Salmonella infections occur mainly via ingestion of contaminated food. Ingested bacteria are usually killed by the acid in the stomach but when they do survive they can cause enteritis. Certain conditions that reduce the acidity in the stomach predispose to infection (e.g.infants, H2 pr Proton pump inhibitor use and pernicious anemia). It has been predicted that about one million organisms need to be ingested to cause infection.
Infection manifests with fever, loose stools, vomiting, dehydration and cramping pain.
Treatment
Salmonella enteritis is usually self-limiting and does not need antibiotic therapy. Fluid management and symptoms control are the mainstay of the treatment.
However, antibiotics may be indicated in the following high risk groups:
Infants especially in the first 3 months of life
Elderly
Immunocompromised hosts
Individuals with prosthetic heart valves or joints
Salmonella is sensitive to a variety of antibiotics including fluoroquinolones(ciprofloxacin, ofloxacin, levofloxacin), azithromycin, trimethoprim/sulfamethoxazole(Bactrim/Septran) or amoxicillin.
Carrier state
Carrier state is defined as having positive stool cultures for >12 months. It can occur in 1 in about every 200 patients with salmonella enteritis. The bacteria resides in the biliary tree. Chronic antibiotic therapy (Ampicillin) or surgery is needed.
Showing posts with label Microbiology. Show all posts
Showing posts with label Microbiology. Show all posts
Pneumonia - causes and organisms
1) Gram-Positive Bacteria
-Streptococcus pneumoniae is the most common cause of pneumonia(20 - 60% of all community-acquired pneumonia-CAP in adults).
-Staphylococcus aureus causes only about 2% of CAP but 10 - 15% of hospital-acquired pneumonias. It is the organism most often associated with viral influenza.
-Streptococcus pyogenes or Group A streptococcus.
2) Gram-Negative Bacteria
These cause infections in patients with chronic lung conditions like cystic fibrosis and chronic lung disease.
-Haemophilus influenzae
-Klebsiella pneumoniae may be responsible for pneumonia in alcoholics and other people who are physically debilitated.
-Streptococcus pneumoniae is the most common cause of pneumonia(20 - 60% of all community-acquired pneumonia-CAP in adults).
-Staphylococcus aureus causes only about 2% of CAP but 10 - 15% of hospital-acquired pneumonias. It is the organism most often associated with viral influenza.
-Streptococcus pyogenes or Group A streptococcus.
2) Gram-Negative Bacteria
These cause infections in patients with chronic lung conditions like cystic fibrosis and chronic lung disease.
-Haemophilus influenzae
-Klebsiella pneumoniae may be responsible for pneumonia in alcoholics and other people who are physically debilitated.
-Pseudomonas aeruginosa is an important cause of nosocomial pneumonia. It is a common cause of pneumonia.
-Moraxella catarrhalis, Neisseria meningitidis and E. Coli are other rare gram negative bacteria causing pneumonia.
3) Atypical Pneumonia
-Mycoplasma pneumoniae is the most common atypical bug causing pneumonia. Mycoplasma is a tiny bacterium that lacks a cell wall. The pneumonia caused by it is commonly called "walking pneumonia."
-Chlamydia pneumoniae disease is usually mild but can be severe in babies and elderly.
-Legionella pneumophila causes Legionnaires' disease. It is contracted by breathing in drops of contaminated water (especially from air coolers and air conditioners). Outbreaks are often reported in hotels, cruise ships, and office buildings.
-Workers exposed to pigeons, parrots, parakeets, and turkeys are at risk for psittacosis, a lung disease caused by the bacteria Chlamydia psittaci.
4) Viral Pneumonia
-Influenza. Pneumonia is a major complication of the flu and can be very serious(usually staphylococcal)
-Respiratory syncytial virus usually infects infants and causes bronchiolitis. It can also cause pneumonitis.
-Parainfluenza virus, Adenoviruses, Herpes viruses, Avian influenza(Type A influenza subtype H5N1 in birds/Swine flu) are other relatively uncommon causes of pneumonia.
