earth is a watery place. Seventy-one percent of the earth is covered in water;
and oceans account for 96.5% of the total earth’s water (USGS, 2016) and
freshwater is 2.5% (Wikipedia, 2017).
water is basically defined with these characteristics: colourless, odourless
and tasteless. It is a major constituent of cells, bodies of living organisms
and water bodies e.g. rivers, streams, oceans, seas, lakes, ponds, etc. It is
an excellent solvent for a vast array of chemicals.
ability of water to serve as a general solvent accounts for the various
impurities affects its characteristics and reduces its qualities.
1.1.The Water Cycle
hydrologic or water cycle describes how water molecules move from the earth’s
surface to the atmosphere and back, in some cases, below the surface. The cycle
is powered by energy from the Sun and is a continuous exchange of moisture
between the oceans, land and the atmosphere. (NASA, )
1.2.Uses of Water
is very essential to life, it is home to a vast array of species and is used
industrially and domestically. It powers human activities such as
transportation, recreation, electricity generation, irrigation, fire extinction
and is also a food source for man and other species.
quality is defined as a range of variables which limit water use. Water quality
is influenced by a number of natural and human factors. Natural factors are
categorized under geological, climatic or hydrological influences. For example,
high salinity is a quality of arid or coastal waters (WHO, 1996). Human
intervention greatly affects water quality. An example is hydrological changes
e.g. the building of dams, diversion of flows, draining of wetlands, etc.; and
more obviously, pollution. The discharge of waste which may be domestic,
industrial, urban, agricultural, etc. and other wastewaters significantly
affects water quality.
use determines its quality. Although water may be available in large
quantities, its usually unsuitable quality limits its uses. Because of the more
demanding quality of domestic and industrial water-use, they are normally
associated with prior water treatment. However, the less demanding uses include
transportation and electricity generation, which don’t have particular
necessities regarding quality (Sperling, 2007). Along these lines, the study of
water quality is important, not just to portray the consequences of a specific
polluting activity or agent, but to permit the choice of processes and
strategies that will comply with the desired water use.
refers to water that has been used, for example, for domestic or industrial
purposes and contains solid or liquid waste products which might be chemical or
biological. The reason for which the water is utilized decides the composition
of the wastewater. These uses differ with climate, social and economic
situation and population type. Household sewage comprises of roughly 99.9%
water. Other parts include organic and inorganic, suspended and broke down
solids, together with microorganisms (Von
Municipal sewage/wastewater comprises for the most
part of water (99.9%) alongside relatively small concentrations of suspended
and dissolved organic and inorganic solids. A portion of the natural substances
show in sewage incorporate synthetic detergents, soaps, lignin, fats, proteins
and their decay items, and also different regular and manufactured natural
chemicals from chemical industries.
Total solids, composed of floating matter, settleable
matter, colloidal matter and matter in solution; biodegradable organics,
usually measured in terms of biochemical oxygen demand (bod) and of chemical
oxygen demand (cod); pathogens, some which transmit diseases; nutrients, mainly
nitrogen and phosphorus that leads to eutrophication; priority pollutants that
could be carcinogens, mutagens or highly toxic; refractory pollutants, like
pesticides, phenols and surfactants, that can resist to conventional methods of
treatment; organic pollutants, like oil; heavy metals, very harmful to humans,
animals and the environment; dissolved inorganics such as sodium, calcium and
sulphate; and pharmaceuticals that can affect humans and animals.
Pathogens in wastewater can include bacteria,
protozoa, helminths, viruses, or prions. It is worthy of note that the presence
of pathogens in wastewater will be a function of the epidemiological health of
a community; a higher infection rate in the community will cause higher
pathogen concentrations in that community’s wastewater.
Pathogenic organisms are typically killed in
wastewater or biosolids through disinfection procedures such as chlorination,
ultraviolet (UV) radiation, or heat exposure. To safely reuse wastewater
effluent or biosolids, it is imperative that pathogenic materials are
adequately eliminated such that public and environmental health is not
compromised for the sake of water and energy conservation (Drexler et al., 2014).
Table 1: Pathogenic organisms potentially present in
raw and treated water
in raw sewage (number per 100 ml)
in biologically treated water (number per 100 ml)
Carries out all life processes
Average size: 0.2–5 mm
3 x 102
5 x 102
5 x 102
Carries out all life processes
Average size: 0.1–1 mm
Carries out all life processes
Average size: 1 mm–30 cm
Single piece of
acid or ribonucleic acid
Needs host for reproduction
Average diameter: 20–300 nm
Norwalk agent (norovirus)
Detected in 3.1%
Detected in 5.6%
secondary and tertiary
Present in secondary
et al, 2014.
