Gram Negative Bugs Flashcards
Basics of Gram - bacteria:
what color do they stain, wall structure, habitat?
Don’t retain crystal violet stain used in the gram staining method -> red
- have thin peptidoglycan layer of the cell wall (Gram + has a much thicker one) is sandwiched between an inner cytoplasmic cell membrane and the bacterial outer wall membrane
- All have a lipopolysaccharide outer membrane of cell wall - endotoxin
- Most, with few exceptions, don’t form spores
- live in a wide range of habitats -> large intestines (enteric), zoonotic, respiratory, soil, water
- some are true pathogens and some are opportunists.
Medically relevant gram - cocci include 3 species responsible for?
- gonorrhea
- meningitis
- pneumonia
Medically relevant gram - bacilli include species responsible for?
- respiratory illness
- urinary infections
- GI problems
- and many other ailments
Importance of the lipopolysaccharide (LPS)?
outer leaflet of outer membrane -> acts as an endotoxin
- if gm - bacteria enter blood stream, LPS can cause a toxic reaction which results in fever, increased RR, low BP
- this may lead to life threatening endotoxic sepsis and shock
- the presence of LPS also triggers an innate immune response and prod. of cytokines, which in turn, leads to inflammation, which can also produce host toxicity.
2 genera of gram - cocci
- Neisseria
- Moraxella cararrhalis: resides in the resp. tract and causes tracheobronchitis and pneumonia
Neisseria meningitidis & N. gonorrheae features
non-motile, gm -
usually diplococci
aerobic
Neisseria gonorrheae
Gonorrhea may be most prevalent bacterial STI
- 2nd most commonly reported notifiable STI in US
- may be over 1 million infected
Where does gonorrhea present?
infection of cervix
-infection of urethra (men, inflammatory response -> purulent discharge)
How does gonorrhea present and how can it progress?
- urethral infections
- dysuria and fever
- male infection may extend to prostate and epididymis, causing sterility, infection of urethra -> discharge
- It can progress to systemic disease: arthritis, endocarditis, meningitis
- Gonorrhea neonatorum (ophthalmia neonatorum) is an eye infection during passage through birth canal, can lead to blindness.
Neisseria meningitidis
- causes meningitis, septicemia
- only natural reservoir is the human nasopharyngeal mucosa
- 10% nasal carrier rate
- transferred: direct contact or droplets
subclinical/minimal disease of N. meningitides
transient meningococcemia, short febrile flu-like episode, cleared spontaneously
overt disease of fulminant meningeal sepsis
- massive and rapid proliferation in the bloodstream
- blood culture: +, usually also involves meninges
- rapid clinical deterioration
- fever, severe HA, vomiting, neck/back pain, stiffness, petechial rash, altered mental status, shock, organ failure.
Overt disease of meningitis
Why does shock and DIC occur in FMS/meningitis?
shock: endotoxin causes capillary leakage, poor vascular tone, intravascular micro thrombi, myocardial dysfunction
- C3a, C5a, inflam. mediators cause vasodilation, capillary leakage
- hypoperfusion -> shock
DIC: endothelial damage -> hemorrhages, micro thrombi (See in hands)
- endotoxin and cytokines create more of an inflammatory response -> deadly cycle
Dx of FMS or meningitis?
early dx is difficult but crucial!
- later stages: FMS- skin lesions appear 6-12 hours after, easier to recognize disease
- meningitis: skin lesions 12-18 h after onset, no lesions in 20% of pts
bacteriologic dx: FMS - gm stain of skin lesion biopsy specimen
- meningitis: only CSF +
Therapy for FMS/meningitis
survival little improved during last few decades
Most impt principles:
- therapy should never be delayed by dx procedures
-abx are most imp part of tx
- Cefotaxime or ceftriaxone + vanco
-pts in contact: prophylatic abx rochephin
Outcome of meningitis:
mortality and sequelae
Moraxella catarrhalis
gm - cocci that causes infections of:
- upper and lower resp (part imp cause of bronchopulm. infection in elderly, pts with chronic lung disease)
- middle ear
- eye
- CNS
- joints
Resistant to PCNs, SMX/TMP, tetracyclines
- SO tx with fluoroquinolones, most 2nd and 3rd cep, macrolides, and augmentin
Aerobic gm - nonenteric bacilli
- pseudomonas & burkholderia: opportunistic pathogen
- Brucella & Francisella: zoonotic pathogens
- Bordetella & Legionella: mainly human pathogens
- Alcaligenes: opportunistic pathogen
Pseudomonas
small gm - rods w/ single polar flagellum
- free living: mainly in soil, sea water, fresh water, also colonize plants and animals
- impt decomposers and bioremediators
- freq contaminants in homes and clinical settings
