Gram Negative Bacteria section provides High Yield Information needed for USMLE, COMLEX, Medical School, Residency, and as a practicing Physician.
Table Of Contents
LadyofHats / Public domain
Graevemoore at English Wikipedia / CC BY-SA
Gram Negative Cocci
Neisseria Species
- Features:
- Oxidase positive
- Gram Neg
- Diplococci
- Grows on Chocolate Agar, inhibited on blood agar.
- VPN special agar enriched with vancomycin, polymixin, and nystatin
- Thayer martin AKA VPN agar SELECTIVE AGAR
- MAC Deficiency; unable to form the MAC complex due to complex c5-c9 being inhibited
- c5-c9 MAC Deficiency
- Virulence Factors:
- Pilli allows attachment to surfaces and display antigenic variation
- IgA protease cleaves IGA at its hinge point, facilitates survival along mucosal surfaces
- Types:
Neisseria Gonorrhea
- Features:
- Gram negative diplococci
- Oxidase positive
- Chocolate agar and Thayer martin agar cultures
- Complement deficiency of C5-9–> increase susceptibility
- Glucose fermenter
- Virulence factors: Pilus and IgA protease
- Sexually transmitted infection
- Facultative Intracellular
- Causes:
- STI- genitalia of men and women
- Purulent discharge: thick (thicker than chlamydia)
- Men: prostatitis, orchitis, urethritis
- Women- ascends–> PID
- Can cause Fitz Hugh Curtis syndrome if spreads to peritoneum
- Polyarthritis
- Congential infection
- If pregnant mother is untreated–> transfer of infection to newborn during delivery
- Purulent conjunctivitis – first 5 days of life
- STI- genitalia of men and women
- Treatment:
- DOC Ceftriaxone
- Co-infection of Chlamydia: Macrolide: Azithromycin or Doxycycline
Neisseria meningitides
- Feature:
- Gram negative diplococci
- Oxidase positive
- Encapsulated
- Chocolate agar and Thayer martin agar cultures
- Glucose fermenter AND maltose
- Virulence factors:
- Pilus and IgA protease
- Spread:
- In close quarters by respiratory droplets- Colonizes in nasopharynx
- Increased susceptibility in:
- Complement Deficiency of C5-9
- Sickle Cell disease patients
- Causes:
- Meningitis with petechial rash
- Waterhouse Friderichsen Syndrome destruction of adrenals due to vasoconstriction caused by hypovolemia
- Treatment:
- Ceftriaxone
- Prophylaxis:
- Rifampin
Gram Negative Rods
E coli
- Features:
- Gram-negative rod
- Lactose fermenter
- Encapsulated
- Catalase positive
- Fimbriae – pili to cause UTI
- Causes:
- UTI- most common cause
- Gram-negative sepsis
- Neonatal meningitis
- EHEC: O157H7
- Transmission by eating undercooked meat
- Bloody diarrhea
- Can cause HUS- Shiga like toxin
- Shiga-like toxin:
- ETEC: Traveler’s diarrhea
- Transmission via water source
- Recent travel usually to Mexico
- Heat-labile and stable toxins
- Watery diarrhea
- Heat-Labile Toxin:
- Heat-Stable Toxin:
Klebsiella
.jpg)
- Features:
- Gram negative rod
- Immotile
- Encapsulated
- Nosocomial infection
- Clinical Feature:
- Currant Jelly Sputum
- Cavitary lesions on CXR- may be mistaken for TB
- Causes:
- Pneumonia and UTI
- Multi-drug resistant
- 3 A’s of Klebsiella
- Alcoholics commonly affected
- Abscess commonly produced
- Aspiration commonly started
- Treatment:
- Carbapenem
Enterobacter
Serratia
Salmonella
- Features:
- Gram negative rod
- Motile
- H2S positive – enteric bacteria
- Encapsulated
- Acid labile – easily degraded in stomach acid
- Types:
- – Salmonella Typhi
- In gallbladder of chronic carriers
- Red macules/rose spots in abdomen
- Typhoid fever- constipation and diarrhea/pea soup
- – Salmonella Enteritidis
- Eating undercooked chicken
- Inflammatory diarrhea
