DR.T.V.RAO MD 1

Dr.T.V.Rao MD

SOCIO-MICROBIOLOGYBIOFILMS AND QUORUM SENSING IN

INFECTIOUS DISEASES

DR.T.V.RAO MD 2

• Sociomicrobiology" is part of the broader discipline "Microbiology", the study of organisms (bacteria, yeast, molds, viruses and protists) that cannot be observed with the naked eye, but having critical mechanisms for propagation.

SOCIOMICROBIOLOGY

DR.T.V.RAO MD 3

SOCIOMICROBIOLOGY

• The term "sociomicrobiology" was introduced by Matt Parsek & Peter Greenberg in 2005 (Trends in Microbiology, 13:27-33) and refers to the group behavior of micro-organisms, Two topics that form the core of sociomicrobiological research are microbial biofilm formation and cell-cell communication (quorum sensing).

DR.T.V.RAO MD 4

INTRODUCTIONQuorum sensing is cell to cell signaling mechanism that enables the bacteria to collectively control gene expression.

This type of bacterial communication is achieved only at higher cell densities.

Bacteria release various types of molecules called as auto inducers in the extracellular medium, these molecules are mediators of quorum sensing.

When concentration of these signaling molecules exceed a particular threshold value, these molecules are internalized in the cell and activate particular set of genes in all bacterial population, such as genes responsible for virulence, competence, stationary phase etc .

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• The study of group behavior in microbes

• • Debate over environmental vs. genetic determinates

• • Biofilms and quorum sensing

• • Model for dissecting social behavior at a genetic level

SOCIOMICROBIOLOGY ADVANCES THE UNDERSTANDING MICROBES

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BACTERIA ARE DYNAMIC CREATURES

• Bacteria are dynamic creatures that are able to regulate their metabolism and lifestyle in response to a variety of environmental cues. These cues include changes in their chemical, physical, and biological surroundings. In recent decades, microbiologists have come to appreciate that bacteria are even able to recognize changes in their own population density. Cell density-dependent regulation has

been termed "quorum sensing."

• iosynthetic and regulatory prodigiosin mutants of Serratia

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• Microbes run much of our body. The human micro biome in our gut, mouth, skin, and elsewhere, harbors 3,000 kinds of bacteria with 3 million distinct genes. (Our own cells struggle by on only 18,000 genes or so.)…This biotech century will be microbe enhanced and maybe microbe inspired….Confronting a difficult problem we might fruitfully ask, “What would a microbe do?”

MICROBES RUN IN OUR BODY AS NORMAL FLORA

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• Models to understand biology of sociality

• To develop new medicines to treat devastating bacterial infections

• Understanding bacteria

• Sociomicrobiology• The “new” science of

• Tools for synthetic biology

MICROBES DO HAVE SOCIAL LIFE AND WELL ADOPTED WHY DO WE WORK

ON IT?

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• In the past decade, significant debate has surrounded the relative contributions of genetic determinants versus environmental conditions to certain types of human behavior

GENETICS X ENVIRONMENT

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• A structured community of bacterial cells enclosed in a self-produced polymeric matrix.

• -Biofilms are a protective mode of growth that allows survival in hostile environments.

• -Bacteria in biofilms are inherently resistant to killing.

WHAT IS A BIOFILM?

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BIOFILMS ARE …….

• Biofilms are multicellular aggregates of bacteria and yeast that congregate on surfaces.

• Biofilm may form on any surface exposed to biofilm-forming bacteria and some amount of water.

• Biofilms are formed to protect the bacteria from host defenses, antibiotics, and from harsh environmental conditions.

DR.T.V.RAO MD 12

BIOFILMS ARE COMMUNITIES OF MICROORGANISMS

• Biofilms are communities of microorganisms that develop on surfaces in most natural and artificial environments. Biofilm maturation requires cell contact with a surface and cell-cell adhesion counteracting the shear forces of the environment. Biofilms are characterized by a surface covered by a high number of cells (a film) encased in a self-produced extra cellular matrix, are highly heterogeneous environment, both at structural, physiological and specific levels and biofilm bacteria express still under-explored specific biological properties such as a characteristic increased tolerance to biocides

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• Biofilms are found almost everywhere in nature, including rivers, lakes, soil, water pipes, and even inside the human body

• Bacterial biofilms are often a cause of infections associated with medical implants such as catheters and IV lines and other medical devices.

WHERE ARE BIOFILMS FOUND?

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BIOFILMS ARE CONCERN IN EVERY ASPECT OF LIFE

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THE DYNAMICS OF GROWING BIOFILM

• Quorum Sensing:• What is it?

• How does it work?

• Heterogeneous structures:

• How do these cells use polymer gel for locomotion?

• What are the mechanisms of pattern (structure) formation?

