Introduction to bacteriology, Lecture notes of Microbiology

Download Introduction to bacteriology and more Lecture notes Microbiology in PDF only on Docsity!

INTRODUCTION TO

BACTERIOLOGY

NURSING STUDENTS

DR. INNOCENT AFEKE UHAS

At the end of this course, the student should be able to:

1. Classify bacteria physiologically and relate the classification to practical application in a hospital setting
2. Relate structure of bacteria to function
3. Classify bacteria structurally and relate the classification to daily application in a hospital

Physiological Classification of Bacteria

oClassification based on nutritional requirement Nutrition- unique to the group of bacteria but basically require C,N,H,O

• Autotrophs - derive their own nutritional requirement
• Heterotrophs- derive from their host or already manufactured food from the environment. Have chemical components for protein synthesis oClassification based on Oxygen requirement for growth
• If oxygen is the electron acceptor the process is aerobic e.g. of aerobes Pseudomonas spp., Brucella spp. Bordetella spp. and Francisella spp
• Most clinically significant aerobes can also thrive under conditions of reduced oxygen and are called facultative anaerobes

• However if the electron acceptor is any other inorganic molecule other than oxygen then it is anaerobic metabolism Bacteria that survive on this type of metabolism are anaerobes e.g. Clostridium spp. Practical applications

1. Sample collected on a swab for aerobic cultures 2.Samples from deep tissues for anaerobic cultures
2. Blood culture for anaerobes
3. Tissue biopsy from internal organs for culturing anaerobes

o Classification based on Temperature requirement for growth

✓Psychrophilic bacteria:

• These grow best at about 20 o C but also down to - 10 o C in unfrozen media.
• Psychrophilic bacteria can cause food spoilage at low temperatures.
• Several of the microorganisms found in the soil and water belong to this group ✓Mesophile:
• These organisms grow between 25 o C and 40 o C, with an optimum growth temperature close to 37 o C
• Some such as Pseudomonas aeroginosa may grow at even lower temperatures between 5- 43 o C
• None of the mesophilic bacteria are able to grow below 5 o C or above 45 o C.
• Most pathogenic bacteria belong to this group

✓Thermophilic bacteria:

• These grow at temperatures above 45 o C
• Often their optimum growth temperatures is between 50 o C and 70 o C.
• Growth of some bacteria occur at 80 o C
• Bacteria in this group are mainly spore formers and are of importance in the food industry especially in processed foods Practical applications

1. Most clinical important bacteria are Mesophiles ( 37 o C body T o )
2. Very few are Psychrophiles e.g Mycobactrium ulcerans (Buruli ulcer)
3. No known clinical important bacterium that is Thermophiles
4. We store blood in the fridge (2- 8 o C) to kill mesophilic bacteria
5. Heating of food prevent the transmission of most clinical bacteria

Practical Applications

1. Vaginal douching with alkaline chemicals make it prone to infection (vaginitis) e.g. Bacterial vaginosis
2. Alkaline food are more prone to vibrio cholera contamination than acidic ones
3. The human stomach with very low pH kills most bacteria ingested in food
4. The pH and the salt contents of the skin (sweat) makes it unhabitable for most pathogenic bacteria

Structural Classification of Bacteria

Anatomy of a Bacterial Cell

• Outer layer – two components:
• Rigid cell wall
• Cytoplasmic (Cell/ Plasma) membrane : present beneath cell wall
• Cytoplasm – cytoplasmic inclusions, ribosomes, mesosomes and nucleoid
• Additional structures – plasmid, slime layer, capsule, flagella, fimbriae (pili), spores

Gram stain technique

Exceptions (1)Some bacteria e.g. Mycobacteria (Mycobacterium tuberculosis, ulcerans and leprae) and Norcadia spp do not stain well with the Gram

• although they are Gram Positive bacteria, they have a thick lipid layer which does not allow the Gram stain to permeate the cell wall
• We use special staining technique for these bacteria called Acid Fast Staining or Ziehl-Neelson (Z-N) staining technique

Practical Application: bacterial cell wall classification

1. Selection of antibiotics to treat appropriate bacterial infection
   • Narrow spectrum antibiotics (Gram + or Gram - )
   • Broad spectrum antibiotics (both Gram + and Gram - )
2. Selection of appropriate disinfectant/sterilant in the hospital
   • Phenolic based disinfectant e.g. Dettol and carbolic soaps are effective disinfectants for mycobacteria in hospital setting like Chest Clinics
   • Glutaldehydes for spore forming bacteria
3. Persistent postpartum infection caused by Mycoplasma spp

Classification based on the SHAPE of Bacteria

• Cocci – spherical/ oval shaped major groups
• Bacilli – rod shaped
• Vibrios – comma shaped
• Spirilla – rigid spiral forms
• Spirochetes – flexible spiral forms
  • Actinomycetes – branching filamentous bacteria
  • Mycoplasmas – lack cell wall