are needed adverse effects may result. It is citrate, catalase, and oxidase positive. Pseudomonas aeruginosa is found in soil, water, skin flora, and most man-made environments throughout the world. It thrives not only in normal atmospheres, but also in low-oxygen atmospheres, thus has colonized many natural and artificial environments. It uses a wide range of organic material for food; in animals, its versatility enables the organism to infect damaged tissues or those with reduced immunity.

The symptoms of such infections are generalized inflammation and sepsis. If such colonization occurs in critical body organs, such as the lungs, the urinary tract, and kidneys, the results can be fatal (Balcht & Smith, 1994). Because it thrives on moist surfaces, this bacterium is also found on and in medical equipment, including catheters, causing cross-infections in hospitals and clinics. It is also able to decompose hydrocarbons and has been used to break down tarballs and oil from oil spills (Itah, 2005). P. aeruginosa is not extremely virulent in comparison with other major pathogenic bacterial species – for example Staphylococcus aureus and Streptococcus pyogenes – though P. aeruginosa is capable of extensive colonization, and can aggregate into enduring biofilms (Hoiby, 2010).

Klebsiella pneumoniae

Klebsiella pneumoniae is a Gram-negative, non-motile, encapsulated, lactose-fermenting, facultative anaerobic, rod-shaped bacterium. It appears as a mucoid lactose fermenter on MacConkey agar. Although found in the normal flora of the mouth, skin, and intestines (Ryan & Ray, 2004), it can cause destructive changes to human and animal lungs if aspirated, specifically to the alveoli resulting in bloody sputum. The most common condition caused by Klebsiella bacteria outside the hospital is pneumonia, typically in the form of bronchopneumonia and also bronchitis. These patients have an increased tendency to develop lung abscess, cavitation, empyema, and pleural adhesions. It has a death rate around 50%, even with antimicrobial therapy. In the clinical setting, it is the most significant member of the genus Klebsiella of the Enterobacteriaceae. It naturally occurs in the soil, and about 30% of strains can fix nitrogen in anaerobic conditions (Postgate, 1998). As a free-living diazotroph, its nitrogen-fixation system has been much-studied, and is of agricultural interest, as K. pneumoniae has been demonstrated to increase crop yields in agricultural conditions (Riggs et al., 2001).

Escherichia coli

Escherichia coli also known as E. coli, is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus Escherichia that is commonly found in the lower intestine of warm-blooded organisms (endotherms) (Tenaillon et al., 2010) (Singleton, 1999). Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in their hosts, and are occasionally responsible for product recalls due to food contamination (Vogt and Dippold, 2005). The bacterium grows massively in fresh fecal matter under aerobic conditions for 3 days, but its numbers decline slowly afterwards (Russell & Jarvis, 2001).

Faecal–oral transmission is the major route through which pathogenic strains of the bacterium cause disease. Cells are able to survive outside the body for a limited amount of time, which makes them potential indicator organisms to test environmental samples for faecal contamination (Thompson, 2007). A growing body of research, though, has examined environmentally persistent E. coli which can survive for extended periods and grow outside a host (Ishii & Saowsky, 2008) (Montealegre et al., 2018). E. coli is the most widely studied prokaryotic model organism, and an important species in the fields of biotechnology and microbiology, where it has served as the host organism for the majority of work with recombinant DNA. Under favourable conditions, it takes up to 20 minutes to reproduce.

BACTERIAL RESISTANCE TOWARDS ANTIBACTERIAL AGENTS

Antibacterial resistance is the ability of bacteria to resist the effects of medication that once could successfully treat the bacteria. Antibiotics resistance occurs when bacteria change in some way that reduces or eliminates the effectiveness of drugs, chemicals, or other agents designed to cure or prevent infections. The bacteria survive and continue to multiply causing harm. Bacteria can do this through several mechanisms. Some bacteria develop the ability to neutralize the antibiotic before it can do harm, others can rapidly pump the antibiotics out, and still others can change the antibiotic attack site so it cannot affect the function of the bacteria.

Antibiotics kills or inhibits the growth of susceptible bacteria. Sometimes one of the bacteria survives because it has the ability to neutralize or escape the effect of the antibiotic, that one bacterium can then multiply and replace all the bacteria that were killed off, this time they have developed resistance to the antibiotics used against them.

Bacteria that were at one time susceptible to an antibiotic can also acquire resistance through mutation of their genetic material or by acquiring pieces of DNA that code for the resistance properties from other bacteria.

Antibacterial resistance from bacteria has become a worldwide troubling concern and the search for new antibacterial and antimicrobial agents and drugs is important. This is the major importance of this study.

LIMITATION OF STUDY

This study was limited to isolating only bacterial species from earthworm castings, it doesn’t cover the isolation of other microorganisms including actinomycetes.