Microbiology: Gram Negative Cocci

Question 1

Niesseria Gonorrhoeae

Answer 1

• Aerobic diplococci (in pairs) that are oxidase and catalase positive
• Produces acids by oxidation of glc
• Grows on chocolate agar, but not blood agar, dry conditions, or FAs
• Pili mediate attachment to cells, transfer of genetic material, and mobility (all pathogenic, virulence factor)

Question 2

Pathogenesis of N gonorrhoeae

Answer 2

• Acquired by sexual contact (obligate human pathogen), infects sub-epithelial cells in mucous membranes of urethra in men and endocervix in women
• Pili, PorB, Opa, LOS (lipo-oligosaccharide, endotoxin) stimulate IgG3 production and facilitate penetration and binding (except LOS, instead stimulates inflammation/TNF-a release)
• Can avoid degradation if internalized
• Meningococcal disease occurs in absence of specific Abs directed against the capsule
• High prevalence, low mortality rates (can lead to corneal scarring)
• Both genders experience purulent discharge from genitals, dysuria
• Organism cannot infect squamous epithelial vagnial cells in post-pubescents
• Females may develop ascending genital infections (salpnigitis, tubovarian abscesses, pelvic inflammatory disease)

Question 3

Gonococcemia

Answer 3

• Gonococcal bacteremia leads to disseminated gonococcal infections
• Often affects skin and joints, can cause numerous untreated asymptomatic infections
• Manifestations are fever, migratory arthralgias, arthritis, purulent rash/skin lesions
• Peri-hepatitis, pharyngitis
• Purulent conjunctivitis may affect newborns especially during delivery
• Anorectal gonnorhea in homosexual men

Question 4

Epidemiology of Gonorrhoeae

Answer 4

• Only occurs in humans (no reservoir except asymptomatic infected persons)
• Most men are initially symptomatic, half of women have mild or asymptomatic infections
• 2nd most common STI after clap, higher rates in poorer regions, in black people, and people w/ multiple sexual encounters
• Women at 50% risk on exposure, men at 20% risk on exposure
• Symptoms may clear in a few weeks and asymptomatic carrier can be established

Question 5

Diagnosis of Gonorrhoeae

Answer 5

• Gram stain is sensitive for testing purulent exudates
• Must be confirmed by culture of exudate (chocolate agar, selective media) that contains cysteine and energy source (glc, lac, pyr)
• Use selective media and non-selective media since vancomycin in selective media kills some strains of gonorrhoeae
• Blood cultures only effect during 1st week of gonococcemia
• Oxidase positive, definitive identification guided by pattern of oxidation of carbs (glc)

Question 6

Treatment of Gonorrhoaea

Answer 6

• Penicillin not used due to B-lactamase, PBP2, cell wall changes
• Now also resistant to tetracycline, erythromycin, aminoglycosides
• Some are resistant to fluoroquinolones and ciprofloxacin
• Tx is combination of ceftriaxone or ciprofloxacin plus doxycycline
• No vaccine available, prophylaxis for exposed adults and newborns available. Condoms too

Question 7

Neisseria meningitidis

Answer 7

• Aerobic diplococci, oxidase and catalase positive
• Acids produced by oxidation of glc and maltose
• Pili mediate attachment to cells, transfer of genetic material, and mobility (all pathogenic, virulence factor)
• 2nd most common cause of community-acquired meningitis in adults, can cause fatal sepsis and bronchopneumonia
• 12 serogroups based on Ag differences of capsules
• Por B interferes w/ degranulation of neutrophils, LOS has endotoxin activity
• Fe is essential for growth/metabolism

Question 8

Pathogenesis of meningitidis

Answer 8

• Infection by aspiration of infective particles, which attach to epithelial cells of mucosal surfaces and enter bloodstream (usually through naso/oropharyngeal)
• Blood borne bacteria may enter CNS if not treated
• Are internalized by phagocytosis and avoid intracellular death (via capsule), replicate, and migrate to sub-endothelial spaces causing diffuse vascular damage from LOS endotoxin
• Can only infect patients who lack Abs against capsule or non-capsular Ags, or patients that have late-acting complement)
• low prevalence but high mortality, begins often w/ skin lesions (small to larger ones)

Question 9

Meningococcemia

Answer 9

• With or without meningitis is life-threatening
• causes thrombosis of small vessels and multi-organ involvement, bilateral destruction of adrenal glands
• May present as chills, fever, malaise, headaches
• Milder and chronic form can occur: fever, arthritis, skin lesions
• Possible pneumonia, is usually preceded by resp. tract infections. Symptoms are cough, chest pain, rales, fever

Question 10

Acute bacterial meningitis

Answer 10

• Abrupt headache, meningeal signs (cervical rigidity, thoracolumbar rigidity hamstring spasm, exaggerated reflexes), fever
• High mortality untreated, low mortality treated
• Incidence of neuologic sequelae is low (just hearing deficits and/or arthritis
• Children may show non-specific signs such as fever and vomiting

Question 11

Epidemiology of meningitidis

Answer 11

• Humans are only carriers
• Almost all infections caused by serogroups A, B, C, Y, and W135 (Y and W135 most associated w/ pneumonia)
• Serogroups B, C, and Y in Europe and America
• Serogroups A and W135 in developing countries
• Transmitted by respiratory droplets, higher rates in low SES (socioeconomic setting) populations
• Asymptomatic carrier occurs from 1-40%. Oro/nasopharyngeal carriers common in children
• Most outbreaks caused by A, sporadic cases by B, C, and Y

Question 12

Diagnosis of meningitidis

Answer 12

• Most characteristic symptom is skin rash (usually petechiae lesion)
• Once septic the bacteria can be seen in WBCs from blood samples when gram stained
• Culture methods: it is inhibited by toxic factors in media, anticoagulants in blood
• Oxidative positive diplococci that grows on chocolate agar or selective media
• Definitive ID from pattern of oxidation of carbs

Question 13

Tx of meningitidis

Answer 13

• Susceptible to penicillin (occasional low levels of resistant)
• If patient can’t take penicillin, cephalosporin or chlormamphenicol are recommended
• Prevention includes prophylaxis by antibios
• Conjugate vaccine is available for children
• Group B has weak immunogen and doesn’t provide immunity response (no vaccine has B parts)
• Vaccination w/ suspension of serogroup A can be used to control outbreaks and for those at risk of getting the disease (complement deficiency)