Gram Negative Bacteria

Question 1

Bordetella pertussis

Answer 1

Gram-negative coccoid
Special features: aerobic/facultative anaerobic
Disease: whooping cough
Epi: kids , no bacteremia
Unique diagnostic methods: Bordet-Gengou media for nasopharyngeal culture
Treatment/notes: TDAP vaccine; treatment: macrolides/azalides, quinolones +/- tetracycline

Question 2

Haemophilus influenzae

Answer 2

Gram-negative coccoid
Special features: aerobic/facultative anaerobic
Diseases: sinusitis, infant meningitis
Epi: rare because of vaccine
Virulence factor: capsule
Transmission/Pathogenesis: same as pneumococcus
[cell wall proteins bind to sialic acid, platelet activating factor receptors, IgA protease inhibits IgA, removed via IgG-mediated opsonization in spleen
Signs/symptoms: persistent, severe sinusitis
Treatment/notes: Amoxicillin, steroids?

Question 3

Anaplasma spp. (includes phagocytophilium)

Answer 3

Gram-negative coccoid
Special features: vector-borne, intracellular
Diseases: HGA (human granulocytic anaplasmosis)
Epi: NE, West, summertime, elderly
Virulence factors: P-selectin ligand allows infection of white cells
Transmission/pathogenesis: bite from deer tick (lxodes scapularis, reservoir for nymphs is small mammals e.g. white-footed mouse, white-tailed deer for adults) –> infect WBCs
Signs/symptoms: flu-like symptoms, varying severity, no rash
Unique dx methods: PCR, serologic, peripheral smear for murulae (bodies on phagosomes)
Treatment/Notes: doxycycline

Question 4

Ehrlichia spp.

Answer 4

Gram-negative coccoid
Special features: vector-borne, intracellular
Disease: Human Monocytic Ehrlichiosis (HME)
Epi: central, SE, summertime, elderly
Virulence factors: P-selectin ligand allows infection of white cells
Transmission/Pathogenesis: bite from lone star tick (amblyomma americanum, white tailed deer is reservoir) –> infect WBCs (monocytes or granulocytes)
Signs/symptoms: flu-like symptoms, varying severity, no rash
Unique dx methods: PCR, serologic peripheral smear for morulae (bodies on phagosomes)
Treatment/notes: doxycycline

Question 5

Vibrio Cholera

Answer 5

Gram-negative comma-shaped
Special features: non-lactose fermenting, oxidase (+)
Diseases: cholera
Epi: 3-5 M cases, 100K deaths
Virulence factors: cholera toxin (ToxR gene), colonizing factor
Transmission/pathogenesis: high inoculum ingested via contaminated food or water (may be fecal-oral), enterotoxin acts on small intestine
Signs/symptoms: 75% asymptomatic, diarrhea with dehydration, tenting of skin but no fever, shedding 1-2 wks s/p infection
Treatment/notes: oral rehydration solution, IV if severe, vaccine

Question 6

Campylobacter jejuni

Answer 6

Gram-negative comma-shaped
Special features: non-lactose fermenting, oxidase (+)
Disease: food poisoning
Signs/symptoms: bloody diarrhea

Question 7

Neisseria meningitidis

Answer 7

Gram-negative diplococcus
Special features: maltose-fermenting
Disease: meningitis (adults)
Epi: adolescents, military, travelers, sub-Saharan Africa
Virulence factors: pili, capsule, Lipopolysaccharide
Transmission/pathogenesis: binds factor H, inhibits lysis, encapsulated so IgG and complement must be functional, type IV pilus binds to ciliated epithelial cells
Signs/symptoms: meningococcemia, fulminant sepsis, progressing rapidly to meningitis
Unique dx methods: Lumbar puncture, preceded by CT if risk of herniation
Treatment/notes: 3G cephalosporin; prophylaxis: rifampin/cipro/ceftriaxone; conjugate vaccine exists for kids + teens

Question 8

Neisseria gonorrhoeae (GC)

