Rods Notes

Chapter 2 Acyanotic Defects NOTES RODS MICROBE OVERVIEW ▪ Rod shaped bacteria (bacilli), Gramnegative, non-spore forming BACTEROIDES FRAGILIS osms.it/bacteroides-fragilis PATHOLOGY & CAUSES ▪ Flora of oral cavity, GI tract (primarily large intestine), genitourinary tract of individuals who are biologically female; responsible for variety of infections ▪ Obligately anaerobic, non-motile ▪ Beta lactamase positive → resistance to beta lactam antibiotics ▪ Fastidious → difficult to isolate ▪ Grows in 20% bile ▪ Usually involved in widespread polymicrobial anaerobic Gram-negative bacilli infections (AGNB) ▫ Intra-abdominal, skin/soft tissue, pulmonary RISK FACTORS ▪ Prior antibiotic use ▪ ↓ blood supply (e.g. trauma, malignancy, surgery, shock, vascular disease) ▪ Tissue necrosis ▪ Disruption of intestinal mucosa ▪ High risk for aspiration pneumonia (e.g. alcoholism, coma, stroke) ▪ Bronchial obstruction → lung abscesses SIGNS & SYMPTOMS ▪ Foul-smelling discharge, tissue necrosis, formation of abscesses, gas production in tissues/discharges DIAGNOSIS DIAGNOSTIC IMAGING CT scan ▪ Abscesses/presence of gas in infected site ▫ Highly suggestive of anaerobic infection LAB RESULTS ▪ Rapid enzymatic test ▪ Polymerase chain reaction (PCR) assays ▪ Direct needle aspiration OSMOSIS.ORG 523

TREATMENT MEDICATIONS ▪ Antimicrobials ▫ Recovered anaerobes mixed with aerobic organisms; clindamycin, metronidazole, carbapenems, tigecycline, beta-lactam/beta-lactamase inhibitors, cefoxitin SURGERY ▪ Drain abscesses, relieve obstructions BARTONELLA HENSELAE osms.it/bartonella-henselae PATHOLOGY & CAUSES ▪ Zoonotic microbe; affects skin (most common), regional lymph nodes, internal organs (e.g. liver, spleen); small, pleomorphic; fastidious, slow growing; requires specific culture conditions; grows in lysis centrifugation tubes; detected with Warthin–Starry (WS)/silver stain ▪ Natural reservoir ▫ Domestic cats, usually young cats ▪ Mode of transmission ▫ Infection follows cat scratch, bite, exposure to cat feces/fleas Commonly associated diseases ▪ Cat-scratch disease (CSD) ▫ Usually affects children ▪ Bacillary angiomatosis (BA) ▫ Rare vasoproliferative disorder; usually occurs in severely immunocompromised individuals (e.g. due to HIV) COMPLICATIONS CSD ▪ Lymph nodes necrosis; can disseminate, cause life-threatening complications involving visceral organs (e.g. liver, spleen), central nervous system (CNS), eyes BA ▪ Potentially fatal if untreated 524 OSMOSIS.ORG SIGNS & SYMPTOMS ▪ May be asymptomatic CSD ▪ Usually develops 1–3 weeks after inoculation ▪ Regional lymphadenopathy/lymphadenitis (most common) ▫ Usually unilateral; lymph nodes drain site of inoculation; tender, swollen lymph nodes ▪ Rare ▫ Low grade fever, malaise, ↓ appetite, abdominal aches ▪ Cutaneous erythematous lesion at site of inoculation; regresses spontaneously after 1–4 weeks ▪ Visceral organs → hepatomegaly, splenomegaly ▪ Eyes → neuroretinitis, parinaud oculoglandular syndrome ▪ Central nervous system (CNS) → encephalopathy BA ▪ Usually affects skin → red papules, nodules/ subcutaneous masses DIAGNOSIS LAB RESULTS ▪ Difficult to culture; incubation takes 2–4 weeks ▪ PCR assays

