Bact

• Non-spore-forming, non-branching, catalase-positive bacilli


  • Corynebacterium
  • Rothia
  • Listeria

  
• Corynebacterium


  • Slightly curved, gram-positive rods with nonparallel sides and slightly wider ends, producing the "club shape" or coryneform
  • Can be divided into non-lipophilic and lipophilic species

  
• Lipophilic Corynebacteria


  Fastidious organisms that are difficult to grow; grow slowly on standard culture media; cultures must be incubated for at least 48 hours before the growth to be detected

  
• When we talk about lipophilic organism, the growth is enhanced if lipids are included in the culture media
• Corynebacterium diphtheriae


  • Major virulence factor is the diphtheria toxin, a heat-labile protein of 62,000 daltons (Da) composed of 2 fragments: Fragment A responsible for the cytotoxicity, Fragment B responsible for binding to receptors on human cells and mediating the entry of fragment A into the cytoplasm

  
• Respiratory diphtheria


  1. Sudden onset with exudative pharyngitis, sore throat, low-grade fever, and malaise; a thick pseudomembrane develops over the pharynx; in critically ill patients, cardiac and neurologic complications are most significant

  2. Mode of transmission is through aerosol, through nasopharyngeal route, or nasal-oral discharges

  3. Exotoxin can lead to the pseudomembrane formation

  4. Patients have a "bull's neck" appearance
• Cutaneous diphtheria


  A papule can develop on the skin, which progresses to a non-healing ulcer; systemic signs can develop
• Microscopy of Corynebacterium


  • Highly pleomorphic gram-positive bacillus
  • Palisades (cells lie in parallel rows) or as individual cells lying at sharp angles to another in "V" and "L" formations
  • Club-shaped swellings and beaded forms are common
  • Often stain irregularly, especially when stained with methylene blue
  • Metachromatic areas of the cell: Babès-Ernst granules

  
• Culture characteristics of Corynebacterium


  • Facultative anaerobe
  • Optimal growth temperature of 37°C
  • Multiplication occurs within the range of 15°C to 40°C
  • Grows on nutrient agar, Loeffler serum or Pai agars
  • Have a very small zone of α-hemolysis
  • Cystine-tellurite blood agar (CTBA) is a selective and differential culture media: presence of potassium tellurite inhibits many non-coryneform bacteria, and Corynebacterium diphtheriae, Corynebacterium ulcerans, Corynebacterium pseudotuberculosis form black or brownish colonies due to the reduction of tellurite

  
• Identification of Corynebacterium


  • Catalase positive
  • Non-motile
  • Brown halo on CTBA for Corynebacterium diphtheriae, Corynebacterium ulcerans, Corynebacterium pseudotuberculosis
  • Corynebacterium diphtheriae lacks urease production, ferments glucose and maltose producing acid but not gas, and reduces nitrate to nitrite

  
• In vitro test for toxigenicity of Corynebacterium diphtheriae

  ELEK TEST - immunodiffusion test where the organism is streaked on low iron content culture media parallel to each other, and a filter paper strip with diphtheria anti-toxin is placed in the center. Positive result is indicated by lines of precipitation.

  
• Treatment for diphtheria


  Prompt administration of anti-toxin, drug of choice is Penicillin, Erythromycin used for penicillin-sensitive individuals
• Other Corynebacteria