Answer 8

Gram-negative diplococcus
Special features: non-maltose fermenting
Disease: gonorrhea
Epi: 15-24 yo, second most common bacterial STI, esp MSM
Virulence factors: porin, pillin, OPA
Transmission/pathogenesis: porin degranulates PMNs, pilin necessary for infection, OPA affects tight junctions + cell-cell signaling; blocks antibodies and complement
Signs/symptoms: 2-5 day incubation period followed by purulent urethral discharge (men), endocervical disease/pain/purulence (women), pharyngitis, gonococcal opthalmia, PID, rectal infection, disseminated infection (more likely in complement deficit)

Question 9

Haemophilus ducreyi

Answer 9

Gram-negative pleomorphic
Special features: fastidious (requires complex nutritional environment)
Disease: chancroid
Epi: M>F, in Africa; STI
Transmission/Pathogenesis: direct sexual contact
Signs/symptoms: multiple painful ulcers (vs. painless in syphilis), lymphadenitis (buboes)
Unique dx methods: culture on chocolate agar (“school of fish”)
Treatment/notes: macrolides, cephalosporin, quinolone

Question 10

Chlamydia trachomatis (STI-chlamydia)

Answer 10

“Gram-negative pleomorphic”
Special features: obligate intracellular
Epi: 3M/yr, most common bacterial STI in US, 13-19 yo
Transmission/Pathogenesis: often transmitted together with GC, elementary body is infectious extracellular, enters cell as reticulate body, which replicates using host ATP and releases more elementary bodies
Signs/symptoms: urethritis in men, + cervicitis, PID in women, conjunctivitis in newborns, can lead to Reiter’s syndrome (+reactive arthritis –> “can’t see, pee, or climb a tree”)
Unique dx methods: PCR (NAAT)
Treatment/notes: azithromycin or doxycycline

Question 11

Chlamydia trachomatis (pneumonia)

Answer 11

“Gram-negative pleomorphic”
Special features: obligate intracellular
Epi: Neonates (1-3 mo)
Transmission/Pathogenesis: infects non-ciliated columnar cells, multiply in alveolar macrophages
Signs/symptoms: increased eosinophils, not PMNs; no fever, staccato-like cough, tachypnea, perihilar infiltrates
Unique dx methods: serology (4x rise in titer) or nucleic acid test on eye discharge
Treatment/notes: macrolides/azalides (erythromycin), quinolones +/- tetracycline

Question 12

Chlamydophila pneumoniae

Answer 12

“Gram-negative pleomorphic”
Special features: obligate intracellular
Epi: school age children, elderly
Transmission/Pathogenesis: prolonged incubation period, indolent
Signs/symptoms: pneumonia
Unique dx methods: PCR, serology
Treatment/notes: macrolides, doxycycline, levofloxacin

Question 13

Chlamydia psittaci

Answer 13

“Gram-negative pleomorphic”
Special features: obligate intracellular
Disease: pneumonia
Epi: exposed to birds (parrots)
Transmission/pathogenesis: inhaled
Signs/symptoms: increased eosinophils, can see fever, rash, CNS symptoms, hepatitis, pericarditis
Unique dx methods: serology; diffuse, hazy CXR
Treatment/notes: macrolides/azalides, quinolones +/- tetracycline

Question 14

Rickettsia akari

Answer 14

Gram-negative Pleomorphic
Special features: vector-borne, intracellular
Disease: rickettsial pox
Epi: urban areas
Transmission/pathogenesis: mus musculus (house mouse) is reservoir, mite is vector
Signs/symptoms: swollen lymph nodes, necrotic eschars
Unique dx methods: clinical
Treatment/notes: self-limited without treatment, can use doxycycline

Question 15

Francisella tularensis

Answer 15

Gram-negative pleomorphic
Special features: vector-borne, intracellular
Disease: pneumonia
Epi: rabbits
Virulence factors: same as RMSF
[Weak Lipopolysaccharide, OmpB (outer membrane protein B, adherence to endos), RickA (activates host cell actin, pushes to cell surface)
Transmission/pathogenesis: mus musculus is reservoir, mite is vector

