3 - Bacteriology: Gram Negative Bacteria

Neisseria meningitidis

Gram negative “kidney bean” diplococci, encapsulated, aerobic, ferments glucose and maltose

Neisseria gonorrhoeae

Gram-negative "kidney-bean" diplococci, insignificant capsule, ferment glucose only

Meningitis

Aged 2-18 yrs, with fever, headache, stiff neck, and an increased level of PMNs in spinal fluid. The patient most likely has?

Meningococcemia

When meningococci disseminate into the bloodstream, leading to multiorgan disease, consumptive coagulopathy, petechial or purpuric rash (purpura fulminans).The patient most likely has?

Waterhouse-Friderichsen Syndrome

Most severe form of meningococcemia; high fever, shock, DIC, adrenal insufficiency (bilateral hemorrhagic destruction of adrenal grands)

A, C, Y, and W-135

Memory Aid: “YWCA! 🎵 (like the YMCA song)”

Vaccine contains what capsular polysaccharide strains of N. meningitidis?

Late-acting complement components (C5b–C9)

Deficiency of what complement components predisposes a patient to Neisseria infection?

Penicillin G

(no significant resistance)

Treatment of choice for Meningococcemia?

Chlamydia trachomatis

What organism usually has co infection with N. gonorrhoeae, hence recommendations include Doxycycline for treatment?

Lipooligosaccharide (LOS)

Toxicity of gonococcal infections are largely attributable to?

Neisseria gonorrhoeae

Most common cause of urethritis, PID, and septic arthritis in sexually active adults?

Fitz-Hugh-Curtis syndrome (perihepatitis)

History of PID, right upper quadrant pain, and “violin-string adhesions” between the liver and abdominal wall. The patient possibly has?

Nucleic acid amplification test (NAAT)

Gold standard for the diagnosis of gonorrheal infections?

Ceftriaxone 500mg IM single dose

plus

Doxycycline 100mg orally 2x a day for 7 days

If pregnant: use Azithromycin instead of Doxycycline

Treatment of choice for gonorrheal infection?

Haemophilus influenzae type b

Gram negative rods, (coccobacillary), fastidious organism, with Polyribitol phosphate capsule

Haemophilus influenzae

Gram negative rods, (coccobacillary), fastidious organism, need X (hemin) and V (NAD) factor for growth, satellite phenomenon around S. aureus colonies, positive Quellung test

Haemophilus influenzae type b

Most common cause of epiglottitis; also causes meningitis, otitis media and pneumonia

Haemophilus ducreyi

Gram negative rods, (coccobacillary), fastidious organism, need X (hemin) for growth, associated with painful genital ulcers (soft chancre)

Bordetella Pertussis

Pertussis or Tuspirina:paroxysmalpattern of hackingcoughs,accompaniedbyproduction of copious amounts of mucus, that end withan inspiratory "whoop"

Small gram-negative rods, causes whooping cough

ADP-ribosylation ;

activates G proteins that increases cAMP

Mechanism of action of pertussis toxin?

tracheal cytotoxin

damages ciliated cells

Bordetella pertussis toxin that causes the "whooping" ?

Catarrhal phase

Phase of Pertussis where antibiotics are most effective?

Paroxysmal phase

Phase of Pertussis where antibiotics are ineffective; Also where the characteristic “whoop” is seen

Legionella pneumophila

Poorly gram negative rods, facultative intracellular bacteria, visualized with silver stain, cultured on charcoal yeast extract agar

Legionella pneumophila

Atypical pneumonia associated with confusion, non-bloody diarrhea, hyponatremia, proteinuria and hematuria. Which organism is the likely cause?

Legionella pneumophila

Causative agent of Pontiac Fever and Legionnaire's disease

Escherichia coli

Most common cause of community-acquired UTI, lactose-fermenting, facultative gram-negative rods

Enteroaggregative E. coli (EAEC)

Strain of E. coli associated with persistent watery diarrhea in children and patients infected with HIV

Enterohemorrhagic E. coli (EHEC)

vs. shigella-like manifestation of EnteroinvasiveE. coli (EIEC)

Strain of E. coli associated with bloody diarrhea (after eating hamburger); hemorrhagic colitis and hemolytic uremic syndrome (HUS); shiga-like toxin

hemolytic anemia, thrombocytopenia, and uremia

E. coli O157:H7 is themost prominent serotype

Triad of hemolytic uremic syndrome (HUS)

Proteus mirabilis

Organism associated with “swarming” on agar; urea rapidly hydrolyzed (smell of ammonia)

Vibrio spp.

