Microbes and Multicellularity: The Biofilm Concept

Professor Adriano G DuseChief Specialist, Chair & Academic

Head: Division of Clinical Microbiology and Infectious Diseases

NHLS & Wits School of Pathology

Objectives for this Lecture:By the end of this lecture, students must be able to:

Define a bacterial biofilm Describe the composition, and interrelationship of bacterial cells,

within a biofilm Briefly discuss the interactions of microbial cells within a bacterial

biofilm with particular reference to cell-to-cell signaling (quorum sensing)

Understand the mechanisms of resistance of biofilm-embedded cells to antimicrobial agents

Discuss the clinical relevance of bacterial biofilms in infective processes and medical device associated infections

Illustrate all of the above by describing the “foreign body” effect and infection

The Biofilm Concept

• NOT NEW – A van Leeuwenhoek, 1683 !

The Biofilm Concept

• Assemblage of microbial cells, irreversibly associated with a surface, enclosed in matrix of mainly polysaccharide material

• Sessile versus planktonic microbial cells• Biofilm matrix may also contain non-

cellular materials• Form on a variety of surfaces: living

tissues, medical devices, industrial / natural aquatic systems

The Biofilm Concept

• Assemblage of microbial cells, irreversibly associated with a surface, enclosed in matrix of mainly polysaccharide material

• Sessile versus planktonic microbial cells• Biofilm matrix may also contain non-

cellular materials• Form on a variety of surfaces: living

tissues, medical devices, industrial / natural aquatic systems

The Biofilm Concept

• Assemblage of microbial cells, irreversibly associated with a surface, enclosed in matrix of mainly polysaccharide material

• Sessile versus planktonic microbial cells• Biofilm matrix may also contain non-

cellular materials• Form on a variety of surfaces: living

tissues, medical devices, industrial / natural aquatic systems

Biofilms And Antimicrobial Resistance

Biofilms And Hospital-Acquired Infections

Main nosocomial infections (NIs) acquired by biofilms are:

1. Bacteremia– 87% of (N) bacteremias have an indwelling vascular device– England: 0.6/1000 pt days; ICUs: 9/1000 pt days; > 40% S aureus, 17% CoNS, ~ 9%

enterococci– US: ~ 300 000 cases of CR-bacteremia in 2001

2. Urinary tract infections – account for ~ 30% of all NIs– 95% of (N) UTIs are catheter-related– Of all patients with a urinary catheter: 30% bacteriuria 6% clinical UTI– Risk of UTI increases by 5% for each day catheter is in situ

3. Pneumonia– Occurs in ~ 1% of all patients, accounting for 40% of all surgical ICU infections– Incidence of VAP ranges from 7 to > 40% (mono- / polymicrobial, Gram – ves & + ves

4. Surgical wound infections: not necessarily a biofilm infection per se but relevant

Biofilms In Infectious Diseases

Two types of medically important biofilms:

1. Those that develop on surfaces of implanted medical devices

2. Those that form directly on host tissues

Biofilms And Device-Related Infections

• Central venous catheters (CVCs)• Urinary catheters• Endo tracheal tubes and ventilator tubing• Prosthetic heart valves• Orthopaedic devices• Endoscopes & post-disinfection rinsing tanks

The Foreign Body Effect