Lecture 7: Gram Negative Bacteria

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Questions and Answers

Which of the following is NOT a clinical manifestation associated with Helicobacter pylori?

Bacteremia (correct)

GERD

Gastritis

Peptic ulcer disease

What is a component of the first-line quadruple therapy for Helicobacter pylori treatment?

Azithromycin

Ciprofloxacin

Doxycycline

Clarithromycin (correct)

Which of the following characteristics is associated with Vibrio species?

Anaerobic growth only

Gram-positive cocci

Facultative anaerobes (correct)

Lactose non-fermenting

What type of agar is used for the growth of Vibrio species?

TCBS agar Signup and view all the answers

What condition is associated with Vibrio vulnificus?

Cellulitis and bacteremia from oyster ingestion Signup and view all the answers

What is the role of the tests used for identifying Enterobacteriaceae?

Rapid identification of the family Signup and view all the answers

Which of the following bacteria is a lactose non-fermenter present in the Enterobacteriaceae family?

Salmonella Signup and view all the answers

What characteristic makes Enteroinvasive E. coli (EIEC) distinct among other E. coli pathotypes?

Is non-motile Signup and view all the answers

Which of the following can be concluded about Escherichia coli regarding UTI?

It is the most common cause of UTI and usually motile. Signup and view all the answers

What is the mechanism by which Enterotoxogenic E. coli (ETEC) causes diarrhea?

ADP ribosylation of Gs leading to an increase in cAMP Signup and view all the answers

What is the primary type of infection caused by typable Haemophilus influenzae (Hib)?

Pneumonia Signup and view all the answers

Which of the following properties correctly describes Campylobacter jejuni?

Motile, curved rod that is microaerophilic Signup and view all the answers

What type of vaccine is used to prevent infections caused by Haemophilus influenzae type b?

Conjugate vaccine Signup and view all the answers

Which test is NOT commonly used to diagnose Haemophilus influenzae infections?

Serum glucose test Signup and view all the answers

What is the recommended dose schedule for the DTaP vaccine?

2, 4, 6, 12-15 months, and booster 4-6 years Signup and view all the answers

What is the primary mechanism by which Neisseria meningitidis evades the immune system?

Forming a polysaccharide capsule Signup and view all the answers

Neisseria gonorrhoeae is most symptomatic in which percentage of males?

90% Signup and view all the answers

Which feature is used to uniquely identify Neisseria meningitidis from Neisseria gonorrhoeae?

Maltose metabolism Signup and view all the answers

What is the most common clinical sign of meningitis caused by Neisseria meningitidis?

Nuchal rigidity Signup and view all the answers

Which of the following treatments is typically used for Neisseria gonorrhoeae infections?

Ceftriaxone and Azithromycin Signup and view all the answers

What type of agar is used for culturing Neisseria meningitidis?

Thayer Martin Agar Signup and view all the answers

Which of the following complications is associated with Neisseria meningitidis infections?

Waterhouse-Friderichsen syndrome Signup and view all the answers

What is a key characteristic of Neisseria gonorrhoeae in terms of its pathogenicity?

Intracellular pathogen Signup and view all the answers

Which serotype of Neisseria meningitidis is the most common and least immunogenic?

Serotype B Signup and view all the answers

How do respiratory droplets relate to the transmission of Neisseria meningitidis?

They facilitate respiratory transmission. Signup and view all the answers

Which organism is a major cause of neonatal meningitis?

Escherichia coli Signup and view all the answers

What characteristic is associated with Klebsiella pneumoniae?

Lactose fermenter Signup and view all the answers

Which pathogen is particularly associated with nosocomial UTIs and catheter septicemia?

Serratia marcescens Signup and view all the answers

What is a key virulence factor of Proteus spp.?

Hydrogen sulfide production Signup and view all the answers

Which statement is true regarding Serratia marcescens?

It produces red pigments known as prodigiocin. Signup and view all the answers

Which condition is NOT commonly associated with Klebsiella pneumoniae?

Hemolytic uremic syndrome Signup and view all the answers

What type of infections is Proteus vulgaris most commonly associated with?

Nosocomial infections Signup and view all the answers

Which characteristic differentiates P. mirabilis from P. vulgaris?

