systematic bacteriology 2

Question 1

Enterobacteria?

Answer 1

Enterobacteriaceae is a large family of Gram-negative bacteria
that includes many pathogens responsible for a variety of infections in
humans and animals. They are commonly found in the intestinal tract and can
cause diseases ranging from gastrointestinal infections to systemic infections.

The family Enterobacteriaceae includes several genera, such
as:
* Escherichia (e.g., E. coli)
* Salmonella (e.g., S. typhi)
* Shigella (e.g., S. dysenteriae)
* Klebsiella (e.g., K. pneumoniae)
* Enterobacter (e.g., E. cloacae)
* Serratia (e.g., S. marcescens)
* Proteus (e.g., P. mirabilis)
* Yersinia (e.g., Y. pestis)

Question 2

General characteristics of Enterobacteria:

Answer 2

Gram-negative: Rod-shaped bacteria.
* Facultative anaerobes: Can grow in both the presence and absence of
oxygen.
* Oxidase-negative: Do not produce the enzyme cytochrome oxidase.
* Fermentative metabolism:Capable of fermenting glucose and other
sugars.
* Motility: Some are motile with peritrichous flagella, while others are non
motile.
* Capsule production:Some, like Klebsiella, produce a prominent
polysaccharide capsule.

Question 3

Enterobacterial species frequently
colonize the _________________, especially in
frequently hospitalized or
immunosuppressed individuals

Answer 3

genitourinary
tract and oropharynx

Consequently, the
Enterobacteriaceae are the most
common gram-negative pathogens
isolated in microbiology
laboratories, capable of causing both
community-acquired and nosocomial
infection in virtually every organ
system

Question 3

what is pathobiont?

Answer 3

pathobiont is an organism that is native to the host’s microbiome that
under certain environmental or genetic changes can become pathogenic
and induce disease (potentially pathogenic).

Pathobionts differ from opportunistic pathogens in the sense that they
are normally native to the microbiome, where opportunistic pathogens
are acquired from outside the microbiome

Question 4

What is an opportunistic infection?

Answer 4

opportunistic infection is an infection caused by pathogens (Bacteria,
Fungi, parasites or viruses) that take advantage of an opportunity not
normally available.

Question 4

Pathogenicity: Enterobacteriaceae can cause a
range of infections:

Answer 4

1. Gastrointestinal Infections:
2. Escherichia coli: Can cause diarrhea, urinary tract infections (UTIs),
   and neonatal meningitis. Pathogenic strains include ETEC, EHEC,
   EPEC, and EAEC.
3. Salmonella: Causes gastroenteritis (non-typhoidal Salmonella) and
   typhoid fever (Salmonella typhi and Salmonella paratyphi).
4. Shigella: Causes bacillary dysentery or shigellosis, characterized by
   severe diarrhea with blood and mucus.
5. Respiratory Infections:
6. Klebsiella pneumoniae: Known for causing pneumonia, particularly in
   hospital settings (nosocomial infections), and is associated with high
   antibiotic resistance.
7. Urinary Tract Infections:
8. Proteus mirabilis: Known for causing UTIs and is characterized by its
   ability to produce urease, leading to the formation of kidney stones.
9. Systemic Infections:
10. Yersinia pestis: Causes plague, a severe systemic infection with a high
    mortality rate if untreated.

Question 5

Virulence Factors:

Answer 5

• Endotoxins: Lipopolysaccharides (LPS) in the outer membrane cause a
  strong immune response.
• Exotoxins: Various toxins, such as Shiga toxin from Shigella dysenteriae
  and certain strains of E. coli.
• Adhesins:Surface proteins that enable bacteria to adhere to host cells.
• Capsules: Protect bacteria from phagocytosis.
• Siderophores: Molecules that bind and transport iron into bacterial cells,
  essential for growth.
• Antimicrobial resistance

Question 5

Enterobacteria: Structural and antigenic
Features

Answer 5

• Rod-shaped organisms, generally 1 to 3 μm in length and 0.5 μm in
  diameter, with a genome typically consisting of a single circular
  chromosome, although multiple plasmids may be present in the cytoplasm.

