Clinical Microbiology Flashcards
What are the main actions of antibiotics?
- Inhibit cell wall formation
- Inhibit protein synthesis
- Inhibit DNA synthesis
- Inhibit RNA synthesis
Give some examples of antibiotics that inhibit cell wall formation?
penicillin
cephalosporins
Give some examples of antibiotics that inhibit protein synthesis?
aminoglycosides (cause misreading of mRNA)
chloramphenicol
macrolides (e.g. erythromycin)
tetracyclines
fusidic acid
Give some examples of antibiotics that inhibit DNA synthesis?
quinolones (e.g. ciprofloxacin)
metronidazole
sulphonamides
trimethoprim
Give some examples of antibiotics that inhibit RNA synthesis?
rifampicin
Features of campylobacter jejuni?
-Most common cause of acute infective diarrhoea
-Spiral, gram negative rods
-Usually infects caecum and terminal ileum.
-Local lymphadenopathy is common
-May mimic appendicitis as it has marked right iliac fossa pain
-Reactive arthritis is seen in 1-2% of cases
Features of shigella spp.?
-Members of the enterobacteriaceae
-Gram negative bacillii
-Clinically causes dysentery
-Shigella soneii is the commonest infective organism (mild illness)
-Usually self limiting, ciprofloxacin may be required if individual is in a high risk group
Features of salmonella?
-Facultatively anaerobic, gram negative, enterobacteriaceae
-Infective dose varies according to subtype
Salmonellosis: usually transmitted by infected meat (especially poultry) and eggs
Features of E.coli?
MAIN TYPES:
-Enteropathogenic
-Enteroinvasive: dysentery, large bowel necrosis/ulcers
-Enterotoxigenic: small intestine, travelers diarrhoea
-Enterohaemorrhagic: 0157, cause a haemorrhagic colitis, haemolytic uraemic syndrome and thrombotic thrombocytopaenic purpura
Features of yersinia enterocolitica?
-Gram negative, coccobacilli
-Typically produces a protracted terminal ileitis that may mimic Crohns disease
-Differential diagnosis acute appendicitis
-May progress to septicaemia in susceptible individuals
-Usually sensitive to quinolone or tetracycline
What are the features of vibrio cholera?
-Short, gram negative rods
-Transmitted by contaminated water, seafood
-Symptoms include sudden onset of effortless vomiting and profuse watery diarrhoea
-Correction of fluid and electrolyte losses are the mainstay of treatment
-Most cases will resolve, antibiotics are not generally indicated
what are typhoid and paratyphoid caused by?
Salmonella typhi and Salmonella paratyphi (types A, B & C) respectively
Symptoms of typhoid/paratyphoid?
- initially systemic upset
- relative bradycardia
- abdominal pain, distension
constipation: although
Salmonella is a recognised cause of diarrhoea, constipation is more common in typhoid - rose spots: present on the trunk in 40% of patients, and are more common in paratyphoid
Complications of typhoid/paratyphoid?
- osteomyelitis (especially in sickle cell disease where Salmonella is one of the most common pathogens)
- GI bleed/perforation
- meningitis
- cholecystitis
- chronic carriage (1%, more likely if adult females)
What is Streptococcus bovis septicaemia associated with?
carcinoma of the colon
(also endocarditis)
gram +VE
Features of S.Aureus?
Facultative anaerobe
Gram positive coccus
Haemolysis on blood agar plates
Catalase positive
What can S.Aureus cause?
cutaneous infections
abscesses
Exo and entero toxin may result in toxic shock syndrome and gastroenteritis respectively
Ideal treatment of S.Aureus?
penicillins although many strains now resistant
Features of S.pyogenes?
Gram positive, forms chain like colonies, Lancefield Group A Streptococcus
Produces beta haemolysis on blood agar plates
Rarely part of normal skin microflora
Catalase negative
Treatment of S.Pyogenes?
penicillin, macrolides may be used as an alternative
What does S.pyogenes release?
proteins/ virulence factors: hyaluronidase, streptokinase which allow rapid tissue destruction
Superantigens such as pyogenic exotoxin A which results in scarlet fever
What does H.pylori release?
urease that breaks down gastric urea> Carbon dioxide and ammonia> ammonium>bicarbonate
Produces hydrogenase that can derive energy from hydrogen released by intestinal bacteria
what does Hlpylori colonise?
usually gastric antrum
Irritates resulting in increased gastrin release and higher levels of gastric acid
Is Hpylori gram positive or negative?
Gram negative, helix shaped rod, microaerophillic
Risks of H.Pylori?
10-20% risk of peptic ulcer, 1-2% risk gastric cancer, <1% risk MALT lymphoma.
Diagnosis of H.pylori?
serology (approx. 75% sensitive). Biopsy urease test during endoscopy probably the most sensitive
Features of staphylococcus epidermis?
tends to colonise plastic devices and forms a biofilm
(difficult to eradicate without removal of device e.g. breast implant)
what is malignant otitis external cause by?