  • Corynebacterium amycolatum: Recovered from human specimens, part of normal skin biota, flat and dry, matte or waxy appearance, non-lipophilic, resistant to many antimicrobials
  • Corynebacterium jeikeium: Most common cause of Corynebacterium-associated prosthetic valve endocarditis in adults, also causes other infections, lipophilic and strict aerobe, drug of choice is Vancomycin
  • Corynebacterium pseudodiphtheriticum: Does not show pleomorphic morphology, often appear in palisades, grows well on standard media, reduces nitrate, produces urease, respiratory tract infections can mimic respiratory diphtheria
  • Corynebacterium pseudotuberculosis: Primarily a veterinary pathogen, causes granulomatous lymphadenitis in humans, produces diphtheria toxin and a brown halo on CTBA
  • Corynebacterium striatum: Non-lipophilic and pleomorphic, considered a commensal or skin contaminant but can cause nosocomial infections, shows resistance to many antibiotics but susceptible to vancomycin
  • Corynebacterium ulcerans: Also a veterinary pathogen, produces a brown halo on CTBA, grows well on SBA, does not reduce nitrate unlike C. diphtheriae, urease positive
  • Corynebacterium urealyticum: Most commonly associated with UTIs, lipophilic and strict aerobe, nitrate negative, catalase positive, urease positive

  
• Rothia


  • Gram-positive cocci that can appear rodlike, belong to the family Micrococcaceae
  • Nitrate positive, nonmotile, esculin hydrolysis positive, urease negative
  • Approximately two thirds of the isolates are catalase positive
  • Rothia mucilaginosa is linked to bacteremia, endocarditis, pneumonia
  • Rothia dentocariosa is a member of the normal human oropharyngeal flora and found in saliva
  • Microscopic characteristics: Resembles coryneform bacilli, forms short, gram-positive bacilli and branching filaments, produces coccoid cells

  
• Listeria monocytogenes


  • Virulence factors: Hemolysin (listeriolysin O) damages phagosome membrane, catalase, superoxide dismutase, phospholipase C, surface protein (p60) induces phagocytosis
  • Causes listeriosis, most common in newborns, immunocompromised adults, and pregnant women
  • Gram-positive coccobacillus found singly, in short chains, or in palisades
  • Grows well on SBA, chocolate agar, nutrient agars, brain-heart infusion medium and thioglycolate broth, prefers slightly increased CO2, colonies are small, round, smooth, and translucent with narrow zone of α-hemolysis
  • Optimal growth temperature 30°C to 35°C, but can grow at 4°C (cold enrichment technique used to isolate from polymicrobial specimens)
  • Hippurate hydrolysis positive, catalase positive, bile esculin hydrolysis positive, motile at room temperature with "tumbling motility", produces positive CAMP reaction

  
• Non-spore-forming, non-branching, catalase-negative bacilli

  • Erysipelothrix rhusiopathiae
  • Arcanobacterium and Trueperella
  • Gardnerella vaginalis

  
• Erysipelothrix rhusiopathiae


  • Gram positive, catalase negative, non-spore-forming, pleomorphic rod that has a tendency to form long filaments
  • Usual route of infection is through cuts or scratches on skin
  • Can be found worldwide; commensal pathogen on vertebrates and even invertebrates
  • Only species in this genus that can cause disease in humans

  
• Clinical infections caused by Erysipelothrix rhusiopathiae


  1. Erysipeloid: Localized skin disease, occurs on fingers by direct inoculation

  2. Septicemia: Associated with endocarditis

  3. Generalized, diffuse cutaneous infection
• Microscopy of Erysipelothrix rhusiopathiae


  • Thin, rod-shaped, gram-positive organism that can form filaments, arranged singly, in short chains

  
• Alase-negative bacilli


  • Erysipelothrix rhusiopathiae
  • Arcanobacterium and Trueperella
  • Gardnerella vaginalis

  
• Erysipelothrix rhusiopathiae


  One of three species in the genus Erysipelothrix
• Erysipelothrix rhusiopathiae


  • Gram positive, catalase negative
  • Non-spore-forming
  • Pleomorphic rod that has a tendency to form long filaments
  • Usual route of infection is through cuts or scratches on skin
  • Can be found worldwide; commensal pathogen on vertebrates and even invertebrates
  • Only species in this genus that can cause disease in humans

  
• Erysipeloid


  Localized skin disease; occurs on fingers by direct inoculation [seal finger and whale finger]
• Septicemia


