Exam 6 FOOD MICR

CDC estimates that Salmonella causes:

1.2 million illnesses
450 deaths every year (USA)

Salmonella infection is most common in:

June, July, and August

Salmonella - Taxonomy

Foodborne INFECTION
Facultative
Gram (-)
Rods
Family - Enterobacteriaceae
Motile - Peritrichous flagella (all over their surface) - there are also non-flagellated variants

Two Species of Salmonella

Salmonella enterica (former 'group I, II, IIIa, IIIb, IV, VI')
Salmonella bongori (former 'group V')

2500+ Serovars in 5 Subspecies of S. enterica

I - enterica
II - salamae
IIIa - arizonae
IIIb - diarizonae
IV - houtenae
VI - indica

All Former Group V are S. bongori:

old naming scheme = S. typhimurium
new naming scheme = S. enterica Typhimurium or S. Typhimurium (serovar not italicized)

New serovars are named after:

the place where they were first isolated - International standard

CDC Salmonella Subtyping:

Tier 1 : based on Serotyping (using antibodies)
Tier 2 : based Molecular Typing: PFGE genotyping (DNA fingerprinting; within a subtype) Now replaced with Whole Genome Sequencing (WGS), even better detailed info.

Host-adaptation:

pathogens that have evolved so long and so closely with specific hosts that they have learned to modulate biochemical processes in the 'adapted hosts', but infection of other hosts may not be as severe

Host-adapted to Humans:

S. Typhi (typhoid fever),
S. Paratyphi A and C (paratyphoid fever)
Most severe Salmonella illnesses (highest mortality rates)

Host adapted to Animals:

S. Gallinarum (poultry),
S. Dublin, S. Abortusovis (cattle)
S. Typhisuis (swine)
Can still cause illness in humans

Un-adapted (to any particular animal):

Foodborne Pathogens

Another definition of Host Adaptation is the

"ability of a pathogen to circulate and cause acute disease in a specific host population as a predominant reservoir."

Reservoirs of Salmonella:

Poultry and Poultry Products
Meat: Beef and Swine
Fish
Most commonly found pathogen in meat products (ahem!, what about Campylobacter?)
USDA Testing Fruits and Vegetables

Distribution of Salmonella:

Primary Habitat of Salmonella that cause FBI
Water
Other Body Organs
Carriers
Animal Feeds
Food Products

Primary Habitat of Salmonella that cause FBI

Intestinal Tract of Animals
Birds/poultry, reptiles, farm animals, human, insects (un-adapted)

Water:

Stagnant water, irrigation ponds

Other Body Organs

Spleen, liver, bile, lymph nodes

Carriers

Shedding in Feces

Animal Feeds:

USDA Study-49% of feeds contaminated

Regulatory Status:

FDA and USDA
USDA manufacturing performance stds

FDA and USDA Regulatory Status:

Zero Tolerance in Ready-to-Eat (RTE) foods

USDA manufacturing performance stds.

Beef carcasses (steers and heifers) - 1% incidence
Pork - 8.7% incidence
Ground Beef - 7.5%
Broilers - 20%
Ground turkey - 49%

SPI 1, 2, 3, 4 =

Salmonella Pathogenic Islands 1, 2, 3, 4

Small Intestine:

Duodenum
Jejunum
Ileum => Peyer's Patches

Lymphatic system: Immunity and Spread of Infection

The lymphatic system plays an integral role in the immune functions of the body. It is the first line of defense against disease. This network of vessels and nodes transports and filters lymph fluid containing antibodies and lymphocytes (good) and bacteria (bad). The spleen also helps the body fight infection. The spleen contains lymphocytes and another kind of white blood cell called macrophages, which engulf and destroy bacteria, dead tissue, and foreign matter and remove them from the blood passing through the spleen. When bacteria are recognized in the lymph fluid, the lymph nodes make more infection-fighting white blood cells, which can cause swelling.

Antigens transported across the intestinal epithelium by M cells are delivered to the

Peyer's patches and drain into the mesenteric lymph nodes (MLNs).