Chapter 96 Rods Biopsy ▪ CSD: granulomatous inflammation of lymph nodes, stellate microabscesses; organisms visualized using WS/silver stain ▪ BA: biopsy of lesions; Bartonella demonstrated with WS stain Serologic test ▪ Indirect immunofluorescence antibody (IFA)/enzyme immunoassay (EIA) Nonspecific findings ▪ ↑ erythrocyte sedimentation rate (ESR), ↑ C-reactive protein (CRP) in CSD OTHER DIAGNOSTICS ▪ Clinical findings suggestive of Bartonella infection with history of contact with cat Figure 96.1 The histological appearance of an lymph node excised from an individual with cat-scratch disease. There are numerous neutrophils which form characteristic stellate, or star-shaped, microabscesses. TREATMENT MEDICATIONS CSD ▪ Usually self-limited within 2–4 months; antimicrobial therapy with azithromycin prevents life-threatening complications; alternative agents include doxycycline, rifampin BA ▪ Erythromycin, doxycycline, tetracycline Figure 96.2 The histopathological appearance of bacillary angiomatosis. There is a proliferation of small capillaries surrounded by mixed inflammatoru cells, histiocytes and bacterial colonies. OSMOSIS.ORG 525

ENTEROBACTER osms.it/enterobacter PATHOLOGY & CAUSES ▪ Opportunistic microbe; nosocomial, various organ system infections; Enterobacteriaceae family; motile, nonfastidious; fast lactose fermenter, pink colonies on MacConkey agar (lactose containing medium); grows in aerobic, anaerobic conditions, rapidly on selective, nonselective agars; expresses fimbria; hemolysin, urease positive ▪ Commonly isolated species: E. cloacae, E. aerogenes ▪ Natural reservoir ▫ Soil, water, intestinal flora; occasionally respiratory tract ▪ Mode of transmission ▫ Endogenous: transfer from flora to adjacent sterile sites ▫ Exogenous: direct/indirect contact of mucosal surfaces with Enterobacter Commonly associated diseases ▪ Lower respiratory tract infections ▫ Tracheobronchitis, pneumonia, lung abscess, empyema ▪ Urinary tract infections (UTIs) in hospitalized individuals ▫ Cystitis, pyelonephritis, prostatitis ▪ Bloodstream infections (BSI) ▪ Skin, soft tissue infections ▫ Cellulitis, fasciitis, myositis, skin abscesses, wound infections ▪ Intra-abdominal infections ▫ Abscesses, peritonitis following intestinal perforation/surgery ▪ Uncommon ▫ Endocarditis, septic arthritis, osteomyelitis, CNS, ocular infections RISK FACTORS ▪ More common in neonates, elderly individuals 526 OSMOSIS.ORG ▪ Prolonged hospitalization ▪ Invasive procedures (e.g. post-surgery infections) ▪ Prior antibiotic therapy ▪ Invasive devices (e.g. venous catheterization) ▪ Underlying conditions ▫ Malignancy, chronic obstructive pulmonary disease (COPD), diabetes mellitus (DM), burns ▪ Mechanical ventilation ▪ Immunosuppression COMPLICATIONS ▪ Septic shock SIGNS & SYMPTOMS ▪ Non-specific, depends upon organ system affected ▪ UTIs ▫ Frequency, urgency of urination, dysuria DIAGNOSIS DIAGNOSTIC IMAGING Chest X-ray/CT scan ▪ Respiratory infections Abdomen CT scan/ultrasound ▪ Abdominal infections LAB RESULTS ▪ Urinalysis for UTIs Microbe identification ▪ Gram staining, culture

Chapter 96 Rods TREATMENT MEDICATIONS ▪ Antimicrobials ▫ Carbapenems, aminoglycosides, fluoroquinolones, trimethoprimsulfamethoxazole, polymyxins SURGERY ▪ Drain abscesses OTHER INTERVENTIONS ▪ Remove invasive devices (e.g. central venous catheters) ESCHERICHIA COLI osms.it/escherichia-coli PATHOLOGY & CAUSES ▪ Frequent cause of variety of infections; Enterobacteriaceae family; encapsulated, motile; certain strains hemolytic (betahemolytic on blood agar); fast lactose fermenter (pink colonies on MacConkey agar); nonfastidious; beta-galactosidase positive (breaks down lactose into glucose, galactose); iron uptake system ▪ AKA E.Coli ▪ Natural reservoir ▫ Intestinal, vaginal flora ▪ Mode of transmission ▫ Person-to-person contact, contaminated food/water, dislocation from intestinal tract ▪ Growing conditions ▫ On selective media; aerobic, anaerobic; eosin-methylene blue (EMB) agar for isolation (colonies with green metallic sheen); 15–45°C/59–113°F (some strains more heat resistant) ▪ Virulence factors ▫ Fimbriae, K-capsule, lipopolysaccharides (LPS) endotoxin ▪ Pathogenic factors ▫ Fimbriae → cystitis, pyelonephritis ▫ K-capsule → pneumonia, neonatal meningitis ▫ LPS endotoxin → septic shock Commonly associated diseases ▪ Genitourinary tract infections ▫ Leading cause of cystitis, pyelonephritis, prostatitis ▪ Intra-abdominal infections ▫ Enteric infections, abscesses, cholecystitis, spontaneous bacterial peritonitis (E. coli most common cause) ▪ Pneumonia ▪ Meningitis (in neonates) TYPES Enteroinvasive (EIEC) ▪ Invades intestinal mucosa → necrosis, inflammation → dysentery Enterotoxigenic (ETEC) ▪ Heat-labile toxin (LT) → over-activates adenylate cyclase (cAMP) → ↑ Cl- secretion in gut, water efflux ▪ Heat-stable toxin (ST) → overactivates guanylate cyclase (cGMP) → ↓ resorption of NaCl, water in gut ▪ Produces LT, ST → travellers’ diarrhea (watery), mimics Vibrio cholerae illness Enteropathogenic (EPEC) ▪ Adheres to apical surface, flattens villi, prevents absorption → diarrhea Enterohemorrhagic (EHEC) ▪ Most commonly isolated serotype O157:H7 ▪ Produces Shiga-like toxin → enhances cytokine release ▫ Necrosis, inflammation → dysentery ▫ Endothelial damage → formation of microthrombi → hemolysis OSMOSIS.ORG 527