Question 6

Antigenic and pathogenic features of enterobacteria:

Answer 6

Enterobacteriaceae share common antigenic features and pathogenicity factors
that can be correlated with:
* Lipopolysaccharide (LPS) with a common ‘core’ (R antigen), somatic ‘O’
antigen (thermostable) that varies even within the same species (group-specific)
and lipid A with toxic activity (endotoxin)
* Polysaccharide capsule or mucous layer (K antigen; in Salmonellae Vi antigen)
* Flagellar antigens, if present (H antigen, protein-like, thermolabile) K and H antigens
can be expressed or non-expressed (phase variation) contributing to the pathogenesis
(immunoevasion)
* Siderophores for iron sequestration (often a limiting factor for infection)
* Type III secretory systems (‘molecular syringes’ for introducing bacterial proteins
into target cells; encoded by plasmids)
* Drug resistance: some are multi-drug resistant

Question 7

Enterobacteria: pathogenic action (1)

Answer 7

Complex mechanisms: antiphagocytic activity of surface structures (mucous layer
polysaccharides and capsule), adhesiveness (specific fimbriae), endotoxin,
antigenic mimicry, enterotoxins
Enterobacteria can be distinguished based on the mechanism of pathogenic
action into:
* Invasive (intestinal)
Shigellae, Salmonellae, and some types of E. coli produce type III
secretory systems (often encoded by plasmids), ‘molecular syringes’ that
inoculate enterocytes with bacterial proteins that act on the cytoskeleton,
favoring the intracellular encapsulation of the bacterium and its spread to
neighboring cells, with evident histopathological changes and dysenteric-like symptoms
* Non-invasive (intestinal)
some E. coli strains localize in the small intestine (ileum) and elaborate
enterotoxins that act by stimulating the secretory activity of the intestinal mucosa without tissue damage (exclusively diarrhoeic symptoms)

Question 8

Enterobacteria: pathogenic action (2)

Answer 8

Enterobacteria can cause various clinical manifestations distinguishable in:
* Exclusively intestinal infections
(various forms of enteritis or gastroenteritis)
* Infections with extra-intestinal localization
(urinary infections such as cystitis, pyelitis, etc.) generally caused by E. coli and others
* Systemic infections
(typhus and paratyphus) in which involvement of the intestine is accompanied by Spread
of the infection throughout the body by blood and/or lymphatics

Question 9

Habitat and Significance of E.coli:

Answer 9

1)Intestinal Commensal: E. coli is
a common resident in the
intestines of humans and warm
blooded animals. It predominantly
inhabits the large intestine where
it thrives in both aerobic and
anaerobic conditions.
2)Environmental Indicator: The
presence of E. coli in the
environment, particularly in water,
is a key indicator of fecal
contamination. This makes it an
important marker for assessing
water quality and safety

Question 9

• Metabolic Capabilities of E. Coli:

Answer 9

• Nutrient Utilization: E. coli can
  grow using glucose as its sole
  organic source. This characteristic
  is often exploited in laboratory
  cultures.
• Lactose Fermentation: Most E.
  coli strains can ferment lactose,
  which is a key feature used in
  microbiological media like
  MacConkey agar to differentiate
  them from non-lactose fermenting
  bacteria. However, it’s important
  to note that some E. coli strains
  lack this ability.

Question 10

Serotypes of E. Coli:

Answer 10

• Antigenic Diversity: E. coli can be
  classified into numerous serotypes
  based on its surface antigens. The
  classification involves:
• O Antigens: These define the
  serogroup.
• K Antigens: These are
  capsular antigens.
• H Antigens: These are flagellar
  antigens.
• This antigenic diversity helps in
  identifying and tracking different E.
  coli strains, especially in clinical
  diagnostics and epidemiological
  studies.

Question 10

Beyond diarrheal illness, _________ has the capability to cause extraintestinal
disease, including infection of the peritoneum, liver, and biliary system

Answer 10

E. coli

Furthermore, E. coli is the single most common cause of urinary tract infection
(UTI) and a major pathogen causing meningitis, septicemia, pneumonia,
cellulitisand even bone and joint infection.