Cell Receptors:

1. Binding & Transport of nutrients
2. Trigger for internal cell Regulation
3. Trigger for Cellular Uptake

Peyer's Patches (M-cells)

general microbial uptake area
has underlying lymphatic tissue (professional phagocytic cells engulf salmonella)

Phagocytosis (macrophage)

uptake by professional phagocytic cells
evagination of pseudopod-like arms

Endocytosis (intestinal epithelial cells)

uptake by invagination of epithelial surface
Salmonella can 'induce' uptake by epithelia. cells

Vesicles (phagosome, endosome, lysosome)

entrap bacteria in lysosomal vesicles (SCV)
vesicles discharge antimicrobials

Normal Outcome of Phagocytosis (Endocytosis)

Phagocytosis: By 'professional' phagocytic cells (macrophage, dendritic cells)
Endocytosis: "Receptor-mediated Endocytosis" - can be induced by nonprofessional phagocytic cells (intestinal absorptive epithelia cell/enterocyte).

Lysosome antimicrobial activity:

1. Toxic oxygen radicals (oxididizing)
2. Low pH (4.5-5.0)
3. Protease (degrades protein)
4. Lysozyme (degrades carbohydrate)
5. Enzymes (> 40 acid-hydrolases; activity is enhanced at low pH)

Chromosome harbors 2 large areas of virulence genes called 'Pathogenic Islands':

SPI1 (Salmonella Pathogenic Island 1)
SPI2 (Salmonella Pathogenic Island 2)

SPI1 -

encodes genes for invasion of epithelia and intestinal inflammation
Encodes for T3SS-1 (Type 3 Secretion System 1)
Stimulates actin polymerization for uptake of surface-bound Salmonella

SPI2 -

encodes genes for intracellular survival and replication in SCVs (Salmonella-containing vesicles).
Encodes for T3SS-2 (Type 3 Secretion System 2)
Inhibits cell defense mechanisms

Salmonella Pathogenesis ('Trigger')

Surface adhesins bind GI epithelial cells
SPI-1 (Salmonella Pathogenic Island 1)
Engulfment (phagocytosis, RME)
Vesicle formation
SPI-2 (Salmonella Pathogenic Island 2)
As many as 6 different Pathogenic Islands

Surface adhesions bind GI epithelial cells

Adhesins: surface pilli, flagella

SPI-1 (Salmonella pathogenic Island 1)

SPI-1 encoded genes (many)
T3SS-1 ('syringe1')
Injection of SPI-1 factors
Actin polymerization

Vesicle Formation:

SPI-1 encoded genes (many) T3SS-1 ('syringe1') Injection of SPI-1 factors Actin polymerization

SPI-2 (Salmonella Pathogenic Island 2)

SPI-2 encoded genes
T3SS-2 ('syringe2')
Injections of SPI-2 factors
Inhibit cell defense systems

Trigger:

The Type 3 Secretion System (T3SS/TTSS) is often referred to as a 'trigger' mechanism for pathogenesis because of the T3SS injection system (as opposed to a 'zipper' mechanism

Epithelial Cell Entry Mechanisms:

Zipper mechanism (L. monocytogenes)
Trigger mechanism (Salmonella)

Salmonella Pathogenesis: (T3SS)

T3SS-1 (cell entry factors)
T3SS-2 (SCV/intracellular survival factors)

Current Salmonella Issues:

Shell Egg-Related Salmonellosis
Liquid egg pasteurization
Intact shell egg pasteurization
Live Poultry Associated Salmonella Outbreaks
Multi-Drug Resistant Salmonella
Salmonella 'Quantification'

Shell Eggs:

Surface originally has a 'protein cuticle' layer
Cuticle/surface may be contaminated with feces/bacteria (Salmonella?)
Cuticle is meant to protect the egg
Cuticle layer is washed away during washing of shell eggs
Underlying shell surface is porous and the pores are large enough to allow bacteria to enter
Bacterial entry through pores are facilitated by warm eggs being cooled too rapidly (creates negative pressure)

Salmonella Enteritidis (SE):

egg-associated outbreaks
phage-type 8 (U.S.) vs. phage-type 4 (U.K.)
USDA-FSIS "Outbreak Traceback Program"
mid-70's to mid-90's - SE from 5% to > 30% of all Salmonella outbreaks
Eggs from infected flocks diverted from sale as 'shell eggs' (pasteurized liquid egg is OK)
Results from transovarian infection in hens egg yolks become contaminated during egg formation in the hen uteri, resulting in internalized S. Enteritidis.

