The Gram-Negative
Medically Important Bacteria
Chapter 20
Oxygen requirements: aerobes, facultative anaerobes, obligate anaerobes
ENDOTOXIN - lipopolysaccharide of outer membrane - Lipid A
= macrophages release interleukins, tumor necrosis factor, et al.
Septic shock - bp, reduced circulation to heart brain kidneys, lungs
Nausea, tachycardia, cold clammy skin, weak pulse
I. Aerobic Gram-Negative Nonenteric Bacilli (do not ferment sugars)
Pseudomonas - free-living, soil, seawater, freshwater, plants, animals;
Small gram-negative , single polar flagellum, oxidative, (NO4),
pigments (green, brown, red, yellow)
Metabolically versatile: protease, amylase, pectinase, cellulase, et al.
Pseudomonas aeruginosa -
resist soaps, dyes, quats, drugs, drying, temp = chronic nosocomial pathogen
"opportunistic" pathogen - debilitated, immunocompromised, injury
Characteristic blue green, fluorescent "pyocyancin"
most at risk: burns, tumors, cystic fibrosis
causes: pneumonia, UTI, abscess, ear and eye infections
septicemia: endocarditis, meningitis, bronchopneumoia
usually produces: skin rash, UTI, ear infection, corneal infections w/ contacts
multiple drug resistances
Treatment: 3rd generation cephalosporins, aminoglycosides, carbenicillin, polymixin, quinolones, monobactams
Brucella abortis (cows), Brucella suis (pigs) - zoonosis
Brucellosis = Malta fever, undulant fever, Bang's Disease
(
-cross placenta, cause abortion
-in humans - fever (no abortion) slaughterhouse, handlers, vets enters thru breaks in skin, mucous membranes;
-phagocytes release cells, waves of fever (chills, sweating, headache, muscle pain, weakness, weight loss), focal infections in liver, spleen, bone marrow, kidneys.
Treatment: tetracycline & streptomycin for 3-6 weeks (why?)
Francisella tularensis - Tularensis, Rabbit Fever
Former
Rabbits, rodents, wild animals, arthropod vectors - ticks, flies, mites, mosquitoes
Route of entry: skin, eyes, bites, ingestion, inhaled
Infective dose:10-50 cells Incubation time: hours to weeks
Symptoms: headache, backache, fever, chills, weakness
Or skin lesion, swollen glands, conjunctivitis, pharyngitis, GI tract, pneumonia
Treatment: streptomycin, gentamycin, tetracycline
Bordetella pertussis - Whooping Cough, pertussis
Acute respiratory infection, severe in infants <6 months DPT vaccine
Virulence factors: receptors bind to ciliated epitheleum; toxins kill cells
build up mucus and block airways
catarrhal stage - cold-like
paroxysmal stage - coughing fits, inspiration "whoop"
Treatment: erythromycin
Legionella - Legionnaire's diease
200 Legionnaires,
Gram-negative motile short rods, to filaments, fastidious - charcoal extract medium
Legionella pneumophila - fresh water, aerosols, nosocomial in debilitated
Symptoms: rising fever, cough, diarrhea, abdominal pain - lung consolidation, impaired respiration, impaired function
Treatment: erythromycin and/or rifampin
II. Enterobacteriacae
Gram-negative, small non-spore-forming rods, aerobic, ferment when no O2 (facultative anaerobes) soil, water, decaying matter, large bowel.
Diarrheal illness (5M/yr), most common cause of death, nosocomial infections, medical devices
Ferment glucose, Nitrates to Nitrites, oxidase negative, catalase +, often motile
Coliforms - ferment lactose quickly
Noncoliforms - non or slow lactose fermenters
Biochemical Characterisitics - lactose,
IMViC = indole, methyl red, Voges-Proskauer and citrate.
