Gram Negative Bacteria Flashcards Preview

Inhibits leukocyte function by producing cAMP in the presence of host cell calmodulin

Localized tissue destruction in infection

Peptidoglycan fragment that inhibits/kills ciliated cells and is pro-inflammatory 

Highly communicable

Via droplets

Most contagious during the catarrhal stage

Upper airway

1. Incubation (2 weeks)
2. Catarrhal stage: mild coughing and sneezing, patient is very infectious
3. Paroxysmal stage: explosive cough followed by whoop during inhalation, may lead to exhaustion/cyanosis/vomiting/convusions, resolution is very slow

Catarrhal stage

Atypical lymphocytosis

Collected from nasopharynx

Grown on Bordet-Gengou medium or charcoal-containing medium

Cultures are rarely positive after 4 weeks of symptoms

Antibiotic treatment for Bordetella pertussis infection is most effective in the catarrhal stage, before the "whooping" symptoms begin

After the onset of the paroxysmal stage, antibiotic treatment is not as effective at altering the course of disease

Macrolides

(TMP/SMX may also be effective)

Whole-cell killed vaccine combined with toxoid vaccines against tetanus and diphtheria 

Poor long-term efficacy of pertussis component; seizures and hyporesponsive episodes; frequent side effects in kids

DTap: uses acellular components of Bordatella pertussis (detoxified pertussis toxin, FHA, pertactin, fimbriae) to generate immunity

Tdap booster (reduced amounts of diphtheria and pertussis components)

Pregnant women should receive Tdap with each pregnancy

Brucella are small aerobic Gram-negative coccibacilli 

Brucellosis in humans as well as cattle, goats, and hogs

Exposure to infected animalks (contact with mucous membranes, cuts in skin, inhalation) or consumption of unpasteurized milk or other dairy products

Veterinatians, meat inspectors, others who work with meat/animals

Macrophages

Fever*, chills, malaise, and drenching sweats

Infection can be chronic and last for weeks or months

(Fever may be undulant; rise and fall)

Isolation of organism from blood or biopsy specimens, though Brucella spp. may take from 2-4 weeks to grow

Serological tests are also available

• Doxycycline + rifampin/gentamicin/streptomycin
• Vaccine for animals not humans

Francisella tularensis are small, metabolically facultative, Gram-negative coccibacilli 

(similar in morphology to Brucella)

Contact with rabbits, squirrels, muskrats, beavers, and deeper through tiny breaks in skin, exposure of mucous membranes, ingestion, or inhalation (also via ticks)

Skinning rabbits on a hunting trip

Macrophages

Site of innoculation is ulcerated

Regional lymphadenopathy

Fevers and chills

Possible pneumonia and dissemination to multiple organs

• Francisella tularensis is difficult to grow in the lab and requires media
• Serological assay available

• Streptomycin or gentamicin
• Vaccine recommended for laboratory workers and others who have frequent contact with infected animals

Culture specimen from infection on routine lab media

• Plump, gram (-) rods
• Hypermucoviscous strains overproduce capsule and have a hypermucoid appearance

On MacConkey agar

• Turns the agar pink (can ferment lactose)

Pasteurella multocida are small Gram-negative coccobacili that are part of the normal respiratory flora of some animals (especially cats and dogs)

Very resistant to antibiotics!

If positive for extended-spectrum beta-lactamase (ESBL)

• Use carbapenem

If positive for kelbsiella pneumoniae carbapenemase (KPC) or New Delhi Metalocarbapenemase (NDMC)

• Use aminoglycoside, colistin, ceftazidime, avibactam, meropenem-vabobactam 

Cat or dog bite

Zoonotic infections can be acquired both directly and indirectly from animals

Neisseria are Gram-negative diplococci

All encode SHV Beta-lactamase on chromosome

• Resistant to ampicillin, amoxicillin

Some encode Extended-spectrum beta-lacatamase (ESBL)

• Resistant to all beta-lactams except carbapenem

Some encode Klebsiella pneumonia carbapenemase (KPC) or New Delhi Metalocarbapenemase (NDMC)

