**2. Bacterial detection approaches**

The conventional bacterial detection techniques such as colony count, biochemical and immunological procedures (ELISA) [6], and the modern (PCR) [7] approaches are currently widely in use; however, these approaches are time consuming as these need enrichment step. Consequently, there is a need to develop rapid and sensitive detecting methods. To this end, the use of biosensor, which can sense bacteria at diverse concentrations, are considered well applicable platform owing to their low cost, simplicity, and sensitivity [5]. **Figure 1** shows different bacterial detection approaches and **Table 1** summarizes comparative study of different bacterial detection methods.

**159**

*Principle and Development of Phage-Based Biosensors DOI: http://dx.doi.org/10.5772/intechopen.86419*

> Trained users, laborious

users, laborious,

users, laborious,

Simple, automatic

Simple, automatic

Simple, Automatic

*screening approaches, adapted and modified from [5].*

**Personals Cost and** 

**detection time**

Cheap, 5–7 days

Costly, approx.: 4 h

Expensive, 0.5–2 h

Very expensive, 0.5–2 h

**Tools Live and** 

Costly, 1–4 h Specialized No No

Cheap, 0.5–2 h Simple Yes Yes

**dead cells detection**

High-tech No No

Simple No Yes

Simple Yes No [2, 13, 14]

Simple No Yes [2, 15, 16]

**On spot detection** **Ref.**

**Bacterial detection method**

Culture & colony count

Nucleic acids-basedbiosensor

Antibodiesbased-biosensor

Phage-basedbiosensor

**Table 1.**

PCR Trained

ELISA Trained

**2.1 Traditional culturing methods**

**2.2 Immunological methods**

**2.3 Molecular techniques**

their rejection.

**2.4 Biosensor**

Finally, different biochemical tests are performed [8].

In such methods, bacteria existing in a sample are cultured on different types of media so that to confirm their existence and isolate them. Two main culturing approaches are used, quantitative and qualitative. By qualitative culturing technique, the target bacterial colonies are produced on selective or differential media. In quantitative culturing technique, the specific bacteria are propagated to form specific colonies which can be calculated to evaluate the sum of microorganisms.

*A comparison between culture and colony count, advanced molecular, and novel biosensors-based bacterial* 

Immunological approaches, such as ELISA, depend upon the reaction of an antigen with a particular specific antibody. This method is unable to differentiate among living and dead cells and also antibodies production is very expensive [6].

Molecular procedures involve the use of DNA for the detection of target bacteria. For example, PCR, first pronounced in 1980s, is nowadays frequently used for detection of bacteria [7]. Molecular approaches are popular for their high sensitivity and rapidity. Dedicated apparatuses, skilled operators and expensive nature mark

According to the proposed definition of biosensor by IUPAC, "Biosensor is a self-controlled imitated device, that is comprise a bio-recognition constituent (bio-prob/bio-receptor), connected to a transducer to translate the biological signal

### **Figure 1.**

*Representation of various bacterial detection approaches.*


#### **Table 1.**

*Biosensors for Environmental Monitoring*

after bacterial infection [5].

bacterial detection methods.

*Representation of various bacterial detection approaches.*

**2. Bacterial detection approaches**

step for specificity and are laborious and expensive. These restrictions can be potentially overwhelmed by developing a biosensor. Biosensor development needs a specific and sensitive bio-probe that can withstand elevated temperature, extreme pH and remain active in diverse and complicated environment. Bacteriophages being sensitive and specific to host bacterium, and showing activity in diverse ionic concentrations are potent agents in biosensor development for detection of bacteria. Phages naturally deliver specificity in recognition of particular bacterial strain to attach, and specifically sense preferred bacterial spectra. Swift recognition offered by phage-based detection can improve the tracing and remediation of bacterial contamination [3]. The main issue that comes with development of phage based biosensor is active and oriented phages immobilization on substrate surface. The benefit of phage immobilization during biosensor development is that phages remain active for long time period, retain physiological activities with high densities, and having high bacterial cells capture efficiencies. Thus, showing improved detection limits that leads to possible development of phage-based biosensor for rapid and accurate bacterial detection [4]. Bacteriophage based biosensor development involve the following phage related approaches: (i) Observing the released phage particles during lytic cycle in the presence of host bacterium, (ii) monitoring released intracellular lysed cell component in the course of phage-mediated bacterial lysis, (iii) detection of inhibited bacterial growth in the presence of specific phages, (iv) use of stained phages for bacterial capture, and (v) observing the expression of cloned reporter gene in genetically modified phages that is expressed

The conventional bacterial detection techniques such as colony count, biochemical and immunological procedures (ELISA) [6], and the modern (PCR) [7] approaches are currently widely in use; however, these approaches are time consuming as these need enrichment step. Consequently, there is a need to develop rapid and sensitive detecting methods. To this end, the use of biosensor, which can sense bacteria at diverse concentrations, are considered well applicable platform owing to their low cost, simplicity, and sensitivity [5]. **Figure 1** shows different bacterial detection approaches and **Table 1** summarizes comparative study of different

**158**

**Figure 1.**

*A comparison between culture and colony count, advanced molecular, and novel biosensors-based bacterial screening approaches, adapted and modified from [5].*

### **2.1 Traditional culturing methods**

In such methods, bacteria existing in a sample are cultured on different types of media so that to confirm their existence and isolate them. Two main culturing approaches are used, quantitative and qualitative. By qualitative culturing technique, the target bacterial colonies are produced on selective or differential media. In quantitative culturing technique, the specific bacteria are propagated to form specific colonies which can be calculated to evaluate the sum of microorganisms. Finally, different biochemical tests are performed [8].

## **2.2 Immunological methods**

Immunological approaches, such as ELISA, depend upon the reaction of an antigen with a particular specific antibody. This method is unable to differentiate among living and dead cells and also antibodies production is very expensive [6].

#### **2.3 Molecular techniques**

Molecular procedures involve the use of DNA for the detection of target bacteria. For example, PCR, first pronounced in 1980s, is nowadays frequently used for detection of bacteria [7]. Molecular approaches are popular for their high sensitivity and rapidity. Dedicated apparatuses, skilled operators and expensive nature mark their rejection.

#### **2.4 Biosensor**

According to the proposed definition of biosensor by IUPAC, "Biosensor is a self-controlled imitated device, that is comprise a bio-recognition constituent (bio-prob/bio-receptor), connected to a transducer to translate the biological signal

#### **Figure 2.**

*Schematics representation of a generalized biosensors, reframed from [12].*

into a computer readable signal and is then presented on computer and analyzed [9] (**Figure 2**). The bio-probes used in general are bacteriophage, enzyme, whole cell, nucleic acid and antibody. The transducer is electrochemical, optical, or mass based, or combination of these. Typical features of biosensors include; selectivity, reproducibility, detection limit, stability, biocompatibility, sensitivity and linearity [10]. Biosensors are commonly used in medical, diagnostic, quality control, veterinary, food and dairy industry, viral and bacterial diagnostic, agriculture industry, drug production, mining, industrial waste water control, defense and military [11]. Classification of biosensor is based on the recognition element, that is, bio-probe (bacteriophage, enzyme, whole cell, nucleic acid and antibody) used or the type of transducer (electrical, optical, or thermal signals etc.) involved. A representative biosensor is comprised of analyte (target to be sensed), bio-receptor (bio-molecule that identifies the analyte), transducer (responsible for signal transduction) and electronics (display the transduced signal) [5].