5) Anaerobic Bacteria
This usually results from aspiration. This may happen in children and adults with chronic neuromuscular disorders, after a head injury or general anesthesia, or under the effects of drugs or alcohol.
6) Opportunistic infections
-Pneumocystis carinii, renamed Pneumocystis jiroveci in 2002, is a parasite. It was originally thought to be protozoa but is now classified as a fungus.
-Mycobacterium tuberculosis, avium etc.
-Cytomegalovirus
7) Chemical pneumonia:
Exposure to chemicals can also cause inflammation and pneumonia.
-Moraxella catarrhalis, Neisseria meningitidis and E. Coli are other rare gram negative bacteria causing pneumonia.
3) Atypical Pneumonia
-Mycoplasma pneumoniae is the most common atypical bug causing pneumonia. Mycoplasma is a tiny bacterium that lacks a cell wall. The pneumonia caused by it is commonly called "walking pneumonia."
-Chlamydia pneumoniae disease is usually mild but can be severe in babies and elderly.
-Legionella pneumophila causes Legionnaires' disease. It is contracted by breathing in drops of contaminated water (especially from air coolers and air conditioners). Outbreaks are often reported in hotels, cruise ships, and office buildings.
-Workers exposed to pigeons, parrots, parakeets, and turkeys are at risk for psittacosis, a lung disease caused by the bacteria Chlamydia psittaci.
4) Viral Pneumonia
-Influenza. Pneumonia is a major complication of the flu and can be very serious(usually staphylococcal)
-Respiratory syncytial virus usually infects infants and causes bronchiolitis. It can also cause pneumonitis.
-Parainfluenza virus, Adenoviruses, Herpes viruses, Avian influenza(Type A influenza subtype H5N1 in birds/Swine flu) are other relatively uncommon causes of pneumonia.
5) Anaerobic Bacteria
This usually results from aspiration. This may happen in children and adults with chronic neuromuscular disorders, after a head injury or general anesthesia, or under the effects of drugs or alcohol.
6) Opportunistic infections
-Pneumocystis carinii, renamed Pneumocystis jiroveci in 2002, is a parasite. It was originally thought to be protozoa but is now classified as a fungus.
-Mycobacterium tuberculosis, avium etc.
-Cytomegalovirus
7) Chemical pneumonia:
Exposure to chemicals can also cause inflammation and pneumonia.
Vibrio cholera
This organism can not survive in acidic pH. Hence any condition that causes decrease stomach acidity will cause it to proliferate.
Influenza - antigenic drift and shift explained.
Influenza viruses are constantly evolving by reassortment of their genetic material. Mutations cause minute changes in the hemagglutinin and neuraminidase antigens on the surface of the virus. This change is gradual(increasing with each division cycle) and is called antigenic drift. Since the strains produced by drift are somewhat similar to the older strains, some people are still immune and some others will be partly immune (and get a milder illness).
It is due to this antigenic drift that a new vaccine has to be manufactured and reimmunization is recommended each year.
In contrast, antigenic shift occurs when influenza viruses reassort. The virus acquires completely new antigens—for example by reassortment between avian strains and human strains. If a human influenza virus is produced that has entirely new antigens, everybody will be susceptible, and the novel influenza will spread uncontrollably, causing a pandemic.
It is due to this antigenic drift that a new vaccine has to be manufactured and reimmunization is recommended each year.
In contrast, antigenic shift occurs when influenza viruses reassort. The virus acquires completely new antigens—for example by reassortment between avian strains and human strains. If a human influenza virus is produced that has entirely new antigens, everybody will be susceptible, and the novel influenza will spread uncontrollably, causing a pandemic.
Methicillin Resistant Staphylococcus Aureus (MRSA)
Methicillin resistance is most often due to alteration of Penicillin Binding Proteins in the wall of the bacteria.
Toxins that act by increasing cyclic AMP
Toxins that increase cAMP:
CHOLERA
ANTHRAX
M=E.coli labile toxin
PERTUSSIS
CHOLERA
ANTHRAX
M=E.coli labile toxin
PERTUSSIS
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