• Why is polymer gel so effective as a protective environment?

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• Biofilms are important survival mechanisms for bacterial cells. According to in vitro studies, they can avoid attack by host defenses. it is difficult for phagocytic cells to engulf bacteria in biofilms. Also, biofilms are much more resistant than planktonic cells to antimicrobial agents. The bacteria within the biofilm remain healthy, and the biofilm can regrow. Repeated use of antimicrobial agents on biofilms can cause bacteria within the biofilm to develop an increased resistance to biocides.

BIOFILMS ARE ADVANTAGEOUS TO MICROORGANISMS

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• In medicine, biofilms spreading along implanted tubes or wires can lead to pernicious infections in patients. Biofilms on floors and counters can make sanitation difficult in food preparation areas.

• Dental plaque is a yellowish biofilm that build up on the teeth. If not removed regularly, it can lead to dental caries.

BIOFILMS IN MEDICINE

DR.T.V.RAO MD 18

WHY RESEARCH ON BIOFILMS?

• Due to the morphology of biofilms, bacteria capable of forming them are highly resistant to antibiotics, making treatment very difficult.

• In the US alone, one million nosocomial (hospital acquired) infections each year are caused by bacterial biofilms, leading to longer hospitalization, surgery, and even death.

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BIOFILMS AND INFECTIONS:

• Biofilms are responsible for Otitis Media, the most common acute ear infection.

• Biofilms play a role in Bacterial Endocarditis (infection of the inner surface of the heart and its valves).

• Biofilms form frequently in patients with Cystic Fibrosis (a chronic disorder resulting in increased susceptibility to serious lung infections).

• Biofilms also play a role in Legionnaire's disease (an acute respiratory infection resulting from the aspiration of clumps of Legionnella biofilms detached from air and water heating/cooling and distribution systems).

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• A process that enables bacteria to communicate using secreted signaling molecules called auto inducers

• This process enables a population of bacteria to regulate gene expression collectively and therefore, control behavior on a community-wide scale.

QUORUM SENSING

Henke and Bassler, 2004

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Environmental Pseudomonas

PA colonization-ASYMPTOMATIC

Model of Chronic Pseudomonas aeruginosa Infection in Cystic Fibrosis

Bacterial Adaptation

• Alginate/mucoidy• Auxotrophy

Increased bacteria - SYMPTOMATIC

Lung

Disease• surface modifications• Increased PQS

(biofilm, virulence,

antibiotic resistance)

Innate Immune Selective Pressure

• Structuring of multicellular communities

• Stress survival

• Production of

• Antibiotics

• Pigments

• Host tissue degrading enzymes

BEHAVIORS CONTROLLED BY QUORUM SENSING

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• Cell-cell communication can occur within and between bacterial species, and between bacteria and their eukaryotic hosts.

QUORUM SENSING CAN OCCUR …..

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• Bacteria use Quorum sensing to mastermind

behaviors including

• Mating

• Releasing toxins

• Causing disease (virulence )

QUORUM SENSING HELPS IN …

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HOW PATHOGENIC BACTERIA USE QUORUM SENSING

These changes culminate in an infection that can ambush and overwhelm our immune system defenses.

The bacteria appear relatively innocuous as they quietly grow in number.

When their population reaches a certain level, instant changes occur in their

• Behavior

• Appearance

• Metabolism

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QUORUM SENSING SYSTEMS: GRAM NEGATIVE BACTERIA

• Lux I/R systems

• Auto inducers: acylated homoserine lactone

• Lux I-type enzymes synthesize acylated homoserine lactone (AHL) auto inducers by ligating a specific acyl moiety to the homocysteine moiety of S-adenosylmethionine (SAM)

• LuxR-type proteins bind their cognate autoinducers and control transcription of target genes.

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QUORUM SENSING SYSTEMS: GRAM POSITIVE BACTERIA

• Two-component systems involved

• Autoinducers: modified oligopeptides

• The signals are synthesized as precursor peptides, which are subsequently processed and secreted

• Sensor histidine kinases detect the extracellular peptide autoinducers, autophosphorylate and transmit sensory information via phosphorylation of a response regulator

• Response regulator changes gene expression

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THE CHAIN OF COMMAND IN BACTERIAL COMMUNICATION

LuxRMaster Regulator

Protein

Qrr1

Qrr2

Qrr3

Qrr4

Sm

all

RN

A m

ole

cule

s (s

RN

As

)

Qrr = Quorum Regulatory RNA

Signals from sRNAs turn LuxR on and off

Signals from LuxRcontrol quorum-sensing

AI-2AI-2 attaches to LuxR to

initiate cellular communication

LuxRMaster Regulator

Protein

Qrr1

Qrr2

Qrr3

Qrr4

Sm

all

RN

A m

ole

cule

s (s

RN

As

)

Qrr = Quorum Regulatory RNA

Signals from sRNAs turn LuxR on and off

Signals from LuxRcontrol quorum-sensing

AI-2AI-2 attaches to LuxR to

initiate cellular communication

DR.T.V.RAO MD 29

QUORUM SENSING IN P. AERUGINOSA

P. Aeruginosa

•Major cause of hospital infection in the US.•Major cause of deaths in intubated CF patients, and IV fed patients.