Salmonella Enteritidis Shell Egg Outbreak 2010:

From May 1 to November 30, 2010, approximately 1,939 illnesses were reported that are likely to be associated with this outbreak.
CDC - observed a 4-fold increase in Salmonella Enteritidis (SE) outbreaks through PulseNet (i.e, 200 cases/wk vs. typical 50/wk).
FDA, USDA, CDC, and state partners conducted traceback investigations and found many of these restaurants or events received shell eggs from a single firm, Wright County Egg, in Galt, Iowa.
Over 500 million eggs were recalled.
Contamination of egg layers resulted from providing contaminated feed to pullets (young hens) that were then distributed to their 2 main egg production facilities in Iowa.
This resulted in production of eggs that were internallycontaminated with Salmonella.
This event pushed FDA to address contamination of animal feeds through FSMA

3 Ways Eggs can get Infected with Salmonella:

Contamination of egg surface through the pores of the shell
Descending Infection: contamination by oral uptake, infection of GI tract, infection of ovaries via systemic spread of infection
Ascending Infection: infection of hen via cloacal opening that ascends to the ovaries

Salmonella Enteritidis

Estimated that 1-in-20,000 commercial retail eggs may be contaminated
Resulting in increased production of pasteurized liquid eggs:
from elderly scared to eat shell eggs,
from egg producers forced to shift contaminated shell eggs to pasteurized liquid egg
Egg BeatersTm refrigerated egg substitute
reduced (no) cholesterol due to absence of the egg yolk

Pasteurization of Intact Shell Eggs:

Pasteurization of shell eggs to eliminate Salmonella Enteritidis
using hot air system (Stein, Inc)
obtained up to 7-log reduction of SE
evaluated for the egg industry
implemented in a few markets in the US

Commercially Available Pasteurized Intact Shell Eggs:

Patented by Pasteurized Eggs, L.P. (Laconia, NH)
Manufactured by Heat and Control, Inc. (Hayward, CA)
The system pasteurizes up to 5,000 dozen/hour using an automated batch process
Flats of fresh eggs are loaded onto carriers and transferred through a warm bath of aerated water
The egg carriers are then immersed in a bath of chilled water, and then sealed to prevent future contamination.

To prevent illness from bacteria:

Keep eggs refrigerated, cook until yolks are firm, and cook foods containing eggs thoroughly.

By virtue of pasteurization, ____________________ is excluded from that requirement.

Davidson's Pasteurized Eggs

Small Scale Egg Pasteurization:

Leda Technologies: Castor & Pollux pasteurizes eggs without coagulating the yolk targeting home/small businesses

Current Issues: Live Poultry-Associated Outbreaks

2013 Multistate Outbreak of Human Salmonella Typhimurium Infections Linked to Live Poultry in Backyard Flocks
A total of 316 persons infected with the outbreak strain of Salmonella Typhimurium have been reported from 37 states. Among 199 ill persons, with 51 (26%) hospitalized. 59% of ill persons are children 10 years of age or younger.
81% of ill people reported contact with live poultry in the week before their illness began.
97% of ill persons reported purchasing live poultry from agricultural feed stores.
A total of 113 locations of feed stores representing 33 feed store companies were identified.
Traceback investigations have identified 18 mail-order hatcheries that supplied poultry to these feed stores.

Multi-Drug Resistant Salmonella

S. Typhimurium DT 104
Chromosomal Antibiotic Resistance (ACSSuT)
Acquired Resistance to Fluoroquinolones and Trimethoprim
Emerging in US
"DT" : 'Definitive/Determinative Type'

Chromosomal Antibiotic Resistance (ACSSuT)

Ampicillin
Chloramphenicol
Streptomycin
Sulfa Drugs
Tetracyclines

S. Typhimurium DT 104

has contributed to FBI in N.A., U.K., and Europe
resistant to multiple antibiotics
increased in England & Wales from 500 cases in 1991 to 4,006 in 1996
more prevalent in dairy cattle
epidemic strain: DT104 (definitive type or phage type)
60 Md plasmid carries most antibiotic resistance

Antibiotic Resistant Salmonella:

Multistate Outbreak of Multidrug-Resistant Salmonella Heidelberg Infections Linked to Foster Farms Chicken
As of October 17, 2013, a total of 338 persons infected with seven outbreak strains of Salmonella Heidelberg have been reported from 20 states and Puerto Rico.
40% of ill persons have been hospitalized, and no deaths have been reported.
Most ill persons (75%) have been reported from California.
Epidemiologic, laboratory, and traceback investigations conducted by local, state, and federal officials indicate that consumption of Foster Farms brand chicken is the likely source of this outbreak of Salmonella Heidelberg infections.
The outbreak strains of Salmonella Heidelberg are resistant to several commonly prescribed antibiotics. This antibiotic resistance may be associated with an increased risk of hospitalization or possible treatment failure in infected individuals

Multi-Antibiotic-Resistant Genes ('Cassettes')

Series of antibiotic resistance genes in close proximity (ABCRes related pathogenic islands).
Can be transferred to different strains together
Selective enrichment by 1 antibiotic can lead to resistance from the other ABCRes genes on the cassette.

