Gram Positive Rods- Exam 2

What are some general characteristics of corynebacterium?

• Non spore forming, nonbranching

• Gram positive bacilli

• ‘Club shaped’

• Opportunistic pathogen

• Can be divided into two groups: nonlipophilic and lipophilic

• Catalase positive

What is the main virulence factor of Corynebacterium diphtheria?

Diphtheria toxin

What is the diphtheria toxin?

Exotoxin produced by strains of C. diphtheria that are infected with a lysogenic corynephage. Its toxicity is measure by the toxins ability to block protein synthesis in the host cell.

• Generally nontoxic unless exposed to trypsin

• 2 fragments:

  • A: responsible for the cytotoxicity

  • B: binds to the human host cell

What are the two clinical infections of C. diphtheria?

Respiratory and cutaneous diphtheria

Respiratory diphtheria

• Worldwide, but less common in the US due to vaccine availability

• Humans are the only natural host

• Spread through droplets or hand-to-mouth

• Typical incubation period is 2-5 days

• Symptoms:

  • Low grade fever, malaise, sore throat.

  • Infects the tonsils or pharynx

• Toxin is produced locally, causing necrosis of host cells.

  • Creates the characterisitc of illness (hard plaque in throat)

Cutaneous diphtheria

• Common in tropical regions

• Systemic complications are less common, more localized

• Ulcers with gray membrane

• Transfered by person-to-person contact

Microscopic identification of C. diphtheria

• Pleiomorphic GPR

• Palisade formation or sharp angles

• Club-shaped

• babes-Ernst granules

Culture characteristics of C. diphtheria

• Facultative anaerobe

  • Grows best at 37 degrees C in aerobic conditions

• Grows best on agar containing blood or serum

• Other nutrient agars:

  • Loeffler medium

  • SBA- small zone of beta hemolysis

  • CTBA agar- not recommended for ID alone

General identifiers of C. diphtheria

• Catalase positive

• Nonmotile

• Produces brown halo on CTBA

• Negative urease

• Reduces nitrate

• Ferments glucose and maltose

What is the test used to determine the toxigenicity of C. diphtheria?

Elek test

Corynebacterium amycolatum

• Normal skin organism

• FOund in prosthetic joint or hardware infections

• Flat, dry colonies with a matte or waxy appearance

• Resistant to beta-lactams, fluoroquinolones, clindamycin, and aminoglycosides

Corynebacterium jeikeium

• Normal skin organism

• Found in prosthetic valve endocarditis

• In immunocompromised, found with invasive procedure infections, central line catheters, hardware, etc.

• Lipophilic, strict aerobe

• Nonhemolytic

• Negative urease

• Resistant to penicillin, cephalosporins, macrolides, and aminoglycosides

Corynebacterium pseudodiphtheriticum

• Normal respiratory inhabitant

• Found in respiratory infections in immunocompromised patients

  • Ventilator pneumonia in COVID cases

• Not pleimorphic, evenly stains, palisade morphology

• Produces urease, reduces nitrates

Corynebacterium psuedotuberculosis

• Veterinary pathogen: sheep contact

• Granulomatous lymphadenitis

• Dermonecrotic toxin

• Produces brown halo on CTBA

• Produces urease

• On SBA: yellow colonies

Corynebacterium striatum

• Skin and nasopharynx microbiota

• Commensal organism

• Device-related infections

• Nonlipophilic, pleimorphic. Shiny convex colonies

  • Striations in colonies

• Resistant to penicillin, other beta-lactams, macrolides, fluoroquinolones

• Vancomycin susceptible

Corynebacterium ulcerans

• Produces diphtheria toxin

• Isolated from ulcers and pharyngitis

• Vet pathogen

  • Causes mastitis in cows

  • Contact with animals or unpasteurized products

• Brown halow in CTBA

• Beta hemolysis in SBA

• Urease positive

Corynebacterium urealyticum

• Associated with UTIs

• Lipophilic, strict aerobe

• Nitrate negative, Catalase pos, Urease pos

• Resistant to beta-lactams, aminoglycosides, trimethoprim-sulfamethoxazole

Rothia spp.