Question 16

Rickettsia prowazekii

Answer 16

Gram-negative pleomorphic
Special features: vector-borne, intracellular
Disease: Endemic Typhus
Epi: war, unsanitary conditions
Transmission/pathogenesis: human is reservoir, human body louse is vector, infection occurs when infected feces are scratched into bite
Signs/symptoms: fever, myalgia, cough, severe headache, delirium, centrigually spreading rash, multi-organ failure and death 40% of the time, can reactivate (Brill-Zinsser disease
Treatment/notes: doxycycline

Question 17

Rickettsia rickettsii

Answer 17

Gram-negative pleomorphic
Special features: vector-borne, intracellular
Disease: Rocky Mountain Spotted Fever (RMSF)
Epi: most common in SE, south, usually during summer, * purpura, spreads to palms and soles; very serious illness
Unique dx methods: immunohistochemistry on skin biopsy, serology, but generally diagnose clinically and treat right away
Treatment/notes: doxy (regardless of age)

Question 18

Salmonella enteritidis

Answer 18

Gram-negative rod
Special features: lactose non-fermenting, oxidase (-), facultative anaerobic
Disease: (non-typhoid) food poisoning
Epi: chicken, eggs
Virulence factor: capsule
Transmission/Pathogenesis: most animals colonized; eating undercooked chicken or eggs
Signs/symptoms: gastroenteritis

Question 19

Salmonella typhi

Answer 19

Gram-negative rod
Special features: lactose non-fermenting, oxidase (-), facultative anaerobic
Disease: typhoid fever
Virulence factor: capsule
Transmission/pathogenesis: fecal-oral
Signs/symptoms: fever, HSM, salmon pink rash, leukopenia

Question 20

Shigella spp.

Answer 20

Gram-negative rod
Special features: lactose non-fermenting, oxidase (-), facultative anaerobic
Diseases: food poisoning, dysentery
Virulence factor: enterotoxin, shiga toxin
Transmission/Pathogenesis: low inoculum, person-person or fecal contamination, invades intestinal epithelial cells
Signs/symptoms: 12 hr incubation period –> watery diarrhea –> bloody diarrhea; shedding for 1-4 weeks after infection
Treatment/notes: shiga toxin stops protein synthesis in cells, kills them (not all shigella has shiga)

Question 21

Pseudomonas aeruginosa

Answer 21

Gram-negative rod
Special features: lactose non-fermenting, oxidase (+), facultative anaerobic
Diseases: RTI, hot-tub rash
Epi: recent flu, structural lung defect, CF
Signs/symptoms: malignant otitis externa, ecthyma gangrenosum (black necrotic center with raised hemorrhagic ring outside)
Treatment/notes: extended-spectrum penicillins, quinolones, aminoglycosides (AGs), carbapenemes, ceftazidime (3G cephalosporin), cefepime (4G cephalosporin)

Question 22

Escherichia coli

Answer 22

Gram-negative rod
Special features: lactose-fermenting, facultative anaerobic
Diseases: uncomplicated UTI, neonatal meningitis, diarrhea, hemolytic uremic syndrome
Epi: O157: H7 responsible for multiple outbreaks
Virulence factors: toxins (can include shiga-like toxins)
Transmission/pathogenesis: GI tracts of many animals, humans –> release enterotoxin (ETEC, traveler’s diarrhea), or cytotoxin (EHEC, have Shiga toxin)
Signs/symptoms: impaired motility with ETEC, bloody diarrhea from low inoculum with EHEC; HUS may result (hemolytic anemia, thrombocytopenia, acute kidney injury)
Treatment/notes: 3G cephalosporin, quinolones, aminoglycosides, carbapenemes, extended-spectrum penicillins, aztreonam