(microangiopathic hemolytic anemia), platelet consumption (thrombocytopenia), ↓ renal blood flow (acute renal failure) → hemolytic uremic syndrome (HUS) ▫ O157:H7 most common serotype SIGNS & SYMPTOMS ▪ Depends on organ system affected ▪ Clinical manifestations generally nonspecific, except in enteric infections ▫ EHEC: bloody diarrhea, malaise, fever ▫ EIEC: dysentery, mimics shigellosis; bloody diarrhea, abdominal pain, tenesmus ▫ ETEC: watery diarrhea (travellers’ diarrhea), nausea, abdominal pain ▫ EPEC: fever, watery diarrhea; can last > two weeks; typically affects children DIAGNOSIS LAB RESULTS ▪ Culture to isolate E. coli, gram staining, ↑ fecal leukocytes (except ETEC), PCR assays ▪ Complete blood count ▫ Leukocytosis ▪ Urinalysis in UTIs ▪ Pyuria ▫ Leukocyte esterase + → evidence of white blood cell (WBC) activity ▪ Proteinuria, bacteriuria ▪ Nitrite test + → ↓ urinary nitrates → marker of infection 528 OSMOSIS.ORG TREATMENT MEDICATIONS ▪ Antimicrobial treatment (UTIs, pneumonia, meningitis, intra-abdominal infections, sepsis) ▫ Third-generation cephalosporins, quinolones, doxycycline, trimethoprim/ sulfamethoxazole (TMP/SMZ) ▪ Antidiarrheal medications ▫ Contraindicated in children, EIEC infections ▪ EHEC ▫ Antibiotics contraindicated; can increase risk of HUS, thrombotic thrombocytopenic purpura (TTP) complications ▪ ETEC ▫ Antibiotics useful; reduce diarrhea duration OTHER INTERVENTIONS ▪ Most enteric infections self-limited, managed conservatively ▫ Fluid, electrolytes correction

Chapter 96 Rods KLEBSIELLA PNEUMONIAE osms.it/klebsiella-pneumoniae PATHOLOGY & CAUSES ▪ Causative agent of infections, usually occur in immunocompromised individuals; major cause of hospital-acquired infections; Enterobacteriaceae family, facultative anaerobe, nonmotile; possesses prominent polysaccharide capsule; beta-lactamase positive (resistant to ampicillin, amoxicillin; susceptible to cephalosporins); urease positive, lactose fermenter, iron uptake system ▪ Natural reservoir ▫ Flora of human mouth, intestine; soil, water Commonly associated diseases ▪ Pulmonary infections ▫ Pneumonia, empyema, lung abscesses, bacteremia ▪ UTIs ▫ Cystitis, pyelonephritis, prostatitis, abscesses ▪ Pyogenic liver/splenic abscesses ▪ Infective endocarditis ▪ Spontaneous bacterial peritonitis ▪ Endophthalmitis ▪ CNS infections ▪ Meningitis, brain abscesses ▪ Deep neck infections ▪ Skin, soft tissue infections COMPLICATIONS ▪ Pneumonia can be fatal regardless of treatment SIGNS & SYMPTOMS ▪ Pneumonia presents as bronchopneumonia/bronchitis (acute onset of symptoms) ▫ Productive cough (e.g. mucoid; bloody sputum, AKA “currant jelly sputum”), high grade fever, chills, chest pain, dyspnea, tachypnea, crackles ▪ UTIS (frequency, urgency, dysuria) DIAGNOSIS DIAGNOSTIC IMAGING Chest X-ray ▪ Findings suggestive of pneumonia LAB RESULTS ▪ Complete blood count ▫ Leukocytosis ▪ Specimen culture ▫ E.g. blood, sputum, urine ▫ Gram stain: Gram-negative, rod-shaped capsule appears as clear space TREATMENT RISK FACTORS ▪ Prolonged hospitalization ▪ Prior use of antibiotics ▪ Prolonged use of invasive devices (e.g. catheters) ▪ Underlying medical conditions ▫ Alcoholism, DM, underlying malignancy, hepatobiliary disease, COPD, renal failure ▪ Use of glucocorticoids MEDICATIONS ▪ Antimicrobial therapy ▫ Beta-lactams with beta-lactamase inhibitors, cephalosporins, fluoroquinolones, aminoglycosides, carbapenems SURGERY ▪ Drain abscesses ▪ Debride necrotic issues OSMOSIS.ORG 529