• Resistant to almost all beta-lactams inclucding carbapenem

Klebsiella pneumoniae is typically resistant to most early-line beta-lactam antibiotics

Neisseria menigitidis and Neisseria gonorrhoeae

Meningitis and bloodstream infections

People living in crowded conditions (e.g. students in college dorms) are at particular risk

Antiphagocytic and resists complement-mediated killing

Basis for serogrouping and target of vaccines

Tetanus spores have a reservoir in soil

Serogroup A

Sexually transmitted (gonorrhea)

Local infections such as urethritis and cervicits but can spread regionally to cause epididymitis and pelvic inflammatory disease or systemically to cause disseminated gonorrhea 

Gram negative rods that colonize or infect the GI tract

Diarrhea is mESSYY 

Minnie's pneumonic: 

• E. coli
• Salmonella enterica (Serovars enteritidis and typhi)
• Shigella 
• Yersinia enterocolitica
• Yersinia pseudotuberculosis

Produces pili that change their antigenic make-up during the course of infection (antigenic variation)

Moraxella catarrhalis are small Gram-negative cocci or coccobacilli that cause otitis media, sinusitis, bronchitis, and pneumonia

(morphologically and metabolically resemble Neisseria spp.)

LT

Heat Labile Toxin secreted by ETEC

Normal flora of upper and lower GI tract, respiratory tract, and female genital tract

Opportunistic pathogens (affect compromised host, such as when intestines ruptures or mouth contents aspirate into the lungs)

Prone to form polymicrobial abscesses that also include facultative anaerobic organisms such as E. coli

Bacteroides spp., Prevotella spp., Fusobacterium spp.

Proteus spp

Proteus mirabilis

Proteus vulgaris

UTIs (Hospital Acquired and Community Associated)

Also associated with nosocomial infections

Each cell has hundreds of flagella

Proteus spp.

Proteus is urease positive

• Urease splits urea into ammonium hydroxide + CO2
• This raises urine pH (makes it more alkaline)
• This promotes the formation of struvite kidney stones

UTIs caused by Proteus are associated with "struvite" kidney stones

Proteus is urease positive; 

• Urease -> splits urea into ammonium hydroxide -> raises pH -> Kidney stone formation

Often antibiotic resistant... 

• Nosocomial respiratory infections
• UTIs
• Bloodstream infections

Often antibiotic resistant... 

• Nosocomial respiratory infections
• UTIs
• Bloodstream infections

Often antibiotic resistant... 

• Nosocomial respiratory infections
• UTIs
• Bloodstream infections

• Enterobacter spp.
• Citrobacter spp.
• Serratia marcescens

Serratia marcescens

Proteus spp.

Grows in this pattern due to swarming motility

PAL-VCH 

• Pseudomonas aeruginosa
• Acinetobacter baumanni
• Legionella pneumophila
• Vibrio cholerae
• Campylobacter jejuni
• Helicobacter pylori

Ecthyma gangrenosum: A black eschar indicating cutaneous necrosis caused by Pseudomonas aeruginosa

Pseudomonas aeruginosa

He likely acquired the bacteria from the hot tub

Pseudomonas Aeruginosa

Colors are due to pyocanain and pyoverdin (a siderophore)

May also have a grape-like odor 

Legionella pneumophilia 

Legionella pneumophilia

- Not visualized on gram stain, overgrown by other respiratory flora on normal agar

BCYE agar = buffered charcoal-yeast extract agar

- Contains L-cysteine, agar, and antibiotics to prevent the growth of other bacteria

- Both an enrichment agar and a selective agar

Helicobacter pylori

Look for flagella and curved shape

Helicobacter pylori

Urease positive = cleaves ammonium hydroxide from urea. This creates a less acidic microenvironment in the mucus overlying the epithelium in which H. pylori grows, reproduces, and invades the stomach epithelium.

Pseudomonas aeruginosa is a gram negative, obligate aerobic rod. 