Mechanisms of Antibiotic Resistance (ABCRes):

1. Influx mechanisms (ABC not allowed into cell)
2. Efflux mechanisms (ABC pumped out of cell)
3. Hydrolysis of ABC (ABC digested/inactivated)
4. ABC binding site is changed by genetic mutation (ABC can't bind)
5. ABC binding site is blocked by chemical modification (can't bind)

Transfer/Dissemination of ABCRes Genes

1. Transformation - uptake of naked/free DNA
2. Conjugation - transfer of plasmid DNA
3. Transduction - DNA transfer by phage infection

Old school thinking:

If you use antibiotic 'A' for animal feed, you may be enriching for bacteria with antibiotic 'A' resistance (and you wouldn't want to give people antibiotic 'A'). .....but everything would be OK because you can give people antibiotic 'B', or 'C', or 'D'.

New model (based on data):

There are 'multi-drug resistance' genetic cassettes (like mini-pathogenic islands for multiple antibiotic resistances). .....so even if you give an animal antibiotic 'A', and it enriches for that bacteria with 'A-resistance', you end up increasing the number of bacteria that would also have 'B', or 'C', or 'D-resistances' because they are all together on the same chromosome within the same bacteria. So what happens if you give people antibiotic B, C, or D? (those bacteria will also be resistant to the antibiotics only given to humans).

Antibiotic Resistant Salmonella (Muriana Lab/Salmonella Cultures):

Antibiotic disc assay
Easy to identify antibiotic resistances
Commonly used in the medical field
Dr. Muriana uses them to identify ABCR in bacteria used as inocula for antimicrobial intervention studies (to recover inocula from background bacteria by plating on media containing antibiotics).
In hospital setting, you would be interested in sensitivity, not resistance

Human Pathogen Contamination of Animal Feeds:

Animal feed is the beginning of the food chain in the 'Farm-to-Fork' animal model
Food production animals are the major reservoirs of numerous human foodborne pathogens
Some farms are large enough that they process their own feed (mixer-feeder operations)
Similar problems currently going on with 'pet treats' (Salmonella )

Human foodborne pathogens from Food Production animals:

Campylobacter spp. (1-in-160 O:19 infections results in Guillian-Barré disease)
Salmonella spp. (non-typhi)
E. coli O157:H7 & non-O157 (STEC)
Yersinia enterocolitica

World-Wide Effort to Reduce Overuse of Antibiotics:

Infections with antibiotic-resistant bacteria result in increased mortality, morbidity, and social and economic costs. By 2050, an estimated 10 million deaths per year globally will be attributable to antimicrobial resistance, with a cumulative economic cost of US$100 trillion. Governments around the world have mobilized to address this pressing public health concern at the recent G20 Summit and the meeting of the UN General Assembly.
Further, WHO has created a set of strategies to combat rising antibiotic resistance, which include improving sanitation and hygiene to reduce overall infection rates and optimizing the use (and preventing the overuse) of antibiotics in both humans and animals. There is increasing recognition that widespread antibiotic use in agriculture and aquaculture might contribute to the development of resistance to antibiotics commonly used in human medicine especially given the overlap of antibiotics used for these different purposes.
For example, bacteria in animals that are treated with antibiotics can develop antibiotic resistance, and these bacteria, which might carry resistance genes, can then be transmitted from animals to humans.
This cross-species transmission can occur through food, direct contact between humans and animals, or shared environmental sources such as contaminated water

Highlights of the Proposed Rule:

New Current Good Manufacturing Practices
Hazard Analysis and Risk-Based Preventive Controls (similar to HACCP)

New Current Good Manufacturing Practices

(would establish CGMPs that specifically address the manufacturing, processing, packing, and holding of animal food).
Hygienic personnel practices and training;
Facility operations, maintenance, and sanitation;
Equipment and utensil design, use, and maintenance
Processes and controls; & Warehousing and distribution

Hazard Analysis and Risk-Based Preventive Controls (similar to HACCP)

Each owner, operator, or agent in charge of a facility would be required to comply with the hazard analysis and risk-based preventive controls.