Indole metabolism Signup and view all the answers

What type of toxin does Vibrio cholerae produce that leads to watery diarrhea?

Cholera toxin Signup and view all the answers

Which serotypes of Vibrio cholerae are primarily associated with epidemics?

Serotype O1 and O139 Signup and view all the answers

What clinical manifestation is characteristic of cholera?

Perfuse watery diarrhea Signup and view all the answers

Which of the following statements about the Enterobacteriaceae family is true?

They are facultative anaerobes. Signup and view all the answers

What is the primary treatment for cholera infection?

Fluid replacement and antibiotics Signup and view all the answers

What is the shape of bacteria belonging to the Enterobacteriaceae family?

Rods Signup and view all the answers

What indicates a significant loss of potassium in a cholera patient?

Hypokalemia Signup and view all the answers

Which of the following bacteria within the Enterobacteriaceae family is known to be non-motile?

Shigella Signup and view all the answers

What does the Vi antigen refer to in Salmonella enterica?

Capsular antigen Signup and view all the answers

What does the Enteropluri® Tube specifically identify?

Gram negative rods associated with enteric infections Signup and view all the answers

Study Notes

Medically Important Gram-Negative Bacteria

These bacteria are a diverse group, crucial in various medical contexts.
Learning objectives focus on key characteristics, diseases, and virulence factors.
Neisseria spp. and Moraxella spp. exhibit distinct morphologies, features, and common diseases, also outlining their key virulence factors.
Enterobacteriaceae family members are noted for their differing oxidase and lactose fermentation tests, distinguishing opportunistic from primary pathogens and serological classification (O, H, and K antigens).
Gram-negative organisms like Pseudomonas aeruginosa, Burkholderia cepacia, Acinetobacter baumannii, Vibrio spp., Campylobacter spp., Helicobacter pylori, Haemophilus spp., and Bordetella pertussis each possess specific morphologies, virulence factors, and related illnesses.
These organisms' features and classifications are covered in Murray's Medical Microbiology (9th edition), specifically chapters 23 through 29.

Gram (+ve) and Gram (-ve) Bacteria

Gram-positive bacteria have a thick peptidoglycan layer, while gram-negative bacteria have a thin peptidoglycan layer.
Their contrasting structures affect how antibiotics affect them, leading to differential susceptibility.
Gram-positive cell walls contain lipoteichoic acid and are sensitive to certain antibiotics.
Gram-negative cell walls contain lipopolysaccharides (endotoxins), endotoxins are released when the bacteria die, leading to inflammation and possible shock.

Neisseria species

Bean-shaped gram-negative diplococci (pairs).
Non-spore-forming, intracellular pathogens.
Aerobic, requiring carbon dioxide for optimal growth.
Most are oxidase and catalase positive.
All metabolize glucose, but only N. meningitidis metabolizes specifically maltose.
Neisseria species grow on modified Thayer Martin Agar.

Neisseria meningitidis

Second most common cause of community-acquired meningitis.
Transmitted via respiratory droplets.
Encapsulated, capnophilic (5% CO2).
Metabolizes glucose and maltose.
A significant percentage of humans carry it in their nasopharynx.
Key virulence factors include a polysaccharide capsule and pili for attachment.

Virulence and Pathogenesis of N. meningitidis

Polysaccharide capsule: Antiphagocytic, protecting the bacteria from attack.
Various serotypes (A, C, W-135, Y, B). Serotype B is most common and least immunogenic.
Pili: Attachment to respiratory epithelium.
IgA protease: Colonization of mucosal membranes.
Lipooligosaccharide (LOS) endotoxin: Fever, shock.
Complement deficiency (C6-C9): Increased risk of Nisseria infections.

Clinical Signs and Manifestations of N. meningitidis

Meningitis: Fever, headache, and stiff neck ("nuchal rigidity").
Vomiting is a common symptom.
Complications: Septicemia (Waterhouse-Friderichsen syndrome), Adrenal insufficiency, and Intravascular coagulation.
Diagnosis using Gram stain and culture, or possibly rapid PCR of CSF.

