Bacterial Identification Techniques in Clinical Scenarios
Real World Scenarios Utilizing Plating Techniques for Pathogen Identification
Scenario 1: Diagnosing Bacterial Infection in a Patient
Situation Overview
A patient arrives at the hospital experiencing severe abdominal pain.
The doctor suspects a bacterial cause, likely a foodborne illness.
Initial Actions
The doctor orders a bacterial swab to collect samples from the patient.
The objective is to identify the causative agent to determine the appropriate treatment plan.
Test Results
Initial test indicates the presence of a gram-negative bacillus that is motile.
It is noted that typical clinical practice includes ordering blood tests concurrently to check:
White blood cell counts.
Blood biochemistry, which aids in identifying the infection and determining if immediate intervention is necessary.
Challenges with Initial Data
Gram-negative bacilli can cause a variety of diseases; specific characteristics are necessary to narrow down the identity of the bacteria further.
Example pathogens: Salmonella and Shigella, which can exhibit similar symptoms.
Steps to Identify Bacteria
Obtain a Pure Culture
Begin with the mixed culture obtained from the clinical specimen.
Utilize selective and differential media for subsequent identification.
Plating Techniques
Use MacConkey Agar:
Selective for gram-negative bacteria.
Differential for lactose-fermenting bacteria.
Positive lactose fermentation on MacConkey indicates that Salmonella and Shigella can be excluded.
Further Identification
Plate onto EMB (Eosin Methylene Blue) Agar:
While Klebsiella can grow, E. Coli will produce a metallic green sheen indicative of its presence.
Positive identification now suggests that the bacteria is E. Coli.
Using Sorbitol MacConkey Plate
To distinguish between pathogenic and non-pathogenic strains of E. Coli:
The sample does not ferment sorbitol and exhibits slow growth, confirming it is a pathogenic strain.
Confirmatory Tests
If additional confirmation is required, Polymerase Chain Reaction (PCR) can be employed.
Treatment Protocol
Common treatment includes:
Antibiotics to combat the infection.
Supportive care to prevent dehydration of the patient.
Scenario 2: Identifying Source of Staphylococcus Outbreak
Situation Overview
Two cleaning crews are responsible for cleaning different areas in an office:
Company One: Cleans bathroom sinks and toilets.
Company Two: Cleans floors.
Several office workers treated for a Staphylococcus infection, raising concerns about non-compliance with sanitary practices from a cleaning crew.
Initial Sample Collection
Samples taken from:
Various surfaces around the building.
Cleaning tools like mops and sponges to test for pathogen spread.
Initial test results indicate:
Both companies' samples show gram-positive cocci and are non-motile, which is inconclusive regarding clusters or chains of cocci.
Identifying the Pathogen
Confirming the presence of Staphylococcus, the next step is to differentiate between the strains using:
Mannitol Salt Agar Plate:
Allows for differentiation between staphylococcal strains based on mannitol fermentation ability.
Test Results from Mannitol Salt Agar:
Company One: Negative for mannitol fermentation.
Company Two: Positive for mannitol fermentation indicating Staphylococcus aureus presence.
Conclusion
Company Two identified as the source of the Staphylococcus aureus outbreak through the positive fermentation results on the selective media.
Appearance on the differential plate would show the yellow fermenter characteristic of staphylococcus aureus.
Verification Process
Ensure the method of swabbing was correctly applied, proceeding from a mixed culture to a pure culture to ascertain that a specific colony is responsible for the pathogen.