Food microbiology

1
Food microbiology

• Chap. 12 Vibrio species

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Introduction

• Over 20 Vibrio species have now been described
  at least 12 are capable of causing infection in
  humans, although with the exception of Vibrio
  cholerae and V. parahaemolyticus, little is know
  about the virulence mechanisms the employ
• Of the 12 pathogen, 8 are directly food associated

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Introduction

• Vibrio, the predominant bacterial genus in
  estuarine waters, are associated with a great
  variety of seafood
• Approximately 40 to 60 of finfish and shellfish
  at supermarkets may contain Vibrio spp., with V.
  parahaemolyticus and Vibrio alginolyticus most
  commonly isolated
• Vibrios are most frequently isolated from
  molluscan shellfish during the summer months

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Characteristics of the organism

• Many different enrichment broths have been
  described for the isolation of vibrios, although
  alkaline peptone water remains the most commonly
  used
• These are frequently coupled with
  thiosulfate-citrate-bile salts sucrose (TCBS)
  agar or other plating media

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Epidemiology

• The numbers of vibrios in both surfaces water and
  shellfish correlate with seasonality, generally
  being greater during the warm-weather months
  between April and October
• Seasonality is most notable for Vibrio vulnificus
  and V. parahaemolyticus infections, whereas some
  vibrios, such as Vibrio fluvialis, occur
  throughout the year

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7
Characteristics of disease

• The outcomes of infections depend on an
  individuals underlying health (e.g., patients
  with chronic liver disease are more likely to
  succumb to severe illness)
• An exception to this generalization is V.
  cholerae O1/O139, which can readily make
  noncompromised individuals sick

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Characteristics of disease

• Most cases are associated with a recent history
  of seafood consumption, especially eating raw
  oysters
• Because vibrios are part of the normal estuarine
  microflora caused by fecal contamination, Vibrio
  infections will not be controlled through
  shellfish sanitation programs
• It is therefore essential that raw seafood be
  kept cold to prevent significant bacterial growth
  and that it be properly cooked before consumption

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Characteristics of disease

• Symptoms of fooodborne illness for the two most
  common Vibrio species differ and are worth noting
• Symptoms of V. vulnificus foodborne illness
  generally include fever, chills, and nausea,
  diarrhea is generally not experienced
• Mortality occurs in 40 to 60 of cases

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Characteristics of disease

• The most common symptoms of V. parahaemolyticus
  infection are diarrhea, abdominal cramps, nausea,
  and vomiting
• Mortality is extremely low

11
Susceptibility to physical and chemical treatment

• Generally, vibrios are sensitive to cold, and
  seafood can be protective for vibrios at
  refrigeration temperatures
• Thermal processing is a very effective means of
  reducing populations of Vibrio in foods
• The U.S. Food and Drug Administration recommends
  steaming shellstock oysters, clams, and mussels
  for 4 to 9 min at 450oC

12
Susceptibility to physical and chemical treatment

• Frying shucked oysters for 10 min at 375oC or
  baking oysters for 10 min at 450oC
• Thorough heating of shellfish to an internal
  temperature of at least 60oC for several minutes
  should kill pathogenic Vibrios
• High hydrostatic pressure has an additional
  advantage in that the process perfectly shucks
  the oyster

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Susceptibility to physical and chemical treatment

• A large variety of dried spices, the oils of
  several herbs, tomato sauce, and several organic
  acids exhibit bacterial activity
• The process of depuration, in which
  filter-feeding bivalves are purified of certain
  bacteria by pumping bacterium-free water through
  the bivalves tissues, removes Salmonella and
  Escherichia coli, but not Vibrio

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V. cholerae

• V. cholerae O1 causes cholera, one of the few
  foodborne illnesses with epidemic and pandemic
  potential
• Important distinctions within the species are
  made on the basis of production of cholera
  enterotoxin (cholera toxin CT), serogroup, and
  potential for epidemic spread
• Not all V. cholerae strains of the O1 serogroup
  produce CT

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V. cholerae

• Suspected V. cholerae isolates can be cultured on
  a standard series of biochemical media used for
  identification
• DNA probe are useful in distinguishing
  CT-producing strains of V. cholerae through the
  detection of CT (ctx) genes
• V. cholera is part of the normal, free-living
  bacterial flora in estuarine areas
  non-O1/non-O139 strains are much more commonly
  isolated from the environment than are O1
  strains, even in epidemic settings in which fecal
  contamination of environment might be expected

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V. cholerae

• The persistence of V. cholerae within the
  environment may be facilitated by its ability to
  assume survival forms, including a viable but
  nonculturable (VBNC) state
• Long-term carriage of V. cholerae in humans is
  extremely rare and it not important in the
  transmission of disease
• Patients who have not been treated with
  antibiotics may continue to excrete vibrios for 1
  to 2 weeks

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V. cholerae

• Asymptomatic carriers are most commonly
  identified among household members of persons
  with acute illness in various studies, the rate
  of asymptomatic carriage in this group has ranged
  from 4 to almost 22
• The critical role of water in the transmission of
  cholera has been recognized for more than a
  century

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V. cholerae

• The range of food items implicated in the
  transmission of cholera includes crabs, shrimp,
  raw fish, mussels, cockles, squid, oysters,
  clams, rice, raw pork
• When fooodborne outbreaks occur and a number of
  different foods are suspected, foods with an acid
  pH can be eliminated