LEGIONELLA PNEUMOPHILA osms.it/legionella-pneumophila PATHOLOGY & CAUSES SIGNS & SYMPTOMS ▪ Gram-negative, facultative intracellular (stain poorly with Gram stain); best visualized by silver stain; appears in specimens as short rod; longer, filamentous in culture; grows best on charcoal yeast extract medium with cysteine, iron; serogroup 1 most commonly associated with human infections ▪ Natural reservoir ▫ Water sources (e.g. air conditioning systems, tubing systems of domestic water supplies, water-cooling towers) ▪ Mode of transmission ▫ Water aerosol inhalation Legionnaires’ disease ▪ Incubation period ▫ 2–10 days ▪ Atypical pneumonia ▫ Mild cough (may cough bloody mucus), high grade fever, chills, dyspnea, chest pain, rales ▪ GI ▫ Diarrhea, nausea, vomiting, abdominal pain ▪ CNS ▫ Confusion, lethargy, headache, focal neurologic signs, hallucinations Commonly associated diseases ▪ Legionnaires’ disease ▫ Atypical form of pneumonia ▪ Pontiac fever ▪ Rare self-limited upper respiratory tract infection ▪ Extrapulmonary disease (rare) ▫ Heart most common extrapulmonary site (e.g. myocarditis, endocarditis) Pontiac fever ▪ Acute onset ▪ Mild, febrile, flu-like syndrome RISK FACTORS ▪ ↑ age, immunosuppression, smoking, chronic lung disease, organ transplant, renal failure, cardiac disease COMPLICATIONS ▪ Pneumonia ▫ Progresses rapidly, can be fatal (esp. immunosuppressed individuals) ▪ Renal failure 530 OSMOSIS.ORG DIAGNOSIS DIAGNOSTIC IMAGING Chest X-ray/CT scan ▪ Legionnaires’ disease ▫ Unilateral ▪ Diffuse, patchy inflammation of interstitium → consolidation involving ≥ one lobe LAB RESULTS ▪ Nonspecific findings ▫ Hyponatremia, thrombocytopenia, leukocytosis, hypophosphatemia ▪ Culture of respiratory specimens ▫ Many neutrophils, few microorganisms ▪ Urinary antigen test using enzyme-linked immunosorbent assay (test of choice along with culture) ▫ Rapid; sensitive, specific; legionella persists in urine for weeks

