Gram-Negative Bacteria

first step in ID. stains bacteria either purple (Gram +) or pink/red (Gram -). tells us about the structure of the cell wall. super fast, basic info.

Gram stain

3 multiple choice options

grow the organism in a controlled environment. use automated systems like Vitek to speed up ID and analyze biochemical profil

cultures

3 multiple choice options

a fancy mass spectrometer for bacteria. very fast and accurate. think of it like fingerprinting the bug.

Matrix-Assisted Laser Desorption/Ionization - Time of Flight

3 multiple choice options

done after the organism is identified. helps figure out which antibiotics will work (and which ones won't). critical for choosing targeted therapy.

susceptibility testing

3 multiple choice options

purple stain

Gram positive cocci or bacilli.

1 multiple choice option

red stain

Gram negative bacilli

1 multiple choice option

thick peptidoglycan wall traps crystal violet = purple.

Gram (+)

1 multiple choice option

thin peptidoglycan + outer membrane = safranin stain = pink.

Gram (-)

1 multiple choice option

often appear rod-shaped (bacilli) on stain, especially if you're dealing with enterics.

Gram-negative

1 multiple choice option

thinner peptidoglycan wall (only ~20% of total wall content). more complex, multi-layered: outer membrane (unique to Gram - bacteria), periplasmic space, and inner cytoplasmic membrane

Gram-negative cell wall

1 multiple choice option

endotoxin = toxic AF; triggers cytokine storm, sepsis, fever, DIC.

Lipid A

3 multiple choice options

structural stability.

core polysaccharide

3 multiple choice options

channels for hydrophilic molecules. also play a role in antibiotic resistance (some bacteria close these to keep drugs out – rude!).

porin channels

3 multiple choice options

thick peptidoglycan (murein), contains teichoic acids, no outer membrane, and stains purple

gram-positive bacteria

3 multiple choice options

outer membrane with LPS (O-antigen, Lipid A), porin channels. periplasmic space with thin peptidoglycan layer, enzymes and beta-lactamases (defensive weapons!). inner membrane = similar to all bacteria. stains pink

gram-negative bacteria

3 multiple choice options

only _____________________ has LPS, porins, and an outer membrane. antibiotic resistance often stems from these features (esp. beta-lactamase in the periplasm).

Gram-negative

1 multiple choice option

rare compared to bacilli.

Gram-negative cocci

3 multiple choice options

select all that apply:

which of the following are Gram-negative diplococci (they look like two beans smushed together), oxidase positive, and have unique virulence and transmission routes?

1. Neisseria gonorrhoeae

2. Neisseria meningitidis

Gram negative cocci, oxidase +. usually appear as diplococci (pairs of kidney-shaped cells). likes to grow in mucous membranes—super important for pathogenesis

Neisseria gonorrhoeae

3 multiple choice options

Neisseria gonorrhoeae:

primary route of transmission: __________

can colonize lower genital tract (cervix, urethra), rectum, oropharynx, conjunctivae (neonatal transmission!). also spreads perinatally—can cause neonatal conjunctivitis (ophthalmia neonatorum)

sexual

3 multiple choice options

Neisseria gonorrhoeae:

incidence = ~200 cases per 100,000 people. most common in ages 20-24. most are __________________ —especially in females, which is why routine STI screening is 🔑

asymptomatic

3 multiple choice options

young sexually active woman with dysuria and vaginal discharge + intracellular Gram-negative _________________ = N. gonorrhoeae

diplococci

3 multiple choice options

Gram negative diplococci. has a capsule made of polysaccharides—super important: basis for serogrouping, basis for vaccine development (serogroups A, B, C, W, Y). serogroups B & C are most common in North America.

