gram-negative bacteria Flashcards

Question

what species are involved in gram-negative - rod - anaerobic?

Answer 1

bacteriodes

Answer 2

Non-motile rods Strict (obligate) anaerobes Commensal flora (large intestine) - most abundant (30-40% of the total) >1010/g faeces (outnumbers E. coli 20:1) Opportunistic - tissue injury (surgery, perforated appendix or ulcer) Predominantly peritoneal cavity infections (peritonitis, intraabdominal abscesses are most common) can lead to bacteraemia Most frequent cause of anaerobic infections, usually B. fragilis (although it is only 0.5-1.0% of total commensal Bacteroides) Often present in polymicrobial infections with enterobacteria Presence of facultative anaerobes depletes O2, allowing anaerobes such as Bacteroides to proliferate Treatment requires specific anti-anaerobe antibiotics e.g. metronidazole

Answer 3

- Neisseria - Neisseria meningitidis - Neisseria gonorrhoeae

Answer 4

Gonorrhoea - second most common STD worldwide 82.4 million (2020) Cases doubled in the UK last year Person-to-person only Infection can be asymptomatic (~10% men, ~50% women) Usually characterised by urethritis with additional infection of female genitalia Serious complications in women - can lead to salpingitis and/or PID if infection ascends Proctitis, gingivitis, pharyngitis depending on sexual preference Multi-drug resistance arising Non-capsulated

Answer 5

Nasopharyngeal carriage in 5-10% population (asymptomatic) Person-to-person (aerosol) transmission (universities) Pathogenesis: Low level bacteraemia (asymptomatic) or septicaemia (sepsis) Meningitis: invasion of the meninges - bacteria enter CSF of subarachnoid space Very high mortality from septicaemia if not treated Requires rapid diagnosis! Virulence determinants of N. meningitidis Capsule is major virulence determinant (serogroup B - 90% cases in UK) LPS (membrane ‘blebs’) Cytokine cascade Sepsis

Answer 6

Non-flagellated diplococci Fastidious – humans only known reservoir Two species of medical importance: N. meningitidis N. gonorrhoeae

Answer 7

- Borrelia burgdorferi - Leptospira interrogans - Treponema pallidum

Answer 8

Long, slender, helical, highly flexible Most are free-living and non-pathogenic Pathogenic varieties difficult to culture Modified outer membrane (“outer sheath”) Treponema and Borrelia lack LPS, replaced by a different glycolipid Endoflagella (‘axial filaments’ = periplasmic flagella) Located between peptidoglycan and outer membrane Fixed at each end of the bacterium and confers shape Overlap in the centre of the bacterium Propels bacterium in a corkscrew motion Swim faster in high viscosity medium “Hides” antigenic flagellum Three medically important genera

Answer 9

Lyme disease (zoonosis) (~300 cases in UK) Infects small mammals (rodents) Acquired by tick larvae feeding on infected animal Transmitted to humans by tick nymphs (adults easier to spot!) Bull’s eye rash, flu-like symptoms (fever, fatigue, headache) Dissemination via lymphatics/blood to other organs Neurological problems in 10-15% patients, joints → arthritis Most symptoms arise due to immune response

Answer 10

Leptospirosis (zoonosis) Rare in UK Common infection of rats Systemic infection of the rat, excreted in faeces and urine Proximity of rats to water often means water sources are colonised Rivers, streams country parks, lakes Contact of infected animal urine with mucous membrane or abraded skin Flu-like symptoms Severe form (Weil’s disease) in 10-15% infected individuals 2-4 week incubation period, clinical multi-organ infection occurs Liver infection leads to cell destruction and jaundice Acute renal and hepatic failure Pulmonary distress Haemorrhage

Answer 11

Syphilis (STD) 2,800 cases in UK – increasing again Primary stage Localised genital infection (ulcer (“chancre”)) Days-weeks post-infection Highly transmissible phase Secondary stage (~50% cases) Systemic Skin (rash), swollen lymph nodes, joint pains, muscle aches, headache, fever 1-3 months post-infection Still highly transmissible Tertiary stage (~30% cases) ‘Gummas’ (granulomas) in bone and soft tissue Cardiovascular syphilis (aorta) Neurosyphilis (brain and spinal cord) Occurs several years post-infection Non-infectious form

Answer 12

Very small, non-motile Obligate intracellular parasites Many species live asymptomatically as endosymbionts in amoebae, invertebrates and vertebrates Cannot culture in bacteriological media - detect by serum Abs or PCR Detects presence of anti-Chlamydia antibodies in serum May be the result of a previous infection Test must not be used to detect a current infection without an alternative confirmatory test Also referred to as NAA (nucleic acid amplification) or NAAT (nucleic acid amplification test)

Answer 13

C. trachomatis (3 biovars): Trachoma biovar (serotypes A-C) → trachoma → blindness Eye-to-eye transmission via hands, fomites or flies Genital tract biovar (serotypes D-K) Most common STD - infects epithelial cells of urethra (both sexes) and vagina Can ascend to uterus and ovaries (PID, infertility) Usually asymptomatic (i.e. 70-80% cases in women) Conjunctivitis (STD), hand-to-eye transmission Lympho granuloma venereum (LGV) biovar (serotypes L1-L3) Causes LGV (an STD) - invasive urogenital or anorectal infection Endemic to the tropics, cases rising in Europe/N. America C. pneumoniae Respiratory tract (mild or “walking” pneumonia) ~10% community acquired pneumonias C. psittaci Mainly birds Psittacosis (zoonotic infection), severe pneumonia

gram-negative bacteria Flashcards

(38 cards)