1.4.3. Wastewater as
a Reservoir of Antibiotic Resistance Bacteria and Genes
Antibiotics enter wastewater through
human excrement, flushing of excess pills, landfill leachate, or agricultural,
veterinary, or hospital waste and have the ability to influence or disrupt
biological processes in wastewater treatment. Some antibiotics may attack
activated sludge and nitrifying bacteria, reducing treatment efficiency
(Drexler, et all, 2017)
Wastewater treatment plant design and
operation may influence effluent residual antibiotics and antibiotic-resistant
bacteria but wastewater treatment itself may positively select for resistant
bacteria Increased presence of antibiotics in the environment can reduce their
efficacy by encouraging bacteria to develop antibiotic-resistant genes, which
has helped almost every bacterial pathogen to be resistant to at least one
clinical antibiotic (Munir et al., 2011).
An increase in antibiotic resistance and the transfer of resistance genes in
environmental samples such as wastewater can result from uncontrolled and
extreme use of antibiotics in human and animal populations (Pruden et al., 2012; Khan et al., 2013). The increase in antibiotics puts a selective
pressure on bacteria. By eliminating or inhibiting susceptible bacteria,
antibiotics exert a pressure in favour of resistant bacteria.
The unchecked consumption of
antibiotics by humans and animals would imply that antibiotics residues, antibiotic
resistant bacteria and their associated resistance genes would be disseminated
into the environment, especially when insufficient treatment procedures are put
in place to eliminate the excess antibiotics (Hong et al, 2013). The contaminants would pose a serious challenge for
water reuse, therefore, more deliberate actions must be taken to manage sewers
and other environmental reservoirs for the collective reduction of antibiotic
resistance and prevent the development of more resistant superbugs.
Genus Staphylococci belong to the family Staphylococcaceae and its current
classification is as follows:
& Landolo, 2014)
The name Staphylococcus is derived from the Greek staphylo (bunch of grapes) and coccus (a grain or berry), hence Staphylococcus – the grapelike coccus. They
are Gram positive bacteria with having diameters of 0.5-1.5?m and characterized
by individual cocci which divide in more than one plane to form grape-like
clusters (Hayashida et al., 2009).
They are non-motile, non-spore forming facultative
anaerobes that grow by aerobic respiration or by fermentation yielding mainly
lactic acid. Capsules may be present in young cultures, but they generally are
absent in stationary phase cells. Most species of Staphylococcus have a relatively complex nutritional requirement. Members
of this genus are usually catalase-positive and oxidase-negative, which distinguishes
them from the genus Streptococci,
which are catalase-negative, and have a different cell wall composition to Staphylococci (Wilkinson, 1997). Colony
pigmentation on a nonselective medium, such as tryptic soy agar, can range from
cream-white to bright orange. Most isolates of staphylococci are considered as
Class II biohazards by the American Type Culture Collection (ATCC), while the
remaining species are not known to cause any disease in humans and are listed
as Class I organisms (Gillaspy
& Landolo, 2014).
The National Centre for Biotechnology Information (NCBI),
which maintains a curated classification and nomenclature database in the
public repositories for all organisms with DNA sequences, has recognized and
reported 49 species and numerous subspecies of Staphylococcus. With the
development of high-throughput sequencing technology, whole-genome sequencing
projects have become commonplace for bacteria and other organisms (Gillaspy
& Landolo, 2014).
Table 2: Species of Staphylococcus recognized by the National
Centre for Biotechnology Information (NCBI)
& Landolo, 2014).*********cite NCBI***********
Most species of Staphylococcus
are common inhabitants of the skin and mucous membranes. Some species have been
found to have preferences for certain body sites. For example, Staphylococcus capitis frequently is
found in large numbers on the scalp and forehead of humans, S. aureus colonizes the nares of 25–50% of humans, and S. epidermidis is the primary organism
found on the epidermal layer as part of the normal, protective flora. Species
of Staphylococcus found on humans include
S. aureus, S. epidermidis, Staphylococcus
hominis, Staphylococcus haemolyticus, Staphylococcus
warneri, S. capitis, Staphylococcus saccharolyticus, Staphylococcus auricularis,
Staphylococcus simulans, Staphylococcus saprophyticus, Staphylococcus cohnii, and
Staphylococcus xylosus. Staphylococcus
epidermidis are coagulase-negative staphylococci that are natural
inhabitants of the human skin and account for between 65 and 90% of all staphylococci
isolated. Certain species of Staphylococcus frequently are found as etiological
agents of human and animal infections with S. aureus being the organism most commonly
associated with food poisoning and other human diseases. (Gillaspy
& Landolo, 2014).