Neisseria meningitidis

3 multiple choice options

transmission of Neisseria meningitidis: _____________

requires prolonged close contact (think dorms, barracks). carriers can transmit it without getting sick—there are asymptomatic carriers

respiratory droplets

3 multiple choice options

fever, stiff neck, altered mental status, photophobia

meningitis

3 multiple choice options

rapidly progressive, can lead to purpura, DIC, death. Purpura fulminans is a classic finding in meningococcemia

septicemia

3 multiple choice options

Neisseria meningitidis: 1-2 cases per 100,000. can cause:

endemic outbreaks

3 multiple choice options

college student with sudden high fever, neck stiffness, __________________ = N. meningitidis

petechial rash

3 multiple choice options

Kardashian family

Gram-negative, rod-shaped (bacilli), highly diverse (big range of species, some harmless, some deadly)

found in, human/animal gut (normal flora) and environment (soil, water, plants)

enterobacteriaceae family

3 multiple choice options

select all that apply:

who's in the Enterobacteriaceae crew?

1. E. coli

2. Klebsiella spp.

3. Enterobacter spp.

4. Serratia marcescens

5. Proteus spp.

6. Morganella morganii

7. Citrobacter spp.

8. Shigella spp.

9. Salmonella spp.

UTI king, diarrhea, sepsis

E. coli

3 multiple choice options

pneumonia, UTIs, abscesses

Klebsiella spp.

3 multiple choice options

nosocomial infections

Enterobacter spp.

3 multiple choice options

red pigment producer, also hospital-associated

Serratia marcescens

3 multiple choice options

swarming motility, kidney stones

Proteus spp.

3 multiple choice options

rarer, but still hospital-relevant

Morganella morganii

3 multiple choice options

nosocomial

Citrobacter spp.

3 multiple choice options

dysentery

Shigella

3 multiple choice options

typhoid and foodborne illness

Salmonella spp.

3 multiple choice options

select all that apply:

what are the shared features of the Enterobacteriaceae family?

1. oxidase negative

2. lactose fermenting

3. nitrate reducing

4. Gram-negative rods

select all that apply:

what are some structures of the Enterobacteriaceae family?

1. flagella → mobility (Proteus especially swarms)

2. pili (fimbriae) → adhesion to mucosa

select all that apply:

what are some antigenic structures of the Enterobacteriaceae family?

1. O antigen

2. H antigen

3. K antigen

part of LPS (outer membrane); important for virulence

O antigens

3 multiple choice options

flagellar protein

H antigens

3 multiple choice options

capsule/fimbrial protein (helps immune evasion)

K antigens

3 multiple choice options

cause diarrhea (e.g., heat-labile/stable toxins in ETEC)

enterotoxins

3 multiple choice options

help the bacteria stick to mucosal surfaces: fimbriae (e.g., P-fimbriae in E. coli for UTIs)

adhesions

3 multiple choice options

destroy red cells

hemolysins

3 multiple choice options

fever, inflammation, septic shock. some O-antigens can increase immune evasion.

LPS (endotoxin)

3 multiple choice options

bacteria steal ___________ from the host (which is essential for growth). this gives them a survival advantage, especially during infection

iron

3 multiple choice options

Kim Kardashian

short Gram-negative bacillus (rod-shaped). lives happily in your gut... until she doesn't.

Escherichia coli

3 multiple choice options

E.coli antigenic serotyping: part of LPS (outer membrane)→ 173 types! associated with virulence

O-antigens

3 multiple choice options

E.coli antigenic serotyping: capsule→ especially important in K1 strains → neonatal meningitis

K-antigens

3 multiple choice options

E.coli antigenic serotyping: flagella→ helps with motility

H-antigens

3 multiple choice options

a hemorrhagic strain. produces Shiga-like toxin → bloody diarrhea, hemolytic uremic syndrome (HUS)

K1 strain = crosses blood-brain barrier → neonatal meningitis

O157:H7

3 multiple choice options

#1 aerobic organism in your intestinal flora (GI tract = its natural habitat). also found in meats, soil, water → major contamination risk if hygiene/sanitation is poor

E. coli

3 multiple choice options

E. coli = most common cause, esp. in women

urinary tract infection

3 multiple choice options

E. coli has multiple types (enterotoxigenic, enterohemorrhagic, etc.)

diarrhea

3 multiple choice options

bloodstream infections, esp. in compromised hosts (elderly, catheterized)

bacteremia

3 multiple choice options

E. coli:

#1 cause of ___________________ (especially outpatient)

key virulence factors:

1. P fimbriae - help it cling to uroepithelium

2. hemolysins - break down host cells

3. K antigens - resist immune defenses

UTI

3 multiple choice options

Enterotoxigenic E. coli (ETEC) - produces LT/ST enterotoxins → watery diarrhea

traveler's diarrhea

3 multiple choice options

associated with undercooked beef, spinach, water contamination. produces Shiga-like toxin. can cause HUS = hemolysis, renal failure, low platelets

Enterohemorrhagic E. coli = O157:H7

3 multiple choice options

is high alert: it can lead to bloody diarrhea + renal failure. antibiotics may worsen toxin release → careful with treatment

O157:H7

3 multiple choice options

Khloe Kardashian

large, plump Gram-negative rods due to their thick polysaccharide capsule→ capsule makes them appear extra large on Gram stain and gives colonies a mucoid (slimy) appearance. endotoxin (LPS) is their main virulence factor, but the capsule is their best defense against phagocytosis.

Klebsiella spp.

3 multiple choice options

indole positive→ the indole test helps differentiate species in the lab.

K. oxytoca

3 multiple choice options

indole negative

K. pneumoniae

3 multiple choice options

select all that apply:

what are some clinical diseases associated with Klebsiella spp.?

1. UTIs

2. cholangitis (bile duct infection)

3. pneumonia

4. bacteremia

these bad boys are notoriously resistant due to:

_____________________ - sometimes also carbapenemases (CRE - carbapenem-resistant enterobacteriaceae). BIG clinical issue in ICUs, especially ventilator patients.

plasmid-mediated extended-spectrum beta-lactamases

3 multiple choice options

Kourtney Kardashian

two major species:

E. cloacae (most clinically significant)

E. aerogenes

Enterobacter spp.

3 multiple choice options

1976: multihospital outbreak of ______________ showed how resilient and dangerous Enterobacter can be in hospital settings

nosocomial bacteremias

3 multiple choice options

Enterobacter spp.:

5th leading cause of ____________________. major nosocomial pneumonia pathogen→ especially in ventilated patients or those with invasive lines

ICU infections

3 multiple choice options

produces inducible AmpC beta-lactamase → can initially appear sensitive on cultures but turn resistant during treatment → avoid 3rd-gen cephalosporins; consider carbapenems or cefepime

Enterobacter

3 multiple choice options

produces a red pigment (prodigiosin). common in hospital water and IV fluids. causes pneumonia, endocarditis, and catheter infections

SPICE organism (inducible AmpC β-lactamase)

Serratia spp.

3 multiple choice options

highly motile with swarming motility on agar. produces urease → increases urine pH → struvite kidney stones. smells like rotten eggs (hydrogen sulfide). common in UTIs, esp. in elderly men or with catheters

Proteus spp.

3 multiple choice options

opportunistic and rare, but can cause UTIs, wound infections, and sepsis. also produces urease. some strains resistant to multiple drug classes

Morganella morganii

3 multiple choice options

opportunistic, especially in neonates. can cause meningitis, brain abscesses, bacteremia. also SPICE group → possible beta-lactam resistance

Citrobacter spp.

3 multiple choice options

Gram-negative bacillus (technically part of the E. coli group genetically). non-motile, oxidase negative, does not ferment lactose. virulence = TOXIN. only a very small inoculum (10–100 organisms) is needed to cause disease — this makes it very contagious

Shigella spp.

3 multiple choice options

select all that apply:

what are the four main serogroups of Shigella spp.?

1. A = Shigella dysenteriae (most severe)

2. B = S. flexneri

3. C = S. boydii

4. D = S. sonnei (most common in U.S.)

transmission of Shigella:

___________________ — think poor sanitation, contaminated water, food, public pools, and flies (ew). HIGHLY contagious in daycare centers, prisons, and refugee camps.

fecal-oral route

3 multiple choice options

select all that apply:

what are some indications there may be Shigella involved?

1. high fever

2. bloody diarrhea with mucus (aka dysentery)

3. symptoms appear ~12 hours after ingestion in some cases

serotyped by O (LPS) and H (flagella) antigens

S. typhi and S. paratyphi = causative agents of typhoid fever. humans are the only known reservoir (no animal transmission)

Salmonella spp.