It is found in faucets, drains of hospitals and often has fluorescent pigments

It does not ferment; Catalase (+), oxidase (+) 

CASCQET - E (Like casket-y... kind of a stretch)

• Can survive at high temperatures (42 C)
• Adhesions
• Siderophore-producing 
• Capsule
• Quorum Sensing
• Exotoxin A
• Type III Secretion System
• Endotoxin 

Exotoxin A is secreted by Pseudomonas aeruginosa

It ADP-ribosylates EF-2 of the host ribosome. This inhibits protein synthesis and leads to cell death

(Functions similarly to diphtheria toxin)

Quorum sensing allows bacteria to sense how many of them there are. Each bacteria secretes an autoinducer signal, and can sense the concentration of that signal.

Higher concentration => more bacteria are around => they secrete more toxins since there are enough of them to overpower host defenses 

Pseudomonas aeruginosa has quorum-sensing abilities

Cystic Fibrosis

P. aeruginosa colonizes the lungs of CF patients; it causes repeat infections and is the most common cause of respiratory failure in this population

Pseudomonas aeruginosa

Pneumonia in hospitalized patients

- Usually acute, may be necrotizing

- Also causes other nosocomial infections 

• Folliculitis: associated with under-chlorinated hot tubs
  • (The bacteria can survive and grow in hot temperatures)
• Swimmer's ear
• Osteomyelitis: IV drug users and diabetics

• Cystic Fibrosis patients -> Pneumonia
• Ventilated patients -> Pneumonia
• Burn patients -> Skin infection
• Catheterized patients -> UTI
• Neutropenic patients (undergoing chemo) -> Bacteremia
• IV drug users -> Osetomyelitis
• Diabetics -> Osteomyelitis
• Hot tub users -> Folliculitis

May cause bacteremia and cutaneous necrosis

- Look for an ecthyma gangrenosum (black eschar)

• Grows on many types of lab media
• Gram (-), Catalase (+), oxidase (+)
• Grape-liek odor
• Fluorescent pigments

Siderophores

Pyocyanin and pyoverdin

Very reisistant to antibiotics; use 2 drugs until susceptibility is known

• Choice: Aminoglycoside + beta-lactamase
  • Piperacillin, ceftazidime, cefepime, ceftolozane-tazobactam, imipenem/peropenem, aztreonam
     
• Alternative: Quinolone + piperacillin 

Note: Cefalosporins are not active against P. aeruginosa

Don't use tap water to wash respiratory equipment (P. aeruginosa may be living in hospital faucets)

Be aware that P. aeruginosa may contaminate hospital disinfectants

Acinetobacter baumannii is a gram negative, non-fermenting, bacillus or coccobacillus 

Hospital-acquired infections

• Pneumonia
• Bloodstream infections
• Wound infections

Very resistant to antibiotics!

Choice: carbapenem, amikacin, colistin

Note: Sublactams (beta-lactamase inhibitors) work against some strains

Legionella pneumophilia is a gram negative, obligate anaerobic, facultative intracellular, thin bacillus. 

Oxidase (+)

Serogroup 1 causes 80% of disease

Infects amoebae

Hospitals; faucets and drains

Under-chlorinated hot tubs

Natural bodies of water

Cooling towers of air-conditioning units

Water distribution systems

• Infects macrophages
• Dot - "Defect of Organelle Trafficking" genetic locus
• Type IV secretion system
• Phospholipase C

Legionella pneumophilia promotes coiling phagocytosis

• Promotes the formation of a long, thin, pseudopod by the macrophage
• The macrophage wraps around the bacterium, engulfs it in a coiled vesicle to create a phagosome
• This prevents the fusion of the phagosome with the lysosome
• Legionella pneumophilia ​recruits ribosomes to the phagosome and basically lives in the nice, new remodeled phagosome it has created

Dot stands for "defect of organelle trafficking"

It is a genetic locus posessed by Legionella pneumophilia 

It carries the genes necessary to block phagosome/lysosome fusion, promote ribosome recruitment, and express a Type IV Secretion system

Legionnarie's Disease: Most common and most severe

Pontiac fever: less severe, self-limiting

Legionella pneumophilia 

Phospholipase C is an exotoxin that hydrolyzes phosphatidyl choline in eukaryotic membranes