• GPC, sometimes appear rod-like

• Nitrate pos, Bile esculin pos, Urease neg

• Nonmotile

What are some genral characteristics of Listeria monocytogenes?

• Improtant human pathogen

• Found everywhere

• Causes listeriosis-serious infection

What are the virulence factors of L. monocytogenes?

Internalin, listeriolysin O, phospholipase C, actin polymerizing protein, superoxide dismutas,e surface proteins

What is the most important virulence factor in L. monocytogenes? Why?

• Listeriolysin O

• how the bacteria evades phagocytosis

How are clinical infections of L. monocytogenes usually acquired?

Ingestion of contaminated food products, like raw milk

What demographics are usually affected by L. monocytogenes infections?

• Newborns

• Pregnant women

• Immunocompromised patients

Clinical infections of L. monocytogenes in pregnant women

• Usually occurs during 3rd trimester

• Responsible for spontaneous abortions or stillborns

• Flulike illness

Clinical infections of L. monocytogenes in newborns

Early onset:

• Intrauterine transmission. Casues sepsis

Late onset:

• Meningitis

Clinical infections of L. monocytogenes in immunocompromised patients

• Isolated from the CSF and blood

• CNS infections or endocarditis

Microscopic identification of L. monocytogenes

• Gram positive coccobacillus

• FOund in singles, short chains, or palisade formation

Culture characteristics of L. monocytogenes

• Grows on SBA and CHOC

• Prefers increased CO2 environment

• Beta hemolytic

• Cold enrichment

Identifying features of L. monocytogenes

• Catalase positive

• Positve bile esculin

• Motile, tumbling, umbrella

• Positve growth in 6.5% NaCl

• Positive CAMP with usage of R. equi

General characteristics of Erysipelothrix rhusiopathiae

• Only species to cause disease in humans

• Gram positive, non-spore formin, pleimorphic rod

• Occupational exposure: fish and animal products. Enters host through cuts on skin

Clinical infections of E. rhusiopathiae

• Erysipeloid:

  • Hand lesions

  • 2-7 day incubation

  • Heals within 3-4 weeks

• Septicemia

• Cutaneous infections

Culture characteristics of E. rhusiopathiae

• 5% CO2 environment

• Grows on SBA or CHOC

  • nonhemolytic

Identifiaction of E. rhusiopathiae

• Catalase positive

• Bile esculin negative

• H2S positive

• Urease negative

• Negative nitrate reduction

Arcanobacterium haemolyticum

• Commonly found in pharyngitis in 10-20 year olds

• Catalase negative, Lipase and lecithinase negative

• Beta hemolytic

• Treatment with azithromycin

General characteristics of Gardnerall vaginalis

• Normal biota of the urogenital tract

• Short, pleiomorphic, GPR or gram variable/gram neg coccobacillus

Clincial infections of G. baginalis

• Bacterial vaginosis

  • Discharge and pH or 4.5 or higher

  • Overgrowht of vaginal biota

  • Treated with metronidazole or clindamycin

Microscopic identification of G. vaginalis

Clue cells: squamous epis with bacterial cells clustered aorund them

What is Amsel’s clinical criteria for BV?

• Homogenous white discharge

• Clue cells

• ph greater than 4.5

• Fishy odor

Culture characteristics of G. vaginalis

• 5-7% CO2 environment

• 35-37 degrees C

• SBA growth- pinpoint colonies, no hemolysis

• HBT agar (Human blood)- beta hemolysis, gray, opaque colonies

Identification of G. vaginalis

• Nonmotile

• Catalase neg

• Bile esculin neg

• Produce acid from glucose

• Produce H2S

• Urease pos

General characteristic of Nocardia

• Branched, beaded GPR

• Partially acid-fast

• Can be grown on nonselective media

• Most infections occur in immunocompromised patients

What are the virulence factors of Nocardia?