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V. cholerae

• The explosive, dehydrating diarrhea
  characteristic of cholera actually occurs in only
  a minority of persons infected with CT-producing
  V. cholerae O1/O139
• Most infections with V. cholerae O1 are mild or
  even asymptomatic
• The onset of illness may be sudden, with watery
  diarrhea, or there can be loss of appetite,
  abdominal pain, and simple diarrhea

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V. cholerae

• Initially, the stool is brown with fecal matter,
  but once diarrhea starts, it become a pale gray
  color with a slightly fishy odor
• Mucus in the stool gives the characteristic rice
  water appearance
• vomiting can occur a few hours after the onset
  of diarrhea
• A lower number of bacteria caused illness when
  106 vibrios were given, with food (fish and rice)
  acting as a buffer

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V. cholerae

• Production of CT (and possibly other toxins)
  disrupts ion transport by intestinal epithelial
  cells this leads to the severs diarrhea
  characteristic of cholera with excessive loss of
  water and electrolytes
• V. cholerae produces a variety of extracellular
  products that are harmful to eukaryotic cells
• A number of other virulence factors are involved
  in illness, including colonization factors,
  flagella, LPS, and polysaccharide capsule

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V. parahaemolyticus

• Between 1973 and 1998, a total of 40 outbreaks of
  V. parahaemolyticus infection in the U.S.A. were
  reported to the CDC with gt1000 persons involved
• V. parahaemolyticus are presently 12 O (LPS)
  antigens and 59 K (capsular polysaccharide)
  antigen recognized

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V. parahaemolyticus

• A apecial consideration in the taxonomy of V.
  parahaemolyticus is the ability of certain
  strains to produce a hemolysis, called the TDH,
  or Kanagawa, hemolysin, which is linked to
  virulence in the species
• V. parahaemolyticus occurs naturally in estuarine
  waters throughout the world

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V. parahaemolyticus

• The last source includes at least 30 different
  species, among them clams, oysters, lobster,
  scallops, shrimp, and crab
• Gastroenteritis from V. parahaemolyticus is
  almost exclusively associated with seafood that
  is consumed raw, inadequately cooked, or cooked
  but recontaminated

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V. parahaemolyticus

• V. parahaemolyticus has generation times of 8 to
  9 min at 37oC and 12 to 18 min in seafood hence,
  V. parahaemolyticus has the ability to grow
  rapidly, both in vitrio and in vivo, contributing
  to the infection dose required for illness
• Symptoms may begin 4 to gt30 h after the ingestion
  of contaminated food, with a mean onset time of
  23.6 h

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V. parahaemolyticus

• Primary symptoms include diarrhea and abdominal
  cramps, along with nausea, vomiting, and fever
• The symptoms subside in 3 to 5 days in most
  individuals
• Approximately 105 to 107 CFU is required for
  illness
• The number of V. parahaemolyticus organisms
  present in fish and shellfish are usually no
  greater than 104 cells, suggesting that
  temperature abuse of contaminated food occurs
  prior to consumption

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V. parahaemolyticus

• V. parahaemolyticus possesses at least three
  hemolytic components a thermolabile hemolysin
  gene (tlh), a TDH gene (tdh), and a THD-related
  gene (trh), linked to disease
• Several adhesive factors have been proposed,
  including the outer membrane, lateral flagella,
  and pili and a mannose-resistant, cell-associated
  hemagglutinin

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V. vulnificus

• V. vulnificus is the most serious of the
  pathogenic vibrios in the United States it is
  responsible for 95 of all seafood-borne deaths
• Among the susceptible population at risk for
  infection by this bacterium, primary septicemia
  cases resulting from raw oyster consumption
  typically have fatality rates of 60 it is the
  highest death rate for any foodbrone disease

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V. vulnificus

• The bacterium can produce wound infections in
  addition to gastroenteritis and primary
  septicemias
• Wound infections carry a 20 to 25 fatality rate
  and are also seawater and/or shellfish associated
  
• Surgery is usually required to clean the infected
  tissue

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V. vulnificus

• The isolation of V. vulnificus from blood samples
  is straightforwards, as the bacterium grows
  readily on TCBS, MacConkey, and blood agars
• Isolation from the environment is much more
  difficult

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V. vulnificus

• V. vulnificus is susceptible to freezing,
  low-temperature pasteurization, high hydrostatic
  pressure, and ionizing radiation
• The pathogen can be killed through exposure to
  horseradish-based sauces but they do not kill
  bacteria within the oyster

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V. vulnificus

• V. vulnificus is widespread in estuarine
  environments to location around the world
• The presence of V. vulnificus in water is not
  associated with the present of fecal coliforms
• V. vulnificus is seldom isolated from water or
  oysters when water temperature are low
• In most cases V. vulnificus illness occurs during
  the months of April through October, when the
  water is warmer

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V. vulnificus

• Nearly all cases of V. vulnificus infection
  result from consumption of raw oysters, and most
  of these infections result in primary septicemias
• Symptoms very considerably among cases, with
  onset times ranging from 7 h to several days,
  with a median of 26 h
• Symptoms include fever, chills, nausea, and
  hypotension

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V. vulnificus

• Symptoms typical of gastroenteritis-abdominal
  pain, vomiting, and diarrhea-are not common
• The infectious dose of V. vulnificus is not know
• V. vulnificus is susceptible to most antibiotics

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V. vulnificus

• The polysaccharide capsule, LPS, and a large
  number of extracellular compounds contribute tp
  virulence
• Avirulence strains produce translucent
  acapsular colonies
• Symptoms which occur during V. vulnificus
  septicemia, including fever, tissue edema,
  hemorrhage, and especially the significant
  hypotension, are those classically associated
  with endotoxic shock caused by gram-negative
  bacteria

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