- – Salmonella Typhi
- Treatment:
- Fluoroquinolone or Ciprofloxacin
- Live attenuated vaccine
Shigella
Centers for Disease Control and Prevention Publich Health Image Library, Public domain, via Wikimedia Commons
- Features:
- Gram negative rod
- Acid stable
- Facultative intracellular
- Path:
- Invades lymphoid tissue and enterocytes surrounding M cells–> damage tissues and release cytokines that produce immune response
- Shiga Toxin:
- Causes:
- Gastroenteritis –> Bloody diarrhea
- Leukocytosis
- Children: HUS: prodromal diarrhea and signs of acute renal failure
Gram negative rod with bipolar staining
Yersinia Enterocolitica
- Features:
- Gram negative rod with bipolar staining -safety pin appearance
- Encapsulated
- Transmission via puppy feces or contaminated milk products
- Resistant to cold temperatures
- Commonly infected: Toddlers
- Causes:
- Bloody diarrhea
- Systemic effects: Fever, Leukocytosis, and Abscesses
- Infection of abdomen can lead to:
- Intestinal perforation
- Intussusception
- Paralytic Ileus
- Necrotic small bowel
- RARE
- May mimic appendicitis
Yersinia Pestis
Campylobacter Jejuni
Vibrio
- Features:
- Endemic to developing countries
- Gram-negative rod, Comma shaped
- Acid stable
- oxidase-positive
- Cholera Toxin:
- Types:
- Vibrio cholera, parahaemolyticus, vulnificus
- Vibrio parahaemolyticus and vulnificus contaminate seafood- especially oysters
- Transmission:
- Fecal oral
- Causes:
- Profuse/rice water diarrhea 10-20L/day
- Treatment:
- Oral hydration therapy with electrolytes
Helicobacter
- Features:
- Gram negative helical shape
- Motile- flagella
- Urease positive
- Oxidase positive
- Found in pylorus and antrum
- Causes:
- Ulcers
- >95% duodenal
- Untreated ulcers–> increase risk for adenocarcinoma of stomach/MALToma
- Screening test:
- Urea breath test
- Biopsy during endoscopy
- Treatment
- Triple therapy
- PPI, Amoxicillin, Macrolide- clarithromycin
- Triple therapy
Pseudomonas
- Features:
- Gram negative rod
- Encapsulated
- Oxidase positive
- Catalase positive
- Obligate aerobe
- Turns blue when plated
- Produces fruity grape like odor
- Thrives in aquatic environments
- Exotoxin A:
- Causes:
- “Hot tub folliculitis”
- Gram negative nosocomial pneumonia #1
- Pulmonary infection
- Cystic fibrosis
- Most common cause of respiratory failure in cystic fibrosis in patients
- Osteomyelitis
- Feared infection on burn patients
- Associated with nosocomial UTI
- Skin lesions: pruritic papular pustular folliculitis and cutaneous necrosis- ecthyma gangrenosum
- Otitis externa- swimmer’s ear
- Treatment:
- Antipseudomonal penicillin: piperacillin and tazobactam
- Aminoglycosides
- Fluoroquinolones
Proteus Mirabilis
Bordetella Pertussis
- Features:
- Gram-negative
- Virulence factors and toxins
- Pertussis Toxin:
- Transmission:
- Highly contagious via respiratory droplets
- Causes:
- Whooping cough:
- Nonspecific catarrhal phase 1-2 weeks
- Paroxysmal stage: 2 wks – 2 mos: Characteristic Whooping cough
- Convalescence stage- up to 3 mos
- “100” day cough
- Whooping cough:
- Treatment:
- Macrolides
- To remove bordetella from the respiratory tract
- Macrolides
- Prevention:
- Acellular: purified antigens: DTaP
Haemophilus Influenzae
- Features:
- Gram negative coccobaciliary
- Needs chocolate agar to grow
- Transmission:
- Aerosol droplets
- Causes:
- Pneumonia
- Epiglottitis
- Inflamed epiglottis, inspiratory stridor, drooling – commonly seen in children
- Otitis media
- Meningitis- specifically type B
- Sepsis- common in patients with no spleens
