Gram Positive Bacilli

Bacteriology GRAM-POSITIVE BACILLI I. LISTERIA MONOCYTOGENES Morphology and culture characteristics • Small gram-positive coccobacilli (bacillary 3-6 hours 37°C; coccoid thereafter) • ß-hemolytic on sheep agar • Wide range of temperature does not affect growth • Catalase-positive • Motile (4 flagella-20-2SoC; 1 flagellum at 37°C). Transmission • Worldwide distribution • Humans with disease, healthy carriers • Mammals, birds, ticks, fish, crustacea • Probably lives in plant-soil environment • Contracted by humans and animals by many routes • Oral route probably most common. Clinical manifestations Neonatal infections Genital tract infection in pregnant women with transmission to offspring Granulomatis infantiseptica – “in-utero” infection, presents within 2 days, high mortality rate Late infection: Acquired during or after birth, meningitis (10% of all neonatal meningitides). Adult MENINGITIS Leading cause of meningitis in cancer patients and renal transplant recipients, 30% cases with no underlying disease PRIMARY BACTEREMIA- Increased in pregnant patients with underlying disease ENDOCARDITIS Diagnosis • Isolation of the organism from clinical material • Laboratory personnel must be alerted when suspected-may be assumed to be diphtheroid contaminant • Serologic diagnosis unreliable • Anton test-purulent keratoconjunctivitis in rabbits 24-36 hours after inoculation of organisms into conjunctival sac • Occasionally seen on gram stain as small gram positive intracellular organisms Treatment: Ampicillin, Penicillin alone or with Aminoglycosides

II. ERYSIPELOTHRIX RHUSIOPATHIAE Morphology and culture characteristics • Gram-positive rod • Nonmotile • Microaerophilic • Smooth colonies in acute disease • Rough colonies in chronic disease • Alpha-hemolytic • Neomycin resistant.

Transmission: Distributed worldwide, humans acquire by contact with animal or animal products. Occupational exposure-fish handlers, abattoir employees, butchers, etc. Clinical manifestations • Non-suppurative purplish red lesion at site of inoculation • Painless (may burn and itch) • No systemic symptoms, no lymphangitis • May rarely disseminate; endocarditis, septic arthritis. Diagnosis: Culture of organism from aspirated material, biopsy from lesion margin, or growth from blood culture. Treatment: Penicillin

III. CORYNEBACTERIUM Morphology and culture characteristics • Gram-positive bacilli Isolate on loeffler's medium with addition of tellurite salts • Aerobic and facultatively anaerobic species differentiated by hemolysis • Sucrose fermentation • Nitrate reduction • Urease production. Transmission: C. diphtheriae increased in urban, crowded slums, humans only natural host, transmission by droplet (respiratory) and skin discharge. Other corynebacteriae; usually arise from contact with infected animals.

Clinical manifestations: C. diphtheria; respiratory; tonsillar (most common) membrane spread to pharynx, larynx, and bronchi. Cutaneous ulceration; myocarditis. Elaborates exotoxin causes mucous membrane necrosis with pseudomembrane formation. Distant effects of the toxin include degeneration of myocardium, hepatocytes, and renal parenchymal cells. Other corynebacteria: JK: bacteremia, cutaneous infections, pneumonia, endocarditis (increased incidence in patients with hematologic malignancies). C. ulcerans: pharyngitis, tonsillitis resembling diphtheria. C. pseudotuberculosis: chronic lymphadenitis, eosinophilic pneumonia. C. hemolyticum: pharngitis resembling Group-A streptococcal infection.

IV. CLOSTRIDIA Morphology and culture characteristics • Anaerobic • Spore-forming gram-positive bacilli • Usually grow on blood agar or chopped meat glucose media • Pathogenic species produce soluble toxins • Some saccharolytic and/or proteolytic • More than 60 species recognized, about 30 of them pathogenic, some aerotolerant. C. perfringens: Spore formation not noted in clinical isolates, aerotolerant, fastest growing, non motile. Five types based on production of 4 toxins (alpha, beta, epsilon, iota). All produce alpha toxin, phospholipase C (lecithinase), associated with gas gangrene. Abundant growth in chopped meat glucose media. "Stormy fermentation" in milk media, lactose fermented to acid, causing casein to coagulate, which is then disrupted by gas formation and "target hemolysis" by epsilon and alpha toxins on blood agar.

C. difficile: Spore-forming obligate anaerobe, selective media containing cycloserine, fructose, cefoxitin in agar plus 0.2 percent sodium taurocholate facilitates isolation (chartreuse fluorescence on CCFA). C. tetani: Spore-forming (drumstick appearance) motile, long and thin bacilli, swarming on blood agar plates, no carbohydrate fermentation, heating may increase isolation. C. botulinum: Straight to slightly curved gram-positive rods with rounded ends, motile, produces heat-resistant spores, strict anaerobe. Transmission C. perfringens • Ubiquitous o Meat and poultry products o Part of normal skin, intestinal, and peritoneal flora o Soil • Infection by disruption of integrity of skin, bowel, etc. o Traumatic injury o Surgery C. difficile • GI tract in neonates-64% colonization up to 8 months old • GI tract in adults-3% colonization • Diarrhea, colitis associated with present or prior antibiotic administration C. tetani

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Widespread in feces of domestic animals and man Spores abundant in soil Disease more common in underdeveloped, overcrowded, and economically deprived countries Incidence determined by immunization status of the population Wound, closed infected area, or trauma may serve as portal of entry

C. botulinum • Spores ubiquitous in soil, vary in geographic regions • Disease by ingestion of contaminated food, canned, or prepared. Clinical manifestations C. perfringens Skin and soft tissue infections o Simple contamination o Suppurative infections o Localized infections -Anaerobic cellulitis -Stump infection in amputees -Perirectal abscess -Diabetic foot ulcers -Decubitus ulcers Conjunctivitis, ophthalmitis Suppurative infection (usually polymicrobial) (a) Intra-abdominal -Bowel perforation -Emphysematous cholecystitis (b) Pelvic -Tuba-ovarian and pelvic abscess -Septic abortion (c) Myositis in heroin addicts (d) Aspiration pneumonia, with or without empyema Diffuse spreading cellulitis and fasciitis Gas gangrene Bacteremia Intestinal (a) Food poisoning (b) Enteritis necroticans C. difficile: Pseudomembranous enterocolitis-bloody diarrhea, fever C. tetani: Tetanus: incubation period of days to weeks until muscle tetany occurs. • Local-persistant local muscle contraction, low mortality • Cephalic-rare presentation, follows chronic otitis media, can progress to generalized • Generalized-most frequent presentation; "lockjaw" progressing to opisthotonos, mortality from 10-30%. C. botulinum: Botulism • Symptoms within 12-36 hours after ingestion of contaminated food • In humans, usually types A, B, or E • Constellation of signs Diagnosis Generally a clinical diagnosis, not laboratory isolation of the organism C. difficile • Toxin cytopathic effect

• Proctoscopic findings Treatment C. perfringens • Surgical debridement • Penicillin G if organism is only one present • Clindamycin, or metronidazole if infection is polymicrobial • Antitoxin-controversial • Hyperbaric oxygen-controversial C. difficile • Discontinue antibiotic patient is on when diarrhea occurs • Oral vancomycin or metronidazole C. tetani • Respiratory support • Muscle relaxants (curare-like drugs) • Prevention o Immunization with tetanus toxoid o If injury occurs in high risk patient then tetanus immune globulin indicated C. botulinum • Respiratory support • Antitoxin therapy • Penicillin-controversial