Micro 2 Flashcards
What kind of virus is rotavirus?
Reoviridae
- dsRNA genome - 11 segments
- most important cause of gastroenteritis in young children
- group A assoc. w/ human disease
What is orthoreovirus?
A member of reoviridae
Infects mammals, but not associated with serious disease in humans.
What cells do Rotavirus infect?
How long is incubation?
Tip of villi in sm. intestine
- as few as 10 particles can cause infection
- 1-4 days incubation period
Describe rotavirus pathogenesis
virus capsid proteins attach to glycolipid receptor on the apical enterocytes of sm. intestine villi.
- Damage to sodium and glucose absorptive mechanisms -> increased luminal H2O volume. Viral replication -> acute onset of vomiting and diarrhea
- Activation of intestinal nerves -> secretion of H2O
- Fluid accumulation in lumen of sm. intestine, 10-20 diarrheal episodes / day and severe dehydration
Describe rotavirus structure
Unenveloped, icosahedral, 3 layer protein capsid
Segmented dsRNA genome
capsid contains all enzymes needed for replication
VP4 receptor protein - binds glycolipid of host cell
What are the major coat proteins of rotavirus?
VP4 - outer coat - binds receptor (sialic acid / integrins)
VP7 - outer coat - stripped during endocytosis
VP6 - middle coat - major protein that is tested for in antibody titer
VP2 - inner coat
How is rotavirus infection diagnosed in a lab setting?
Presence of virus particles in feces early in illness
- immune electron micoscopy, ELISA, immunoassay
Rise in titer of Ab to VP6
What are the two most important viruses contributing to diarrheal illness in children?
Rotovirus (reoviridae)
Adenovirus
What type of genetic material is carried by Adenovirus?
dsDNA
What is the most common cause of viral gastroenteritis in older children and adults?
Norovirus
How is norovirus transmitted?
fecal-oral
also contaminated food: shellfish and contaminated water
How long is the Norovirus incubation period and how long does it remain contagious?
incubation: 12-48 hours
From onset of symptoms: highly contagious until at least 3 days after symptoms recede - infectious viral particles may be shed as long as 2 weeks after illness
Norovirus symptoms
Acute onset of vomiting, diarrhea, stomach cramps, headache, fever, chills, myalgia
symptoms resolve 24-48 hours after onset.
How is norovirus spread prevented?
Handwashing - soap and water (alcohol hand-gel is inadequate)
10% bleach to clean surfaces.
What family of viruses is norovirus from?
Calicivirus
What is norovirus genome?
ss+RNA
What virus families do Hepatitis viruses A-E belong to?
Hep A: Picornavirus Hep B: Hepadnavirus Hep C: Flavivirus Hep D: satellite virus - undefined classification Hep E: Hepevirus (Hep - E - virus)
Genomes of Hepatitis A-E
A: ssRNA B: dsDNA C: ssRNA D: ssRNA (-) E: ssRNA
Which Hepatitis viruses produce chronic illness?
B and C
D in the context of association with B (is not infective on its own)
What causes hepatic cellular carcinoma
Chronic viral infection is leading cause (HBV, HCV)
course of chronic illness is 25-50 years
Ultimate cause: constant inflammation and constant stimulation of cellular replacement -> mutation and tumor formation
What was the first successful recombinant vaccine for a human disease?
Hep B vaccine
How is HBV spread?
sexual contact and parenteral exposure
most adults clear infection - 5% do not -> chronic infection
–May be asymptomatic
Describe the HBV genome
Circular, partially double stranded DNA. Full length (-), 20-80% (+)
Describe the process of HBV replication
Genome is circular (-) DNA with partial (+) DNA. In nucleus, cellular DNApol -> full dsDNA
(-) DNA -> full length (+) RNA via host cell RNA pol II
(+) RNA is packaged in new core proteins
viral RNA/DNA dependent DNApol -> full length (-)DNA
(-)DNA copied by viral DNApol -> partial (+) DNA
HBsAg containing envelope acquired on exocytosis
How is HBV prevented / treated?
Recombinant vaccine
Interferon - alpha and/or inhibitors of HBV polymerase
These do not eliminate infection*
Describe Hep D’d genome and what it codes
Small (-)RNA genome (1.7kb)
codes one protein: delta antigen: RNA encapsidation
What is HDV superinfection?
Infection w/ HDV after host is already infected with HBV.
contrast w/ coinfection, where both acquired together
Superinfection -> high mortality (20%)
What family of viruses does HCV belong to?
Flavivirus
Describe HCVs genome
(+)ss linear RNA
How is HCV infection treated?
Combination of interferon-alpha and ribavirin
-can eliminate infection, but IFNa has unpleasant side-effects
2 new drugs w/ this mix -> 70-80% cure rate
How is HCV transmitted?
Contaminated blood products
Injection drug use
Mother to child (uncommon)
sexual contact
what is the leading cause for liver transplant necessity?
HCV infection
What is the course if HAV infection in humans?
Initial infection in intestinal mucosa -> liver -> lymphoid cells
Virus is excreted in large volume (10^8 infective units/ gm feces) in feces.
no chronic infection leading cause of jaundice world wide
Where is HEV infection most common? Who is most severely effected?
Mostly in developing countries - drinking water contaminated w/ feces. May be carried by rats, pigs, deer.
Pregnant women - 20% mortality rate
What are M cells?
Found in mucus membranes of GI - antigen presenting cells
phagocytize bacteria and foreign particles and pass them to macrophages underlying the Mcell
What is MacConkey’s agar?
