Enzymes are proteins that act as catalysts for biological reactions. Enzymes, like all catalysts, speed up reactions without being used up themselves. They do this by lowering the activation energy of a reaction. All biochemical reactions are catalyzed by enzymes. Since enzymes are proteins, they can be denatured in a variety of ways, so they are most active under mild conditions. Most enzymes have optimum activity at a neutral pH and at body temperature. Enzymes are also very specific –they only act on one substrate or one class of related substrate molecules. The reason for this is that the active site of the enzyme is complementary to the shape and polarity of the substrate. Typically, only one kind of substrate will “fit” into the active site. In this experiment, we will work with the enzyme amylase. This enzyme is responsible for hydrolyzing starch. In the presence of amylase, a sample of starch will be hydrolyzed to shorter polysaccharides, dextrins, maltose, and glucose. The extent of the hydrolysis depends on how long it is allowed to react –if the starch is hydrolyzed completely, the resulting product is glucose. You will test for the presence or absence of starch in the solutions using iodine (I2). Iodine forms a blue to black complex with starch, but does not react with glucose. If iodine is added to a glucose solution, the only color seen is the red or yellow color of the iodine. Therefore, the faster the blue color of starch is lost, the faster the enzyme amylase is working. If the amylase is inactivated, it can no longer hydrolyze starch, so the blue color of the starch-iodine complex will persist. You will also test for the presence of glucose in the samples using Benedict’s reagent. When a blue solution of Benedict’s reagent is added to a glucose solution, the color will change to green (at low glucose concentrations) or reddish-orange (at higher glucose concentrations). Starch will not react with Benedict’s reagent, so the solution will remain bl

1. Hospital Acquired Infections
Professor Avijit Das
Head, Department of Microbiology

2. Definition
CDC definition of hospital acquired infections. APIC Infection Control and Applied Epidemiology: Priciples and
Practice St. Louis: Mosby; 1996:A-1-20
Hospital acquired infection is a localized or systemic
condition that results from adverse reaction to the
presence of an infectious agent(s) or its toxin(s) that was
not present or incubating at the time of admission to the
hospital.

3. Hospital acquired infections (Special situations)
 Infection that is acquired in the hospital but does not
become evident until after hospital discharge.
 Infection in a neonate that results from passage through
the birth canal.

4. Special situations (not hospital acquired infections)
 Infection that is associated with a complication or
extension of infection already present on admission,
unless a change in pathogen or symptoms strongly
suggests the acquisition of a new infection.
 In an infant, an infection that is known or proved to
have been acquired transplacentally.

5. Influencing factors
 The microbial agent
The likelihood of exposure leading to infection depends
partly on the characteristics of the microorganisms
including resistance to antimicrobial agents, intrinsic
virulence and amount (inoculum) of infective material.
 Patient susceptibility
Important patient factors influencing acquisition of
infection include age and immune status, underlying
disease, diagnostic and therapeutic interventions etc.
 Environmental factors
These factors include contaminated air-conditioning
system, contaminated water system etc.

6. Methods of transmission in the health-care setting

7. Contact
transmission
Transmission between
a susceptible and an
infected or colonized
person.

8. Droplet
transmission
Droplets generated by
coughing, sneezing etc.

9. Vector
transmission
Transmitted through
insects and other
invertebrate animals.

10. Common vehicle
transmission
Transmitted by contaminated
materials such as blood
products, contaminated
instruments etc.

11. Pathological agents
• Bacteria (most common nosocomial pathogens):
Commensal bacteria-
Staphylococcus epidermidis (causes I.V. infections),
Escherichia coli (causes UTI).
Pathogenic bacteria-
Gram-positive bacteria:
Staphylococcus aureus (causes infection in soft tissue,
bone, blood stream etc. Frequently become resistant
to antibiotics), anaerobic bacterium such as
Clostridium causes gangrene.

12. Gram-negative bacteria:
Enterobacteriaceae, Pseudomonas etc. may colonize
when the host defenses are compromised. They may also
be highly antibiotic resistant. Legionella species may cause
pneumonia.
Viruses:
There is possibility of nosocomial transmission of hepatitis
B and C viruses (transfusion, dialysis, injection etc.),
rotavirus and enterovirus (through oro-faecal route).
Parasites and fungi.
Pathological agents

13. Most common sites of hospital acquired infections

14. Urinary tract infections
• The most common
hospital acquired
infection.
• 80% is associated with the
use of an indwelling
bladder catheter.

