INTRODUCTION TO BACTERIA

Dr. Nilanthi Dissanayake (MBBS, Dip. Micro, MD Micro)Department of Microbiology

Faculty of MedicineUniversity of Peradeniya

OBJECTIVES

1. Major morphological and biological characteristics of infective bacteria that determine visualisation/ID

2. Basis of classification and means by which recognised as a cause of disease in a patient

OBJECTIVES

STRUCTURE

HABITAT? Where are bacteria found

EVERY WHERE BUT – most are non pathogenic

Skin flora Space

IMPORTANCE• Basic life form

• Waste degradation

• Industry

• Antibiotic production

• Vaccine production

CLASSIFICATION• Morphology

A- BacilliB,C,D- CocciE- Spiral

• Stain characteristics

IDENTIFICATION• Culture

• Staining characteristics

• Antigen detection

• Biochemical tests

• Nucleic acid detection

HOST PARASITE RELATIONSHIP

STAPHYLOCOCCI

OBJECTIVES

• Habitat, main mode/s of transmission• Morphology and growth characteristics in

relation to ID• Virulence factors, pathogenicity and main

clinical diseases• Principles of treatment and prevention

Staphylococci……• Gram positive cocci in clumps

• Ubiquitously found in humans, animals and in the environment

• Important human pathogen

Staphylococci……• Several species• Classified using coagulase

Positive – S.aureus

Negative- Coagulase negative Staphylococci (CNS)

S.aureus…… Habitat and transmission

• Normal flora of human and animals

• Abundant in ‘sweaty’ hairy areas – nose, axilla, scalp Skin scales – (10-100,000)/cm2 of skin

• Survives for long periods in environment

• TransmissionDirect or indirect contact

S.aureus….. Virulance and disease• Several virulence factors eg. Adhesins, hyaluronidase, leucocidin, coagulase, staphylokinase, haemolysins

Toxins – exfoliatin, enterotoxins, Panton Valentine Leucicidin (PVL)

• DiseaseLocalSystemicToxin related

Antibiotic Treatment• Development of resistance Penicillinase production

Change of Penicillin binding Proteins or the binding target • Range of antibiotics which can be used for treatment

β lactams - penicillins, cephalosporins, carbapenemsMacrolides – erythomycin, azithromycin,

clarithromycinGlycopeptides – vancomycin, teicoplaninOthers – quinolones, rifampicin, linelozid,

daptomycin

Coagulase negative staphylococci….• Many species, but only few are important

S.epidermidisS.saprophyticus

• S.saprophyticus – common cause of Urinary tract infections in females

- very sensitive to antobiotics

• S.epidermidis- Skin commensal- Not a primary pathogen-Forms biofilms on prosthetic material