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Bacteriology

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Bacteriology Finals
Nonfermenting Gram (-) Bacilli
Pseudomonas, Vibrios spp.
General Characteristics
Grow in MacConkey as colorless colonies : Non lactose fermenter (NLF)
Fail to acidify OF Media, overlaid with mineral oil
o Open tube: yellow
o w/ overlaid mineral oil: green
Fail to acidify TSI Agar
o K/K red/red
Most isolates are Oxidase Positive
o Colorless: Acinetobacter and Stenotrophomonas (negative)
o Dark purple: Pseudomonas and Burkholderia (positive)
Clinically Significant Species
Pseudomonas aeruginosa
o Most commonly isolated species
o It accounts 75% of non-fermenters in nosocomial infection/bacteremias
o It accounts 5% to 15% of all nosocomial infections
3
rd
causative of gram (-) bacillary bacteremia
Most common is E. coli, then second is K. pneumoniae
o Infections:
Bacteremia - Ecthyma gangrenosum of skin (usually in thoracic area in lower
extremities)
wound infection
pulmonary disease (Cystic fibrosis patients)
Nosocomial UTI, endocarditis, meningitis
Others: Otitis externa among divers and swimmers in public recreational
facilities,
: Jacuzzi/hot tub syndrome
Fermentative: Change in color in both tubes.
Enterobacteriaceae, Vibrio, Aeromonas, Plesiomonas and Chromobacterium
Oxidative: Change in color in tubes w/out mineral oil (Open tube)
Acinetobacter, Stenotrophomonas, Pseudomonas, Burkholderia
Nonsaccharolytic : No change in color in both tubes. Alcaligenes, Oligella

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: Nail infection of nail beds with artificial nails
: Keratitis
: Endophthalmitis
Virulence Factor
o Endotoxins LPS (component of its outer membrane), motility, capsule, pili
o Exotoxins
- Enzymes: Protease, hemolysins, lecithinase, elastase and DNase
- Exotoxin A - most important exotoxin; blocks protein synthesis; resemble
Diphtheria toxin
o Alginate - polysaccharide polymer in mucoid strains
- Inherently resistance to a number antimicrobials.
- In patient’s lower pulmonary tract with CF (cystic fibrosis)
Identifying Characteristics
o Strict aerobic
o Pigmented
- Belongs to P. fluorescens (P. putida, P. fluorescens)
- H2O soluble pigments tru short UV light
- PIGMENTS:
Fluorescein (Pyoverdin) green- P. fluorescens/P. putida
Pyocyanin blue (specific to P. aeruginosa) highly specific
Pyorubin red
Pyomelanin brown/black (P. stutzeri)
o Fruity, Grapelike or “corn tortilla-like” odor (2-aminoacetophenone)
o Growth at 42°C
o Selective media: Grows in Cetrimide Agar detergents
o Positive: Acetamide utilization, oxidase, ADH, citrate,
o Strict aerobic
o Culture: SBA beta hemolytic, flat, spreading colony with metallic sheen
Acinetobacter spp.
Clinical significance
o Ubiquitous found in soil, water, foodstuffs
- Adults: 25% of present in skin; 7% in pharynx
- In hospital: ventilators, humidifiers, catheters, etc.
o Opportunistic (1-3% of all nosocomial infection, 2nd most commonly isolated non-
fermenter); burns, trauma
Species
o A. baumannii - Saccharolytic (glucose oxidizing), nonhemolytic strains.
o A. lwoffii - Asaccharolytic, nonhemolytic strains.
o A. haemolyticus - β-hemolytic strains.
Colony
o Short gram (-) coccobacilli (plump) gram (+) in blood culture
o A. baumannii may exhibit purplish hue in MacConkey agar (due to lactose fermenter)