Question 11

E. Coli main pathological pictures features:

Answer 11

1. Endogenous urinary tract infections: from many serotypes, particularly those with P or PAP fimbriae
2. intestinal (exogenous) infections of animal origin (mainly cattle)
   a) EPEC and ETEC strains localize to the small intestine causing diarrheal enteritis through direct action on mucous epithelia (EPEC strains, destruction of microvilli) or through the production of enterotoxins with choleric-like effects (ETEC strains)
   b) EIEC and EHEC or VTEC strains localize in the large intestine and cause dysenteric enteritis either by mucosal invasion (EIEC) or by production of enterotoxins (true or Shiga-like); EHEC infections can be complicated by hemorrhagic colitis, hemolytic uremic syndrome and signs of nerve impairment
3. E. Coli is the most frequent agent of neonatal meningitis from strains carrying the K1 capsular antigen
4. Occasionally, alone or in association with others, E. Coli may cause (endogenous) infections of the abdominal (biliary tract, ileocaecal appendix, peritoneum) or respiratory region

Question 12

UPEC (uropathogenic E. coli) frequently cause:

Answer 12

urinary infections, pathogenicity related to specific adhesins (pilli P, binding to bladder and urinary tract lining cells) and production of hemolysis and necrotising cytotoxic toxin (CNF-1)

Question 12

NMEC (neonatal meningitis E. Coli) causes:

Answer 12

Neonatal meningitis

Question 13

E.coli: strain with enteric activity (enteritis)
This strains produce adhesins and enterotoxins closely related to specific
pathology:

Answer 13

• EPEC (enteropathogenic) strains are the main cause of diarrhea in
  children
• Pathogenicity due to direct or indirect damage of the enterocytes (due to
  inflammatory phenomena of the intestinal mucosa), caused by a peculiar
  localized adhesiveness linked to the presence of an adhesion factor (‘EPEC
  adherence factor’, EAF) consisting of an outer membrane protein encoded
  by a plasmid
• The bacteria adhere tightly to the membrane of enterocytes with signs of
  damage at contact points and destruction of the microvilli of the intestinal
  mucosal epithelial cells without apparent invasiveness
• Clinical manifestations include fever, vomiting, nausea, diarrhea with
  mucus
• Diffuse-adhering strains (DAEC) would exhibit increased adhesiveness

Question 14

Traveler’s diarrhea:

Answer 14

Traveler’s diarrhea is given by the enterotoxigenic (ETEC) and enteroaggregative (EAEC)
strains of E. coli. The symptomatology is very important for water diarrhea, vomiting, cramps, nausea, fever, and hydro-saline depletion caused by the diarrhea. It’s the most important diarrhea in undeveloped countries, where can be potentially lethal. The virulence factors implicated in
this kind of diarrhea are enterotoxins LT and ST, heat-labile or heat stable, encoded by plasmid genes.

Question 15

The Enterohaemorrhagic strains (EHEC):

Answer 15

mainly belong to the O157:H7 serotype and they
produce by lysogenic conversion two potent toxins: SLT1 and SLT2. SLT1 is similar to the
toxin produced by Shigella dysenteriae (Dysenteriae toxin), but they differ for some antigens.
These strains can also go to the blood, giving bloodstream infections or reach the CNS and
kidneys. They can cause hemolytic uremic syndrome (HUS), very serious complication
characterized by acute renal failure, microangiopathic hemolytic anaemia and
thrombocytopenia, especially in children.

Question 15

E. coli therapy for enteritogenic strains :

Answer 15

The exogenous strains are normally transmitted through contaminated food and water. The most important therapeutic approach is to restore the electrolyte balance.
Normally it is not necessary to use antibiotics, only necessary in sepsis clinical manifestation
or in uremic-hemolytic syndrome caused by EHEC strains

Question 16

SHIGELLE:

Answer 16

Shigella is not a colonizer of our intestine, it’s a real pathogen. We use somatic antigens to differentiate the 4 different species of these genera: Shigella dysenteriae, S. flexneri, S. boydii and S. Sonnei. Humans and primates are
the unique hosts of these bacteria that are always pathogenic. They are the etiological agents of bacillary dysentery, characterized by a short incubation period (from a few hours to a few days) and the symptomatology is particular since it’s characterized by violent vomiting and
mucus-sanguineous diarrhea. It gives fever, abdominal pain, tenesmus, and also headache.