  Associated with endocarditis
• Microscopy of Erysipelothrix rhusiopathiae


  • Thin, rod-shaped, gram-positive organism that can form filaments
  • Arranged singly, in short chains, or in a "V" shape
  • Decolorized easily, so it may appear gram variable

  
• Culture characteristics of Erysipelothrix rhusiopathiae

  • Grows on SBA and chocolate agar
  • Nonhemolytic and pinpoint
  • After 48 hours of incubation: smaller, smooth form is transparent, glistening, and convex with entire edges; larger, rough colonies are flatter with a matte surface, curled structure, and irregular edges
  • Often appear -hemolytic

  
• Identification of Erysipelothrix rhusiopathiae


  • Catalase negative
  • Nonmotile
  • Pleomorphic
  • Aerobic or facultatively anaerobic
  • Hydrogen sulfide positive
  • Voges-Proskauer test negative
  • Gelatin stab culture: "test tube brush-like" pattern at 22°C

  
• Arcanobacterium and Trueperella


  • Arcanobacterium haemolyticum
  • Trueperella (Arcanobacterium) pyogenes
  • Trueperella (Arcanobacterium) bernardiae

  
• Arcanobacterium and Trueperella


  • Catalase negative
  • Small colonies on SBA: narrow zone of -hemolysis after 24 to 48 hours of incubation
  • A black opaque dot is observe on the agar when the colony is scraped away
  • Pitting of the agar
  • Lipase and lecithinase positive
  • Exhibits a reverse CAMP reaction (CAMP inhibition reaction)

  
• Gardnerella vaginalis


  • Short, pleomorphic gram-positive rod or coccobacillus
  • Stains gram variable or gram negative
  • Found to be a normal biota of the human genital tract, but can cause infection such as Bacterial Vaginosis

  
• Bacterial vaginosis (BV)


  Nonspecific vaginitis
• Microscopy of Bacterial Vaginosis


  • "clue cells" aids the diagnosis of BV - Large, squamous, epithelial cells with gram positive or gram variable bacilli and coccobacilli clustered on edges

  
• Amsel's Clinical Criteria for Bacterial Vaginosis


  • Homogenous, thin, white discharge that smoothly coats the vaginal walls
  • Clue cells
  • pH of the vaginal fluid greater than 4.5, and reduction of lactobacillus in the vagina; if decreased, the Gardnerella vaginalis will cause infection
  • Fishy odor of vaginal discharge before or after addition of 10% potassium hydroxide, the whiff test

  
• Culture characteristics of Gardnerella vaginalis

  • Grows best in 5% to 7% CO2 at a temperature of 35°C to 37°C
  • Grows on SBA as pinpoint, nonhemolytic colonies
  • Medium of choice: human blood bilayer tween (HBT) agar

  
• Non-spore-forming, branching, aerobic actinomycetes

  • Nocardia
  • Actinomadura
  • Streptomyces
  • Gordonia
  • Rhodococcus
  • Tropheryma whipplei

  
• Nocardia


  • Aerobic, branched, beaded, gram-positive bacilli
  • Resembles fungi, but are true bacteria
  • Partially acid fast

  
• Virulence factors of Nocardia

  • No virulence factors have been identified, although virulence has been correlated with alterations in the components in the cell wall
  • Superoxide dismutase and catalase [provide resistance to oxidative killing by phagocytes]
  • Iron-chelating compound called nocobactin

  
• Pulmonary Nocardiosis


  • Confluent bronchopneumonia
  • Sputum: thick and purulent
  • No sulfur granules, and no sinus tract formation
• Cutaneous Nocardiosis


  • Nocardia brasiliensis is the most frequent cause
  • Pus: pigmented and contain "sulfur granules"
  • Granules: yellow or orange
  • Distinct granular

  
• Microscopy of Nocardia


  • Gram-positive, beaded, branching filaments