week of april 11-15
week of april 11-15 Micr 407
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This 6 page Class Notes was uploaded by Molly Gersbach on Sunday April 24, 2016. The Class Notes belongs to Micr 407 at Clemson University taught by Xiuping Jiang in Spring 2016. Since its upload, it has received 16 views. For similar materials see Food and Dairy Microbiology in Microbiology at Clemson University.
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Date Created: 04/24/16
Salmonella Growth limitations Some survival characteristics: why is salmonella so resistant? o Readily adapts to extremely environmental conditions Most human pathogens die off quickly when environment is not ideal (dry/heat/etc) o Heat shock response Exposed to lethal temperature and the microbe has mechanism to survive. Must lengthen lethal temperature exposure o Acid tolerance response (ATR) Induced neuroprotein under acid conditions to survive S. entertidis o 80% of SE outbreaks associated with Grade A shell eggs o how do eggs get contaminated with SE? transmitted horizontally when hen lays egg, egg is in contact with bed/feces/food/etc. gets into egg when cracked if not cleaned properly transmitted vertically from breading flocks to egglaying hens From hen to egg inside egg, during hen ovulation range of 1400 cells of SE o Low infectious dose – as few as 1520 cells o Incubation time 6 to 48 h and duration of symptoms is 12 days S. typhimurium DT104 o Emerged in UK in 90’s o 90% of all DT104 isolates were resistant to ampicillin, chloramphenicol, streptomycin, sulphonamides, and tetracycline All common antibiotics o Affecting about 68,00 to 340,000 people per year Current status of Salmonella o Know top 5 serotypes: S. enteritids S. typhimurium S. Newport S. javiana S. Heidelberg Control of Salmonella o Food producing animals: competitive exclusion If you expose newly hatched chicks to indigenous healthy chick feces early on, they will have less of a chance to get infected because of competitive exclusion o Proper food handling Cross contamination o Control antibiotic use in agricultural and agricultural practices Escherichia coli G, facultative anaerobe, motile rods Most strains are nonpathogenic o Small population is pathogenic Serological classification o Serogroup (O) based on O antigen of LPS (lipopolysaccharides) – where E. coli O157:H7 comes from LPS: protects G bacteria between inner and outer membranes Serotype (H) – dependent on flagella type Serotype (K) – based on capsule antigen Virotypes of pathogenic E. coli o EPEC Enteropathogenic E. coli Diarrheal Infantile – fatal Traveler’s diarrhea in adults Patchy pattern to host cells Effects due to damage Very invasive of human cells No toxins produced o EAggEC Eneroaggregative E. coli Persistant diarrhea in children Binds small intestinal cells – not invasive Clumps in aggregates on mucosa Enterotoxins Enteroaggregative heatstable toxin Hemolysin – forms pores on blood cells/lyses them o ETEC Enterotoxigenic E. coli Cause diarrhea, no major histological changes, no invasion Virulence factors Adhesion Enterotoxin: heatlabile toxin and heat stable toxin o EHEC Enterohemorrhagic E. coli Caused by E. coli O157:H7, O26:H11, Hemorrhagic colitis Hemolyticalis uremic syndrome (HUS) Thrombotic thrombocytopenic purpurea (TTP) Adhesions Shiga toxins (Stx) or verotoxins Blood diarrhea Invasion of cells o E. coli O157:h7 Characteristics Inability to grow at temps > 44.5*C Inability to product bglucuronidase Possession of an attaching and effacing (eae) gene, shiga toxin (stx) toxins, 60 Mda plasmid Acid tolerance Low infective dose –est. 10 cells ~63,153 cases, 2,138 hospitalizations, and 20 deaths Symptoms Incubation period: 34 days Nonbloody diarrhea Reservoirs Cattle/other ruminants Domestic animals and wildlife: dogs, horses, swine, cats, seagulls, and rats Humans Water, soil, and animal feces Animals are carriers, and during processing if you don’t clean the meat well then it carries over and stays in the meat. Foods implicated in E. coli O157:H7 outbreaks Undercooked ground beef o Ground beef mixes the pathogen into the meat, meaning the inside of the burger will be contaminated as well as the outside o Pink inside is not safe Vegetables, salad bars Apple cider/juice Bean sprouts Fermented dry salami Control of E. coli O157:H7 Food producing animals o Vaccine: bacterial extract by Epitopix o Competitive exclusion Water treatment o One animal sick contaminates other animals through water trough in the pasture Avoid fecal contamination Proper food handling o Don’t leave at room temp for too long Intervention technology such as irradiation Human Noroviruses Norovirus is a 32 nm +sense RNA virus o Means its super small (bacteria is 1,000 nm avg) Belongs to the family Caliciviridae o Includes human Sapporo virus Widespread in children, not super serious First identified after an outbreak of gastroenteritis in Norwalk, Ohio in 1972 Structure o Nonenveloped enteric virus o Genome contains 3 Open Reading Frames (ORF) Relevance o Leading cause of foodborne gastroenteritis Acquired through aerosol – droplets? o Outbreaks are most commonly associated with Nursing homes Schools Catered events Cruise ships Consumption of raw seafood Transmission o Fecal or vomitusoral route Symptomatic and asymptomatic individuals shed the virus in their feces for up to 2 weeks after symptoms subside (longer in immunocompromised inidivudals) Vomitus can spread the virus as well o Person to person – majority 66.1% o Foodborne – 25.9% o Environmental – 0.3% o Waterborne – 0.2% High risk food o Fresh produce/seafood Environment they are grown in increases risk of coming into contact with contamination via water/food handlers Often eaten raw o Fresh produce: Makeup of outer surface can lead to increased chance of harboring pathogens Also decreases decontamination capabilities Pathogenesis/infection o Low infectious dose o Overnight incubation time o +sense strand of genome RNA serves as mRNA upon entering the cell, binding to the ribosomes and translating proteins such as viral polymerase o Incubation time of about 2448 h o Causes gastroenteritis, o Symptoms include vomiting and diarrhea, with or without nausea and abdominal cramps o Selflimiting in healthy adults lasting 2472 h o Possible fatal infection in immunocompromised, young and elderly populations mainly due to dehydration Treatment o Vaccines VLP Mainly uses capsid proteins VP1 with or without adjuvant Protrusion particle Uses the protrusion (P portion of capsid protein ) Vector borne Used to generate live attenuated vaccines by using other viruses Problem with vaccines is that not enough immunity is expressed Many different genotypes and groups o Antiviral Drugs None currently Some in the works would target the binding of HuNov to human HBGA Persistance o Persistence in the environment is one of the leading causes of ongoing outbreaks leading to outbreaks continuing for up to 6 months o Lack of envelope grants resistance to environmental factors like pH, temperature, and humidity o On hands When inoculated with Norovirus RNA viral titer drops by ca. 0.25 log and remains stable through 120 min of testing o Foods Survived for 10 days on RTE refrigerated foods with no reduction in viral titer o Surfaces Can persist for up to 28 days on food preparation surfaces before viral titer starts to decrease o In water Persisted for more than 2 months in artificially inoculated water at 20, 4, and 25 C Decontamination/Inactivation
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