Nosocomial or community acquired pneumonia

Usually severe

• Fever >40.5 C (104 F)
• Respiratory symptoms
• Headahe
• Change in neuro symptoms (headache and confusion_
• Nausea, vomiting, diarrhea
• Hyponatremia (low Na+ in blood)
• Patchy infiltrate in 1 lobe of lung (sometimes)

Legionella pneumophilia

• Smokers
• Alcoholics
• Elderly
• COPD patients
• Immunocompromised patients

• Aspiration of water w/ Legionella pneumophilia from faucets or fountains
• Inhallation of aerosol from air conditioning systems

Note: No person-person transmission

Fever and malaise

Usually self-limiting and not severe

Caused by Legionella pneumophilia

• Visualize with dieterle silver stain  (Poorly visualized with gram stain)
• Grows on BYCE agar (but grows slowly)
• Direct fluorescent antibody
• Urinary antigen test
  • Only detects serogroup 1

Choice/first line: Macrolide or ciprofloxacin

If severe: Rifampin + macrolide or quinolone

Disinfect hospital water systems

Severe gastroenteritis and/or wound infection following cuts exposed to sea water

Life-threatening bacteremia in anyone with iron overload (liver disease)

Liver disease = iron overload

The bacteria grow really well when there is a lot of iron around

Vibrio spp. are gram negative, curved rods that are "comma shaped"

Vibrio cholerae

Vibrio parahemolyticus 

Vibrio vulnificus

Sea water, fresh water

Gastroenteritis due to the ingestion of raw/undercooked seafood

Helicobacter pylori is a gram negative, slender, curved rod that grows best in microaerophilic environments (obligate aerobe that cannot survive in full oxygen)

Urease (+), Oxidase (+), Motile

VU-FAT (You view fat in people's stomachs, where H. pylori lives)

• VacA
• Urease (+)
• Flagella + Curved shape
• Adherence
• Type IV Secretion System 

VacA is an exotoxin that causes the vacuolation of cultured epithelial cells

It is secreted by H. pylori

- VacA (+) H. pylori causes peptic ulcer disease 

Peptic ulcer disease: Increased gastric acid production in the duodenum

Adenocarcinoma, non-Hodgkin lymphoma, MALT lymphoma: H. pylori is a risk factor. MALT lymphoma regresses in 50% of cases with antibiotic treatment

30% of people in the USA are infected with Helicobacter pylori

- Usually asymptomatic with GI inflammation

Poorly visualized with gram stain, does not grow well in culture

• Endoscopy w/tissue biopsy
  • Stain with giesma or silver stain
  • Check urease activity using assay or breath test
• Serologic tests for specific IgG
  • But IgG levels do not fall until 6 months after infection is cleared by abx
• Antibody test to detect H. pylori in stool

• Ingest radiolabeled urea
• If urease is present, it will cleave urea into ammonium hydroxide and CO2
• Pt. will exhale radiolabled CO2

Multi-drug protocol (3-4 drugs)

• Proton pump inhibitor + Clarithromycin + amoxicillin

-OR-

• Proton pump inhibitor + Clarithromycin + metronidazole

Campylobater jejuni is a gram negative, obligate aerobe, that is a curved rod with a little twist

Gastroenteritis, diarrhea

Proper food handling

It is poorly visualized by gram stain and difficult to grow in culture

Diphtheria toxin (Corynebacterium diphtheriae)

Exotoxin A (Pseudomonas aeruginosa)

Type of fever

• F. tularensis = constant
• Brucella  = undulant (rises and falls)

Type of animal that carries it

• F. tularensis = Wild animals
  • Rabbits, beavers, squirrels, muskrats
• Brucella  = Farm animals
  • Cattle, goats, hogs

Distinguishing symptoms

• F. tularensis = painful ulceration
  • May lead to granuloma with caseating necrosis
• Brucella  = anorexia, arthralgia
  • May lead to osteomyelitis, arthritis (esp. in sacroilliac joint)

Infection by Francisella tularensis

Contact with wild animal, fever, ulceration, regional lymphadenopathy 

Treat with streptomycin or gentamicin to prevent systemic spread (pneumonia, dissemination to multiple organs, granuloma formation)