Microbiology: Yersinia and Neisseriae

Yersinia

• Gram(-), short, pleomorphic, non-motile
• Bipolar staining
• Catalase +
• Oxidase -
• Microaerophilic/facultative anaerobe

Yersinia enterocolitica

• Non-lactose fermenter
• G(-)
• Urease +
• Oxidase -
• Grows best at 25°C
• Motile at 25°C, non-motile at 37°C
• Transmission: eating raw or undercooked pork

Pathogenesis and Clinical Findings

• Incubation: 4-7 days
• Early symptoms: fever, abdominal pain, diarrhea
• One to two weeks after onset, some patients develop arthralgia, arthritis, and erythema nodosum, suggesting an immunologic reaction to the infection

Diagnostic Laboratory Tests

• Culture: cefsulodin-irgasan-novobiocin (CIN) agar
• Treatment: self-limited
• Susceptible to: aminoglycosides, chloramphenicol, tetracycline, TMP-SMX, piperacillin, third-generation cephalosporins, and fluoroquinolones
• Resistant to: ampicillin and first-generation cephalosporins

Neisseriae

• Gram(-), nonmotile diplococcus
• Aerobic, acid-producing
• Oxidase +

Neisseria Gonorrhoeae

• Table 20-1 details biochemical reactions (details in table)

Diagnostic Laboratory Tests (Neisseria)

• Specimens: Pus, secretions from urethra, cervix, rectum, conjunctiva, throat, or synovial fluid for culture and smear
• Culture: Modified Thayer-Martin medium (MTM), incubated in 5% CO2 at 37°C
• Transparent or opaque, nonpigmented, and nonhemolytic colonies
• N. flavescens, N. cinerea, N. subflava, and N. lactamica (yellow pigmentation)
• N. sicca: opaque, brittle, wrinkled colonies
• M. catarrhalis: nonpigmented or pinkish gray opaque colonies
• NAAT, ELISA

Neisseria meningitidis

• Most important serogroups: A, B, C, X, Y, and W-135
• Gram(-)
• Oxidase +
• Kidney-shaped diplococcus with a polysaccharide capsule
• Ability to use both glucose and maltose

Neisseria meningitidis: Disease

• Meningococcal meningitis
• Most prevalent in children 6 months to 2 years
• Begins as mild pharyngitis
• Fever, vomiting, headache, and stiff neck
• Pneumonia may be present
• Petechial eruption, progressing to frank purpura
• Vasculitic purpura is the hallmark

Pathogenesis, Pathology, Clinical Findings (Meningitis)

• Humans are the only natural hosts
• Nasopharynx is the portal of entry
• Early symptoms may resemble upper RTI
• Fulminant meningococcemia: severe, high fever, hemorrhagic rash; possible DIC and circulatory collapse (Waterhouse-Friderichsen syndrome)
• Meningitis: most common complication, sudden onset with intense headache, vomiting, stiff neck, progresses to coma within hours
• Acutely inflamed meninges, thrombosis of blood vessels, exudation of PMNs, thick purulent exudate on brain surface
• Meningococcemia: thrombosis in many small blood vessels across organs; perivascular infiltration; petechial hemorrhages, interstitial myocarditis, arthritis, and skin lesions

Meningococcal Disease

• Two most common manifestations: meningococcemia (blood infection), meningitis (spinal cord/brain infection)
• Bacteria enter through nose and throat; spreads to bloodstream; then enters spinal cord and brain membranes

Neisseria spp.: Carbohydrate Utilization test

• Table showing glucose, maltose, and lactose results for N. gonorrhoeae and N. meningitidis

Neisseria gonorrhoeae: Antigenic Structure

• Pili (fimbriae): hair-like appendages, enhance attachment to host cells and resistance to phagocytosis
• Por: prevents phagosome-lysosome fusion; selectively binds to complement components C3b and C4b
• OPA proteins: adhesion within colonies and attachment to host receptors
• RMP (Protein III): resistance to killing by human antibody-complement; interferes with gonococcal binding to phagocytic receptors
• Lipooligosaccharide: resistance to killing by human antibody-complement and interferes with gonococcal binding to phagocytic receptors

Pathogenesis (Neisseria gonorrhoeae)

• Only piliated bacteria are virulent
• Opaque colonies: men with symptomatic urethritis, uterine cervical cultures at mid-cycle
• Transparent colonies: men with asymptomatic urethral infection, menstruating women, invasive forms like salpingitis, disseminated infection

Pathology (Neisseria gonorrhoeae)

• Gonococci attack mucous membranes of the genitourinary tract, eye, rectum, and throat → acute suppuration → tissue invasion → chronic inflammation and fibrosis

Clinical Findings (Neisseria gonorrhoeae)

• Males: urethritis, yellow creamy pus, painful urination, extends to epididymis, fibrosis can occur, urethral strictures
• Females: endocervix infection, urethra and vagina; mucopurulent discharge; salpingitis; fibrosis; obliteration of tubes
• Gonococcal bacteremia: skin lesions (hemorrhagic papules and pustules), tenosynovitis, and suppurative arthritis (knees, ankles, and wrists)
• Gonococcal ophthalmia neonatorum: during passage through an infected birth canal

Treatment (Neisseria gonorrhoeae)

• Uncomplicated genital or rectal infections: Ceftriaxone 1 g IM as a single dose
• Concomitant chlamydial infection: Azithromycin 1 g orally in a single dose or with doxycycline 100 mg orally twice a day for 7 days
• Azithromycin is safe for pregnant women, with doxycycline contraindicated.