Quorum Sensing: The ability of a bacterial colony to sense its size and regulate its activity in response.

Examples: P. aeruginosa

P. Aeruginosa in planktonic (non-colonized) form are non-toxic, but as a biofilm, they are highly toxic and well protected by the polymer gel in which they reside. However, they do not become toxic or begin to form polymer gel until the colony is of sufficient size to overwhelm the immune system. Before this, they cannot be detected bythe immune system.

DR.T.V.RAO MD 30

QUORUM SENSING IN P. AERUGINOSA

Planktonic

Loosely Bound EPS secreting

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“WALL SENSING” IN P. AERUGINOSA

Wall Sensing: The ability of bacteria to differentiate in response toContact with a wall (the substratum).

Planktonic Loosely Bound EPS secreting

DR.T.V.RAO MD 32

• AHL type autoinducers are for intraspecies communications

• AI-2 and its synthase, LuxS, are widespread, existing in many bacterial phyla. AI-2 is suggested to serve as an interspecies bacterial communication signal.

INTRASPECIES VS. INTERSPECIES COMMUNICATIONS

How quorum sensing works?

Signaling compounds, auto inducers AI synthases (luxI gene products)cell density indicators - non-essential aa, acyl homoserine lactones

lactone ring part - binding to a receptor site acyl chain tail – determining the species specificity

- oligopeptides - diketopiperazines - quinolone - furanones

Recognition systems LuxR transcriptional regulatorspecific binding sites for AHL and DNA (sensor/transducer)

Genetic basis regulatory circuit involving both regulatory genes accumulation of AHL - activating gene transcription

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LABORATORY MADE MOLECULES HAVE SOLUTIONS TO COUNTER QUORUM SENSING

AI-2 contains the element boron

AI-2 and similar boron-containing molecules made in the laboratory could serve as decoys to subvert virulence and other quorum-sensing behaviors

Autoinducer 2 may hold the key to disrupting quorum-sensing.

The three general classes of quorum-sensing systems

Modified oligopeptides

Processing and secreation

SHKA R

ATPADP

Class Autoinducer Strain

P. aeruginisaV. fisheriE. carotovoraA. tumefaciensY. enterocolitica

E. coli O157:H7V. harveyiV. choleraeV. vulnificusS. Typhimurium

B. subtilisS. aureusS. pneumoniaeS. epidermidisL. lactis

QS1

G(+)

QS2

AI1

PAI

AI2

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COMMUNICATION BETWEEN PROKARYOTES AND EUKARYOTES

• Chemical communication extends to the eukaryotic hosts with which bacteria engage in pathogenic and symbiotic relationships.

• P. aeruginosa AHLs enter eukaryotic cells and stimulate production of chemokine interleukin 8 (IL-8), which in turn induces the NF-kB transcription factor.

• These responses cause recruitment of neutrophils to the lung, in which they contribute to pulmonary inflammation and tissue deterioration.

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NEED FOR INHIBITION OF QUORUM SENSING

Inhibition of quorum sensing has been proved to be very potent method

for bacterial virulence inhibition.

Several QS inhibitors molecules has been discovered.

QS inhibitors have been synthesized and have been isolated from several

natural extracts such as garlic extract.

QS inhibitors have shown to be potent virulence inhibitor both in in-vitro

and in-vivo, using infection animal models.

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WHAT IS THE NEED FOR QUORUM SENSING INHIBITORS ?

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STRATEGIES FOR QUORUM SENSING INHIBITION

3 strategies can be applied

Targeting AHL signal

dissemination

Targeting the signal

receptor

Targeting signal

generation

Signal precursor

Signal

Signal receptor

Signal precursor Signal precursor

Signal Signal

Signal receptor Signal receptor

X

X

X

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• Further studies are needed on quorum sensing

• regulated gene expression

• – Onset of QS

• – Affects on Onset

• • Architecture and physical flow

• • Functional consequences on biofilm

• community

• • Role in mixed species systems

• • Effects of signal consumption

FURTHER RESEARCH IS NEEDED IN SOCIOMICROBIOLOGY ON ….

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• Created by Dr.T.V.Rao MD for ‘ e’ learning resources for Medical Microbiologists in the

Developing world • Email.

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