Question 17

Invasion by Shigella

Answer 17

All the species are able to invade epithelial cells of our intestine and the specific target is enterocytes. It always produces necrosis. It’s the most potent producer of Shiga toxin that can be produced in different quantities. Shigella invades the intestine attaching the end part of the
cell, a protein on the surface of our enterocytes, and then the bacteria can be introduced in the cell by a vacuole. Shigella blocks the formation of the vacuole and starts multiplying itself in the cytoplasm of the cell inducing necrosis. It also passes to the other enterocytes giving diffused necrosis of the intestinal mucosa. It doesn’t pass the lamina propria

Question 18

Bacillary dysentery

Answer 18

The disease is contracted by ingestion of contaminated food or drinks. It’s a human pathogen so food is contaminated with feces of sick people or healthy carriers. These bacteria are highly infectious so it takes a few bacterial cells to cause infection. They localize at the level of colon mucosa, they don’t spread to the bloodstream.
The mechanism of pathogenicity is the production of endotoxin, in particular of type 1 toxin in the case of S. dysenteriae and S. flexneri, similar to the toxin produced by E. coli. It’s always
transmitted through food/water contaminated with human feces. It’s a real problem in developed countries with high sewage pollution.

Question 19

SALMONELLAE

Answer 19

Another pathogen of this family is Salmonellae. The name comes from the pathologist Salmon
who was the first one to isolate this bacteria, in particular Salmonella choleraesuis, from the
porcine intestine. Sometimes they are commensal of animal intestines, including domestic
mammals, reptiles, birds and insects. Some serotypes like Salmonella enterica Typhi and
Paratyphi are real pathogens for humans, they have adapted to humans and have no other known natural hosts. Other salmonella like salmonella typhimurium have a broad host range and can infect many animals including reptiles and turtles.
The spread of these bacteria in the environment is one of the causes of the spreading of the infection in humans and cause of outbreaks. There are many outbreaks mediated by water
contamited with these bacteria ( water used for agriculture). For instance, there were outbreaks in the USA caused by cantaloupe or tomatoes cultivated with contaminated water, since they can internalize salmonealle and give the pathology after ingestion.

Question 19

Salmonella epidemiology

Answer 19

Salmonella is the main cause of food infections. The infection begins with the ingestion of bacteria. It depends on the temperature of food and water. The reservoirs are usually human or animal intestines. The infection dose depends on the virulent factors of these bacteria but it’s generally higher than Shigella. The transmission can be human-to-human by direct contact with stools (fecal-oral route) or through contact with bacteria found in contaminated food or drinks. One barrier is the chloric acid of our stomach and people that use antacids are more exposed to this infection. The highest rates of infection are in children under 5 years of age, and people older than 70. It’s the most common cause of outbreaks in the community

Question 20

Salmonellae characteristics

Answer 20

They are not different from other gram-negative bacteria we have already seen. They are gram-negative, non-spore-forming, facultatively anaerobic bacilli with a size comparable to that of other bacteria. They produce acid on glucose fermentation, they can reduce nitrates without the production of cytochrome oxidase. Usually, they don’t ferment lactose but a few strains can (1%), so we can’t use McConkey agar as media. The hydrogen sulfite production gives us the possibility to identify salmonella on a media called Bismuth sulfite agar which contains an indicator susceptible to the metabolization of thiosulfate, used to produce hydrogen sulfide, that gives the capacity to the bacteria to form black colonies, very easy to identify.
The genus Salmonella comprises many serotypes, we know more than 2000 serovars, based on antigenic characteristics: somatic-lipopolysaccharide antigen (O antigen or somatic antigen), capsular antigen (K antigen or Vi antigen-specific of S. thypi) and flagellar antigen (H antigen, phase I or II). Salmonella has many pili, in particular, type 1 pilus, though which it binds to endothelial cells of our intestine thanks to the D-mannose receptor (used also by E. coli). The genus Salmonella is widely distributed in the gut microbiota of animals, so it could be commensal, but not in humans. The spread between animals and humans is the reason why we have the outbreaks and the disease. Some serotypes like S. typhi and S. paratyphi, have adapted to humans that are now the only hosts