Neisseria gonorrhoeae

Gram-negative diplococci
Intracellular pathogen
Does not metabolize maltose
Fastidious
Symptomatic in 90% of males and 50% of females.
More prevalent in southern U.S. states.
Infections are frequently underreported.
Key virulence factors are pili for attachment and IgA protease to degrade the immune response.

Virulence and Pathogenesis of N. gonorrhoeae

Pili: Attachment, antigenic variation.
Outer membrane proteins: Antigenic variation.
Lipo-oligosaccharide (LOS): Modified endotoxin.
IgA protease: Hydrolyzes secretory IgA.
Invades mucosal surfaces.

Clinical Signs and Manifestations of N. gonorrhoeae

Males: Urethritis with dysuria (painful urination) and purulent discharge.
Females: Endocervicitis, salpingitis, and possible rectal infections in homosexual males.
Some patients with conjunctivitis.
Diagnosis: NAAT (Nucleic Acid Amplification Test) and culture.
Treatment: Ceftriaxone (IM) and Azithromycin (oral).

Gram-Negative Bacilli

Diverse group of gram-negative rod-shaped bacteria.
Key classifications: non-enteric and enteric.
Pseudomonas aeruginosa, Burkholderia cepacia, and Bordetella pertussis are significant non-enteric varieties.
Haemophilus influenzae and Yersinia pestis are facultative anaerobes, important non-enteric bacilli. Specific pathogens are noted as aerobic and facultative anaerobes respectively.

Pseudomonas aeruginosa

Ubiquitous, water-inhabiting gram-negative rod with a flagellum.
Frequent in hospital environments.
Strict aerobe, opportunistic.
Common in cystic fibrosis (CF) patients, leading to pneumonia.
Resistant to multiple antibiotics.
Some factors leading to tissue damage (phospholipase C and Exotoxin A) are discussed.

Acinetobacter baumannii

Gram-negative, aerobic rods.
Common environmental organisms (soil, water, skin), commonly isolated from patients in hospitals.
Rarely causes disease in healthy individuals, but strains in hospital settings are highly drug-resistant.
Can cause multiple infections (Respiratory tract infections, Urinary tract infections, Wound infections, Septicemia)

Burkholderia cepacia

Gram-negative rod.
Can be found in water, soil, and hospital environments.
Opportunistic organism, frequently associated with respiratory infections, particularly in individuals with cystic fibrosis.
Can spread via person-to-person contact, contact with contaminated surfaces, or exposure to Burkholderia in the environment.
Many strains are antibiotic-resistant, posing clinical challenges.

Bordetella pertussis

Human-specific pathogen.
Highly contagious (person-to-person).
Non-motile, encapsulated gram-negative coccobacillus.
Fastidious, requiring specialized media (Bordet-Gengou or Regan-Lowe agar) for growth.
Associated with lymphocytosis – increased levels of white blood cells, and toxins (Adenylate cyclase toxin and Pertussis toxin).

Virulence and Pathogenesis of Bordetella pertussis

Polysaccharide capsule: Antiphagocytic.
Adenylate cyclase toxin: Inhibits phagocytosis.
Tracheal cytotoxin: Destroys ciliated epithelial cells, and induces apoptosis and potentially dermonecrotic lesions.
Pertussis toxin (PT): Increases cAMP levels.
Filamentous hemagglutinins (FHA): Bacterial attachment.

Clinical Signs and Manifestations of Bordetella pertussis

Whooping cough, a specific paroxysmal cough, with periods of intense coughing.
Other symptoms include fever, headache, sneezing, and anorexia.

Management of Bordetella pertussis

Vaccination is the primary method of prevention.
Diphtheria, tetanus, and pertussis vaccines (DTaP) are given in childhood.
Tdap vaccines are recommended for adolescents and adults.

Haemophilus influenzae

Gram-negative, pleomorphic (varying shape) coccobacilli
Strict human pathogen, typically found in the nasopharynx.
Facultative anaerobe

Campylobacter jejuni

Gram-negative curved, rodshaped organism.
Motile (polar flagellum), microaerophilic (needs a lower oxygen concentration).
Common cause of bacterial diarrhea.
Often associated with undercooked poultry.
Virulence factors include adherence factors (that contribute to mucosal attachment), some O-antigens can cross react and result in demyelination.

