Gram negative bacteria Flashcards

Question

Serovar Typhi

Answer 1

Systemic infection due to dissemination within macrophages. Produces typhoid toxin (DNA-ase activity = genotoxin).

Answer 2

Can differentiate into an elongated hyperflagellated form = surface motility (‘swarming’) Causes catheter-associated UTIs (~30% cases)  pyelonephritis Produces urease (causes urine pH increase) - calcium phosphate precipitation - formation of bladder/kidney stones, catheter blockage.

Answer 3

Environmental. Opportunistic, nosocomial infections (neonates, elderly, compromised) Colonisation of gastrointestinal tract (normal) and oropharynx (less frequently) is benign but can lead to: -UTI -pneumonia (aspiration from oropharynx) -surgical wound infections -bacteraemia = sepsis (high mortality) Multi-drug resistant (resistant to carbapenems)

Answer 4

Ubiquitous, free-living Motile (single polar flagellum) Rod-shaped Opportunistic (serious cause of nosocomial infections) Resistant to multiple antibiotics (& disinfectants) - very difficult to treat Acute infections (due to multiple toxins): Localised Burn/surgical wounds, UTI, Keratitis Systemic (bacteraemic = sepsis) neutropenic patients (leukaemia, chemotherapy, AIDS) ICU patients (ventilator acquired pneumonia) leading cause of nosocomial pneumonia Chronic infections: Cystic fibrosis (CF) patients Common denominator to all infections - compromised host defences.

Answer 5

CF, most common inherited lethal disorder among Caucasians. Defective CFTR = thick mucus produced in lungs. Lungs prone to microbial infection. P. aeruginosa most problematic. P. aeruginosa ‘wild-type’ (non-mucoid). P. aeruginosa ‘CF’ phenotype (mucoid) Isolates that secrete a thick coating of exopolysaccharide: provides additional protection against host defences in the lung Chronic inflammation leading to progressive lung damage and deterioration of lung function Occurs following infection of the CF lung by P. aeruginosa Mainly due to host immune system trying to clear the infection.

Answer 6

Facultative anaerobe Saline environments: commensal to planktonic crustaceans such as copepods Ingestion by shellfish Contamination of drinking water due to flooding of coastal areas or poor sanitation (faecal contamination).

Answer 7

Most severe diarrhoeal disease Characterised by pandemics (7 recorded since 1817) 1P-6P, Indian subcontinent 7P began in Sulawesi (1961)  SE Asia (1963)  Africa (1970)  Latin America (1991)  Caribbean (2010) O1 serotype  epidemics (and occasionally O139 variant) 1.4-4.0 million cases/year, 20,000-140,000 associated deaths

Answer 8

Faecal-oral route (not person-to-person) - high infective dose required Faecal contaminated water (poor sanitation) Undercooked shellfish from risk areas) Incubation, few hours to 5 days (V.c. multiplies in small intestine) Voluminous watery stools (‘secretory’ diarrhoea) Can lose 20 litres fluid/day plus electrolytes Dehydration/death (hypovolaemic shock)  50-60% mortality if untreated No blood, pus or fever (i.e. not dysenteric) i.e. no invasion or damage to mucosa Release of cholera toxin causes pathogenesis Most cases can be treated with ORT

Answer 9

C. jejuni C. coli Spiral rods Unipolar (monotrichous) or bipolar (amphitrichous) flagella Most common cause of food poisoning in UK & US Undercooked poultry Cattle (unpasteurised milk) I.D. 500-800 (low) Mild to severe diarrhoea, often with blood Usually self-limiting (≤ 1 week) Campylobacter shed in faeces for ~3 weeks

Answer 10

Spiral shaped Tuft of polar flagella Discovered in gastric mucus, 1982 (stomach previously thought to be sterile) Present in ~50% global population, but only a fraction develop disease Major role in gastritis and peptic ulcer disease (80-90% of ulcers) Implicated in ~10% cases of gastric adenocarcinoma & mucosa-associated lymphoid tissue lymphoma (linked to production of VacA and CagA toxins) Barry Marshall ingested H. pylori → gastritis → Nobel prize 2005

