ELEMENT 6B: INFECTION & IMMUNITY LECTURE 16: Introduction to Microbiology & Bacterial Forms

LECTURE 16: LEARNING OBJECTIVES The objectives of this lecture are for students to:  Appreciate the wide prevalence and diversity of microbial forms  Understand the consequences of microbial infectious diseases  Realize the different morphologies of microbes  Realize the difference between prokaryotic and eukaryotic cell structure  Be aware of the medically important microbes  Understand the importance of the Gram stain

LECTURE 16: LEARNING OUTCOMES At the end of the lecture you should be able to:  Discuss the omnipresence of microorganisms  Understand that microbes are capable of causing infectious diseases  Appreciate and recognize the various forms and diversity of microbes  Compare and contrast prokaryotic and eukaryotic cell structures  Perform the Gram staining procedure during practicals

 1. Microorganisms can be found in every ecosystem and in close association with every type of multicellular organism  They populate the healthy human body by the billions as benign passengers and even participate in bodily functions …… (give examples)  Bacteria, fungi, viruses, protozoa, helminthes …..their role in the initiation and spread of human diseases. Such microorganisms are characterized as Pathogens

 Most infectious disease is initiated by colonization (i.e. the establishment of proliferating microorganisms on the skin or mucous membranes)  However major exceptions are diseases caused by introduction of organisms directly into the bloodstream or internal organs  Microbial colonization may result in 1 ) Elimination of the microorganism without effecting the host or 2 ) Infection where the organisms multiply and cause the host to react by making an immune or other type of response.

 Infection can have several consequences, including infectious diseases, where the organism causes tissue damage and impairment of body function.(Def. of infection: multiplication of pathogenic bacteria eg Salmonella species even if the person is asymptomatic)

11. PROKARYOTIC PATHOGENS  All prokaryotic organisms are classified as bacteria whereas eukaryotic organisms including fungi, protozoa and helminthes, as well as humans.  Prokaryotic organisms divided into 2 major groups: the eubacteria (which include all medically impt. bacteria) and archae bacteria (a collection of evolutionarily distinct organisms )

A. TYPICAL BACTERIA  Most bacteria have the following shapes : a sphere or coccus, rod shaped or a corkscrew like appearance ( spirochete )  Nearly all bacteria have a rigid cell wall with the exception of the mycoplasma. The cell wall determines the shape of the bacteria. The cell wall also determines whether the bacterium is classified as gram-positive of gram- negative. The cell wall also surrounds the cell membrane. External to the cell-wall may be flagella, pili and/or a capsule.

 Bacteria divide by binary fission. Many bacteria also exchange genetic information carried on plasmids (small specialized genetic elements capable of self replication including transferring antibiotic resistance) B. ATYPICAL BACTERIA  This group include organisms such as mycoplasma, Chlamydia and rickettsia. Although prokaryotic, they lack some significant structural and metabolic capabilities

111. FUNGI  They are nonphotosynthetic, generally saprophytic, eukaryotic. If filamentous, are called moulds whereas the yeast are unicellular.  Fungal reproduction maybe asexual, sexual or both and all fungi produce spores. Pathogenic fungi can cause diseases such as skin infections (superficial mycoses) to serious, systemic infections (deep mycoses)

1V. PROTOZOA  Protozoa are single – celled, nonphotosynthetic, eukaryotic organisms that have many shapes and sizes. Parasites of humans….they can infect all the major tissues and organs of the body.  Both intracellular as well as extracellular parasites in the blood, urogenital region or the intestine. Transmission is by ingestion of the infective stage of the parasite or by an insect bite.

V. HELMINTHS  Helminths are those group of worms that live as parasites. These are multicellular eukaryotic organisms with complex body organization.  Three major groups: tapeworms (cestodes) flukes (trematodes), and roundworms (nematodes). They are parasitic and all major groups can cause disease.

V1. VIRUSES  Viruses are obligate intracellular parasites that do not have a cellular structure.  A virus consists of molecules of either DNA (DNA Virus) or RNA (RNA Virus) but not both surrounded by a protein coat.  A virus may also have an envelope derived from the plasma membrane of the host cell from which the virus is released.  Viruses contain the genetic information necessary for directing their own replication but require the host’s cellular structure and enzymatic machinery in order to complete the process of their own reproduction

Some Possible Outcomes Following Exposure to Microorganism

VARIOUS TYPES OF BACTERIA

Comparison of naked and enveloped virus