Antigens: flagellar (H), capsule +/or fimbri (K), somatic=cell wall=LPS (O)
Serotype HKO
Endotoxins, overcome host defenses and multiply
Virulence factors: endotoxin, enterotoxins, capsules, hemolysins, fimbrae (colonize)
Coliforms
Escherichia coli - most common, non-fastidious
Enterotoxigenic - heat-labile (LT), heat-stabile (ST). fimbrae to attach
Enteroinvasive - invasion and ulceration of mucosa
Enteropathogenic - wasting disease of newborns
Diseases: Infantile diarrhea,
Traveler's Diarrhea - profuse, watery diarrhea, low fever, nausea, vomiting,UTI -
Indicator of fecal contamination (Salmonella spp.)
Other coliforms: Klebsiella pneumoniae: nosocomial prneumonai, meningitis, bacteriemia, wound infections, UTI
Enterobacter and Hafnia, Citrobacter, Serratia
Noncoliform, Lactose-negative enterics
Proteus - ubiqutous, UTI, wounds, pneumonia, septicemia, infant diarrhea, burns
Noncoliform Pathogens
Salmonella typhi - typhoid fever
O, H, and V (capsule)
Motile, ferment glucose with acid and gas, H2S, urease -
Not fastidious, resist bile and dyes, do not loose virulence on cultivation
Typhoid Fever: GI tract, 1k-10k infective dose
Adhere to mucosa of small intestine, progressive invasion -> septicemia
Lymph nodes -> liver and spleen, bacteremia
Fever, diarrhea, abdominal pain
Mesenteric lymph nodes ulcerate, perforate, peritonitis
Treatment: Chloramphenicol
and ampicilin
Chronic carrier - remove gall bladder
Vaccine - killed whole cells (why?)
Other: S. enteriditis,
S. paratyphi, S.schottmulleri,
S. hiirschfield, S. typhimurium
Zoonoses - cattle, poultry, rodents, reptiles, Chickens, eggs, milk
Enteric fevers, gastroenteritis (N/V/D), asymptomatic infections
Treatment: Chlroamphenicol, ampicilin, electrolyte replacement
Shigella - Bacillary dysentery - Shigellosis
Severe abdominal cramps, watery stool with mucus and blood
Shigella dysentery- invades villi of large intestine
Endotoxin = fever Enterotoxin = inflammation, degenration of villi, bleeding, heavy mucus production
Shiga toxin=heat-labile exotoxin
Non-motile, no capsule, not fastidious,no H2S or urease
Infective dose: 200 cells children most affected
Treatment: replace fluids, ampicillin, sulfa-trimethoprim, (nalidixic acid, cephalosporins)
Nonenteric Yersinia pestis - Plague
100 million people died in 6th century
gram-negative rod, bipolar stain
Virulence factors: capsular and envelope proteins protect against phagocytosis and promote intraceluar growth. Coagulase, endotoxin
Epidemiology:
Mammals = "endemic reservoir" harbor microbe w/o disease
Spread to "amplifying hosts" which do develop disease
Fleas bite infected mammal, Y. pestis grow in gut and block esopahgus
Consecutive bites transmit Y. pestis
Pathology:
Infective dose: 3-50 cells
Bubonic - bite to lymph node - inflammation = bubo
Incubation time - 2-8 days - fever. Chills, headache, nausea, weakness, tender bubo
Septicemic - coagulate blood in vessels, subcutaneous hemmorage, purpura to necrosis to gangrene
Pneumonic - lungs, fatal
Treatment: streptomycin, tetracycline, chloramphenicol
Oxidase-postive Nonenteric Pathogens
Pasteurella multocida - zoonose
Chlolera-like in chickens
Hemorrhagic septicemia and pneumonia in cattle
Human - local abscess- joints, bones, lymph nodes
Pulmonary damaged patients risk pneumonia
Treatment: penicillin and tetracycline
Haemophilus
Tiny gram-negative, pleomorphic rods
Fastidious, sensitive
Require blood for hemitin (X factor) cytochomes, catalase, peroxidase
V factor Nicotinamide adenine dinucleotide (AND) coenzyme
H. influenzae - acute bacterial meningitis
Treatment: Chloramphenicol and ampicillin
Hib vaccine
H. aegyptius - conjunctivitis = pinkeye
Subconjunctival hemorrhage
H. ducreyi - chancroid - STD - painful necrotic ulcer on genitalia,
Lymph nodes swell like buboes
Treatment: cotrimoxazole