Chapter 96 Rods ▪ Fluorescent antibody test on sputum specimens ▪ Serological tests ▫ Serum antibodies develop after 8–10 days; fourfold rise in titre/single high titre ▪ PCR using sputum/other specimens (less sensitive than culture) TREATMENT MEDICATIONS ▪ Atypical pneumonia ▫ Macrolides, tetracyclines. fluoroquinolones, rifampicin OTHER INTERVENTIONS ▪ Eradication of organism from responsible water source to control disease NONTYPHOIDAL SALMONELLA osms.it/nontyphoidal-salmonella PATHOLOGY & CAUSES ▪ Causes salmonellosis (foodborne gastroenteritis); Enterobacteriaceae family; motile; encapsulated; facultative intracellular, anaerobes; nonlactose fermenter; oxidase-; possesses type III secretion system, iron uptake system; high infectious dose; H2S production on TSI agar; produces endotoxin ▪ Most common human pathogen ▫ S.enteritidis ▪ Natural reservoir ▫ Humans, animals; poultry, eggs, pets, turtles common sources ▪ Mode of transmission ▫ Food (e.g. undercooked meat, poultry, eggs, milk), fecal-oral route RISK FACTORS ▪ Age (usually affects young children, older adults); season (peak incidence in summer, fall); low gastric acidity (atrophic gastritis, use of acid-suppressive agents); immunodeficiency; sickle cell disease; hemolytic anemia; alcoholism; cardiovascular dysfunction; malignancies; IV drug use COMPLICATIONS ▪ Can disseminate via blood → extraintestinal manifestations (e.g. endocarditis, vascular infections, cholecystitis, hepatic/splenic abscesses) SIGNS & SYMPTOMS ▪ Present 24–48 hours after food ingestion ▪ Loose stools/diarrhea often bloody (can persist for two weeks) ▪ Nausea, vomiting ▪ Fever (resolves within two days) ▪ Abdominal cramps DIAGNOSIS LAB RESULTS ▪ Stool culture, ↑ fecal leukocytes, blood cultures to detect bacteremia; bone marrow aspiration, culture TREATMENT MEDICATIONS ▪ Antimicrobial therapy ▫ Generally not required, prolongs duration of fecal shedding of Salmonella, doesn’t shorten duration of symptoms OSMOSIS.ORG 531

▪ Antibiotics ▫ Only indicated in immunocompromised individuals; antimicrobial agents (e.g. ciprofloxacin) PROTEUS MIRABILIS osms.it/proteus-mirabilis PATHOLOGY & CAUSES ▪ Common cause of community acquired, nosocomial UTIs (e.g. primarily cystitis, pyelonephritis) ▪ Enterobacteriaceae family; highly motile; nonlactose fermenters; oxidase negative; expresses mannose-resistant hemagglutination, calcium dependent/ independent hemolysins; swarming growth in discontinuous manner on agar media; H2S production on TSI agar; resistance to polymyxins, tetracyclines ▪ Urease positive → converts urea to ammonia, CO2 → ↑ urine pH → ammonia combines with magnesium, phosphate → form magnesium-ammonium-phosphate (struvite) stones ▪ Pr. mirabilis causes 90% of infections ▪ Natural reservoir ▫ Intestinal flora ▪ Virulence factors ▫ Fimbria (important for adherence to tissue) Commonly associated diseases ▪ Urethritis, acute prostatitis, pyogenic liver abscesses RISK FACTORS ▪ Hospitalization; ↑ age (most common in elderly); multiple prior UTIs; prior use of antibiotics; urinary tract surgery; urinary catheterization; structural abnormalities/ obstructions of urinary tract; underlying medical conditions (e.g. DM, chronic kidney disease); neurogenic bladder; frequent sexual activity 532 OSMOSIS.ORG COMPLICATIONS ▪ Abscesses, sepsis, meningitis, chronic pyelonephritis, xanthogranulomatous pyelonephritis (chronic destructive granulomatous process of renal parenchyma) SIGNS & SYMPTOMS ▪ Nonspecific, disease-dependent: symptoms commonly associated with urethritis, acute prostatitis, pyogenic liver abscesses DIAGNOSIS DIAGNOSTIC IMAGING Ultrasound/CT scan ▪ Kidneys; indicated if therapy fails X-ray ▪ Struvite stones appear radiopaque LAB RESULTS ▪ Urine culture to isolate Proteus ▪ Complete blood count ▫ Leukocytosis ▪ Urinalysis ▫ Alkaline urine pH (> 7.0), pyuria, bacteriuria