Selects for gram (-) organsisms
Bile salts and crystal violet inhibit gram (+) growth
pH indicator distinguishes between lactose fermenting (pink colonies) and non lactose fermenting organisms
3 types of secretory diarrhea and responsible organisms
Secretory Diarrhea: non-inflammatory, non-invasive
- Bacterial enterotoxigenic: Enterobacteriaceae and Vibrionaceae
- Bacterial neurotoxic: usually a preformed toxin is ingested: C.botulinum, B.cereus, S.aureus
- Non-inflammatory parasitic: G.lamblia, C.parvum
3 types of invasive inflammatory diarrhea and organisms responsible
- Bacterial cytotoxin caused inflammation: C.diff, EHECCCC
- Bacterial invasive infection: Shigella, EIEC, Salmonella
- Parasitic invasive: E.histolytica
Vibrio Cholerae: organisms of interest and characteristics
O1 and O139
Gram neg, oxidase pos, motile (single polar flagella), comma shaped rods
found in brackish water, fresh water ponds, can colonize shellfish
Two types of O1: Classic and El Tor
Classic - highly virulent, but does not survive freely in enviro well
El Tor - less virulent, but survives in environment for long periods
What are V.cholera’s virulence factors?
Motility - single polar flagellum
Adhesion - tcp pili (toxin co-regulated pili) and other adhesins - tight adhesion to intestinal epithelium
Cholera toxin
Describe Cholera toxin and its activity
AB type toxin (A is enzymatic, B is binding, consists if 5 identical units)
ADP ribosylating
B attaches to GM1 ganglioside, A1 is released to enter cell
A1 ADP-ribosylates Gs -> chronic activation of Gs -> massively increased cAMP -> hypersecretion of fluids, chloride ions, inhibition of Na absorption
End result is massive fluid loss
Describe the etiology / pathogenesis of cholera
ingestion of organism via contaminated water or food
10^8 organisms needed for infection - V.cholera sensitive to gastric acid
2-3 day incubation period, high replication
vomiting, high volume watery rice-water diarrhea no PMNs profound dehydration
How is Vibrio cholera identified in the lab?
Stool sample
Culture on TCBS (thiosulfate-citrate-bile salt-sucrose agar) - highly selective for vibrio species
Positive oxidase test
O antigens: O1 and O139 - assoc. w/ cholera toxin producing strains
5 classifications of E.coli and assoc. symptoms
ETEC (Enterotoxogenic): Watery d., cramps and low fever. Infants and travellers. Cytotoxins increase cAMP or cGMP
EAEC / EAggEC (Enteroadhesive): Persistent infant d., also AIDS pts. Sometimes gross blood. Low fever. Aggressive adherence to intestinal mucosa prevents fluid absorption
EPEC (enteropathogenic): copious watery d. w/ mucus in infants. Fever, N/V. Adhere and destroy epithelium of INTESTINE
EIEC (enteroinvasive): watery diarrhea then scant bloody stools. fever. invasion and destruction of epithelium of COLON
EHEC (enterohemorrhagic): watery d. then grossly bloody d. Hemolytic uremia (O157:H7). Cytotoxic verotoxin prevents protein synth.
What is ETEC and how is it identified
Enterotoxic E.coli - causes secratory diarrhea - traveler’s diarrhea, Montezuma’s revenge. Major cause of infant mortality worldwide.
ELISA or agglutination tests for the presence of toxins
DNA probes for LT and/or ST genes
What are the ETEC toxins?
LT - heat labile toxin - destroyed at 100deg C for 30 min, 75% similarity to cholera toxin (AB structure) and same mechanism (B binds GM1, A unit: ADP ribosylation of Gs -> increased cAMP or cGMP) new evidence: Type II secretion
ST - heat stable toxin - not destroyed at 100deg C for 30 min., family of small molecules. Bind membrane bound guanylate cyclase -> chronic elevation of cGMP -> fluid and electrolyte loss
note: both LT and ST are plasmid encoded
How is ETEC spread? What are symptoms?
contaminated food and beverages
most common in tropics and in young
Symptoms: N/V, weakness, dizziness, then watery diarrhea
How do ETEC adhere to a host?
Colonization Factor Adhesions (CFA) - plasmid encoded - allow binding to epithelium of sm. intestine
Bundle forming pilus - similar to Tcp pili of v.cholera
What is EPEC and how is it identified in the lab
Enteropathogenic E.coli: causes severe, often fatal, diarrhea in infants and children primarily in developing countries. Traveller’s diarrhea in adults.
Identified via ELISA and multiplex PCR
How does EHEC attach to host cells?
Bundle forming pilus - non-intimate attachment
Tir and intimin - closer, intimate attachment
-bacteria produce and secrete Tir (type III secretion), which embeds in host cell membrane and binds to bacterial intimin (in bacterial outer membrane), Tir interacts w/ actin cytoskeleton and forms pedestal-like structure beneath organism -> effacement: destruction of pili
Describe the etiology / pathogenesis of EPEC
Fecal - oral spread
Diarrhea not caused by toxin: caused by destruction of microvili (rearrangement of actin cytoskeleton) -> malabsorption and diarrhea
What is clostridium botulinum and how is it recognized in a lab?
Obligate anaerobe, gram (+) rod that produces botulism neurotoxin.
Spore forming
Usually clinical identification w/o culture
Can be grown in O2 free lab environment
Immune assay for toxin in food sample, blood, gastric contents
How does botulinum toxin work?
Usually ingested as a preformed toxin via contaminated food
sypmtoms 12-36 hrs after ingestion
AB toxin - B portion binds ganglioside receptors on nerve cells
Toxin blocks presynaptic release of ACh - prevention of muscle contraction and flaccid paralysis - death via respiratory collapse
Can botulinum toxin be inactivated?