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o A. baumannii colony appears with a blue-grey (cornflower blue) center in EMB (eosin
methylene blue).
Stenotrophomonas maltophilia
Clinical significance
o Identified before as plant pathogen
o In H20, sewage and plant materials
o In hospital, contaminants in blood drawing equipment (collection tubes, disinfectants,
transducers, venous catheters, etc.)
o Opportunistic (3rd most commonly isolated among nonfermenters/nosocomial
infections)
o Intrinsic resistance commonly used antibacterial agent (aminoglycosides, cephalosporin,
carbapenems, penicillin and beta lactams)
Identifying characteristics
o Oxidase negative
o Catalase, DNase positive
o Esculin and Gelatin hydrolysis (+)
o Lysine decarboxylase positive
o BAP lavender green pigment
o MacConkey bluish
o Odor - Ammonia-like smell
o Oxidizes glucose: W(+/-)
o Oxidizes maltose: S(+)
Burkholderia cepacia
Clinical significance
o Opportunistic causing pneumonia in patients with cystic fibrosis or chronic
granulomatous disease
o Isolated/found from irrigation fluids, anesthetics, nebulizers, detergents and
disinfectants.
o Onion bulb rot in plants and foot rot in humans
o Intrinsic resistance to antibiotics
Identifying characteristics
o Colony: Smooth, non-wrinkled and slightly raised
: yellow/green pigment do not fluorescence (P. stutzeri also produce
yellow/green pigment but is wrinkled)
o Odor: dirt like odor in BAP
o Non lactose fermenter (colorless): but become dark pink to red after 4-7 days in
MacConkey
o Most strains are ONPG positive
o Specific selective media (PC Pseudomonas cepacia; OFPBL: oxidative fermentation
base, polymyxin B, Bacitracin, lactose; BCSA B. cepacia, selective agar)

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Burkholderia pseudomallei
Clinical significance
o Disease: “Melioidosis” (pulmonar disease) formation of abscess
- Aggressive granulomatous pulmonary disease with abcess formation of lungs
and viscera
o Bipolar staining (safety pin) in Gram Stain
o Colony: BAP: wrinkled colonies (same with P. stutzeri)
Lactose fermenter
o Selective media: Ashdown media: Wrinkled and deep pink colony to neutral red
with collistin
o “Earthy odor”
o “Sniffing” of plate is discouraged (work on BSC)
Burkholderia gladioli
“Associated with patients with CF (cystic fibrosis) and CGD (chronic granulomatous disease) in
immunocompromised who had lung transplant
Oxidase (-)
Burkholderia mallei
Disease: Glanders: zoonosis affecting livestocks like horses, mules, donkeys. Formation of
nodular lesions in lungs. Coughing, fever and release of infectious nasal discharge.
Local and suppurative pulmonary infection
Potential bioterrorist agent (identified by US government)
Nonmotile; non-pigmented colonies; no distinct odor
Laboratory diagnosis:
1. Nitrate reduction
Nitrate ----Nitrate reductase----> nitrite + sulfanilic acid = (+) pink / (-) colorless
If (-): add zinc dust ((+) control)
Result: pink: true negative
: Colorless: nitrite is converted further to nitrogen gas
(+): Pseudomonas and Stenotrophomonas
(-): Burkholderia, Acinetobacter

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Bacteriology Finals Nonfermenting Gram (-) Bacilli Pseudomonas, Vibrios spp. General Characteristics • • • • Grow in MacConkey as colorless colonies : Non lactose fermenter (NLF) Fail to acidify OF Media, overlaid with mineral oil o Open tube: yellow o w/ overlaid mineral oil: green Fail to acidify TSI Agar o K/K – red/red Most isolates are Oxidase Positive o Colorless: Acinetobacter and Stenotrophomonas (negative) o Dark purple: Pseudomonas and Burkholderia (positive) Fermentative: Change in color in both tubes. Enterobacteriaceae, Vibrio, Aeromonas, Plesiomonas and Chromobacterium Oxidative: Change in color in tubes w/out mineral oil (Open tube) Acinetobacter, Stenotrophomonas, Pseudomonas, Burkholderia Nonsaccharolytic : No change in color in both tubes. Alcaligenes, Oligella Clinically Significant Species Pseudomonas aeruginosa o o o o Most commonly isolated species It accounts 75% of non-fermenters in nosocomial infection/bacteremias It accounts 5% to 15% of all nosocomial infections ▪ 3rd causative of gram (-) bacillary bacteremia ▪ Most common is E. coli, then second is K. pneumoniae Infections: ▪ Bacteremia - Ecthyma gangrenosum of skin (usually in thoracic area in lower extremities) ▪ wound infection ▪ pulmonary disease (Cystic fibrosis patients) ▪ Nosocomial UTI, endocarditis, meningitis ▪ Others: Otitis externa among divers and swimmers in public recreational facilities, : Jacuzzi/hot tub syndrome : Nail infection of nail beds – w ...
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