Viruses, Viroids, & Prions

Human Rotavirus: Structure, Pathogenesis, and Control

The human Rotavirus is a major cause of foodborne infections and gastroenteritis, especially in children. Understanding its structure and control measures is essential in microbiology and public health.

• Genome Type: Rotavirus contains double-stranded RNA (dsRNA) as its genetic material.

• Disinfectant Action: Ethanol (95%) is an effective disinfectant against Rotavirus due to its ability to denature viral proteins and disrupt the lipid envelope.

• Infective Dose: The infective dose for Rotavirus is low, often less than 100 viral particles.

• Replication in Food: Rotavirus does not replicate in food; it requires living host cells for replication.

• Inactivation Methods: Heat treatment, chlorine-based disinfectants, and UV irradiation can inactivate Rotavirus.

• Example: Rotavirus outbreaks are common in childcare centers due to fecal-oral transmission.

Prokaryotic Cell Structures & Functions

Gram Positive vs. Gram Negative Bacteria

Bacteria are classified based on their cell wall structure, which affects their staining properties and resistance to antibiotics.

• Gram Positive Bacteria: Thick peptidoglycan layer, retain crystal violet stain (e.g., Bacillus spp.).

• Gram Negative Bacteria: Thin peptidoglycan layer, outer membrane, do not retain crystal violet (e.g., Escherichia coli).

• Example: Staphylococcus aureus (Gram positive), Salmonella enterica (Gram negative).

Colony Appearance on Food

• Colony Color Variation: Not all bacterial colonies appear white due to pigment production (e.g., Pseudomonas produces green pigment).

Dynamics of Microbial Growth

Hurdle Technology and Growth Curves

Hurdle technology combines multiple preservation methods to inhibit microbial growth in food. Growth curves illustrate the effect of these hurdles on bacteria such as Bacillus cereus.

• Principle: Multiple hurdles (e.g., pH, temperature, preservatives) create unfavorable conditions for microbial survival.

• Growth Curve Analysis: Different hurdles result in distinct lag phases and growth rates, as shown in experimental data.

• Example: Combining low temperature and preservatives delays the exponential growth phase of Bacillus cereus.

Controlling Microbial Growth

Food Safety and Microbial Enumeration

Microbial safety in food production is assessed by quantifying pathogens such as Salmonella spp. using dilution and plating techniques.

• Dilution Plating: Serial dilution followed by plating allows estimation of colony-forming units (CFU) per gram of food.

• Calculation: CFU is calculated using the formula:

• Example Table:

• Microbiological Safety: Ensured by keeping pathogen counts below regulatory limits.

Microbial Metabolism

Fermentation by Saccharomyces cerevisiae

Saccharomyces cerevisiae metabolizes pyruvate via fermentation, producing ethanol and carbon dioxide under anaerobic conditions.

• Pathways: Glycolysis (Embden-Meyerhof-Parnas pathway) followed by alcoholic fermentation.

• Products: Ethanol and CO2 are the main products.

• Equation:

• Application: Used in bread making and alcoholic beverage production.

Cell Membrane & Transport

Endospores of Bacillus spp.: Resistance Mechanisms

Endospores are highly resistant structures formed by certain bacteria, enabling survival in harsh conditions.

• Characteristics: Thick spore coat, dipicolinic acid, low water content.

• Resistance: Endospores resist heat, desiccation, chemicals, and radiation.

• Example: Bacillus subtilis endospores survive boiling temperatures.

Microscopes & Enumeration Techniques

DEFT (Direct Epifluorescent Filter Technique)

DEFT is used for rapid quantification of microbial cells in liquid samples using fluorescence microscopy.

• Steps: Filtration, staining with fluorescent dye, microscopic counting.

• Application: Used in food microbiology for quality control.

Principles of Disease & Epidemiology

Foodborne Pathogens and Disease Transmission

Foodborne diseases are caused by pathogens such as Salmonella, Escherichia coli, and Rotavirus. Understanding their transmission and control is vital for public health.

• Transmission: Contaminated food, water, and surfaces.

• Control Measures: Proper cooking, sanitation, and food handling practices.

• Example: Outbreaks linked to undercooked meat or unpasteurized dairy.

Antimicrobial Drugs & Food Preservation

Preservatives and Antimicrobial Agents in Food

Various chemical and physical methods are used to control microbial growth in food.

• Chemical Preservatives: Sodium benzoate, sorbic acid, nitrates.

• Physical Methods: Heat treatment, refrigeration, irradiation.

• Non-Thermal Methods: High pressure, pulsed electric fields.

• Antimicrobial Agents: Used to inhibit spoilage and pathogenic microorganisms.

Additional info:

• Some questions reference practical microbiological techniques, such as serial dilution, plating, and enumeration, which are foundational in laboratory microbiology.

• Hurdle technology is a modern approach in food microbiology, combining multiple preservation strategies to enhance food safety.

• DEFT is a specialized enumeration method, relevant for rapid microbial assessment in food and water samples.