Yes - boil 10-15 minutes
Spores are not destroyed (can withstand 100deg C for 3-5 hrs)
What are infant and wound botulism?
Infant botulism: infants have incomplete gut microflora. C. botulinum can colonize and produce toxin -> SIDS (v. rare)
-seen in cases of mothers giving infants honey
Wound botulism: colonization of deep wound (anaerobic) - organism found in nature, can contaminate wound, grow and produce toxin
What is the most common form of bacterial food poisoning?
Staph aureus
Describe S.aureus enterotoxin action.
Preformed toxin is ingested and absorbed. Assoc. w/ food being left out - potato salad, cold cuts.
Stimulation of neural receptors in gut - signal to emetic center -> projectile vomiting within hours
Enterotoxin is heat stable
What bacterial food-borne organism is associated with Chinese restaurants / fried rice?
Bacillus cereus
Describe B.cereus toxic effects
2 forms:
- Emetic: (1-6 hrs post ingestion) ingestion of preformed toxin (fried rice held at room temp for a long period). S.aureus like N/V, cramps
- Diarrheal: (8-16 hrs. post ingestion) toxin formed in vivo. Activation of intestinal AC -> elevated cAMP, fluid excretion, diarrhea. meat or veg. foods held at room temp after cooking.
* ** both forms subside ~24 hrs. after onset ***
What is Clostridium perfringens?
Gram (+) rod, anaerobic spore-former.
Similar toxic effect to B.cereus
Assoc. w/ cooked food being left at room temp (meat, veg, gravy)
Abd cramps, N/V, diarrhea, no fever.
Symptoms 8-24 hours after consumption. Toxin produced in GI tract.
What are the symptoms of Giardia lamblia infection?
Acute watery diarrhea, cramping, flatulence.
May develop chronic diarrhea. Symptoms may wax/wane over a long period. Weight loss common.
What is Giardia lamblia and how is it identified?
Protozoan. Flagellated.
Two stage life-cycle: Trophozoite (free-living) cyst (infective)
Identified by microscopic examination of stool, duodenal aspiration, or duodenal biopsy - look for cyst
string test
Antigen test of stool
What is giardia’s incubation period?
7-10 days
What is Cryptosporidium parvum? Describe infection
Protozoan most often isolated in HIV patients w/ diarrhea
severe, prolonged, watery diarrhea in immunocompromised, less severe in normal
Oocyst ingested in contaminated water -> sporozoite in intestine -> Enters intestinal epithelial cells -> sexual / asexual reproduction -> oocysts released and shed in feces
What is Clostridium difficile and how is it identified?
Gram (+) rod, anaerobic, spore forming
Normal flora in ~5% of adults, but can cause inflammatory diarrhea (inflammation of colonic mucosa)
Culturing is not helpful to identification
Toxin test on stool is most helpful: EIA
What are C.diff’s virulence factors?
2 toxins
A: enterotoxin: -> accumulation of viscous bloody fluid in colon. Chemotactic for PMNs -> PMN lysis -> release of inflammatory mediators, fluid secretion, altered membrane permeability, Hemorrhagic necrosis of mucosa.
B: cytotoxin: disrupts actin polymerization and cytoskeletal organization, inhibits protein synthesis - similar in effect to diptheria toxin
What is pseudomembranous colitis?
Can be caused by C.diff infection
pseudomembrane forms at site of epithelial cell destruction - consists of fibrin, mucin, and dead PMNs, leukocytes
Produces watery, sometimes bloody diarrhea, may be mucus present. Abdominal pain and cramps, fever, nausea. In severe cases may be lethal.
What is EHEC?
Enterohemorrhagic E.coli (also STEC (shiga-toxin e.coli) and VTEC (verocytotoxin e.coli))
How is EHEC identified in the lab?
Gram (-) rod, facultative anaerobic
O157:H7 does not fement sorbitol, so can be selected for on sorbitol MacConkey agar
Serotype with anti-O157:57 serum
demonstrate pathogenic activity with vero cells
DNA probe for shigella toxin genes
EHEC virulence factors
Adhesion: Tir and intimin production - tight binding
Toxin: Shiga toxin
Type III secretion: attaching and effacing lesions
What is Shiga toxin?
Produced by EHEC also vero cytotoxin
AB toxin
B binds G3 ganglioside receptor. A subunit enzymatically modifies 28S rRNA of 60S ribosomal subunit - blockade of protein synthesis and cell death
Capillary thrombosis, inflammation of colonic mucosa, hemorrhagic colitis
Shiga Toxin I and II encoded by plasmids (Stx1, Stx2)
Describe the etiology of EHEC
Usually spread via contaminated food (Ground beef)
Small number of organisms can cause infection
Incubation period of 3-4 days - severe crampy watery diarrhea that evolves to grossly bloody diarrhea
Hemolytic Uremic Syndrome: 5-10% of patients - esp. children
-acute renal failure, thrombocytopenia, hemolytic anemia.
-shiga toxin damages renal glomerular cells
How is Shigella identifiable in the lab?
Gram (-), non-motile, lactose neg on MacConkey and Hektoen agars.
Serotyping - 4 groupings:
1. Group A: S. dysenteriae (Shiga bacillus - largest producer of toxin)
2. Group B: S. flexneri
3. Group C: S.boydii
4. Group D: S.sonnei (60-80% of US cases)
Describe Shigella infection and illness
Transmitted by food, fingers, flies, feces
Organisms multiply in sm. intestine, esp. lower sm. intestine.
First 12 hrs: abdominal pain, cramping, fever
12-72 hrs: organism is no longer in upper intestine. pain intensifies, dysentery, tenesmus, lethargy. Many PMN in mucoid stool.