at now, the genus Staphylococcus consists of 52 species and 28 subspecies
(Euzeby, 2016). They are widely divided into two main categories of clinical
importance which are coagulase positive staphylococci and coagulase negative
staphylococci (CONs). Coagulase positive staphylococci produce coagulase and
thus clot blood and are important pathogens such as Staphylococcus aureus, Staphylococcus
hyicus and Staphylococcus intermedius.
The CONs give a negative coagulase test because they do not have the ability to
produce coagulase e.g. Staphylococcus
epidermidis. The coagulase negative strains are common commensals of the
skin; however some species can cause infection (Rogers et al., 2009; Becker et
1.6.Classification of Staphylococci
Staphylococci have been differentiated using biochemical tests such as
coagulase test and DNase test (Mugalu et
al., 2006; Akpaka et al., 2006). Staphylococcus
aureus gives a positive coagulase and DNase test while the majority of CONs
test negative to both coagulase and DNase tests (Kateete et al, 2010).
Staphylococcus aureus is a Gram positive facultative anaerobe occurring in
grape-like clusters. S. aureus tests
positive to DNase and coagulase biochemical tests and ferments mannitol which
differentiates it from CoNS e.g. S. epidermis
(Marie et al., 2016). It is both a commensal bacterium and a human
pathogen. About 30% of the entire human population is colonized with S.
aureus. It is the most common cause of staphylococcal infections such as bacteraemia,
infective endocarditis (IE), device-related, osteoarticular, skin and soft
tissue, pleuropulmonary infections (Tong et
al, 2015). Other infections which occur in immunosuppressed individuals,
especially hospital patients, include pneumonia, deep abscesses, osteomyelitis,
endocarditis, phlebitis, mastitis, meningitis, toxic shock and food poisoning
(Shittu et al, 2011).
A common problem
in hospital and community-acquired infections is methicillin-resistant S. aureus
(MRSA) infections and has been associated with increased costs and
prolonged hospital stay (Nixon et al., 2006).
Coagulase Negative Staphylococci (CoNS)
staphylococci are a heterogeneous class of staphylococci that test negative to
coagulase. In times past, they were thought to be non-pathogenic; however,
because of patient and procedure-related changes CoNS are now one of the major
nosocomial pathogens. Important members of this family include Staphylococcus
epidermidis and Staphylococcus haemolyticus. Many CoNS species
are DNase negative, for example Staphylococcus epidermidis. They
significantly account for infections in preterm infants and foreign body (or
device)-related infections. S. lugdunensis in some aspects resembles S.
aureus in causing infectious endocarditis whereas S. saprophyticus has
been linked with acute urethritis (Becker et al., 2014).
CoNS are typical
opportunistic pathogens and have a significant impact on human health and life.
They colonize different parts of the mucous membranes and skins of animals and
humans and are less commonly involved in clinically manifested infections
(Grice and Segre, 2011; Becker et al., 2014).
Staphylococci in wastewater
bacteria (ARB) have been found in various aquatic environments, including
groundwater and surface water (Kumar et al., 2010). Wastewater is a
significant hotspot for the cultivation and dissemination of antibiotic-resistant
bacteria and antibiotic resistance genes (ARGs) through horizontal gene
transfer (Börjesson et al., 2009). This is explainable by the occurrence
of bacteriophages in wastes which are capable vectors for the horizontal
transfer of antibiotic resistant genes to previously susceptible strains (Colomer-Lluch
et al., 2011).
and extreme use of antibiotics by humans and animals have contributed
significantly to the antibiotic resistance menace by eliminating or inhibiting
the growth of susceptible bacteria, and exerting selective pressure favouring
resistant bacteria. The antibiotic residues have created an environment for the
evolution of resistant strains and these strains proliferate because of their
newly conducive environment.
To curb the menace
of antibiotic resistance, strategic checks and policies must be implemented to
minimize antibiotic misuse.