15. Urinary tract infections
Causative organisms
 Gram-positives
Enterococcus species (14.3%)
Coagulase negative staphylococcus (3.1%)
Staphylococcus aureus (1.4%)
 Gram-negatives
Escherichia coli (18.5%)
Pseudomonas aeruginosa (10.3%)
Klebsiella pneumoniae (5.2%)
Enterobacter species (4%)
Citrobacter species (2%)
Others (5.2%)
 Fungi
Candida albicans (15.3%)
Candida galbrata (3.5%)
Other candida species (6%)

16. Surgical site infections
• They are also frequent.
• 2/100 operations (NNIS-2006, CDC).
• The infection is acquired during
operation itself either
exogenously (e.g. from air,
medical equipment etc.) or
endogenously from flora on the
skin or rarely from blood used in
surgery.

17. Causative organisms
 Gram-positives
Enterococcus species (17.1%)
Coagulase negative staphylococcus (11.7%)
Staphylococcus aureus (8.8%)
Others (9.2%)
 Gram-negatives
Escherichia coli (8.5%)
Pseudomonas aeruginosa (9.6%)
Klebsiella pneumoniae (3.9%)
Enterobacter species (8.4%)
 Fungi
Candida albicans (5.9%)
Candida galbrata (1.3%)
Other candida species (1.7%)
Aspergillus species (0.1%)
Other fungi (1.7%)
SURGICAL SITE INFECTIONS

18. Hospital acquired pneumonia
The most important are patients on ventilators in
intensive care units, where the rate of pneumonia
is 3% per day.

19. Hospital acquired pneumonia
Causative organisms
 Gram-positives
Staphylococcus aureus (17%)
Streptococcus pneumoniae (1.6%)
Enterococcus species (1.8%)
 Gram-negatives
Escherichia coli (4.4%)
Pseudomonas aeruginosa (15.6%)
Klebsiella pneumoniae (7%)
Enterobacter species (10.9%)
Acinetobacter (2.9%)
Citrobacter (1.4%)
Serratia (4.3%)
Other (15.7%)
 Fungi
Candida albicans (5.7%)
Candida galbrata (0.2%)
Other candida species (1%)
Aspergillus species (0.5%)
Other fungi (2.5%)

20. Health-care associated blood stream infections
In Intensive care unit
• 5.9/1000 catheter
• Attributable mortality 12-25%
(NNIS-2006, CDC)

21. Causative organisms
 Gram-positives
Enterococcus species (11%)
Coagulase negative staphylococcus (39%)
Staphylococcus aureus (12%)
 Gram-negatives
Escherichia coli (2.2%)
Pseudomonas aeruginosa (3.7%)
Klebsiella pneumoniae (2.3%)
Enterobacter species (3.8%)
 Fungi
Candida albicans (6.1%)
Candida galbrata (1.8%)
Other candida species (3.6%)
Blood stream infections

22. Ear, nose & throat infections
Causative organisms
 Gram-positives
Enterococcus species (4.9%)
Coagulase negative staphylococcus (15%)
Staphylococcus aureus (13%)
Streptococcus pneumoniae (0.5%)
 Gram-negatives
Escherichia coli (2.6%)
Pseudomonas aeruginosa (10.3%)
Klebsiella pneumoniae (3.4%)
Enterobacter species (7.2%)
Haemophilus influenzae (2%)
 Fungi
Candida albicans (2%)
Candida galbrata (1.4%)
Other candida species (1.7%)
Aspergillus species (0.3%)
Other (2%)

23. Who is affected by hospital acquired infections?
Nosocomial infections typically affect patients who are
immunocompromised because of age, underlying
diseases, or medical or surgical treatments.

24. Root causes of hospital acquired infections (1)
 Lack of training in basic infection control.
 Lack of an infection control infrastructure and poor
infection control practices (procedures).
 Inadequate facilities and techniques for hand hygiene.
 Lack of isolation precautions and procedures.

25. Root Causes of Nosocomial Infections (2)
 Use of advanced and complex treatments without
adequate training and supporting infrastructure,
including—
 Invasive devices and procedures
 Complex surgical procedures
 Interventional obstetric practices
 Intravenous catheters, fluids, and medications
 Urinary catheters
 Mechanical ventilators
 Inadequate sterilization and disinfection practices and
inadequate cleaning of hospital.

26. • General cleaning and disinfection of the ward.
• Maintenance of sterility of surgical instruments,
invasive devices etc.
• Proper dressing technique.
• Limiting antimicrobial prophylaxis during perioperative
period.
• Use of narrow spectrum antibiotic once a pathogen is
recovered.
Prevention of hospital acquired infections