Chapter 96 Rods TREATMENT MEDICATIONS ▪ Uncomplicated UTIs ▫ Cystitis: TMP/SMX, nitrofurantoin, quinolones, fosfomycin ▫ Pyelonephritis: quinolone/ampicillin, gentamicin/third-generation cephalosporin ▪ Complicated UTIs ▫ E.g. diabetes, nephrolithiasis, pregnancy, anatomic abnormalities of urinary tract ▫ Therapy should be prolonged SURGERY ▪ Drainage of collections (e.g. perinephric abscesses) ▪ Removal of struvite renal calculus Figure 96.3 Proteus species spread in a swarming fashion on an agar plate. PSEUDOMONAS AERUGINOSA osms.it/pseudomonas-aeruginosa PATHOLOGY & CAUSES ▪ One of most common causes of hospitalacquired infections in immunocompromised individuals; motile; aerobic; nonlactose fermenter (derives energy from carbohydrates by oxidation); nonfastidious; oxidase, catalase, elastase, leukocidin, hemolysin positive; resistant to many antibiotics ▪ Grows on variety of culture media ▫ Colonies greenish-blue due to production of procyanin (blue), pyoverdin (yellow-green); fruity, grapelike odor ▪ Natural reservoir ▫ Water, soil sources (e.g. rivers, ponds), animals, plants, hospital equipment; hospitalized individuals asymptomatic carriers ▪ Mode of transmission ▫ Direct contact with contaminated materials/infected individuals ▪ Virulence factors ▫ Exotoxin A → inactivates elongation factor (EF-2) → inhibition of protein synthesis → death of host cells ▫ Phospholipase C → degrades membranes ▫ Endotoxin → fever, shock ▫ Mucoid exopolysaccharide → biofilm formation → protection from immune system Commonly associated diseases ▪ Pneumonia; sepsis; genitourinary tract infections; skin, soft tissue infections; ear infections (e.g. external otitis, chronic otitis media); eye infections (e.g. keratitis); GI infections; bone, joint infections (usually affects vertebral column); infective endocarditis RISK FACTORS ▪ Prolonged hospitalization, catheterization, IV drug use, severe burns, contact lenses, eye trauma OSMOSIS.ORG 533

▪ Mechanical ventilation/endotracheal intubation ▫ P. aeruginosa second most common cause of ventilator-associated pneumonia ▪ Cystic fibrosis (CF) → chronic infection with P. aeruginosa ▪ Immune system deficits (e.g. neutropenia, diabetes) COMPLICATIONS ▪ Sepsis/necrotizing pneumonia can be fatal in immunocompromised individuals ▪ Chronic infections in CF → bronchiectasis, pulmonary fibrosis → pulmonary failure ▪ Disseminated intravascular coagulation due to sepsis ▪ Eye infections → vision loss SIGNS & SYMPTOMS ▪ Generally nonspecific, depend on organ system ▪ Eye infections (esp. cornea) extremely painful, rapidly destructive ▪ Ecthyma gangrenosum ▫ Due to sepsis, typically appears in immunocompromised individuals ▫ Well-demarcated, black, necrotic cutaneous lesion; rapidly progressive Figure 96.4 Pseudomonas species will adopt a greenish hue when cultured on cetrimide agar. 534 OSMOSIS.ORG DIAGNOSIS DIAGNOSTIC IMAGING Chest X-ray ▪ Pneumonia ▫ Bilateral bronchopneumonia with nodular infiltrates with/without pleural effusion LAB RESULTS ▪ Culture (blood/other specimens) on selective media ▫ Enhances production of procyanin ▪ Oxidase test ▪ PCR assays ▪ Complete blood count ▫ Leukocytosis ▪ Serological tests ▫ Only individuals with CF/COPD TREATMENT MEDICATIONS ▪ Antimicrobial therapy ▫ Extended-spectrum penicillins, betalactamase inhibitors, aminoglycosides, carbapenems, monobactams, polymyxins, fluoroquinolones, third/ fourth-generation cephalosporins

Chapter 96 Rods SERRATIA MARCESCENS osms.it/serratia-marcescens PATHOLOGY & CAUSES ▪ Opportunistic microbe; uncommon cause of variety of hospital-acquired infections; Enterobacteriaceae family; motile; aerobic; slow, weak lactose fermenter; urease positive (struvite stones in individuals with recurrent UTIs); catalase positive; grows on media at 30–37°C/86–99°F, utilize most carbohydrates with production of acid, gas; produces red pigment (prodigiosin) colonies on agar; often resistant to commonly used antibiotics (e.g. ampicillin, macrolides, firstgeneration cephalosporins) ▪ Natural reservoir ▫ Water, soil sources ▪ Virulence factors ▫ Fimbria, cell surface components, longchain LPS, hemolysin Commonly associated diseases ▪ Respiratory infections (e.g. pneumonia), UTIs, wound infections, CNS infections (e.g. meningitis, cerebral abscesses), intra-abdominal infections, septicemia, endocarditis, otitis externa RISK FACTORS ▪ Neonates, infants ▪ More common in individuals who are biologically male ▪ Prolonged hospitalization; catheterization (e.g. intravenous, urinary catheters); mechanical ventilation; recent surgery/ obstruction of urinary tract; cardiac valve replacement; IV drug use; immune system deficits (e.g. neutropenia, chronic granulomatous disease, DM); head trauma/ brain surgery; contact lenses COMPLICATIONS ▪ Septic shock, stroke (due to endocarditis) SIGNS & SYMPTOMS ▪ Nonspecific, depend upon disease ▪ Symptoms associated with respiratory infections, UTIs, wound infections, CNS infections, intra-abdominal infections, septicemia, endocarditis, otitis externa DIAGNOSIS DIAGNOSTICS IMAGING Chest X-ray ▪ Pneumonia Abdominal ultrasound/CT scan ▪ Abnormalities of urinary tract, intraabdominal infections, abscesses Echocardiography ▪ Valvular vegetations Brain CT scan ▪ Follow with lumbar puncture in individuals with suspected meningitis Figure 96.5 Serratia marcessens grows red colonies when cultured on agar. OSMOSIS.ORG 535