Explain Shigella virulence
Invasiveness: entry via M.cells, passed to macrophage, apoptosis induced, IL-1, inflammatory factors, PMN chemotaxis
PMN open tight junctions allowing Shigella to penetrate epithelium.
Escape from phagosome and movement to epithelial cells. Actin rearrangement “actin based motility” - allows bacteria to move through cell and enter neighbors.
Epithelial cells die after infectoin - ulcerative colitis
Product is bacillary dysentery. Only S. dysenteriae produces toxin which contributes to death of epithelium. Primary virulence is via cell invasion.
What is EIEC?
Enteroinvasive E.coli
Behaves like Shigella - cell invasion, actin rearrangement - cell death - dysentery. Symptoms the same.
No tests to differentiate from other E.coli strains,but can be differentiated from Shigella. Rare.
3 forms of Salmonella infection
Gastroenteritis: most common - 8-48 hour incubation, abrupt onset, low fever, diarrhea, N/V, 2-5 day duration.
Bacteremia: invasion of blood stream following oral ingestion. High spiking fever, septic. Usually no GI symptoms. Rare.
Enteric (Typhoid) Fever: 7-20 day incubation, chills, headache anorexia, myalgia, enlarged spleen and lymph nodes, gradual fever, insidious onset, early constipation followed by bloody diarrhea, lasts several weeks. 1/3 of patients develop maculopapular rash (rose spots) on trunk.
In chronic carriers of Salmonella, where is the organism reservoir?
Gall bladder
What size Salmonella inoculum causes illness?
10^4 - 10^8
Large inoculum needed.
Explain Salmonella’s virulence
Invasion: enter M cells or intestinal mucosa epithelial cells - multiplication within vessicles (phagosomes) -> cell lysis
Type III secretion: Actin rearrangement -> ruffled border
Endotoxin: Lipid A of LPS induces inflammatory response and contributes to mucosal dammage.
How is Salmonella identified in the lab?
Gastroenteritis: culture lactose neg, oxidase neg colonies, serological tests to determine serotype (there are many)
Bacteremia: blood cultures, stool cultures (usually negative)
Typhoid fever: early - blood culture, later - stool
How can Salmonella be differentiated from Salmonella in the lab?
Growth on Hektoen enteric (HE) agar
Salmonella grows distinct black colonies due to H2S production
What is campylobacter infection associated with?
Usually chicken consumption - undercooked
Sometimes other meats, raw milk
What are the symptoms of campylobacter infection?
Fever, malaise, abd. cramps, profuse watery / bloody diarrhea, mucosal inflammation.
How is campylobacter identified?
Small, motile, flagellated bacteria. Comma shaped, gram (-), Oxidase pos (vs. Salmonella and Shigella neg)
Microscopy: stool sample - darting motility
Will not grow on MacConkey
microaerophilic and capnophilic (doesn’t ferment glucose)
What are Campylobacter’s virulence factors?
Flagella - motile in mucus layer of sm. intestine, multiply in mucus
Toxins - enterotoxin, endotoxin, cytotoxin - destroy intestinal cells -> bloody diarrhea
Protein S - surface protien, blocks complement binding - serum resistance to phagocytosis
Autoimmune response: “Guillain-Barre” cross-reaction between host myelin and Campylobacter surface structure
What is Guillain-Barré syndrome as it relates to Campylobacter?
cross-reactivity between organism surface proteins and host myelin
Self-reacting Ab formed -> inflammatory demyelinating polyneuropathy
Symptoms emerge 1-3 weeks post infection. Bilateral weakness,
Yersinia enterocolitica - What and what does it cause?
belongs to family enterobacteriaceae - gram (+) cocci
Zoonotic - transferred from animals to humans (rabbits, rats, livestock)
Causes Enterocolitis with necrosis of Peyer’s patches
-bloody diarrhea, fever, abd. pain lasting 1-2 weeks
-inflammation of messenteric lymph nodes mimics acute appendicitis (esp. in young children)
- transfusion related septicemia (grows in blood at low storage temps)
What bacteria is associated with transfusion related septicemia?
Yersinia enterocolitica
How does H.pylori protect itself from stomach acid?
Urease: Converts urea to ammonia and CO2. Organism is surrounded by a layer of ammonia that protects from acid.
How is H.pylori identified?
Small, gram (-), microaerophilic, motile, curved bacillus
Gastric biopsy for culture, and rapid urease - CLO (campylobacter like organism) test
What toxins does H.pylori produce?
Cytotoxin and mucinase - contribute to tissue destruction and infiltration of inflammatory cells in ulcer formation
How is Listeria monocytogenes identified?
Small, facultative anaerobes, non-spore forming, catalase pos, oxidase neg, B-hemolytic, gram (+) bacillus
How are people infected by Listeria monocytogenes and what is the result?
Listeria is ubiquitous in nature, but usually infection through food - raw veg, raw milk, soft cheese, fish, poultry, meat (including ready-to-eat, like hot-dogs)
Motile bacteria crosses mucosal barrier of intestine and enters blood stream and:
1. is cleared by host immune system
2. infects other organs (esp. in immuno suppressed population) -esp. CNS - meningitis
3. crosses placenta to infect fetus - birth defects, spontaneous abortion
What are 3 roundworms that can infect humans?
Ascaris lumbricoides - intestinal roundworm
Enterobius vermicularis - pinworms
Ancylostoma duodenale and Necator americanus - hookworms
What are symptoms of Ascaris lumbricoides infection?
Often asymptomatic
GI upset, colic, loss of apetite
In heavy infestation worms can ball up in sm. intestine and cause obstruction
What are Taenia saginata and Taenia solium?
