bio 207 lecture 6: food infections, poisoning, spoiling

chemical properties of food can change over time through three major classes of processes

• indigenous enzymes cause meat flesh → proteolysis; sugars → starches

• abiotic oxidation: lipid oxidation → odors

• microbes from food surfaces can cause chemical conversions

sources of microbes from food surfaces include

• skin of food handlers

• soil or manure that plants grow in

• other environmental sources

food spoilage

microbial changes causing a product to become unfit or unpalatable for consumption

types of food spoilage

• acid fermentation → sour taste

• oxidation of fats → rancidity

• decomposition of proteins → putrefaction

• alkaline fermentation → bitter taste

what environmental factors can affect food spoilage?

• pH (deviation from neutral increases likelihood of spoilage)

• temperature

• osmolarity and water availability

• nutrients (more nutrients increase spoilage)

• biological barriers like shells, rinds

• antimicrobial chemicals like spices, herbs

what foods tend to spoil by anaerobic fermentation?

milk, cheese

what foods tend to be spoiled by mesophilic organisms or by abiotic auto oxidation of lipids?

meats

fish are special and tend to be contaminated by

psychrophilic microbes well under refrigeration conditions; fish are special b/c they normally live in cold environements

plants tend to have a lower water content than animal-based foods so they have a (longer/shorter) shelf life

longer

food contamination

presence of human pathogens that can lead to disease

extrinsic risk factors for food spoilage

• storage temperature: microbes multiply rapidly in warm temps

• atmosphere: faster growth in oxygen-rich environments (but microbes will also grow in low-oxygen or anaerobic conditions, improperly canned foods)

food poisoning

presence of toxins produced by microbes are in the food

food infection

presence of pathogens on ingested food that grow and proliferate in the body

physical means of food preservation (avoiding spoilage and illness) include

• dehydration/increase solute

• cool

• heat

• controlled or modified atmosphere (limiting oxygen)

• radiation

chemical means of food preservation (avoiding spoilage and illness) include

• adding organic weak acids that can pass thru cell membranes

• adding sugars/salts to increase osmolarity

• lower pH

pathogens are distinguished from food spoilage organisms in that they

possess highly specific mechanisms for host colonization

• adhesins to make first contact and bind with host cells

• toxins

• secretion systems to deploy toxins

in pathogens, bacterial factors contributing to host colonization and disease are often encoded

together in pathogenicity islands in its genomes

adhesin

any microbial factor that causes attachment

how do viruses attach to host cells? bacteria?

• viruses - use capsid or envelope proteins as “keys” for receptors

• bacteria - use their pili or non-fimbrae adhesins (bacterial surface proteins) that rely on specific surface receptors to bind to the right hosts

two types of bacterial adhesins (pili)

• type I: adhere to carbohydrates on the host membranes

• type IV: involved in “twitching motility,” an active process, where a dynamic attachment is formed w/ assembly and disassembly

type I pili

• found in gram negative bacteria only

• produces a static attachment to host cell w a chain of proteins

• may be found free in the periplasm

type IV pili

• motility/anchoring

• dynamic: pilus fiber can assemble and disassemble to grow/retract

• grows from inner membrane of many gram negative bacteria

• allows bacterial pathogen to break tight junctions between cell walls

• e coli breaks tight junctions between intenstinal cell wall, cells break down physical defense

what type of pili is transported from the cytoplasm through a channel to the outer membrane in a bacterial pathogen?

type IV

retraction of type IV pili pilus can cause

diarrhea

whether an infecting organism can infect a host is in large part determined by

initial attachment

endotoxins

• only in gram-negative bacteria & all gram negative bacteria have them

• part of the lipopolysaccharide (LPS) of the outer membrane

• released when the bacteria ruptures

• hyperactivity host immune systems to harmful levels

• lower toxicity and poorly antigenic

exotoxin

• toxin produced and secreted by bacteria

• proteins

• gram positive and gram negative

• highly toxic and highly antigenic (since they’re proteins)

• kill host cells and unlock their nutrients

LPS endotoxin is composed of

lipid A core glycolipid + polysaccharide chain (O antigen)

clostridium botulism

• example of exotoxin, gram positive, spore-forming rod (anaerobe)

• neurotoxin

• destroyed by high heat above 80C

• rare but very potent and potentially fatal

two ways pathogens deploy toxins

• type II secretion system

• type III secretion system

type II secretion systems

• evolutionarily related to type iv pilus biogenesis (similar polymerization/depolymerization characteristics)

• pilus-like structure that thrusts protein/toxin through the pore and out of the cell

type III secretion system

• flagellar synthesis mechanism

• molecular syringe/needle injects proteins from bacterial cytoplasm → host cell

• triggered by cell-cell contact

• salmonella, yersinia, shigella, escherichia

the genes encoding type III secretion systems are usually found on

pathogenicity islands inherited from other microbial sourcesc

e coli is a special case of toxin deployment because

it has evolved to circumvent the need of a specific host receptor:

• uses type III ss but injects its own receptor (Tir proteins)

• acct as receptors for the host outer membrane

• binding to intimin → strong attachment → cascade/responses in host → damage

gastrointestinal infections are primarily (viral/bacterial)

viral

most common GI viral pathogens are (?) and cause what symptoms?

• rotavirus, norovirus

• diarrhea, vomiting

dysentary

intense gastroenteritis; abdominal pain, passage of blood or mucus in diarrhea; can be caused by food poisoning (faster onset) and food infection

enterotoxin

exotoxin that targets the GI tract; heat stable up to 100C for 30 mins

enterotoxin-based food poisoning

• causes gi disease w/out producing infection

• diarrhea, no fever, absence of blood/pus, large number of watery stools

• caused by secretion of enterotoxins into tainted foods

enterotoxin producing strains include

s aureus, e coli, vibrio cholerae

foodborne infection

• requires consumption of living organisms

• symptoms appear one day or more after ingestion

• thorough cooking before consumption kills organisms (prevents infection)

• can become invasive pathogens infecting internal host environment accompanied by invasive diarrhea

common causes of foodborne infections are

salmonella, campylobacter, e coli

salmonella enterica

• leading cause of foodborne deaths in US

• advantage under refrigeration conditions

• raw eggs, dairy, meat, kitchen utensils

• gram negative rod, facultative anaerobe that is able to grown on food and in gut

• growth in intestines can spread to immune system cells and engulf (invasive); secretes toxins directly into host cell

norovirus

• viral cause of foodborne infection

• small non enveloped single stranded RNA virus

• nausea, vomiting, watery diarrhea