LAB RESULTS ▪ Complete blood count ▫ Leukocytosis, ↑ neutrophils with left shift, possible anemia TREATMENT MEDICATIONS ▪ Antibiotic therapy ▫ Aminoglycosides with antipseudomonal beta-lactam ▫ If infection persists, fluoroquinolones/ carbapenems SURGERY ▪ Drainage of collections (e.g. abscesses) SHIGELLA osms.it/shigella PATHOLOGY & CAUSES ▪ Causes acute infectious diarrhea (shigellosis), one of most common causes of bloody diarrhea; Enterobacteriaceae family; facultative anaerobe; nonmotile; nonlactose fermenter; urease, oxidase negative; resistance to low pH of gastric acids; highly virulent; possesses virulence plasmids; invades colonic mucosa via microfold (M) cells of Peyer patches ▪ Natural reservoir ▫ Human only; part of intestinal tract flora ▪ Mode of transmission ▫ Usually fecal-oral route, contaminated water, food; easy person-to-person spread TYPES ▪ S. dysenteriae: serogroup A ▫ Releases Shiga toxin, causes most severe form of shigellosis ▪ S. flexneri: serogroup B ▪ S. boydii: serogroup C ▪ S. sonnei: serogroup D COMPLICATIONS ▪ Dehydration (due to fluid loss) ▪ Electrolyte imbalance (e.g. hyponatremia, 536 OSMOSIS.ORG hypokalemia) ▪ Reiter’s syndrome ▫ Reactive arthritis, urethritis, conjunctivitis ▫ Affects HLA-B27+ individuals ▪ Hemolytic-uremic syndrome ▫ Hemolytic anemia, thrombocytopenia, acute renal failure ▫ Usually in infections due to S. dysenteriae ▪ Toxic megacolon ▪ Intestinal obstruction SIGNS & SYMPTOMS ▪ Incubation period ▫ 2–3 days/one week ▪ Sudden onset ▫ Abdominal pain ▫ Diarrhea that is initially watery, progresses to bloody (bacillary dysentery) in 50% of cases ▫ Tenesmus ▫ Fever, malaise, headache, anorexia ▪ Less common ▫ Nausea, vomiting

Chapter 96 Rods ▪ Subacute presentation in minority of individuals ▫ Several weeks of waxing/waning diarrhea DIAGNOSIS DIAGNOSTIC IMAGING Colonoscopy ▪ Hemorrhagic, ulcerated mucosa ▪ Most prominent in left colon, ileum also involved ▪ Pseudomembranes TREATMENT MEDICATIONS ▪ Antimicrobial therapy ▫ Shorten duration of symptoms, reduce fecal shedding of organisms, risk of complications; azithromycin orally, thirdgeneration cephalosporin parenterally ▪ Antidiarrheal medications contraindicated ▫ Delay fecal shedding of Shigella OTHER INTERVENTIONS ▪ Most cases self limited (resolve within one week), do not require antibiotics LAB RESULTS ▪ Stool culture ▪ ↑ leukocytes, blood in feces ▪ PCR testing of stools YERSINIA MARCESCENS osms.it/yersinia-marcescens PATHOLOGY & CAUSES ▪ Enterobacteriaceae family; facultative anaerobe, intracellular; motility depends on temperature (motile at 25°C/77°F, nonmotile at 37°C/99°F); nonlactose fermenter; oxidase negative ▪ Important human pathogens ▫ Y. pestis, Y.enterocolitica ▪ Natural reservoir ▫ Y. pestis: ground squirrels, gerbils, voles, rats ▫ Y. enterocolitica: cattle, deer, pigs, birds, pigs ▪ Virulence factors ▫ Adhesins to bind to host cell beta 1 integrins, endotoxin, coagulase, fibrinolysin, iron uptake system (mediates iron capture, transport) TYPES Yersinia enterocolitica ▪ Causes yersiniosis ▫ Gastrointestinal infections (e.g. ileum, appendix, right colon) ▪ Common types ▫ Enterocolitis, terminal ileitis, mesenteric lymphadenitis, pseudoappendicitis ▪ Mode of transmission ▫ Pet feces, inadequately cooked foods, contaminated pork, milk, water Yersinia pestis ▪ Causes human plague ▫ Zoonotic infection, highly fatal if untreated ▪ Subtypes ▫ Wild (sylvatic), urban plague (typically transmitted from rats, more severe) OSMOSIS.ORG 537