Question 21

Pathogenesis of Salmonella

Answer 21

Ingested salmonella go to the intestinal mucosa. We need a high degree of contamination to go over the acidic environment of our stomach and go to the intestinal mucosa. They reach also the small bowel where they compete with the normal microbes to adhere to our
intestinal cells. There’s an interaction with enterocytes, M-cells, or columnar epithelial cells, perhaps mediated by pili of the bacteria, that determines the adherence to intestinal cells transforming the membrane of cells in ruffles that favor the introduction of these cells into vacuoles that lead to infection. It passes from the apical surface of the enterocytes to the basolateral membrane and multiplies in the vacuole and enters the lamina propria, inducing inflammation.
The difference between Salmonella and Shigella is in this characteristic: salmonella goes to the lamina propria, where it replicates and it also goes to lymph nodes causing inflammation in other organs. Salmonella is very commonly found in blood cultures when there is an
important infection. The same doesn’t happen for Shigella, limited to the intestinal mucosa. Salmonella produces also enterotoxin, leading to an invasive infection.

Question 22

Clinical manifestations of salmonella

Answer 22

The clinical manifestation goes from simple gastroenteritis to systematic salmonellosis. With minor salmonellosis, the symptomatology involves tenesmus, diarrhea, and sometimes with vomiting manifestations. Some salmonella as S. Typhi and paratyphoid, are involved in
systemic salmonellosis that gives fever as the main manifestation, not diarrhea.
The degree of infection depends also on the immunological competence of the host: in immunocompromised patients, children, and old people gastroenteritis can manifest with severe symptoms. The worst one is S, typhi which can present with abdominal typhus or typhoid fever.

Question 23

Typhoid fever:

Answer 23

is a human infection caused by S. Typhi.
An important indicator is the fever, since it’s particularly high in this disease (40°C). There’s a high probability of finding the bacteria in the blood and before that in the
stools. It’s not so common to find it in the stool at the beginning of the fever. We use also some serological systems to identify the infection, by looking at the agglutinating antibodies in the serum of patients

Question 23

OTHER ENTEROBACTERIA

Answer 23

Other enterobacteria considered opportunistic pathogens are Erwinia, Cedecea, Kluyvera and
Tatumella. Many of them are opportunistic pathogens and can be isolated in human biological materials, they can colonize and start to be pathogens in different organs, but they don’t have a specific route of pathogenicity. We normally look at the antibiotic sensitivity of enterobacteria because they easily uptake plasmids with antibiotic resistance so it’s easy to find resistance in these bacteria.

Question 24

Immunization methods for Salmonella:

Answer 24

For Salmonella it’s possible to have an immunization vaccination with alive attenuated
bacteria of S. typhi strain TY-21 administered by os.

Question 24

KLEBSIELLA PNEUMONIAE

Answer 24

Klebsiella pneumonia is the second most common enterobacteria
involved in human infections like abscesses, pneumonia, urinary tract infections, etc. The characteristic of these bacteria is that they are capsulated gram-negative, and really slimy, giving the impression of mucous on isolated culture plates. Highly mucoid Klebsiella
pneumonia bearing K1 or K2 capsules has been associated with several clinical syndromes featuring liver abscesses and endophthalmitis, particularly in Southeast Asian countries (found also in Italy in microbiology labs). It’s one of the most important multidrug-resistant bacteria and a concern of WHO since these gram-negative bacilli easily uptake plasmids from the environment and introduce antimicrobial resistance systems in their genome, becoming resistant to many antimicrobial drugs as penicillin, beta-lactams, etc.
A K. Pneumonia clone called Type 258 is involved in a pan-resistant outbreak in the whole world.

Question 25

YERSINIA

Answer 25

Looking at other enterobacteria, we can find the Yersinia genus. Yersinia is an enterobacteria, coccobacillus gram-negative which is specific because the color of the gram-negative
remains at the polar part of the cell, giving color to just that part. Growth and metabolic characteristics are similar to other enterobacteria, but they prefer to grow at temperatures lower
than 37°C. We know 11 species of the genus Yersinia, but only 3 species are pathogenic for humans: Yersinia pestis, Yersinia pseudotuberculosis, and Yersinia enterocolitica. Yersinia pseudotuberculosis and Yersinia enterocolitis have multiple serotypes, always identified by the different somatic and flagellar antigens, while Yersinia pestis is antigenically homogenous, it has only one serotype. Yersinia pestis is immobile, it doesn’t have flagellum or pilis that give a high degree of motility; it grows well on enriched media as blood agar at 25-28°C. The preferred host is the rat intestine. The infection is transmitted by hematophagous
ectoparasites, Xenopsilla cheopis, which infect rats and can infect humans by ingesting blood from infected animals. It introduces the bacillus from the bite of these ectoparasites and leads to the introduction of these bacteria into human blood.