Very unclear, potentially ocrrelated to changes in the cell wall

• Can produce superoxide dismutase and catalase

• Can produce nocobactin

Clinical infections of Nocardia

• Pulmonary infections:

  • COnfluent bronchopneumonia- chronic

• Cutaneous infections

  • Seen in hands and feet

  • Localized abscess that becomes invasive: actinomycotic mycetomas

Microscopic ID of Nocardia

• GPR, branched, beaded

• Commonly found in sputum, exudates/aspirates

• Some granules in cutaneous specimens

Culture characteristics of Nocardia

• Oxidative matabolism

• Does not require specific growth factors

• Can be incubated between 22 and 37 degrees C

• Chalky, velvet, matte appearance. White, yellow, or gray pigment

• Breadcrumb appearance

ID of Nocardia

• Urease, nitrate, lysozyme resistance positive

• Mostly identified through 16s rRNA sequencing

Actinomadura

• Cause mycetoma

• Microscopic morph similar to Nocardia

• Not partially acid-fast

• Cellobiose and xylose positive

Streptomyces

• Saprophytes

• Can casue actinomycotic mycetoma

• Common soil inhabitant

Gordonia

• Aerobic, nonmotile, gram positive/variable

• Partially acid-fast

• Catalse positive, nitrate positive

• Mostly found in the environment

• Secondary infection in immunocompromised

Rhodococcus

• R. equi, most common isolate

• Contact with farm animals and feces

• On gram stain- filaments, partially or fully acid fast

• Salmon pink pigment on SBA

Tropheryma whipplei

• Causes whipple disease

• Facultative intracellular pathogen

• Gram positive actinomycete

• Ubiquitous

General characteristics of Bacillus

• Gram positive/variable

• Facultative anaerobe or aerobic

• Produces spores both aerobically or anaerobically

• Most species can grow on SBA with nonpigmented colonies

• Catalase positive

Virulence factors of Bacillus anthracis

• Glutamic acid capsule

• 3 component protein exotoxin

  • PA, EF, LF

Clinical infections of B. anthracis

• Common livestock disease

  • Contaminated plants with spores

• Bioterrorism agent

Cutaneous B. anthracis

• Wounds are contaminated with spores

• Small pimple to black necrotic area

• Normally localized

Inhalation B. anthracis

• Woolsorter’s disease

• Spores inhaled into parenchyma

• Resembles URI

• High mortality rate

Gastrointestinal B. anthracis

• Spores on undercooked/raw meat

• Abdominal pain, nausea, vomiting

Injectional B. anthracis

• NF, organ failure, shock

Microscopic ID of B. anthracis

LArge, square ended GPR found singly or in chains

Culture characteristics of B. anthracis

• SBA- nonhemolytic, large gray colonie swith irregular margins

• Medua head

Identification of B. anthracis

• nonmotile

• Susceptible to penicillin

• Catalase posiitve, ferments glucose

• Negative gelatin hydrolysis, salicin fermentation

Characteristics of B. cereus

• Common cause of food poisoninga nd other opportunisitc infections

• Similar to B. anthracis in morphology and metabolism

B. cereus at 37 degrees C:

• Hemolytic on SBA

• Motile

• Penicillin resistant

• Hydrolyzes gelatin

• Ferments salicin

• Produces lecithinase

Diarrheal B. cereus food poisoning

• Clinically indistinguishable from C. perfringens

• Incubation: 8-16 hours

• Lasts about 24 hours

Emetic B. cereus food poisoning

• Nausea and vomiting

• Occurs 1 to 5 hours after eating infected food

• Lasts about 9 hours

Are the two types of food poisoning of B. cereus, are they caused by the same enterotoxin?

No, two different enterotoxins

B. cereus eye infections

• Endophthalmitis

• Panophthalmitis

• Keratitis