Pseudomonas aeruginosa
Key features of malignant otitis external?
Diabetes (90%) or immunosuppression (illness or treatment related)
Severe, unrelenting, deep-seated otalgia
Temporal headaches
Purulent otorrhea
Possibly dysphagia, hoarseness, and/or facial nerve dysfunction
What can malignant otitis external progress to?
Progresses to temporal bone osteomyelitis
Treatment of malignant otitis externa?
Anti pseudomonal antimicrobial agents
Topical agents
Hyperbaric oxygen is sometimes used in refractory cases
Main causes fo lactational mastitis?
S.Aureus
Which pathogen is associated with gangrene?
C.perfringes
WHO definitions of diarrhoea?
Diarrhoea: > 3 loose or watery stool per day
Acute diarrhoea < 14 days
Chronic diarrhoea > 14 days
Common causes of osteomyelitis (pathogens)?
S aureus and occasionally Enterobacter or Streptococcus species
In sickle cell: Salmonella species
what sort of virus is hepatitis B?
double-stranded DNA virus
Complications of hepatitis B infection?
Chronic hepatitis (5-10%)
Fulminant liver failure (1%)
Hepatocellular carcinoma
Glomerulonephritis
Polyarteritis nodosa
Cryoglobulinaemia
Treatment of hepatitis B infection?
Pegylated interferon-alpha
lamivudine, tenofovir and entecavir
How are patients screened for MRSA?
nasal swab and skin lesions or wounds
the swab should be wiped around the inside rim of a patient’s nose for 5 seconds
the microbiology form must be labelled ‘MRSA screen’
Suppression of MRSA once carrier identified?
nose: mupirocin 2% in white soft paraffin, tds for 5 days
skin: chlorhexidine gluconate, od for 5 days. Apply all over but particularly to the axilla, groin and perineum
Common cause of bladder calcification?
Schistosoma haematobium causes haematuria
Schistosomiasis is the most common cause of bladder calcification worldwide.
Management of schistosomiasis?
Single oral dose of praziquantel
what is the most common pathogen implicated in cholangitis?
E.coli
[Klebsiella species
Enterococcus species
Streptococcus species ]
Clinical features of cholangiitis?
Charcot’s triad:
Fever (90% cases)
Right upper quadrant pain
Jaundice
Reynolds pentad: Above plus confusion and hypotension
Management of cholangitis:?
ERCP -usually after 72 hours of antibiotics
Percutaneous transhepatic cholangiogram and biliary drain
Features of enterobiasis?
Due to organism Enterobius vermicularis
Common cause of pruritus ani
Diagnosis usually made by placing scotch tape at the anus, this will trap eggs that can then be viewed microscopically
Treatment is with mebendazole
What is Ancylostoma duodenale?
- Hookworms that anchor in proximal small bowel
- Most infections are asymptomatic although may cause iron deficiency anaemia
- Larvae may be found in stools left at ambient temperature, otherwise infection is difficult to diagnose
- Infection occurs as a result of cutaneous penetration, migrates to lungs, coughed up and then swallowed
-Treatment is with mebendazole
What is Ascariasis?
- Due to infection with roundworm Ascaris lumbricoides
- Infections begin in gut following ingestion, then penetrate duodenal wall to migrate to lungs, coughed up and swallowed, cycle begins again
- Diagnosis is made by identification of worm or eggs within faeces
- Treatment is with mebendazole
When is bacteroides fragilis found?
severe peritoneal infections and as it is facultatively anaerobic may be present in pus. It has a pungent aroma.
Risk factors for c.diff?
Broad spectrum antibiotics
Use of proton pump inhibitors
Contacted with persons infected with c.difficile
Management of c.diff?
Consider stopping proton pump inhibitor treatment
First-line therapy is now oral vancomycin 125mg orally 4 times daily for 10 days
Patients who do not respond to vancomycin may respond to oral fidaxomicin
Patients with severe and unremitting colitis should be considered for combination therapy of oral vancomycin and metronidazole. Some cases may require emergency colectomy
What is Fasciola hepatica?
common liver fluke (parasitic trematode)
Infects humans as part of a plant/ food trematode infection
Symptoms of fasciola hepatica?
Acute: fever, nausea, swollen liver, skin rashes, and extreme abdominal pain
Chronic: intermittent pain, jaundice, and anemia.
Treatment of fasciola hepatica?
triclabendazole. Some patients may need ERCP
Classic diphtheria symptoms?
systemic illness that lasts several days. The tonsils or pharynx can be covered in a thick grey membrane which bleeds on attempted removal.
Cervical adenopathy
Bulls neck appearance
What are melanosis coli?
occur as a result of laxative abuse and consists of lipofuschin laden macrophages that appear brown.