- Septic arthritis
- Vaccine:
- Specific type of capsular antigen- type B
- Polysaccharide of capsule conjugated to diphtheria toxoid –> strong IgG response
- Vaccinate at 2-18 months
- Specific type of capsular antigen- type B
- Treatment:
- Beta lactam
- Ceftriaxone: for meningitis or systemic disease
- Prophylaxis:
- Rifampin
Legionella
- Features:
- Gram negative
- Oxidase positive
- Silver stain to visualize
- Clinical presentation:
- Pneumonia associated with hyponatremia
- Neurologic symptoms
- Diarrhea
- High fever
- Causes:
- Legionnaire’s disease
- Potentially fatal, occurs in smokers
- Atypical pneumonia
- CXR patchy infiltrate with consolidation of one lobe
- Definitive diagnosis:
- Culture sputum
- Treatment:
- Macrolides
- Fluoroquinolones- fewer complications
Bartonella Henselae
- Features:
- Gram negative
- Self limited
- Causes:
- Cat scratch disease
- Bacillary angiomatosis
- Cat scratch disease
- Transmission:
- Via cat scratches, causes fever, involves regional lymph nodes
- Commonly seen in:
- Immunocompetent
- Diagnosis:
- Silver stain to visualize
- Treatment:
- Azithromycin
- Transmission:
- Bacillary angiomatosis
- Seen only in:
- Immunocompromised patients: HIV
- Transmitted via:
- Cat scratches of bites
- Presentation:
- Raised vesicular regions all over the skin
- Similar process to Kaposi sarcoma
- Treatment:
- Doxycycline and Macrolide
- Seen only in:
Gram Negative Zoonotic
Brucella
- Features:
- Gram negative zoonotic
- Facultative intracellular
- Associated with cattle and other farm animals
- Transmission:
- Direct contact and indirect contact by consumption of milk or cheese and unpasteurized dairy
- Clinical presentation:
- Nonspecific: fever, chills, anorexia
- Fever: undulating/rises and falls
- Organomegaly – replicates intracellularly
- Osteomyelitis
- Treatment:
- Tetracycline: doxycycline – rarely used on its own
- Rifampin with doxycycline
Francisella Tularemia
Pasteurella Multocida
Mycobacterium Tuberculosis
- Features:
- Gram negative
- obligate aerobe
- Acid fast
- Cord factor- essential for virulence
- Transmission:
- Human to human respiratory droplets
- Causes:
- Progression of TB
- Primary infection –> healed latent, systemic infection/miliary or reactivation of latent
- Primary infect lungs: middle or lower lobes- once healed causes Ghon complex
- Latent infection: primary infection that heals with fibrosis becomes latent
- Systemic progression/miliary TB–> bacteremia – infects any organ but commonly bone, liver, and lymphatics
- Reactivation of latent infection – seen in 5-10% of people. associated with immunosuppression. primarily infects upper lobe. Cough, night sweats, hemoptysis
- Treatment:
- RIPE: Rifampin, Isoniazid, Pyrazidimide, Ethambutol
- Prophylaxis: Rifampin and Isoniazid 9 months
Mycobacterium Leprae
- Features:
- Gram negative rod
- Acid fast bacteria
- Reservoir- Armadillo
- Causes:
- Leprosy/Hansen’s disease
- Thrives in cold temperature: predilection to distal extremities
- Causes:
- Tuberculoid
- Mild symptoms: well demarcated, hairless, hypoesthetic skin plaque – occurs anywhere in the body. Generally well controlled
- Lepromatous leprosy
- Bacteria not confined in macrophage- humoral response
- High transmission from human to human
- Symptoms: symmetric neuropathy: stocking and glove distribution, numerous poorly demarcated lesions “leonine facies”
- Tuberculoid
- Treatment:
- Tuberculoid leprosy
- Dapsone and rifampin 6 months
- Lepromatous leprosy
- Dapsone, Rifampin, and Clofazimine 2-5 years
- Tuberculoid leprosy