Question 26

Y. Pestis virulence factors

Answer 26

The virulence factors of Y. Pestis constitute one of the most complex pathogenicity
apparatuses detected among bacteria. They are encoded by 3 plasmids: Plasmid pYV or pCD1, called also virulon, activated in the host at 37°C in eukaryotic cells. Then it produces a secretory enzyme, Yersinia secretion, that together with the yersinia outer membrane proteins contributes to the necrosis of the cells inducing some pores on the bacterial membrane. Plasmid pFra or pMT1 contains genes coding for a protein called Fraction 1 that forms the capsule of the bacterium that has an antiphagocytic action, and for the so-called murine toxin, a phospholipase D that appears to have an essential role in the colonization of the vector insect. Plasmid pPst or pPCP1 encodes a protein present on the bacterium’s outer membrane that has a protease activity acting as a plasminogen activator, the cause of blood clotting, and enhances the spread of the bacterium in the host.

Question 27

Plague

Answer 27

The incubation of plague, a very important disease present in some areas of the world, is very short (2-7 days). We can distinguish between 3 clinical forms:
* Bubonic plague: limited to the proliferation of bacterium in the lymph nodes near the bite of the parasites. It results in necrosis of lymph nodes. If left untreated, it evolves into septicemia and secondary pneumonia.
* Pneumonic plague: is a fatal disease in less than 4 days. It can also be air-borne: the bacteria can be introduced in our respiratory tract, causing primary pneumonia
* Septicemic plague: it is rare but lethal Plague is one of the most serious calamity of human beings. Now we have only a few places in the world where there are sporadic outbreaks, like in North and South America, and Africa. It’s treated with antibiotics to limit the spread to other countries. The bacteria in neutrophils can
survive thanks to their capsule with antiphagocytic properties so that the lysis of the phagosome
doesn’t happen.

Question 27

Y. Pestis: drug susceptibility and prophylaxis

Answer 27

Y. Pestis is always sensitive to antibiotics, so it can be easily traded with aminoglycosides, tetracyclines, and sulfonamides. The first way to control this plague is through prophylaxis, by controlling infected rodents, and by checking if the bacteria can pass from the rodents to rats.

Question 28

Yersinia pseudotubercolosis

Answer 28

Yersinia pseudotuberculosis is different from Y. Pestis due to the presence of peritrichous or para-polar flagella that give mobility. It ferments sugars without gas production, it has intense urease activity and it’s the etiological agent of micro-abscesses lesions (like liver and spleen)
and can cause very severe septicemia in debilitated hosts. Normally humans can be infected through direct contact with infected animals, in particular mice, guinea pigs, or cats, or by ingesting food contaminated with infected animal feces.

Question 28

Yersinia enterolitica

Answer 28

We can differentiate Y. Pseudotubercolosis and Y. Enterolitica by looking at subgroups
responsible for outbreaks and by looking at the somatic and flagellar antigens. In our lab, we use an easy and modern system to identify this genre of bacteria that is Maldi-toff. Y. Enterocolotica can cause mesenteric adenitis which is a particular syndrome that manifests with fever, and abdominal pain and sometimes can mimic appendicitis but it’s an abdominal infection caused by the passage of Y. Enterocolitica through the mesenteric lymph nodes. It gives also enteritis with dysenteric symptoms and intense diarrhea, especially in children. It’s also very common to have polyarthritis manifestation by the production of an enterotoxin similar to Escherichia coli toxin.