3 multiple choice options

incubation: 1-3 weeks after ingestion. systemic illness, not just GI: high prolonged fever, rose spots on the abdomen, relative bradycardia, hepatosplenomegaly, and constipation or diarrhea

most common in foreign travel: South & East Asia, Africa, and Latin America

typhoid fever

3 multiple choice options

many species cause self-limiting gastroenteritis. common strains: S. enteritidis, S. typhimurium, S. arizonae (from exotic pets like reptiles), S. dublin (unpasteurized milk, raw dairy)

non-typhoid Salmonella

3 multiple choice options

transmission of non-typhoid Salmonella: fecal-oral route (contaminated food/water). 50% of cases = ________________. think eggs, undercooked chicken, pet reptiles, and raw milk

poultry

3 multiple choice options

clinical disease in Salmonella spp.:

nausea, vomiting, abdominal cramps, watery or loose diarrhea. usually self-limited but can cause ______________ in high-risk patients (e.g., infants, elderly, immunocompromised)

sepsis

3 multiple choice options

low inoculum, shiga toxin, bloody diarrhea, daycare, pools

Shigella

3 multiple choice options

travel history, rose spots, long fever, systemic illness

typhoid Salmonella

3 multiple choice options

contaminated poultry/dairy, self-limiting diarrhea

non-typhoid Salmonella

3 multiple choice options

select all that apply:

which of these are the main troublemakers in healthcare settings (they all belong to the Enterobacteriaceae family)?

1. Klebsiella spp.

2. Enterobacter spp.

3. Serratia marcescens

4. Proteus spp.

5. Citrobacter spp.

select all that apply:

Enterobacter are normal flora, but they become pathogenic with which of the following?

1. translocation (like from GI to bloodstream)

2. infection of catheters or surgical wounds

3. exploitation of immunocompromised patients

enzymes that hydrolyze (break down) most beta-lactams, including penicillins, 1st-3rd gen cephalosporins, and aztreonam

extended spectrum beta-lactamases

3 multiple choice options

most commonly associated with ESBLs.

E. coli and Klebsiella spp.

3 multiple choice options

select all that apply:

E. coli and Klebsiella require treatment with which of the following?

1. carbapenems (e.g., meropenem)

2. non-beta-lactam options depending on susceptibility

even carbapenems are no longer effective. extremely dangerous and life-threatening due to limited treatment options. spread rapidly in ICUs via ventilators, central lines, catheters.

carbapenem-resistant enterobacteriaceae

3 multiple choice options

select all that apply:

what are some clinical infections caused by these Enterobacteriaceae and nosocomial organisms?

1. urinary tract infections (UTIs)

2. pneumonia

3. cellulitis

4. CNS infections

5. intra-abdominal infections

select all that apply:

if you see a patient with fever, catheter, ICU stay, or immunosuppression—and the bug is Gram-negative with mucoid colonies or resistance to ceftriaxone—you should IMMEDIATELY think which of the following?

1. ESBL/CRE Enterobacteriaceae

2. consider infection control, narrow abx options, and bad outcomes

the Gram-negative baddie of the ICU. if this pathogen had a personality, it would be the nosocomial villain with a flamethrower and a gas mask.

Pseudomonas aeruginosa

3 multiple choice options

Gram-negative bacillus, oxidase positive (a major lab clue!), non-lactose fermenter (so it's clear or colorless on MacConkey agar). produces a blue-green pigment called pyocyanin (this is unique!)→ it fluoresces under UV light.

Pseudomonas aeruginosa

3 multiple choice options

Pseudomonas aeruginosa:

environmental organism: found in soil, water, hospital surfaces, sinks, mops, respiratory equipment. loves moist areas → ventilator tubing, urinary catheters, wounds, burns. it can colonize human flora, especially in hospitalized or ___________________ patients (i.e. people with cancer, burns, cystic fibrosis)

immunocompromised

3 multiple choice options

Pseudomonas aeruginosa:

rarely causes disease in healthy folks—needs compromised host defenses to invade. opportunistic: thrives when ________________ are down (e.g., neutropenia, chronic wounds, long hospital stays)

immune defenses

3 multiple choice options