Pasteurella

• Non-motile gram(-) coccobacilli
• Bipolar staining
• Aerobes or facultative anaerobes
• Oxidase and Catalase +

Pasteurella Presentation

• Most common presentation: history of animal bite, within hours: redness, swelling, and pain
• Regional lymphadenopathy may be variable
• Fever often low-grade
• Penicillin G - DOC
• Tetracyclines and fluoroquinolones - alternative

Pasteurella Species

• P. multocida: most common in human wounds from cat and dog bites; common cause of hemorrhagic septicemia in animals
• P. bettyae: infections of human genital tract and newborns
• P. pneumotropica: normal flora of mice and rats; causes pneumonia or sepsis when host-parasite balance is disturbed
• P. ureae: mixed flora in human chronic respiratory disease or other suppurative infections.

Anaerobic Bacteria

• Located throughout the human body: skin, mucosal surfaces, high concentrations in the mouth and GI tract (normal microbiota)

Diagnosis of Anaerobic Infections

• Clinical signs: foul-smelling discharge (caused by short-chain fatty-acid products of anaerobic metabolism), proximity to a mucosal surface (anaerobes are part of normal microbiota), gas in tissues (production of CO2 and H2), negative aerobic culture results

Gram-Negative Anaerobes: Bacilli

• Bacteroides: bile-resistant, non-spore forming, slender gram-(-) rods; may appear as coccobacilli; normal bowel flora; often implicated in intra-abdominal infections (e.g., B. fragilis, B. thetaiotaomicron)
• Prevotella: gram-(-) bacilli; may appear as slender rods or coccobacilli; P. melaninogenica (upper respiratory tract infections); P. bivia and P. disiens (female genital tract); brain and lung abscesses, empyema, PID, and TOA
• Porphyromonas: normal oral flora; cultured from gingival and periapical tooth infections; common in breast, axillary, perianal, and male genital infections
• Fusobacteria: most human infections are caused by F. necrophorum and F. nucleatum; F. necrophorum cause severe infections of the head and neck; can progress to Lemierre's disease
• Veillonella: small, anaerobic, gram-(-) cocci; normal flora in the mouth, nasopharynx, and probably the intestine; rarely the sole cause of an infection.

Gram-Positive Bacilli

• Actinomyces: A. israelii and A. gerencseriae are common types; encountered in groin, urogenital areas, breast, axilla, and postoperative mandible, eye, head, and neck infections; chronic suppurative and granulomatous infections produce pyogenic lesions, with interconnecting sinus tracts containing microcolonies of the bacteria embedded in tissue elements; DOC: Penicillin
• Lactobacillus: normal flora of the vagina, rarely cause disease
• Propionibacterium: normal flora of the skin, oral cavity, large intestine, conjunctiva, and external ear canal; opportunistic pathogen; acne vulgaris; cause postsurgical wound infections (prosthetic joint infections, CNS shunt infections, osteomyelitis, endocarditis, and endophthalmitis)
• Eubacterium, Eggerthella, Bifidobacterium, and Arachnia: occur in mixed infections of the oropharyngeal or bowel flora
• Clostridium tetani: ubiquitous; >50% of cases follow minor injuries; tetanospasmin, a potent neurotoxin; preventable with active immunity induced by tetanus toxoid

Gram-Positive Cocci

• Peptostreptococcus: opportunistic; in brain abscesses, pleuropulmonary infections, necrotizing fasciitis, other deep skin and soft tissue infections, intra-abdominal infections and female genital tract infections.

Gram-Positive Bacilli

• Clostridium botulinum: preserved or canned foods, low oxygen levels and low pH, which support growth, neurotoxins as most potent toxins, can be neutralized by specific antibodies
• Clostridium perfringens: causes gas gangrene and food poisoning; produces alpha toxin (necrotizing, hemolytic exotoxin that is a lecithinase)
• Clostridium difficile: causes pseudomembranous colitis, part of the normal GI flora in 2-10% of humans, from diarrhea alone, to marked diarrhea and necrosis of mucosa.

Explore the characteristics, pathogenesis, and diagnostic tests for Yersinia species and Neisseriae. This quiz will challenge your understanding of their unique features, symptoms, and treatment options. Perfect for microbiology students looking to test their knowledge.