Question 29

Curved Gram- Negative Bacteria:
Vibrio - campylobacter and helicobacter

Answer 29

Other gram-negative enterobacteria relevant in pathology are Vibrio
campylobacter and helicobacter. They are studied together since they are
called curved bacteria, characterized by a helicoidal shape. They are motile
since they have super-efficient flagella that give them a high degree of motility.
The most important vibrio is Vibrio cholerae; of campylobacter genera, we
know campylobacter jejuni and among helicobacter, helicobacter pylori.
Vibrio are curved on their major axis, having a C-shaped structure. They are
mobile, with a single polar flagellum, they are asporigens and non-capsulated. Vibrio prefers alkaline medium to grow, so our stomach is not a good environment for them. To give diseases we have to ingest a high degree of bacteria. Vibrio cholerae is the
most important species in human pathology, but other
species of these genera are also known in human diseases such as V. parahaemolyticus, V. alginolyticus and V. vulnificus. They are more common than cholerae now and they are correlated to ingestion of contaminated food or water.
This table shows the Vibrio families: they are very similar to each other, but they manifest in different ways. With Vibrio cholerae you have watery diarrhea that can be present also in other bacteria like V. Parahaemolyticus and V. vulnificus in which the symptomatology is moderate compared to V. Cholerae.

Question 29

VIBRIO CHOLERAE

Answer 29

Vibrio cholerae is a pathogen that is identified in many subtypes correlated by the characteristics of the somatic antigen. All strains can produce an enterotoxin that has high power over our enterocytes to give watery diarrhea. The main important serogroups involved in outbreaks are O1 and O139 which are the only ones responsible for cholera epidemics in the world. In the O1 group, we can distinguish between 3 serological types called Inaba, Ogawa, and Hikojima which have some different biological characteristics. The serogroup O139 is called the El Tor biotype. This scheme shows the genera vibrio and the serogroups important in human pathology. Other species involved in human pathology are V. Parahaemolyticus, vulnificus and alginolyticus.

Question 29

V. cholerae epidemiology

Answer 29

The epidemiology is correlated to the ingestion of contaminated water. The incubation period is very short: in 2 days you can manifest clinical symptoms. It’s very easy to transform a single case into an outbreak, under poor sanitary conditions. It’s endemic in some continents like India and Africa where you can always have little outbreaks of this disease. The first outbreak in the Western Hemisphere was in 1911. Every 5-7 years there’s an outbreak in the world; the last one was El Tor outbreak in East Africa in 2015-2016. The resistance of V. cholerae in the environment is due to its capacity to survive in biofilm form on shellfish and plankton by attaching to their exoskeleton. The biofilm form is a quiescent
form that allows the persistence of the bacteria. In other forms the bacteria is really fragile so it can’t survive in the environment.

Question 30

V. cholerae mechanism of pathogenic action

Answer 30

The mechanism of pathogenic action is first of all the ingestion of food or water (uncooked seafood) contaminated with fecal material, sometimes of human
origin. There’s clinical manifestation after 2-3 days and it remains in the host for 3-4 weeks after recovery. It multiplies
on the intestinal mucosa, with an adhesion that allows the bacteria to penetrate the cells without transforming the
enterocytes, but with the production of exoenzymes that activate adenylate cyclase which starts to exclude, in an
osmotic way, from the cell chlorine, potassium, and sodium giving watery diarrhea. The toxin of cholera is a complex polymer of proteins that attach to membrane cells and activate its active part, the A1, which starts to activate adenylate cyclase that extrudes the ions from the cells giving watery diarrhea.

Question 31

V. cholerae clinical manifestation

Answer 31

Cholera has a rapid onset, with abdominal fullness and discomfort, rushes of peristalsis, and loose stools. It’s characterized by the emission of very large quantities of watery feces, up to 10-14 liters per day, which is the reason why the lethality is due to dehydration of the patient. There’s no trace of blood or mucous in the tools, which are symptoms typical of Shigelle and of the E. coli enterotoxin

Question 32

Diagnosis of V. Cholera associated infections:

Answer 32

The diagnosis is based on suspicion of infection. Bacteriologic diagnosis is accomplished by isolation of V. cholerae from the stools, in the lab, through the use of a particular media that contains thiosulfate-citrate-bile salt-sucrose, the TCBS agar, that gives the correct organic
support for vibrio to grow and it gives yellow colonies on a green background that makes it easier to recognize and identify.