Tapeworms
Taenia saginata - beef tapeworm
Taenia solium - pork tapeworm - can invade gut wall and migrate to other tissues and form cyst - cysticerocosis
What are symptoms of peritonitis?
Abdominal distention, pain, decreased appetite, fever, nausea, thirst, vomiting, absence of bowel sounds.
May be other signs of shock
Three types of peritonitis
Primary - develops without an evident source
Often associated w/ advanced liver disease
-Usually caused by gram (-) rods: E.coli, Klebsiella (>50%)
-~25 % by gram (+) organisms - streptococcus
Only facultative anaerobes - oxygen content of ascitic fluid prevents obligate anaerobes from living
Secondary: Trauma related - spillage of GI or UG organisms into peritoneal cavity. Usually polymicrobial.
Dialysis associated: often involves skin flora. Usually monomicrobial. usually: S. epidermidis, S.aureus, E.coli, Pseudomonas aeruginosa
What are E.coli virulence factors
Adherence - 20 factors
Endotoxin - lipid A (LPS of outer membrane): activates complement -> inflammation; stimulates cytokine release -> septic shock
LPS -> LPS binding protein -> CD14 on monocytes and macrophages -> activation
What organism is most frequently involved in CAPD peritonitis?
S.aureus
What are the virulence factors of S.aureus?
Pili - adherence
Capsule - antiphagocytic, promotes adherence to tracheal epithelium
Endotoxin - LPS - may cause shock
Exotoxin A - increases tissue destruction by inhibition of protein synthesis (similar to diptheria)
Extracellular enzymes - pyocyanin: blue pigment, suppresses other bacterial growth, impairs function of nasal cilia
How do intraperitoneal abscesses usually form?
Complication of general or secondary peritonitis, appendicitis, diverticulitis, surgery or other intra-abdominal pathology. Usually polymicrobial (~4, up to 12) consisting of endogenous flora *Bacteroides fragilis
What is Bacteroides fragilis and how is it identified?
Gram (-), anaerobic, encaspuslated bacillus
Normal flora of GI tract- causes infections when it escapes - major cause of intra-abdominal abscesses
Produces foul-smelling discharge from wound (anaerobic metabolites)
What organisms are commonly associated with congenital infections?
Viruses spread mother -> fetus: HIV, CMV, rubella
Bacteria: L.monocytogenes, T.gondii
What organisms are commonly associated with parinatal infection?
Perinatal: passage down birth canal
L.monocytogenes
E.coli
S.agalactiae (Group B strep )
What organisms are commonly associated with post-natal infection of the newborn?
Organisms that can be spread through milk, saliva, physical contact
L.monocytogenes
S.agalactiae (Group B strep - B-hemolytic)
E.coli
What is the leading cause of bacterial meningitis in newborns?
Group B strep
S.agalactiae - normal flora of female UG tract and GI
How is Streptococcus agalactiae identified?
Gram (+), catalase neg, B-hemolytic, grow as diplococci or short chains in liquid.
In the case of bacterial meningitis - lab evaluation of CSF. Culture needed, but immediate gram stain should be done for empiric treatment.
What are Early and Late Onset Diseases caused by GBS?
EOD: Within first week of birth (usually w/in 24 hrs) -meningitis, pneumonia, bacteremia LOD: After first week of birth -usually meningitis -risk factors less well understood
What are the risk factors for Early Onset Disease involving GBS?
Maternal carriage of GBS
Low anti-capsular IgA
Early delivery
Early / prolonged membrane rupture
What are GBS virulence factors?
Capsule - most important - 9 serotypes (type 3 most assoc. w/ disease)
-sialic acid moiety on terminal sugar - limits C3b deposition and complement activation, thus phagocytosis
Invasion - can invade respiratory epithelium and cross BBB
B-hemolysin - damages respiratory epithelium, cytolytic for brain epithelium, enables crossing of BBB
What E.coli strain is associated with newborn meningitis?
E.coli K1 - normal inhabitant of lg. intestine. Similar to GBS.
Virulence factors of E.coli K1
K1 polysialic capsule: resistance to killing by neutrophils and normal serum, survival in blood and CSF
Invasins: IbeA and IbeB: needed to cross BBB
Type O antigen LPS
S.fimbriae - important for establishing infection
What are symptoms of E.coli K1 meningitis in a newborn?
Variable, and possibly subtle
respiratory distress, fever, poor feeding, abdominal distension
Culture CSF and treat on suspicion
How are Listeria infections of the newborn usually acquired?
From contaminated food.
Mother consumes and transfers to fetus.
Organism exhibits tropism for placenta and fetus.
Usually fatal - stillbirth, spontaneous abortion, premature labor.
Listeriosis of newborn usually acquired during delivery -> meningitis
How is Listeria immunity mediated?
Cell mediated immunity - Listeria is intracellular pathogen
Initial infection: macrophages, then CD8+ Tcells
What are Listeria’s virulence factors in the setting of fetal/newborn infection?
Internalins - allow cell invasion
Listeriolysin O - escape from vacuoles
ActA - recruits host-cell actin for motility and spread cell to cell w/o exposure to extracellular environment.
What is the lifecycle of Toxoplasma gondii?
Oocyst consumed (fecal-oral)
Trophozoite is mature asexual proliferative form - infect cells, replicate, burst cells
Tissue cyst bradyzoite forms once immune response is initiated - cysts can exist in tissue for life of individual.
What happens if a woman is infected with T.gondii for the first time during pregnancy?
Often stillbirth or spontaneous abortion.
Live births: microcephaly, hydrocephaly, motor disturbances, convulsion. May appear normal at birth, but develop problems later (retardation, chorioretinitis)
Subsequent births: no risk of transmission to fetus
What is a primary histologic marker of chronic hepatitis?
