Bacteria

Question 1

Streptococcus pyogenes

Answer 1

Gram positive
Cocci
Form chains

An infrequent, but usually pathogenic, part of skin flora

Treatment of choice = penicillin
In individuals with a penicillin allergy, erythromycin, other macrolides, and cephalosporins have been shown to be effective treatments

Question 2

Klebsiella pneumoniae

Answer 2

Gram negative
Rod

Although found in the normal flora of the mouth, skin, and intestines, it can cause destructive changes to human and animal lungs if aspirated, specifically to the alveoli (in the lungs) resulting in bloody sputum.

Naturally found in soil

If the specific Klebsiella in a particular patient does not show antibiotic resistance, then the antibiotics used to treat such susceptible isolates include penicillin (e.g. Ampicillin), fluoroquinolone broad spectrum antibitic (e.g. levofloxacin), 3rd generation cephalosporin (e.g. ceftazidime)

Usually also requires surgical clearing

Question 3

Neisseria meningitidis (meningococcus)

Answer 3

Gram negative
Diplococcus

hospitalized immediately for treatment with antibiotics.
Because meningococcal disease can disseminate very rapidly, a single dose of intramuscular antibiotic is often given at the earliest possible opportunity, even before hospitalization, if disease symptoms look suspicious enough.
Third-generation cephalosporin antibiotics (i.e. cefotaxime, ceftriaxone) should be used to treat a suspected or culture-proven meningococcal infection before antibiotic susceptibility results are available.

Question 4

Escherichia coli

Answer 4

Gram-negative
facultatively anaerobic
rod-shaped

Often found in normal gut flora

Treat with fluids
Antibiotic used depends upon susceptibility patterns in the particular geographical region. Currently, the antibiotics of choice are fluoroquinolones or azithromycin, with an emerging role for rifaximin (esp in travellers diarrhoea)

Question 5

Clostridium Difficile

Answer 5

Gram positive
Bacilli
Anaerobic, spore-forming

Prevalent in soil
Transmitted faecal-orally
Can become established in colon (e.g. If antibiotics depleted normal flora)
Difficult to treat with antibiotics due to resistance
Usually sensitive to oral Metronidazole & Vancomycin

Question 5

Staphylococcus aureus

Answer 5

Gram positive
Cocci
Grape-like clusters

Frequently found in resp tract & on skin
Common cause of skin/organ infections (incl endocarditis)
Treated with penicillin
But resistant strains (MRSA) treat with vancomycin

Question 6

Typhoid fever (enteric fever/typhoid)

Answer 6

symptomatic bacterial infection due to Salmonella typhi growing in the intestines and blood.
spread facal-orally (eating/drinking contaminated food)

Diagnosis: is by either culturing the bacteria or detecting the bacterium’s DNA in the blood, stool, or bone marrow (most accurate)

Treatment: Where resistance is uncommon, the treatment of choice is a fluoroquinolone such as ciprofloxacin.
Otherwise, cephalosporin such as ceftriaxone or cefotaxime
Antibiotics, such as ampicillin, chloramphenicol, trimethoprim-sulfamethoxazole, amoxicillin, and ciprofloxacin, have been commonly used to treat typhoid fever in microbiology.

Symptoms: may vary from mild to severe and usually begin six to thirty days after exposure.
gradual onset of a high fever over several days, Weakness, abdominal pain, constipation, and headaches
Diarrhea and vomiting are uncommon
Some people develop a skin rash with rose colored spots.
Other people may carry the bacterium without being affected

Prevention: Typhoid vaccine may be effective for up to 7 yrs

Question 7

Traveller’s diarrhoea (most common cause)

Answer 7

three or more unformed stools passed by a traveler within a 24-hour period. commonly accompanied by abdominal cramps, nausea, and bloating.

enterotoxigenic Escherichia coli (ETEC) is the most common pathogen

Treatment: oral rehydration, fluoroquinolone antibiotics 3-5days
(Trimethoprim-sulfamethoxazole and doxycycline are no longer recommended because of high levels of resistance to these agents)

Question 8

Legionella pneumophila (legionnaire’s disease)

Answer 8

Gram-negative, nonencapsulated, aerobic bacillus with a single, polar flagellum

invades and replicates inside macrophages
a facultative intracellular parasite that can invade and replicate inside amoebae in the environment, which can thus serve as a reservoir for L. pneumophila, as well as provide protection from environmental stresses, such as chlorination.

Can cause pneumonia

Treatment: Macrolides (azithromycin or clarithromycin) or fluoroquinolones (levofloxacin or moxifloxacin): levofloxacin first line with resistance to azithromycin

Question 9

Pseudomonas aeruginosa

Answer 9

Gram negative, bacillus, aerobic (but a facultative anaerobe)

Commonly colonises lungs of those with CF;
can develop special characteristics that allow the formation of large colonies (“mucoid” Pseudomonas) - rarely seen in those without CF

Thrives in moist & hypoxic environments (e.g. Catheters/urinary tract, lungs)

Can infect damaged tissue in those with compromised immunity

Frequently isolated from non-sterile sites, so can show colonisation without infection

If isolated from sterile site, treat with antibiotics:
aminoglycosides (e.g. gentamicin)
quinolones (e.g. ciprofloxacin)
cephalosporins (e.g. ceftazidime, but not ceftriaxone)
antipseudomonal penicillins (e.g. carbenicillin, mezlocillin)
carbapenems (e.g. meropenem)
polymyxins
monobactams

Shows natural resistance to wide range of bacteria