Growth promotants (antibiotics, ABCs):

Antibiotics used at low doses in feeds are considered to improve the quality of
the product with lower fat and higher protein content (Hughes et al., 2002).
This is called "subtherapeutic" use because the antibiotics are used at levels
lower than normally used to kill bacteria to eliminate a disease.
Benefit is considered to decrease the environmental impact that livestock production has on the world by producing more livestock weight on less feed than would otherwise be needed without 'growth promotants'

Various theories (not really understood why it works):(Antibiotics as 'growth promotants in animal feed')

Growth promotants help to decrease the amount of feed needed to produce food (reduce bacterial use of food nutrients in the gut; more feed is available to the animal).
Sub-therapeutic levels of ABCs reduce bacterial inflammation of the GI tract saving the body a lot of 'energy' = translates to more growth

Otherside of the Issue: (Antibiotics as 'growth promotants in animal feed'):

Antibiotic 'selective pressure' promotes the selection and presence of antibiotic-resistant bacteria.
Antibiotic resistant bacteria can genetically transfer antibiotic-resistance genes among themselves (integrons/ transposons + ABC-resistance => mobile gene cassettes)
Human foodborne outbreaks with antibiotic-resistant bacteria are getting more difficult to treat because of the greater appearance of these organisms

FDA Phasing out Certain Antibiotic Use in Farm Animals

FDA is working with the industry to curtail the use of antibiotics (ABCs) as growth stimulants
FDA Guidance for Industry (Dec. 11, 2013) lays out the strategy and starts the implementation period to phase out ABCs in certain animal feeds.

FDA Guidance for Industry (GFI) #213:

New Animal Drugs and New Animal Drug Combination Products Administered in or on Medicated Feed or Drinking Water of Food-Producing Animals:
Recommendations for Drug Sponsors for Voluntarily Aligning Product Use Conditions with GFI #209

Veterinary Feed Directive (VFD):

Jan 1, 2017: FDA moving all human-medically important drugs (antibiotics) to the VFD drug process (to gain greater control over antibiotics given to animals).
Attempt to combat antibiotic resistance derived from giving antibiotics in animal feeds as 'growth promotants'

Growth promotants (antibiotics, ABCs):

Requesting drug companies to revise label claims, removing growth promotion and feed efficiency as allowable uses, effectively preventing veterinarians from writing VFD orders for these purposes.
Farmers must work with a licensed veterinarian with whom they have an established veterinarian-clientpatient relationship (VCPR) in order to receive permission to order and use feed containing a VFD drug.
This relationship must be established and recognized by the veterinarian prior to any VFD order being written.
Feed distributors will require a valid VFD, provided by the veterinarian, prior to supplying customers with the regulated feed product. VFDs will need to be renewed every 6 months, based on renewal guidelines set by FDA.
Not all antibiotics will be considered VFD drugs. The use of injectable antibiotics will not be affected. At this time, FDA has only moved antibiotics essential to human medicine and being fed to animals to VFD status.
Also, as a part of the new FDA changes, water soluble antibiotics, which are important to human medicine, will now require a prescription from a veterinarian. This transition of water soluble drugs will include Aureomycin® Water Soluble Concentrate (Chlortetracycline).

Fast Food Chains Announcing Elimination of Foods Grown with Antibiotics:

Fast food chains have a lot of 'clout'
They didn't wait for FDA regulations to take effect
They went forth and said "we are not buying foods that were raised with antibiotics in feed"
This type of pressure was more effective than FDA 'voluntary requests

Salmonella 'Quantification':

Constituent Update - July 8, 2022
FSIS to Include Salmonella Quantification in Raw Poultry Rinse Samples
FSIS awarded a contract to bioMérieux to incorporate its non-enrichment quantification system for Salmonella, 'GENE-UP™ QUANT Salmonella,' into the agency's laboratory system. USDA-FSIS evaluated commercially available quantification systems and determined that this technology is the most appropriate for use in the high throughput FSIS laboratory environment.
A future Constituent Update will announce when the method is available and when it will be implemented in all three FSIS food testing laboratories.
Salmonella quantification is a significant step in FSIS' efforts to reduce Salmonella illnesses associated with poultry and to modernize the diagnostic capabilities of the FSIS food testing laboratories. Using this new system, FSIS will be able to measure the amount of Salmonella present in a regulatory sample, not solely its presence or absence.