Bridging fibrosis w/in hepatic lobules from central vein to portal triad
What are the most common initial symptoms of viral hepatitis?
Malaise, weakness, N/V, anorexia, vague dull RUQ pain, low grade fever - all precede jaundice if it occurs (50-80% of pts do not experience jaundice)
Jaundice and dark urine usher in icteric phase - bring pt. to doctor.
Also - smokers lose appetite for smoking.
what is the effect of circumcision on STI transmission? Why?
Reduces risk of acquiring HIV by 51-76% (hetersexual)
Large population of macrophages, CD4+ cells in nonkeratinized inner mucosal cells of foreskin.
Also: decreased incidence of HPV, HSV - 2, syphilis, and trichomonas.
No effect: N.gonorrhoeae, C.trachomatis
Female partners: decreased risk for HSV, BV, trichomonas
What symptoms are associated with urethritis?
May be asymptomatic
Urethral discharge - purulent / mucopurulent
Dysuria, burning, pain, pruritus (itching)
What are the causes of urethritis?
Most involve N.gonorrhoeae Often polymicrobial Chlamydia (if gon, at least 30% likliehood of having Chlamydia) Mycoplasma genitalium etc
Arthritis-dermatitis is the classic presentation for what?
Disseminated Gonococcal Infection
Bacteremial spread of Gonorrhea
What are the symptoms of Neisseria gonorrhoeae infection?
Urethritis - mucopurulent discharge Mucopurulent cervicitis - vaginal discharge dysuria Pelvic Inflammatory disease in 10-20% Disseminated gonococcal infection pharyngitis, conjunctivitis
How is Gonorrhea diagnosed?
Gram stain of urethral, cervical, or anal swab
-Gram (-) diplococci within or associated w/ PMNs
-sensitive and specific
Culture - Modified Thayer Martin media (2-3 days)
-can test susceptibility
-preferred for pharynx and rectum
DNA probe, PCR, NAAT (nucleic acid amplification test)- best (very highly sensitive and specific - near 100%)
What medium is N.gonorrhoeae grown on?
Modified Thayer Martin
What is treatment for Gonorrhea?
Cephalosporins - resistant to FQ, Penicillin, tetracycline
Ceftriaxone 250mg IM or
Cefixime 400 mg (single dose PO) or
Cefpodoxime 400mg (single dose PO)
Always include treatment for chlamydia - azithromycin or doxycycline
Who is more likely to be an asymptomatic carrier of gonnorhea: male or female?
Female
Who is more likely to be an asymptomatic carrier of chlamydia: male or female?
Common in both
What can be said about women w/ positive cervical culture for chlamydia?
Probable upper genital tract infection
Who should be screened for chlamydia?
All young women, annually (<25) regardless of sexual risk.
Older women w/ risk factors
No routine screening in males
How is chlamydia diagnosed?
Women: urine or swab from endocervix or vagina
Men: urine or urethral swab, anal swab
Culture, immunofluorescence EIA - no longer used
Nucleic Acid Hybridization
NAAT - best sensitivity, modern standard
What is therapy for chlamydia?
1g single dose of azithromycin - preferred
or - doxycycline 100mg bid 7days
amoxicillin in pregnant patients
What is the most likely cause of urethritis if non-gonococcal?
Mycoplasma genitalium - most often (10-25%)
then Chlamydia trachomatis
No identifiable pathogen - frequent finding
How is non-gonococcal urethritis treated?
1g single dose azithromycin - preferred
or - doxycycline 100mg bid 7 days
M.genitalium often fails with doxy, and increasing resistance to azithromycin
What bacteria are commonly associated with PID?
N.gonorrhoeae 30-50%
C.trachomatis 25-40%
Mixed bacteria 25-50%
Natural vaginal flora also common - reduction in lactobacilli -> overgrowth, infecton
What organism is associated with chancroid?
Hemophilus ducreyi
What are the symptoms of Syphilis?
Slow development (12-40 days incubation)
Primary painless ulcer at site of inoculation (penis, vagina, vulva, mouth)
No purulence
Painless inguinal lymphadenopathy
What are the stages of syphilis?
Primary infection: painless ulcer, painles lymphadenopathy
Secondary (6weeks - 6mos): multiple mucocutaneous lesions, fever, alopecia, lymphadenopathy, meningitis
Tertiary (months - years): gumma (necrotic sores)
What is the modern algorithm for identification of Treponema pallidum (syphilis)?
EIA or CIA -> if pos: quantitative RPR -> if pos, syphilis
if neg: TP-PA (treponema pallidum particle agglutination assay) -> if pos: syphilis, if neg: syphillis unlikely
How is syphilis treated?
Early: Benzathine Penicillin - IM
Latent / asymptomatic neurosyphilis: Benzathine Penicillin - IM weekly, for 3 weeks
Neurosyphilis: IV Benzyl Penicillin X 10days (IV Cephtriaxone)
How do we know if syphilis treatment is working?
4 fold drop in titer in 6mos (early syph) or in 24 mos (latent/ late)
What causes gential herpes?
HSV 1 and 2
2 primarily, but 1 is on the rise
2 does not infect mouth
What are the symptoms of genital herpes?
Multiple painful, shallow genital ulcers May be missed Constitutional changes (F>M) Fissures (F) lymphadenopathy, cervicitis, urethritis
What is treatment for genital herpes?
7-10 days treatment: acyclovir famcyclovir valacyclovir can't eradicate virus, but goal to decrease viral shedding and recurrences.
How is Herpes diagnosed in the lab?
Direct Fluorescent Antibody test
Culture (specific, not sensitive)
PCR
Type specific IgG serology - commercial kits
What is the most frequently reported infectious disease is the US?
