Gram-Negative-Organisms (3).docx

**Gram Negative Organisms** **Diplococci** ***Neisseria species*** - Aerobic, Gram-negative, nonmotile, diplococcus - N. gonorrhea can grow under anaerobic conditions - Individual cocci - Kidney bean-shaped - Oxidase test positive - Oxidize carbohydrates - Culture: Thayer-Martin/...

**Gram Negative Organisms** **Diplococci** ***Neisseria species*** - Aerobic, Gram-negative, nonmotile, diplococcus - N. gonorrhea can grow under anaerobic conditions - Individual cocci - Kidney bean-shaped - Oxidase test positive - Oxidize carbohydrates - Culture: Thayer-Martin/Modified Thayer-Martin - Mueller-Hinton Agar - With 5% chocolate sheep blood - Antibiotics - **Colistin** - Inhibit growth of other gram neg bacteria other than Neisseria - Vancomycin - inhibit gram positive - Nystatin - inhibit yeast Selective and enriched medium. ***Neisseria gonorrhea*** - Small, mucoid, oxidase-positive colonies - **Ferments glucose only** - Culture Appearance - "Opaque Colonies" = specimen came from symptomatic male - "Transparent Colonies" = specimen came from asymptomatic male - Habitat- human genital tract - Transmission by sexual contact or during passage through birth canal - Specimens: urethra, cervix, rectum, conjunctiva, throat, synovial fluid - Gram stain: **many diplococci within PMNS (presumptive diagnosis)** - **Gold standard test: Nucleic Acid Amplification Tests (NAATs** **Spectrum of disease** - **Gonococcal urethritis** - Urethritis and epididymitis in men - Most common cause of urethritis - **Ophthalmia neonatorum** - Purulent conjunctivitis in newborns - **Cervical gonorrhea** - Can progress to pelvic inflammatory disease ***Neisseria meningitidis*** - Encapsulated - large polysaccharide capsule - **Ferments glucose and maltose** - Oxidase-positive colonies on chocolate agar - Habitat -- URT - Transmission via respiratory droplets - High carriage rate in **close quarters** - Dormitories, camps, travel **Spectrum of disease** - **Meningitis** - Most common cause among 2-18 yrs old - Fever, headache, stiff neck, increased PMNs in spinal fluid - **Meningococcemia** - Meningococci disseminates into the bloodstream - Multiorgan disease, consumptive coagulopathy, petechial or purpuric rash **(purpura fulminans)** - **Waterhouse-Friderichsen Syndrome** - Most severe form of meningococcemia - High fever, shock, widespread purpura, disseminated intravascular coagulation, thrombocytopenia, adrenal insufficiency **Coccobacilli** ***Haemophilus influenzae*** - Found in the upper respiratory tract - Non motile, small gram-negative (coccobacillary) rods - Fastidious organism - Flat, grayish, translucent colonies on chocolate agar - **Satellite phenomenon** *around S. aureus* colonies - Hemolysis by *S. aureus* liberates factor V needed by *H. influenzae* - Positive quellung test **Quellung Test** - A Quellung reaction is a biochemical reaction in which antibodies bind to a bacterial capsule, allowing species with a positive Quellung reaction to be visualized under a microscope. **Diagnosis:** - Requires factor X (hemin) and V (NAD) for growth - **X -- hemin** - **V - NAD** (can be replaced by nicotinamide adenine dinucleotide (NAD) - Grown on IsoVitaleX-enriched chocolate agar - Satellite phenomenon- grows around colonies of Staphylococci - Colonies of Staphylococci on sheep blood agar cause the release of NAD, yielding the satellite growth phenomenon **Spectrum of disease** - Sinusitis, otitis media, pneumonia - Meningitis - Epiglottitis - COPD exacerbations ***Haemophilus ducreyi*** - Small gram-negative rods in strands - **Requires X factor** but not V factor - Causes **chancroid** ***Bordetella pertussis*** - minute, Gram-negative coccobacilli resembling H. influenza - **Bordet-Gengou agar or Regan-Lowe charcoal medium** - Habitat: URT - Transmission via respiratory droplets **Spectrum of disease** - **Pertussis** - **Hacking coughs** accompanied by production of copious amounts of mucus, that end with an **inspiratory "whoop"** - Prevention: acellular vaccine in combination with diphtheria and tetanus toxoids (DTaP) **Bacilli** ***Pseudomonas aeruginosa*** - **Obligate aerobe** - Oxidase-positive, non-lactose-fermenter - Culture - Grown on **Cetrimide agar** - Greenish, metallic colonies on blood agar - Produces pyocyanin, pyoverdin - **Sweet grape-like odor** - Habitat - environmental water sources (eg humidifiers) - Inhabits skin, URT, and colon of people - Transmission via water aerosoles, aspiration, fecal contamination **Spectrum of disease** - **Skin and Soft Tissue Infections** - Burn wound infections - Hot tub folliculitis - Green nail syndrome - **Ear Infections** - Otitis externa - Swimmer's ear - Chronic suppurative otitis media - **Pneumonia** - Ventilator-acquired pneumonia - High-risk CAP in immunocompromised - **Urinary Tract Infection** - One of the most common cause of nosocomial UTIs ***Salmonella spp.*** - Facultative anaerobes - Non-lactose-fermenting - Produces H2S - Motile - Widal test detects antibodies in patient's serum - Cultured in **XLD medium** - Habitat - human colon only **(S. typhi)** - Enteric tract of humans and animals, e.g., chickens and domestic livestock ***(S. enteritidis)*** - Transmission via fecal-oral route **Spectrum of disease** - **Enterocolitis** - Nausea and vomiting, then progresses to abdominal pain and nonbloody diarrhea - **Typhoid fever** ***Shigella spp.*** - Slender, nonmotile Gram-negative rods - Facultative anaerobes - Oxidase negative - Non lactose fermenter - H2s non-producer - Culture media: **XLD** - Convex, circular, transparent colonies with intact edges ***Proteus Mirabilis*** - Facultative anaerobic gram-negative rods - non-lactose-fermenting - urease-positive - swarming motility - wave-like pattern extending from the point of inoculation **Spectrum of Disease** - **Complicated UTI** - UTI associated with nephrolithiasis - staghorn calculi form on renal calyces - Urea hydrolyzes the urea in urine -\> forming ammonia -\> increase ph -\> alkaline urine -\> struvite stones (staghorn calculi) ***Escherichia coli*** - facultative gram-negative rods - lactose-fermenting colonies on EMB or MacConkey agar - **green metallic sheen** on EMB agar - habitat is human colon - colonizes the vagina and urethra - Transmission: - ascending infection in UTI - during birth in neonatal meningitis - fecal--oral route in diarrhea **Spectrum of Disease** - **UTI** - most common cause - **Intestinal infection** - 4 strains: ETEC, EPEC, EHEC, EIEC - **Neonatal meningitis** - 2nd most common cause - **Hemolytic Uremic Syndrome** - Triad: hemolytic anemia, thrombocytopenia, and uremia - **Pyogenic liver abscess** ***Klebsiella pneumoniae*** - Urease positive - Facultative, non motile, gram-negative rods with **large polysaccharide capsule** - Habitat: URT and GIT - Transmission: aspiration/inhalation or ascending spread of fecal **Spectrum of Disease** - **Lobar Pneumonia** - **UTI** **Comma-shaped** ***Campylobacter jejuni*** - Comma-, or, S-shapeed - Seagull wing appearance - Microaerophilic - Positive oxidase and catalase tests - Grows well at 42C on **Skirrow agar** - Habitat - human and animal feces (cattle, chickens, and dogs) - Transmission via fecal-oral route **Spectrum of disease** - one of the **most common causes of bacterial gastroenteritis** - watery, foul-smelling diarrhea followed by bloody stools accompanied by fever and severe abdominal pain - Disease association - **Guillain-Barré syndrome** - Campylobacter infection is the most commonly identified cause of GBS - **reactive arthritis (Reiter syndrome)** ***Vibrio cholerae*** - Comma-shaped gram-negative rods - Motile - **Shooting star motility** - Oxidase-positive - ferments **sucrose and mannose** but not arabinose. - cultured on **thiosulfate citrate bile salts sucrose (TCBS) agar** - Convex, smooth, round colonies, opaque and granular in transmitted light - Produces **yellow colonies** (sucrose fermented) on TCBS agar that are readily visible against the dark-green background of the agar - Spiral, curved, or fusiform rod-shaped - Motile, **oxidase-positive, catalase-positive, urease-positive** - Microaerophilic - Habitat - human stomach - Transmission via ingestion **Spectrum of disease** - **Peptic Ulcer Disease** - Recurrent pain in the upper abdomen - Frequently accompanied by bleeding into the gastrointestinal tract - **Disease Associations** - **Gastric carcinoma** - **MALT lymphomas**