Question 33

Treatment of V. Cholera associated infections:

Answer 33

V. Cholerae are sensitive to a broad spectrum of antibacterial drugs like tetracyclines, chloramphenicol, sulphonamides, etc. However the first line of therapy is the rehydration of the patient. After that, the infection could be self-limited spontaneously.
There are many immunization methods used for people who travel to endemic countries. The most used are oral vaccines with low pathogenic serotypes of virions.

Question 34

V. PARAHAEMOLYTICUS, V. ALGINOLYTICUS AND V. VULNIFICUS

Answer 34

V. parahaemolyticus is a marine micro-organism that causes a less severe form of diarrhea and mild intestinal symptoms, resulting from ingestion of raw shellfish or crustaceans colonized by these bacilli. It produces thermostable hemolysin, lethal to guinea pigs and mice. It also produces thermolabile hemolysin. It occasionally infects wounds of people bathing in
contaminated water.

Question 34

CAMPYLOBACTER

Answer 34

Campylobacter is another type of gram-negative enterobacteria. It’s a quite recent pathogen (1970), as the cause of the serological agent of avian meat. It colonizes the intestines of avians, so it’s often found in avian farming. They are gram-negative rods, curved and helicoidal. They grow in microaerophilic environments, rich in oxygen. They have polar flagella that give them a S shape and seagull appearance under the microscope. They infect animals and could be the cause of cattle and sheep abortion. Sometimes they can infect humans via the fecal-oral route. The most important campylobacters involved in human pathology are campylobacter jejuni and campylobacter coli. They grow in rich media.

Question 35

Campylobacter jejuni

Answer 35

Campylobacter jejuni is the second most common etiological agent of diarrhea in humans together with
salmonella. It has many virulence factors as LPS antigens on the membrane and capsule. There are minor relevant species, but in humans, we can find most commonly only jejuni and coli

Question 36

HELICOBACTER

Answer 36

Helicobacter is the last enterobacteria we look at today. It’s a recently recognized pathogen because it was discovered in the 1970s. It’s found in the gastric mucosa of many mammals and humans. It colonizes the intestines of 1/3 of humans in the world. There are different species
involved in axial disease. For people, the most important species is helicobacter pylori, the cause of gastritis.

Question 37

Helicobacter pylori

Answer 37

It has a similar morphology to campylobacter. It likes microaerophilic environments. It’s oxidase and catalase positive. It has 5-6 polar flagella that give the ability to have adherence capacity to our mucosa. It has high ureic activity as a virulence factor that allows the organism to survive in low pH environmental conditions, like our gastric environments, by the generation of ammonia that allows us to recognize it more easily (ammonia in the breath of patients). The urease is produced in amounts so great that its action can be demonstrated within minutes of placing H pylori in the presence of urea.
It’s present in the stomach of 30-50% of adults in developed countries. The mode of
transmission is not well known, but it’s presumed to be person to person by the fecal-oral route or by contact with gastric secretions. It’s the etiological agent of gastritis, gastric ulcers, and duodenal ulcers. It causes these diseases thanks to a virulence factor called Cag+ which is also responsible for some gastric adenocarcinoma. It’s also linked to a gastric mucosa-associated lymphoid tissue lymphoma called MALT, which is not so common.

Question 37

H. pylori pathogenicity

Answer 37

The motility provided by the flagella allows the organisms to go to the gastric mucosa and adhere, and multiply on the surface of the cells. It produces exotoxins like vacuolating cytotoxin (VacA) that cause apoptosis in gastric cells by inducing necrosis. This is an electron microscopy image in which we can see how
the bacteria can adhere to the surface of our gastric cells and penetrate the cells. After penetrating the surface of gastric
mucous it causes the necrosis and apoptosis of the cells

Question 38

Diagnosis of H. pylori?

Answer 38

The diagnosis is achieved through endoscopic examination, with biopsy and culture of the gastric mucosa to see the presence of Helicobacter. It needs a very particular environment to
grow, so the main methods of diagnosis are serology, urea breath test, and by looking at the antigen present on the stools.

Question 39

Treatment of H. pylori?

Answer 39

The treatment is very long, with a combination of more than 4 different antibiotics together like tetracycline, metronidazole, and a protein pump inhibitor like omeprazole, and bismuth subsalicylate that contribute to the reduction of gastric acid symptoms. The treatment must be at least 2 weeks long and it may be difficult for some patients to tolerate