- use aerobic respiration, don’t ferment carbohydrates
- produce oxidase and catalase
- many produce water soluble pigments
Pseudomonas aeruginosa
- common inhabitant of soil and water
- intestinal resident in 10% people
- resistant to soaps, dyes, quaternary ammonium disinfectants, drugs, drying
- Freq. contaminant of ventilators, IV solns, anesthesia equipment
- opp. pathogen
Pseudomonas aeruginosa common cause of what infections, complications, presentation, tx
- common cause of nosocomial infections in hosts w/ burns, neoplastic disease, cystic fibrosis
- complications: pneumonia, UTI, abscesses, otitis(see blue green gunk in ear), and corneal disease
- endocarditis, meningitis, bronchopneumonia
- grape like odor
- greenish-blue pigment (pyocyanin)
- multidrug resistant
- tx w/ cephaloporins, aminoglycosides, polymixin, quinolones (oflaxacin: good for otitis), & monobactams
Brucella -> Brucellosis
- tiny gm - coccobacilli
- 2 species: brucella abortus (cattle), brucella suis (pigs)
- aka: brucellosis, malta fever, undulant fever, band disease -> zoonosis transmitted to humans from infected animals
- fluctuating pattern of fever (weeks to a year)
- tx w/ combo of tetracycline and rifampin or streptomycin
- animal vaccine available
- potential bioweapon
- *the bacteria can spread to humans w/ contact of infected meat or placenta of infected animals, or unpasteurized milk and cheese
Brucellosis infection
- brucellosis: in humans usually assoc. w/ consumption of unpasteurized milk and soft cheeses made from milk of infected animals
- affects all age groups and both sexes
- can be insidious & may present in many atypical forms
- sxs are mild but may present as acute febrile illness which may persist & progress to a chronically incapacitating disease w/ severe complications
- carefully monitored in Mt but is present, still persists in elk and bison in greater yellowstone region
Francisella tularensis & Tularemia
- facultative intracellular coccobacillus
- causes tularemia: zoonotic disease of mammals, endemic to northern hemisphere, particularly rabbits (rabbit fever)
- transmitted by contact w/ infected animals, water and dust or bites by vectors
- HA, backache, fever, chills, malaise, and weakness
- 10% death rate in systemic and pulmonic forms
- intracellular persistence can lead to relapse
- tx: gentamicin or tetracycline
- attenuated vaccine
- potential bioterrorism agent
Bordetella pertussis
- minute, encapsulated coccobacillus
- causes pertussis or whooping cough
- acute respiratory syndrome
- 100 day cough
- often severe, life-threatening complications in babies
- reservoir: healthy carriers
- transmission by direct contact or inhalation of aerosols
Virulence factors of Bordetella pertussis
- receptors that recognize and bind to ciliated resp. epithelial cells
- toxins that destroy and dislodge ciliated cells: loss of ciliary mechanism leads to buildup of mucus and blockage of the airways.
Vaccine and tx for Bordetella pertussis
Tdap: acellular vaccine contains tetanus toxoid and protection against diphtheria and pertussis.
tx: macrolides -> azithromycin
Legionella pneumophila and Legionellosis
-widely distributed in water
- organisms inhaled in aerosolized mist
- live in close assoc. w/ amoebas
- 1976 epidemic of pneumonia afflicted 200 American Legion members in Philly and killed 29 hence the name legionellosis
AKA: legionnaires dises and pontiac fever
Presentation of legionellosis and treatment
Most prevalent in males over 50, nosocomial disease in elderly.
- fever, cough, diarrhea, abdominal pain, pneumonia fatality rate: 3-30%
Tx: azithro
The most common aerobic and non-fastidious bacterium in the gut?
Escherichia coli -> most prevalent enteric bacillus
- 150 strains
- some have developed virulence through plasma transfer, others are opportunists
Pathogenic strains of E. coli -> Enterotoxigenic E. coli
enterotoxigenic E. coli: causes severe diarrhea due to heat-labile toxin and heat-stable toxin - stimulate secretion and fluid lost alsi has fimbriae (spikes -> attachment pili)
Pathogenic strains of E. coli -> Enteroinvasive
causes inflammatory disease of the large intestine
Pathogenic strains of E. coli -> enteropathogenic
linked to wasting form infantile diarrhea
Pathogenic strains of E. coli -> enterohemorrhagic
O157:H7 strain, causes hemorrhagic syndrome and kidney damage
How does E. coli present?
pathogenic strains frequent agents of infantile diarrhea of many forms is the greatest cause of mortality among babies
- causes 70% of traveler’s diarrhea
- causes 50-80% UTI in women
- colifrom count: ind. of fecal contamination in water