Comma-shaped gram negative rods, motile (shooting star motility), oxidase-positive, cultured on TCBS agar

Campylobacter jejuni

Comma-shaped gram negative rods, positive oxidase and catalase tests, microaerophilic, "sea gull wing" shaped

Helicobacter pylori

Curved gram-negative rods, urease-positive, microaerophilic, causes PUD, and associated with gastric carcinoma and MALT lymphomas

Proteus mirabilis Klebsiella pneumoniae Helicobacter pylori Ureaplasma urealyticum

Urease positive bacteria:

Pseudomonas aeruginosa

Gram negative rods, obligate aerobe, non-lactose fermenting, oxidase-positive, with sweet grape-like odor and pyocyanin (blue-green pigment)

Klebsiella pneumoniae

Urease-positive; facultative gram-negative rods with large polysaccharide capsule, associated with ESBL activity in drug resistant strains

Bacteroides fragilis

Anaerobic, gram-negative rod, predominant anaerobe of human colon, causes abdominal abscess and peritonitis

Brucella abortus

Small gram-negative rods without a capsule, causative agent of Brucellosis (undulating fever) by ingestion of contaminated dairy or direct contact

Francisella tularensis

Small gram-negative rods, causative agent of tularemia

Yersinia pestis

Non-motile, with striking bipolar staining (safety pin), causative agent of bubonic plague

Pasteurella multocida

Short, encapsulated gram-negative rod that exhibits bipolar staining, with buttery colonies with musty odor due to indole production

Salmonella spp.

Gram negative rods, motile, oxidase negative, H2S producer

Shigella spp.

Gram negative rods, non-motile, oxidase negative, H2S non producer, with low infective dose

Xylose-Lysine-Deoxycholate(XLD) medium

Culture medium for Salmonella and Shigella

Salmonella choleraesuis

Organism associated with osteomyelitis in patients with sickle cell anemia

gallbladder

In Typhoid fever, predilection for invasion of this organ can result in establishment of chronic carrier state

Stepwise pattern fever

Fever pattern of Typhoid Fever

Bone marrow culture

Most sensitive diagnostic modality, for Typhoid fever, but rarely indicated in clinical practice

Widal Test

Test that detects antibodies for Salmonella in the patient's serum

Rose spots

Faint, salmon-colored, blanching, maculopapular rash (trunk and chest) of Typhoid Fever

Shigella sonnei

(Duval’sbacillus)

Most common cause of bacillary dysentery

Shigella dysenteriae type 1

(Shiga bacillus)

Most severe form of bacillary dysentery; most common cause of epidemic dysentery

Cholera

Disease described with watery diarrhea in large volumes (rice-water stools), severe hypovolemia, may have sunken eyes, decreased skin turgor, wrinkled hands and feet (‘washerwoman's hands’)

ADP-ribosylation leads to stimulated Gs protein → increased cAMP

Mechanism of action of Choleragen

V. parahaemolyticus

Vibrio spp. associated with ingestion of contaminated raw seafood

V. vulnificus

Vibrio spp. associated with

trauma to skin, especially in shellfish handlers, or by ingestion ofraw shellfish

Fluid and electrolyte replacement; tetracycline or azithromycin shortens duration

Treatment for Cholera

Campylobacter infection

Most commonly identified cause of Guillain-Barré syndrome (GBS)

Campylobacter jejuni

Most common cause of bacterial gastroenteritis; associated with Reiter Syndrome

Skirrow agar

grows well at 42°C

Culture medium for Campylobacter jejuni

urethritis, uveitis, and arthritis

Memory aid: “can’t see (uveitis), can’t pee (urethritis), can’t climb a tree (arthritis)"

Triad of Reiter Syndrome

Amoxicillin (Metronidazole if with penicillin allergy) + Clarithromycin + PPI

Triple therapy for H. pylori

Bismuth + Metronidazole + Tetracycline + PPI

Bismuth-based quadruple therapy

Klebsiella pneumoniae

Most common cause of pneumonia in alcoholics, usually nosocomial, with thick, bloody sputum ("currant-jelly" sputum)

