Corynebacterium and Other Non–Spore-forming Gram-Positive Rods Corynebacterium sp. Listeria monocytogenes Erysipelothrix rhusiopathiae

Case Study A 76-year-old woman is receiving corticosteroid therapy Complained of fever and headache for 7 days CBC count showed an elevated white cell count CSF analysis showed 250 WBC/cu mm Glucose 30 mg/dL Protein 180 mg/dL Culture grew beta-hemolytic colonies on sheep blood agar, gram-positive pleomorphic rods Catalase positive, motile at room temperature CAMP-factor positive

Points to Consider What type of infection was suspected in this particular patient? What predisposing risk factors were presented by the patient? How are these organisms differentiated from other groups with similar characteristics? What clinical forms of infections are associated with these groups of organisms? Other points to consider

Corynebacterium Species: General Characteristics Morphology Gram-positive, non–spore-forming rods Arrange in palisades: “L-V” shape; “Chinese characters” Pleomorphic: “club-ends”

Corynebacterium Species General characteristics Found as free-living saprophytes Members of the usual flora of humans and animals Corynebacterium diphtheriae is the most significant pathogen Other species may cause infections in the immunocompromised hosts

Other Corynebacteria Significant Corynebacterium species C. xerosis C. pseudodiphtheriticum C. pseudotuberculosis C. jekeium C. ulcerans Rhodococcus equi Arcanobacterium haemolyticum

C. diphtheriae: Agent of Diphtheria Toxigenic Corynebacterium diphtheriae Worldwide distribution rare in places where vaccination programs exist Exotoxin as the virulence factor Diphtheria toxin Toxin is produced by certain strains Lysogenized by bacteriophage with toxin gene (tox+) Toxin is antigenic

Toxigenic Corynebacterium diphtheriae Toxin consists of two fragments A: Active fragment Inhibits protein synthesis Catalyzes transfer of ADPR to link with EF2 ADPR.EF (inactive) Leads to cell/tissue death B binds to specific cell membrane receptors Binds to specific cell membrane receptors Mediates entry of fragment A

Clinical Forms of Diphtheria Respiratory Acquired by droplet spray Unimmunized individuals are susceptible Nonrespiratory Systemic Skin and cutaneous forms

C. diphtheriae: Causative Agent of Diphtheria Respiratory disease–diphtheria Incubation period–2 to 5 days Symptoms: sore throat, fever, malaise Toxin is produced locally, usually in the pharynx or tonsils Toxin causes tissue necrosis Forms a tough grey to white pseudomembrane

Clinical Infections: Non-Respiratory Disease Systemic infections Toxin is absorbed in the blood stream and carried systemically Affects the kidneys, heart, and nervous system Death occurs due to cardiac failure

Clinical Infections: Non-Respiratory Disease Cutaneous form More prevalent in the tropics Infections occur at the site of minor abrasions Maybe superinfected with Streptococcus pyogenes and/or Streptococcus aureus

Laboratory Diagnosis Microscopic morphology Gram-positive, non–spore-forming rods, club-shaped Appear in palisades and give "Chinese letter" arrangement Produce metachromatic granules or “Babes’ Ernst” bodies Loeffler methylene blue stain of Corynebacterium sp.

Laboratory Diagnosis: Cultural Characteristics Loeffler's slant or Pai's slant—Used to demonstrate pleomorphism and metachromatic granules; "Babes’ Ernst bodies" Serum Tellurite or modified Tinsdale- brown or grayish to black halos around the colonies Growth of C. diphtheriae on blood agar

Laboratory Diagnosis Identification Toxigenicity testing Confirm identification by fermentation reactions Toxigenicity testing Elek test— Immunodiffusion test

Differentiating Characteristics of Corynebacterium Species

Listeria Monocytogenes: General Characteristics Gram-positive, non–spore-forming rods Widespread in nature Known to infect a wide variety of animals Human exposure is limited; direct or indirect Transient colonization occurs without disease

Listeria monocytogenes: Clinical Infections Adults Septicemia/meningitis in the compromised/elderly Mild flu-like syndrome in pregnant women could be fatal to fetus Neonatal Early onset from intrauterine transmission results in sepsis; high mortality rate Late onset manifests as meningitis; lower mortality rate

Laboratory Diagnosis: L. monocytogenes Identification Microscopic morphology Gram Positive non–spore-forming coccobacillary Cultural characteristics Grows well on blood agar; colonies produce a narrow zone of hemolysis similar to Group B Streptococcus

Laboratory Diagnosis: L. monocytogenes Identification Catalase positive Motility: Motile at 25o C; "umbrella" type Tumbling motility in hanging drop preparations “Umbrella” motility pattern (Left) typical for L. monocytogenes

Laboratory Diagnosis: L. monocytogenes Identification CAMP test Produces a “block” type of hemolysis in contrast to “arrow”-shape produced by Group B Streptococcus CAMP test with Listeria monocytogenes Positive CAMP test for Group B Streptococcus

Differentiating Characteristics between L Differentiating Characteristics between L. monocytogenes and Other Gram Positive Bacteria

Erysipelothrix rhusiopathiae: General characteristics Gram positive, non–spore-forming, pleomorphic rods Distributed in nature Can cause disease in animals (swine, turkey, sheep) Humans acquire the infection through occupational exposure

Erysipelothrix rhusiopathiae: Clinical Infections Erysipeloid Self-limiting localized infection at the site of inoculation Produces painful swelling, usually on the hands or fingers Heals within 3 to 4 weeks Endocarditis May occur in those who have had valve replacements Disseminated infections may occur, but rarely

Laboratory Diagnosis: Erysipelothrix rhusiopathiae Microscopy Pleomorphic, gram-positive thin rods that may form long filaments, may be arranged singly, in short chains, or in a V shape

Laboratory Diagnosis: Erysipelothrix rhusiopathiae Identification Catalase negative CO2 is required Grows on blood or chocolate agar—colonies may appear gray or translucent with alpha hemolysis Distinguishing characteristic: Production of H2S on TSI

Characteristics of Corynebacterium, Listeria, and Erysipelothrix

Points to Remember Distinguishing characteristics of the genera Listeria, Corynebacterium, and Erysipelothrix from other gram positive bacteria Clinical infections caused by each of these groups Risk factors are associated with these infections Biochemical and microscopic features of each of these species