Helicobacter pylori

Gram-negative, microaerophilic, spiral-shaped bacterium.
Motile (flagella)
Lactose non-fermenter.
Urease positive
Common cause of gastritis and peptic ulcers.
Can potentially lead to chronic/life-long infection if untreated.
Key virulence factors include urease, vacA, and type IV secretion system which neutralize gastric acid and facilitate mucosal colonization & attachment.

Clinical Signs and Manifestations of Helicobacter pylori

H. pylori is associated with various digestive problems.
These include gastritis (inflammation of the stomach lining), peptic ulcers, and potentially gastric adenocarcinoma.

Vibrio cholerae

Gram-negative, curved rods.
Facultative anaerobes.
Single polar flagellum.
Oxidase positive
Human reservoir (colon)
Outbreaks associated with contaminated water.
6 serotypes; only 01 & 0139 related to epidemics.

Virulence and Pathogenesis of Vibrio cholerae

Heat-labile enterotoxin (composed of 6 subunits): ADP-ribosylation of G proteins, leading to increased cAMP levels, resulting in loss of water and electrolytes.

Escherichia coli

Gram-negative, facultative enteric rods.
Most common cause of UTIs and normal intestinal flora.
Motile (some strains).
Doesn't produce H2S, urease -, citrate - and indole + and lactose+. -Numerous pathotypes exist, including enteropathogenic E. coli (EPEC), enterotoxigenic E. coli (ETEC), enterohemorrhagic E. coli (EHEC), and uropathogenic E. coli (UPEC).
Different types are associated with certain diseases (like EHEC causing hemorrhagic colitis and UPEC related to urinary tract infections).

Klebsiella pneumoniae

Gram-negative encapsulated, non-motile rods.
Lactose fermenter.
Common GIT pathogen.
Frequent nosocomial infection (hospital acquired infection).
Patients with medical devices and/or underlying illnesses have a higher risk of infection.
Significant antibiotic resistance (extended-spectrum beta-lactamases, fluoroquinolones, and aminoglycosides, and carbapenems).

Serratia marcescens

Gram-negative, motile rods.
Opportunistic pathogen.
Lactose fermenter; produces red pigments, (such as prodigiosin).
Associated with nosocomial infections, catheter-related septicemia, and burn infections.
Drug resistance is increasing; antibiotic treatment success is decreasing.

Proteus spp.

Gram-negative rods.
Urease positive, lactose non fermenters.
Produce hydrogen sulfide (H₂S).
Important in Struvite stone formation.
Commonly found as normal microbiota in the human GI tract.
P. mirabilis is most common; P. vulgaris are less common, but may be more associated with hospital settings.

Salmonella

Gram-negative motile rods.
Lactose nonfermentative.
H2S production.
Classification of species and varieties is significant (2500 serotypes).
Can cause enteritis, typhoid.
Some serotypes are more commonly associated with gastroenteritis from the consumption of contaminated meals.

Shigella

Gram-negative, non-motile rods.
Lactose nonfermenters
Does not produce H2S.
Humans are the only reservoir, commonly transmitted via the fecal-oral route.
Mainly a disease of infants and young children/school aged children.
Key virulence factors for invasion are the types of toxin and their associated mechanism of action; specifically Shiga toxin and its mechanism of action.

Yersinia enterocolitica

Gram-negative facultative rods.
Motile at 25°C, non-motile at 37°C
Urease +, but does not ferment lactose.
Usually found in colder climates or contaminated meat, milk.
Can cause enterocolitis and post-infectious arthritis.

Yersinia pestis

Gram-negative coccobacilli.
Non motile
Facultative intracellular.
Important zoonotic pathogen (transmitted via fleas.
Plague is a disease that can occur in bubonic, pneumonic, and septicemic forms.
Different cycles of infection are detailed, in both wild and domestic situations.

Enterobacteriaceae Identification

Key tests for identifying members of the Enterobacteriacea family are lactose fermentation, H2S production, motility, and Voges-Proskauer.

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Test your knowledge on clinical manifestations and treatments related to various bacteria, including Helicobacter pylori and Enterobacteriaceae. This quiz covers identification tests, infections, characteristics, and therapies for specific pathogens. Perfect for students in microbiology courses or healthcare professionals looking to refresh their knowledge.