Proteus mirabilis

Organism associated with formation of struvite stones; UTI associated with nephrolithiasis (formation of staghorn calculi on renal calyces)

magnesium ammonium

phosphate

Composition of struvite stones

Pseudomonas aeruginosa

Organism which causes hot tub folliculitis, green nail syndrome, malignant otitis externa in diabetics, ecthyma gangrenosum, burn wound infections

Acinetobacter baumanii

Pleomorphic aerobic gram-negative bacillus commonly isolated from the hospital environment and hospitalized patients

Oriental rat flea (Xenopsylla cheopis)

Vector of Yersinia pestis

Haemophilus aphrophilus Actinobacillus actinomycetemcomitans Cardiobacterium hominis Eikenella corrodens

Kingella kingae

Associated with subacute bacterial endocarditis

Bacteria included in the HACEK group?

Treponema pallidum

Helically coiled, spiral, or corkscrew shaped bacilli, not seen on Gram-stain because too thin, cannot be cultured in vitro, microaerophilic

Leptospira interrogans

Thin, coiled spirochetes, with hook at one or both pointed ends (Shepherd's crook), obligate aerobe, grown on Ellinghausen-McCullough-Johnson-Harris (EMJH) medium or Fletcher medium

Mycobacterium tuberculosis

Slender, aerobic, acid-fast rods, with high lipid content (mycolic acids and wax D), and grows slowly on Löwenstein-Jensen medium?

Secondary Syphilis

Characterized with condyloma lata, maculopapular rash, fever, headache, malaise, anorexia, lymphadenopathy

Hutchinson teeth, 8th nerve deafness, interstitial keratitis

Hutchinson triad of congenital syphilis

VDRL

Non treponemal test useful for neurosyphilis?

Non treponemal tests

(RPR, VDRL)

Test for monitoring of treatment, can be used as test of cure

Benzathine penicillin G 2.4 MU IM

Treatment of choice for early Syphilis

Jarisch-Herxheimer reaction

Influenza-like symptoms few hours after receiving penicillin, from release of toxic products from dying or killed spirochetes

jaundice, bleeding, uremia

Triad of Weil Syndrome

respiratory failure

(massive pulmonary hemorrhage)

Most common cause of death in Weil Syndrome?

Acute Leptospiremic Phase

Phase of Leptospirosis where fever, chills, intense headache, calf tenderness, and conjunctival suffusion are usually seen?

Borrelia burgdorferi

Seen in Stage 2 Lyme Disease

Bacteria associated with Bell's Palsy, myocarditis (AV block), meningitis?

Borrelia recurrentis

Causative agent of Louse borne relapsing fever

Pediculus humanus humanus

Transmits Borrelia recurrentis

Doxycycline

Antibiotic for mild Leptospirosis

Penicillin G

Antibiotic for severe Leptospirosis

Borrelia burgdorferi

Weakly staining, gram negative spirochetes, largest medically-important spirochete which is the causative agent for Lyme disease

bite from deer ticks (Ixodes scapularis, Ixodes pacificus)

Borrelia burgdorferi is transmitted by?

erythema chronicum migrans

typical Bull’s eye configuration

Characteristic skin lesion of Stage 1 of Lyme Disease?

acrodermatitis chronica atrophicans

Stage 3:autoimmune migratory polyarthritis(onionskinlesions), acrodermatitis chronica atrophicans

Skin lesion seen in Stage 3 of Lyme disease?

Doxycycline

DOC for early localized or disseminated Lyme disease

Cord factor

Most important virulence factor of Mycobacterium, which inhibits WBC migration, causes characteristic serpentine growth pattern, and induces TNF-α release?

Ziehl-Neelsen (Hot method) or Kinyoun (Cold method)

Staining technique for acid fast bacteria?

Disseminated (Miliary TB)

Yellowish 1-2mm granulomas that appear like millet seeds scattered throughout the lung

Lymph node (Scrofula)

Most common site of extrapulmonary tuberculosis?

Choroidal tubercles

Pathognomonic finding in Miliary TB?

10 mm

90% of patients with

how many mm induration on Tuberculin Skin Test have a MTB infection?

> 15 mm

Essentially all patients with how many mm induration on Tuberculin Skin Test are infected?