Unit 2: Environmental and sterility testing, nosocomial infection
Applied Bacteriology notes · PTU syllabus (BMLS307-18)
On this page
Unit summary
The laboratory protects patients from hospital infections by monitoring air, fluids and surfaces. This unit covers bacteriological examination of air, sterility testing of IV fluids, surveillance of the hospital environment and the laboratory's role in controlling nosocomial infection.
After this unit you can
- Examine air by settle plates and air samplers
- Test IV fluids for sterility
- Plan environmental surveillance
- Explain the laboratory's role in infection control
PTU syllabus topics
- Bacteriological examination of air (settle plate method, air sampling instruments)
- sterility testing of IV fluids
- bacteriological surveillance of the hospital environment
- role of the microbiology laboratory in nosocomial infection control
Surveillance
Track infection rates
Environmental sampling
Air, surfaces, water
Sterility testing
IV fluids, equipment
Outbreak investigation
Typing the organism
Antibiogram
Guide empirical antibiotic use
Topic 1
Bacteriological examination of air
Settle plate method
Open blood agar plates exposed for a set time; colonies counted
Simple; uses the 1/1/1 schedule (1 hour, 1 metre above floor, 1 metre from walls)
Slit sampler
Air sucked through a slit onto a rotating plate
Counts per cubic metre
Sieve (Andersen) sampler
Air through perforated plates
Sizes particles
Centrifugal sampler
Air spun onto agar strips
Portable
- Acceptable limits (operation theatres): empty theatre about 35 CFU/m³ or less; settle plate counts are reported per plate per hour. Ultra-clean air (laminar flow) for joint replacement theatres.
Topic 2
Sterility testing of IV fluids
- 1
Sample aseptically in a biosafety cabinet
- 2
Membrane filtration (preferred) or direct inoculation
- 3
Media: fluid thioglycollate (anaerobes and aerobes, 30–35 °C) and soybean–casein digest broth (fungi and aerobes, 20–25 °C)
- 4
Incubate 14 days
- 5
Inspect daily for turbidity
- 6
Include positive and negative controls
- Any growth means the batch fails (after excluding laboratory contamination).
Topic 3
Surveillance of the hospital environment
- Surfaces
- Swabs or contact plates from operation theatres, ICUs, labour rooms
- Water
- Dialysis water, drinking water (coliform counts)
- Equipment
- Endoscopes, ventilator circuits
- Hands
- Hand hygiene audits
- Targeted sampling
- During outbreaks rather than routine sampling everywhere
Topic 4
Nosocomial infection and the laboratory's role
- Nosocomial (hospital-acquired) infections: appear 48 hours or more after admission — catheter urinary infection, ventilator pneumonia, central line bloodstream infection, surgical site infection; often caused by resistant organisms (MRSA, ESBL, carbapenem-resistant Klebsiella, Acinetobacter).
- Accurate identification and susceptibility
- Guides treatment
- Surveillance data
- Infection rates and antibiograms
- Alert organisms
- Rapid reporting of MRSA, CRE, C. difficile
- Outbreak investigation
- Typing of isolates (serotyping, PCR, sequencing)
- Infection control committee
- Member; advises on policies
- Sterilisation monitoring
- Biological indicators
Key terms
- Settle plate
- Agar plate exposed to air to catch falling microbes
- Sterility testing
- Testing that a product contains no viable microbes
- Nosocomial infection
- Infection acquired in hospital
- Alert organism
- Pathogen needing urgent infection control action
- Antibiogram
- Summary of local antibiotic susceptibility
Quick revision
- Settle plates (1/1/1), slit, sieve and centrifugal samplers.
- Sterility testing: membrane filtration, FTM and SCDB, 14 days.
- Surface, water, equipment and hand surveillance.
- Nosocomial infections; laboratory roles.
Important exam questions
Practice questions written to the PTU exam pattern for this unit's syllabus: short answers (Section A style) and long answers (Sections B and C style).
Short-answer questions
- Q1.What is the 1/1/1 schedule?
- Q2.Name the media used for sterility testing.
- Q3.How long are sterility tests incubated?
- Q4.Define nosocomial infection.
- Q5.Name two alert organisms.
- Q6.Why is isolate typing done in outbreaks?
Long-answer questions
- Q1.Describe the bacteriological examination of air.
- Q2.Describe sterility testing of IV fluids.
- Q3.Explain the role of the microbiology laboratory in controlling nosocomial infections.
Stuck on this unit?
Message SBS on WhatsApp for help with Applied Bacteriology, or to ask about studying B.Sc MLS at Synetic.