Chlamydia
Gonorrhea is #2
Lymphogranuloma venereum
Caused by Chlamydia trachomatis (serotypes L1-3)
More common in developing countries
Persistent Chlamydia infection - begins with small papule on genitalia, anus, or rectum - heals in a few days
Regional lymphadenopathy - systemic symptoms (fever, rash, nausea)
No treatment
How is chlamydia cultured?
Indirectly. Can’t culture the organism itself, but can culture the cells that it inhabits
epithelial or reticular cells
Describe Chlamydia’s lifecycle
Two stages:
Elementary Body - infectious - enters cell to form RB
Reticulate Body - non-infectious, metabolically active
EB enters epithelial cells, inhabits endosome and converts to RB which multiplies extensively. Under stress, can remain in RB stage. Otherwise, binary fission -> EB which are released.
What happens in persistent Chlamydia infection?
Under stressful conditions, remains in cell as RB
Downregulation of major outer membrane protein (MOMP),
Increased production of stress factors (hsp60, hsp10) -> chronic inflammation
Refractory to Abx
How is chlamydia treated?
Tetracycline, erythromycin common treatments
Erythromycin and amoxicillin used in pregnant women and infants
Are B-lactams effective against Chlamydia?
No - may drive infection into persistent state
Are men or women more likely to be asymptomatic Chlamydia carriers?
Women
What are Opa genes in Gonorrhea?
Outer membrane proteins -> opaque cell appearance
Involve in binding host cells - close contact, possibly invasion
Several Opa genes - constantly transcribed, only translated if start codon is in frame
CTCTTT segments added/ lost - may shift start codon out of frame - control mechanism of expression
Does infection with N.gonorrhoeae confer immunity?
No
Describe pathogenesis of Treponema pallidum
Infection: sexual contact w/ active lesion (primary or secondary)
Invasion of mucus membranes - multiplication and spread -> lymphatics
systemic spread before primary lesion forms
3-4 weeks: primary chancre forms and heals in 4-6 weeks
2-10 weeks after healing: 2ndary syph: fever, sore throat, rash, lesions on hands and feet and face
Clear infection or latency
Tertiary syph - months later: granulomatous lesions (gumma) of skin, bones, joints. Neurosyphilis, CV syph. organism rare in tertiary lesions.
When can a fetus become infected with T.pallidum? How diagnosed?
Infection can occur at any stage of pregnancy.
Fetal anti T.pallidum IgM is diagnostic
How does congenital syphilis usually present?
Normal at birth and for 3-8 weeks. then fail to thrive, rhinitis, pneumonia
25% mortality
What are P-pili, what do they bind? mannose sensitivity?
Primary virulence factor in Uropathogenic E.coli
Bind globobiose (glycosphingolipids) and P group antigens on RBC -> agglutination in lab
Mannose insensitive
Induces IL6,8, PMN chemoattractive -> inflammation
HIV treatment goals
Reduce moridity and improve survival
Restore and maintain immunologic function
Maximal, durable viral load suppression
Prevent vertical transmission (Mother -> child)
Improve quality of life
What is first line treatment for HIV?
2 NRTIs
1NNRTI
1 “boosted” PI
Raltegravir - integrase inhibitor
What is the preferred NNRTI used in HIV?
Efavirenz
except in 1st trimester of pregnancy or women with high pregnancy potential
Preferred alternative: Nevirapine
What is Ritonavir?
Is a protease inhibiting drug, but not used as such. Is a potent inhibitor of CYP3A4, which is used to extend the life of other protease inhibitors.
–BOOSTING
What is the preferred NRTI combo used in HIV treatment?
Tenofovir and Emtricitabine
-available as co-formulation
Uropathogenic E.coli virulence factors
P-pili Type-1, Type-S fimbriae Adhesins (AfaD, AfaE, Dr) Toxins (Hemolysin, cytotoxic necrotizing factor-1) K antigen LPS (endotoxin)
What are S.saprophyticus virulence factors?
S.saprophyticus surface-associated protein (Ssp) - adhesin
Hemagglutinin / Fibronectin Binding Protein - adhesin
Hemolysin - not in all strains
Urease - stones
What is the etiology/ pathogenesis of S.saprophyticus?
UTI pathogen - cystitis, not pyelonephritis
Natural inhabitant of colon - self infection
More common in females
Sexual activity increases risk of UTI
Increased risk w/ spermicide nonoxynol-9
Klebsiella pneumoniae virulence factors in UTI
Type 1 and 3 fimbriae
Capsule
LPS
Urease
Proteus mirabilis virulence factors in UTI
MRP - mannose resistant proteus like hemagglutinin
PMF - proteus mirabilis fimbriae
flagella
urease - high concentration of ammonium - alkalinize urine, stones
What is Bile esculin used for?
Differentiation of Enterococcus from Streptococcus
Enterococcus grows - blackens medium
What are the virulence factors of Enterococcus in UTI?
Aggregation substance (Asa1)- plasmid exchg and adhesion
Cytolysin - lyse RBC -> iron for growth
Sex pheromone - Neutrophil chemoattractant (can enter PMN)
What are host defenses against UTI?
normal flora flushing effect of urine sloughing epithelium high osmolality, low pH of urine insignificant immune defense
In what infections should anti-GI motility agents not be used?
In infectious diarrhea w/ the following:
bloody diarrhea, Shiga-toxin producing E.coli, C.diff
How is Salmonella treated?
Treatment generally not recommended except extreme cases or certain morbidities
-Cipro, Amp/Amox, TMP/SMX, 3rd gen ceph, Azithro
check susceptibility!
Treatments for E.coli GI infection?