▪ Clinical forms ▫ Bubonic (more common), septicaemic, pneumonic (least common, high mortality rate) ▪ Mode of transmission ▫ Fleas from rats, other rodents COMPLICATIONS Yersinia enterocolitica ▪ Reiter’s syndrome, myocarditis, erythema nodosum, kidney disease, mucosal ulceration, bowel necrosis (due to mesenteric vessel thrombosis), septicemia (fatal if untreated) Yersinia pestis ▪ Bubonic plague → sepsis → secondary pneumonic plague/meningitis ▪ Systemic plague → hypotension, disseminated intravascular coagulation, multiorgan failure ▪ Pneumonic plague (rapidly fatal if untreated) SIGNS & SYMPTOMS Yersinia enterocolitica ▪ Enterocolitis (most common) ▫ Abdominal pain, acute diarrhea, low grade fever, nausea, vomiting ▪ Abdominal tenderness ▫ Right lower quadrant, mimics appendicitis (pseudoappendicitis) ▪ Extraintestinal features of pharyngitis, arthralgia, erythema nodosum (painful, red/ purple lesions, resolve spontaneously) Yersinia pestis ▪ Incubation period ▫ 2–8 days ▪ Bubonic plague (sudden onset) ▫ fever; painful lymphadenopathy (bubos), inguinal lymph nodes frequently involved; chills, fatigue ▪ Septicemic plague ▫ Fever; malaise, GI symptoms (nausea, vomiting, diarrhea) 538 OSMOSIS.ORG ▪ Pneumonic plague (sudden onset): ▫ Dyspnea, high grade fever, chest pain, cough with blood-containing sputum DIAGNOSIS DIAGNOSTIC IMAGING Ultrasound/CT scan ▪ Yersinia enterocolitica: exclude appendicitis Colonoscopy ▪ Yersinia enterocolitica: aphthoid lesions in cecum; elevations, ulcers in terminal ileum Chest X-ray ▪ Yersinia pestis: pneumonic plague LAB RESULTS Yersinia enterocolitica ▪ Identification of microbe ▪ Stool culture ▫ Cefsulodin-irgasan-novobiocin (CIN) agar ▫ In extraintestinal disease, cultures of lymph nodes/blood may be positive ▪ PCR assays ▪ ↑ leukocytes in stool, blood ▪ Serological tests ▫ Tube agglutination, enzyme-linked immunosorbent assay (ELISA) Yersinia pestis ▪ Nonspecific findings ▫ Leukocytosis, thrombocytopenia ▪ Isolation of organism in blood culture ▫ Positive cultures in individuals with bubonic, septicemic plague ▪ Peripheral blood smear ▫ Wright–Giemsa stain reveals rodshaped bacteria, Wayson stain reveals characteristic “safety pin” appearance ▪ Rapid antigen testing in sputum/serum ▪ Serological tests ▫ Fourfold rise in serum antibody titers between acute, convalescent phase ▪ PCR assays

Chapter 96 Rods OTHER DIAGNOSTICS Yersinia pestis ▪ Clinical findings suggestive of plague, history of traveling to plague-endemic areas TREATMENT MEDICATIONS Yersinia enterocolitica ▪ Antimicrobial therapy ▫ TMP/SMX, aminoglycosides ▫ Alternative agents: third-generation cephalosporins, tetracyclines, fluoroquinolones Figure 96.6 The black, necrotic fingers of a man infected with Yersinia pestis. Yersinia pestis ▪ Antimicrobial therapy ▫ Aminoglycosides (streptomycin/ gentamicin) ▫ Alternative agents: doxycycline, tetracycline, fluoroquinolones, chloramphenicol OTHER INTERVENTIONS Yersinia enterocolitica ▪ ↑ fluid intake, good nutrition OSMOSIS.ORG 539