7/30/2019 sss222

1/6

Introduction

Ingestion of pathogens may result in different infections. These probably are confined to

gastrointestinal tract or initiated in the gut before spreading to other parts of the body.

There are many of microbial pathogens that are able to infect the gastrointestinal tract.

These microbial pathogens are divided into different categories based on their size,

characteristics and so on. Bacteria are the most common microbes that cause

gastrointestinal tract infection. They can be acquired by the fecal-oral route through

fecal-contaminated food, water and fingers. The pathogens usually must be ingested in

adequate number to cause infection. There are several terms of symptomes used to

describe the gastrointestinal tract infection. Firstly, gastroenteritis, this is characterized by

gastrointestinal symptoms, (nausea, vomiting, diarrhea and abdominal discomfort).

Salmonella, Shigella, Staphylococcus, Campylobacter jejuni, Clostridium, Escherichia

coli and yersinia are the most common species of bacteria that cause gastroenteritis.

Secondly, diarrhea, this is characterized by fluid stool and usually due to the disease of

small intestine and involving increased fluid and electrolyte loss. Thirdly, dysentery, this

is an inflammatory disorder of the gastrointestinal tract mostly associated with blood and

pus in the feces. Pain, fever, and abdominal cramps are symptoms of this disorder and

usually resulting from large intestine disease. Last description term is called enterocolitis;

this is an inflammation involving the mucosa of both the small and large intestine (1). All

of these terms are helpful in identifying the case. The clinical history of the patient also is

very important to make the diagnosis. For example, the cases that we had to investigate

which were three known cases, the fist one was for a 16 year old male presented to his

7/30/2019 sss222

2/6

local doctor with 2 days history of gastroenteritis, his symptoms are nausea, vomiting

followed by abdominal pains and diarrhea. These would help in the diagnosis because it

seems to be one of the pathogens that cause gastrointestinal symptoms. In case study 2,

the patient is suffering from fever, night sweat, severe headache and non productive

cough. There is also a history for a cluster of cases of typhoid fever occurred in the

country town of patient. These symptoms and history would give hint that the case

supposed to be salmonella typhi although we cannot exclude other species unless we do

further investigations. In the case study 3, the patient is 22 year old presented to her local

doctor with a history abdominal pains, fever and watery diarrhea followed by classical

dysentery including blood and mucus in his/her stool. These symptoms are typical for the

third class description (dysentery) and doing further investigations are suggested to reach

the final diagnosis. The importance of clinical history and symptoms in the provisional

diagnosis is very clear as they lead us to the way that we should follow in the

investigations and avoiding consuming many tests. It is very important to get the correct

diagnosis of the case to can prescribe the treatment accurately; this will help the patient to

recover quickly, moreover avoiding any complication of the disease. Therefore, to rashes

that identifying the above organisms by examining their gram morphology and colony

characteristics, with prime importance being given to simple biochemical tests Aims of

the practical exercises is to provide practical knowledge and skills to work at graduate

level in a diagnostic laboratory on the Enterics bench. To work most effectively, i.e. to

interpret results and troubleshoot, it is essential that scientists understand the basic

principles of diagnostic microbiology and are able to recognize and select potential

pathogens in mixed culture. A good understanding of microbial pathogenesis is becoming

7/30/2019 sss222

3/6

increasingly important with the use of tests to detect potential virulence factors, e.g.

toxins.

Discussion

There were three unknown organisms successfully isolated and identified in the

laboratory. It is very important to make sure that while identifying the organism; it is

isolated, purely streaked and not contaminated with others. However, the process for

investigation or diagnosis of any pathogens has to be followed correctly. Starting with

identification and analyzing the clinical not of the patient for example, patient name,

gender, age, type of specimen and symptoms that appear in the patient and finishing with

interpretation the result all to be handled properly. The clinical history of the patient is

the very important step to be considered to reach successful diagnosis. So for lab scientist

the first important thing in the lab after conceder the clinical not is the choice of media,

for example, in case study one, no growth on the plate of skirrows medium (SK) would

exclude campylobacter spp, whereas the growth of bacteria on desoxycholate citrate agar

(DCA), xylose lysine desoxycholate agar (XLD) and hektoen agar (HEK) would rule in

salmonella and shigella spp. The morphological features may give a clue of the suspected

bacteria. The biochemical tests are the next step to be considering so that it can be easy to

differentiate between salmonella and shigella. Based on the results in table one and two

the biochemical tests suggest that the case is more likely salmonella spp. in addition, API

10S and serology are supposed to give the exact serotype and if then sending the report to

7/30/2019 sss222

4/6

the reference lab for the confirmation that will be more accurate to rich the correct

identification. In case study one there is no unusual findings and all results are fit with the

known case. In case no 2, the results are the same to case no 1 except the gas from

glucose is negative which differentiates salmonella typhi from other salmonella

serotypes. Ornithine decarboxylase also is suggested here because it gives negative result

with salmonella typhi and positive with other salmonella serotypes (3). Unusual finding

in this case study is that urea it was positive and that was from the second colony that has

been choose from the media which may reflect non pathogenic disorders therefore it

excluded. In the case study three , the selective media, morphological features and

biochemical tests suggest that the case is more likely shigella spp. the serology test has

been done and the result is positive with shigella flexneri. In this practical exercise we

choose two colons in each case study because we sow slightly different colonies with size

from what we normally suspect in thus cases. So in cause study one we choose two

colonies from XLD agar first was red colonies with black center and the second was red

colonies very small in size and the reason from that is just to be more accurate in identify

the bacteria but the result was the same for the both colonies that have been picked but in

cause study two we choose two colonies but the result was different. In case study two ,

two different colones was first choosen from HEK agar which is green most raised

colonies and the second was blue green colonies with black center and the result where

the same for both colonies exabte in urea test is was positive in the second colony and

negative in the first one so we excluded the second colony because it is may reflect non

pathogenic disorders and that thing is not our interest in this practical exrsaus. finaly in

case study three we also chooses two different colonies first one from XLD agar red

7/30/2019 sss222

5/6

colony and green colonies from HEK agar and the result where different from each other

as it shown in table 3 above but we excluded the second colonies because it give us

positive urea test and that reflect non pathogenic disorders. The purity plat for all case

where cheeked and it was pure with no other bacteria growth but if it is not pure all the

biochemical test cannot be readied and that mean also that we need to do the exrsaus

from the beginning. Moreover, contamination of the specimens also does carry wrong

diagnosis. That is why; all ten equipments were sterilized before use. It is being

suggested to work closely to the flame inside microbiology lab to avoid any kind of

contamination.

Finally, procedures were followed accurately. It is very important to ensure that the total

procedure has been conducted with appropriate steps, confirming to avoid any false

justification. In this regard, taking time to think and analyze the situation, rather than

hurrying with the total procedure, can ensure a realistic and true performance.

We can recommend the followings to improve the experiment of identifying unknown

mixtures:

Organization: For each test, all the records need to be kept properly and

accurately in an organised way. Also, all the tests are being advised to do

separately rather than altogether.

There are few tests which might not provide positive or negative report; in this

case, nothing to be worries, as still organism can be identified.

Period of time enhancement.

7/30/2019 sss222

6/6