Question 23

Klebsiella granulomatis

Answer 23

Gram-negative rod
Special features: lactose-fermenting, facultative anaerobic
Diseases: klebsiella
Epi: STI; PNG, India
Virulence factor: capsule
Transmission/pathogenesis: aka calymmatobacterium granulomas
Signs/symptoms: no lymph node involvement, painless
Treatment/notes: 3G cephalosporin, quinolones, aminoglycosides, carbapenems, extended-spectrum penicillin, aztreonam

Question 24

Klebsiella pneumoniae

Answer 24

Gram-negative rod
special features: lactose-fermenting, facultative anaerobic
Disease: pneumonia
Virulence factor: capsule
Signs/symptoms: currant jelly sputum
Treatment/notes: 3G cephalosporin, quinolones, aminoglycosides, carbapenems, extended-spectrum penicillin, aztreonam

Question 25

Bacteroides fragilis

Answer 25

Gram-negative rod Special features: *obligate anaerobic* Disease: *90% of peritoneal infections, appendicitis* Virulence factors: capsular polysaccharide complex (CPC) Transmission/pathogenesis: part of endogenous gut flora, helps synthesize vitamin K and deconjugate bile acids; CPC leads to abscess formation Treatment/notes: metronidazole, 2G cephalosporins, carbapenems, extended-spectrum penicillins with beta-lactamase inhibitors (e.g., piperacillin-tazobactram)

Question 26

Legionella spp.

Answer 26

Gram-negative rod special features: poorly staining Disease: *Legionnaire's Disease (CAP=community-acquired pneumonia)* Epi: immunocompromised, hospitalized Transmission/pathogenesis: grow in water (e.g., old pipes), aspiration or inhalation --> invasion of phagosome, intracellular replication, microabscesses Signs/symptoms: 10 days, flu-like illness, pneumonia, very high (e.g., 105F), multilobar infiltrates, microabscesses, increased WBCs, abnormal liver function test, renal panel Unique dx methods: urinary antigen, serology > 1:128 Treatment/notes: macrolides or levofloxacin, prevent by sterilizing water

Question 27

Treponema pallidum pallidum

Answer 27

Gram-negative spirochete Special features: motile Disease: syphilis Epi: STI; MSM, commercial sex workers, HIV, etc. Transmission/pathogenesis: direct contact with primary or secondary syphilitic lesion, transmission in 1/3 of contact (very high, vs. HIV < 1%); 3 week incubation Signs/symptoms: *primary=painless ulcers (chancre, mucous patches, condyloma lata)* *secondary* = lymphadenopathy/*red rash on palms + soles*/alopecia *tertiary*=less infectious, more difficult to treat (gummatous, visceral granulomas, syphilitic aortitis); *neurosyphilis*= tabes dorsalis (dorsal horn), Argyll-Robertson pupil Unique dx methods: non-treponemal VDRL/PRP to screen; treponemal fluorescent antibody test (FTA-ABS) to confirm; dark field microscopy Treatment/notes: long-term penicillin --> if allergic, consider desensitization, especially if pregnant --> if can't be desensitized, try doxycycline; look out for Jarisch-Herxheimer reaction (cytokine storm at first 24-36 hours of therapy)

Question 28

Leptospira spp.

Answer 28

``` Gram-negative spirochete Special features: saprophytic Disease: Leptospirosis Virulence factor: capsule Unique dx methods: darkfield microscopy ```

Question 29

Borrelia burgdorferi

Answer 29

Gram-negative spirochete Special features: vector-borne Disease: Lyme disease Epi: most common vector-borne dz in US; NE; summer Virulence factors: OSPs (outer surface proteins), DbpA+B, TLR1/2 induces IFN Transmission/pathogenesis: bite from nymphs of deer tick (Ixodes scapularis) feeds for 24+ hours --> infects WBCs Signs/symptoms: erythema migrans (large spreading *bull's eye lesion*) --> Bell's palsy (unilateral CN VII), meningitis, radiculopathy, myalgias, arthralgias, heart block, pericarditis, post-Lyme syndrome (autoimmune?) Unique dx methods: erythema migrans is pathognomonic, antibodies, CSF Treatment: doxycycline + amoxicillin + ceftriaxone