Answer 11

Exclusively human reservoir Nasopharyngeal carriage in 25-80% population (non-capsulate strains) Transient carriage of capsulate strains occurs in 5-10%

Answer 12

Opportunistic infections seen mainly in young children and adult smokers: - Meningitis* (age <5 yrs), 5-10% of adult cases - Bronchopneumonia - Epiglottitis*, sinusitis, otitis media - Bacteraemia* (often associated with pharyngitis) - Pneumonia in CF, COPD, HIV patients *infections caused by capsulate strains (invasive) – uncommon in healthy adults

Answer 13

Fastidious Requires ‘factor X’ (haem) and ‘factor Y’ (NAD) Cultured on chocolate agar Non-motile.

Answer 14

Capsule - invasive strains are capsulate (‘encapsulated’) Can penetrate nasopharyngeal epithelium Resistance to phagocytosis and complement system 6 different capsule serotypes (a-f) Hi b strains are the main cause of meningitis ‘Hib’ vaccine has reduced the incidence Commensals and upper respiratory tract pathogens are non-capsulate (‘unencapsulated’) referred to as ‘non-typeable’ H. influenzae (NTHi) Incidence increasing LPS (‘endotoxin’) Inflammation Complement resistance

Answer 15

Short (sometimes oval) rods (‘coccobacilli’) Fastidious Humans - only known reservoir (obligate human pathogen) Pertussis (whooping cough) B. parapertussis causes mild pharyngitis Highly contagious (low I.D.) - aerosol transmission Non-specific flu-like symptoms (~7 d), followed by paroxysmal coughing https://www.youtube.com/watch?v=l5SHtdczSBc Non-invasive Produces two toxins Pertussis toxin CyaA Hypersynthesis of cAMP  suppresses innate immune function particularly macrophage phagocytosis

Answer 16

Discovered 1976 Legionnaires’ disease - severe inflammatory pneumonia (1-3% of all pneumonias) Immunocompromised (elderly, alcoholics, smokers) Severe (15-20% mortality) Infection from man-made aquatic environments air-conditioning cooling towers, shower heads, nebulisers, humidifiers… Replicate within freshwater protozoa - intracellular parasite of amoeba Can survive and replicate within alveolar macrophages Upregulates pro-inflammatory genes in alveolar macrophages Excessive influx of neutrophils into lungs → inflammation.

Answer 17

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 18

Non-flagellated diplococci Fastidious Two species of medical importance: N. meningitidis N. gonorrhoeae Humans are the only known reservoir.

Answer 19

Meningococcus Nasopharyngeal carriage in 5-10% population (asymptomatic) Rises to 20-90% during outbreaks Person-to-person (aerosol) transmission (universities, barracks, Haj) Pathogenesis: Crosses nasopharyngeal epithelium and enters bloodstream Low level bacteraemia (asymptomatic) or septicaemia (sepsis) Meningitis: invasion of the meninges - bacteria enter CSF of subarachnoid space second most frequent cause of meningitis in young children 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) Anti-phagocytic Noncapsulated N.m. only found in nasopharynx - not pathogenic LPS (membrane ‘blebs’) Cytokine cascade Sepsis

Answer 20

Gonococcus 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 Note: gonococci are non-capsulated (unlike pathogenic N. meningitidis)

Answer 21

Leptospira Treponema Borrelia

Answer 22

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 23

Lyme disease (zoonosis) (~300 cases in UK) B.b. infects small mammals (rodents) B.b. 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 24

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 25

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 All stages are treatable with ABx but treatment is longer for tertiary stage syphilis and tertiary damage cannot be reverted.

Answer 26

Rickettsia Chlamydia Coxiella

Answer 27

Very small, non-motile Obligate intracellular parasites Many species within this group 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 28

Unique growth cycle: 2 developmental stages: Elementary bodies (EBs) Rigid, extracellular form, ~0.3 μm, dormant Infectious Enter cell through endocytosis Prevent phagosome-lysosome fusion ↓ differentiates into... Reticulate bodies (RBs) Fragile, intracellular form, ~1.0 μm, metabolically active Replicative Non-infectious Acquire nutrients from host cell

Answer 29

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 mucous membranes 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