FQ, TMP/SMX, Cephalosporins
- usually 3 days
- check susceptibilities!!
V.cholera treatment?
1 dose - 300mg Doxycycline
Giardia treatment
-10 days of Metronidazole
Diarrhea in ped patients - avoid what drugs? What is preferred?
Tetracyclines and FQ
- TMP/SMX, penicillins / cephalosporins are better
What are the symptoms of CMV infection?
90% asymptomatic
Infectious mononucleosis, hepatitis, thrombocytopenia, myocarditis
What is the risk of transmission from pregnant mother to fetus of CMV?
40%
How is CMV isolated for testing and how is diagnosis made?
Virus isolated from buffy coat, urine, or cervical secretions
Tests used:
IgG titer (rapid 4x increase in specific titer)
PCR rapid diagnosis
Measurement of specific IgM (persists 4-8 months after infection)
What is the treatment for congenital CMV?
gancyclovir (IV) or valgancyclovir (oral)
Not recommended if asymptomatic!!!
How is congenital CMV diagnosed?
virus isolated from saliva or urine in first 2 weeks of life
What are the symptoms of congenital CMV? Mortality rate?
10% asymptomatic
Petechiae, jaundice, hepatic and splenic enlargement, thrombocytopenia, conjugated hyperbilirubinemia
Neurologic abnormality: microcephaly, seizures, hypotonia, intracranial calcifications
Sensorineural hearing loss (30%)
Eye abnormalities
Neurodevelopmental delay
Dental abnormalities
15-30% mortality. Survivors: long-term sequelae
What are the symptoms of perinatal CMV infection?
Most subclinical / asymptomatic.
Most common illness is self-limited pneumonitis (severe if infant premature)
No long-term deficits
What are three ways in which neonatal HSV infections present?
SEM : skin, eyes, mucus membranes (40%)
Localized CNS involvement (w/ or w/o SEM) (34%) - seizures, lethargy, apnea. In CSF: pleocytosis, elevated protein
Disseminated: (22%) - adrenal glands, liver, kidneys, heart, etc. Mortality for disseminated - 55% (80% w/o therapy)
Treatment for neonatal HSV infection?
Acyclovir or vidarabine (unusual, but eye-drop formulation available)
Fetal Varicella syndrome
Occurs when mother contracts varicella (not shingles) in first 20 weeks of pregnancy (small risk - 1.2%)
- scarring of infant (cutaneous)
- hypoplastic extremities (usually unilateral, usually lower limbs)
Neonatal varicella
contracted from mother during last 3 weeks of preg
-If maternal infection occurs w/in 5 days before or 2 days after delivery - lesions at 5-10 days of age.
Neonatal varicella treatment
Acyclovir
If mother develops varicella 5 days before or 2 days after delivery - VZV Immunoglobin ASAP
What results from Parvovirus B19 infection?
20% asymptomatic
Fifth disease
Erythema infectosum - skin rash - slapped cheek
In adults - flu like, symmetric polyarthropathy
Chronic - anemia, transient aplastic crisis (virus shuts down RBC production - problematic in sickle cell patients)
Fetal Parvovirus B19 infecion
Can result in hydrops fetalis or death (risk cardiac dysfunction
Toxoplasma gondii infection
80-90% asymptomatic
may be flu-like - muscle aches, lymphadenopathy
responsible for 1-5% mononucleosis cases
Complications - myocarditis, hepatitis, encephalitis, deafness, pneumonia
Tissue bound cysts - latent phase of infection - life long
Treatment of maternal toxoplasmosis
spiramycin - attempt to prevent fetal infection
If fetal infection confirmed - folic acid antagonists - pyrimethamine and sulfadiazine
What organisms are most commonly responsible for sepsis neonatorum?
Group B strep Coagulase neg staph Other strep E.coli H.influenzae C.albicans
In early onset GBS sepsis, what is the usual focus of inflammation?
Usually lungs
Meningitis can also occur
In late onset GBS sepsis, what is the focus of infection?
No focus of inflammation.
Bacteremia is most common presentation
followed by development of meningitis.
Common presentation and cause of mononucleosis
Fever, exudative mononucleosis, lymphadenopathy, hepatosplenomegaly, atypical lymphocytes in peripheral blood
Usually caused by EBV
Also CMV
T.gondii (1-5%)
Treatments for infectious mononucleosis
Bed rest in acute phase
Avoid sports until spleen is no longer palpable
Steroids may be used for some symptoms: massive splenomegaly, tonsillar swelling, hemolytic anemia, hemophagocytic syndrome
Describe the course of HHV-6
Incubation 9-10 days, transmitted via respiratory secretion
Roseola (exanthem subitem, sixth disease)
Fever >102deg F for 3-7 days then macular or papular rash for 2 days (spread from trunk outward)
What organism(s) cause Impetigo?
Usually Group A Strep
Also S.aureus
What causes scalded skin syndrome?
soluble exotoxin of S.aureus
What antibiotics are used for CA-MRSA?
Vancomycin - doesn't penetrate lungs Daptomycin - limited lung pen. inactivated by surfactant Linezolid TMP/SMX Clindamycin (~15% resistant) Doxycycline/minocycline
What is Kawasaki disease?
Unknown etiology - vasculitis of all vessels most severely affecting med. sized arteries
Must have 4 of these:
-bilat. non-exudative conjnctival infections
-changes of oral mucosa
-changes of hands and feet
-rash
-cervical lymphadenopathy >1.5cm
AND
disease not explained by any other process
Presents with fever >39C, always cardiac involvement
How is Kawasaki disease treated?
IV Immunoglobin - 2/kg over 10-12 hrs.
repeated if fever persists
Aspirin 80-100 mg/kg/day divided q6 hrs.