Listeria Monocytogenes:

Gram-positive, intracellular foodborne human pathogen
Psychrotroph - Can grow from 4o to 44oC
15 species of Listeria: L. monocytogenes (humans) L. ivanovii (animals)
99% cases of human listeriosis considered foodborne
Zero tolerance in ready-to-eat (RTE) foods (FDA & USDA)
25-30% mortality observed in large outbreaks
Readily forms biofilms => processing facilities

Early appearance of Listeria:

Bacterium monocytogenes was known to infect animals (initially rabbits, then sheep) as far back as 1920's (Murray).
Name 'Listeria' was given by J. Pirie (1940).

Pathogenicity in Humans (Listeria):

Unidentified organisms were also detected in human blood/tissue in the 1940's-1950's
Organisms isolated from lesions in stillborn infants were identified as Listeria (J.H. Seeliger).
It was not clear how humans were acquiring the organism

Listeria Monocytogenes has a ________ incubation period compared to other FBI's

Longer

The long incubation period presents a problem whereby:

1) The organism infection may be ongoing during this time
2) The ability to determine what food was involved; it may not be available any longer

Significance of Listeriosis (Rates of Hospitalization):

The rate of hospitalization is higher than other FBI's by a significant margin

Route of Infection Listeria

GI Infection (Peyer's Patches & M-cells, & GALT)

GALT:

Gut Associated Lymphoid Tissue

Non-specific uptake mechanism:(Listeria)

Peyer's Patches/M-cells
Most bacteria
Nothing extraordinary needed
Specialized cells/region but they take up bacteria indiscriminately

Non-specific attachment mechanism: (Listeria)

Intestinal epithelial surface
Bacteria attach with bacterial fimbrae, pili, flagella to initiate infection
Salmonella, E. coli
Attachment induces uptake to start infection

Specialized attachment / infection mechanism (Listeria):

Specific receptor on intestinal epithelial that bacteria bind to L. monocytogenes
L. monocytogenes Internalin A protein binds to epithelial cells E-cadherin receptor protein

Infectious Route-GI:

Phagocytosis (Macrophage)
Endocytosis (Intenstinal epithelial cells)
Vesicles (Phagosomes, endosome, lysosome)
Illness
Peyer's Patches (M-Cells)

Illness:

diarrhea, fever, vomiting
worse - if survives immunological onslaught
septicemia, systemic infection

L. Monocytogenes Attachment and Inducement of 'Phagocytic-Like' Epithelial Cells

Internalin A mediates attachment to Ecadherin receptor on cells of the intestinal epithelium and other tissues. InlA is secreted, but is covalently bound to the peptidoglycan.
Internalin A/B attach via 'zipper' method (as opposed to the 'trigger' method by T3SS).
Internalin B mediates attachment to the 'Met Receptor' of hepatocytes and therefore mediates infection of the liver. InlB is secreted, loosely bound, often found in culture supernatant.
Both, the E-cadherin and Met receptors are 'trans-membrane' proteins and induce phagocytic-like uptake by non-phagocytic cells by mobilizing actin polymerization.

Listeria Monocytogenes (Intracellular pathogen on the move)

1. GI tract adhesion(E-cadherin) Intestinal Epithelium
2. Invasion (internalin; InlA/InlB)
3. Encapsulation (metalloprotease)
4. Encapsulation (peroxyredoxin)
5. Escape (hemolysin, LLO)
6. Membrane dissolution (phospholipase C, PLC) 6. Propulsion (actin polymeriz.)
7. Cellular escape (septicemia)
8. Macrophage capture, survival, spread
9. Tissue infiltration (liver, kidney, spleen)
10. Brain stem infiltration (meningitis, encephalitis)

Listeria Monocytogenes (Intracellular pathogen on the move):

A)Direct Invasion • Single membrane vesicle
B)Cell-to-Cell Spread • Double membrane vesicle • Lmono is doubly protected

Hard to contain L. monocytogenes in membrane vesicles:

1.Phospholipase C (PLC) - digests vesicle lipid bilayer PI-PLC: phosphatidylinositol-specific phospholipase C PC-PLC: phosphaticylcholine-specific phospholipase C Dissolves lipid bilayer membranes
2.Hemolysin (Listerialysin, LLO) - forms pores (holes) in vesicle LLO: hemolysin (L. monocytogenes) More activity at acidic pH (as occurs in vesicles) Forms 'membrane pores' in the lipid bilayer

How does Listeria monocytogenes get to all these tisues?

They take a 'biological taxi' ride in a Macrophage! or surviving entrapment in some other travelling professional phagocytic cell