Sunday, December 2, 2007

Medical Microbiology- PBL 1

Learning issues:
1. Define the possible diagnosis
2. List down the possible causative agent

Case Study 1
Patient: Female/27 years old
Signs and symptoms: Fever, chills and dysuria
Suspected Diagnosis: Urinary tract infection
Specimen collected: Urine

The female patient in case 1 was diagnosed with urinary tract infection. UTI occurs due to the infection of microorganisms in the bladder,urethra and kidneys. It can be further classified as cystitis( bladder infection) or pyelonephritis( kidney infection). The patient showed common UTI symptoms seen in cystitis like dysuria(painful urination), fever and chills, but did not complain of back pain, or haematuria, hence it is likely that she is suffering from cystitis.

UTI occurs more frequently in woman as compared to men, due to the short urethra they have, allowing entry of bacteria into the urinary tract. The most common cause of UTI is Escherichia coli, a normal flora in the intestine and colon that enters and invades the urethra causing an infection. The second most likely bacteria that can cause UTI is Staphylococcus saprophyticus, as it usually infects woman in between the age of 20-40. Other microbes such as Klebsiella pneumoniae, Proteus mirabilis and Enterococcus species can also cause UTI, however, their occurrence is very low .

They are eliminated because:
a) Enterocoocus species usually occurs in patients who have undergone urinary tract surgery.
b) Proteus mirabilis often infect recurrent UTI patients that have structural abnormalities in their urinary system.
c) Klebsiella pneumoniae is involved in hospital-acquired infection and commonly infect immunocomprised individuals.

Most possible diagnosis: Escherichia coli and Staphylococcus saprophyticus
All the above characteristics were not observed in the patient and hence can be eliminated.
The two most likely cause of UTI are Escherichia coli and Staphylococcus saprophyticus.

Case Study 2
Patient: Female/29 years old
Signs and symptoms: Diarrhea
Suspected Diagnosis: Enterocolitis
Specimen collected: Stool

Types of enterocolitis:
1) Necrotizing enterocolitis
●Gastrointestinal disease that mostly affects premature infants, NEC involves infection and inflammation that causes destruction of the bowel intestine or part of the bowel.
● NEC typically occurs within the first 2 weeks of life, usually after milk feeding has begun

2) Autistic enterocolitis
●Autistic enterocolitis is a controversial term first used by British gastroenterologist Andrew Wakefield to describe a number of common clinical symptoms and signs which he contends are distinctive to autism.
● The existence of autistic enterocolitis is controversial, as the methodology of Wakefield's studies has been criticized and his results have not been replicated by other groups

3) Salmonella enterocolitis
● Most common type of food poisoning
● Infection in the lining of the small intestine caused by the bacteria Salmonella.
●Symptoms include diarrhea and abdominal pain

Most possible diagnosis: Salmonella enterocolitis
Reasons: Since necrotizing enterocolitis affects mainly infants but the patient is a 29-year-old female, it is highly unlikely that she is suffering from this disease. Moreover, it is not known to the medical technologist that the patient is suffering from autism. Hence, there is very low chance of her suffering from autism enterocolitis. The symptoms of salmonella enterocolitis include diarrhea which is one of the complaints as told by the female patient.

Case Study 3
Patient: Female/67 years old
Signs and symptoms: Fever, chills, bladder distension (bladder stretching); on indwelling catheter
Suspected Diagnosis: Urinary tract infection
Specimen collected: Urine

Indwelling catheters
Indwelling catheters avoid distension by emptying the bladder continuously into a bedside drainage collector. Individuals with indwelling catheters are encouraged to maintain a high fluid intake in order to prevent bacteria from accumulating and growing in the urine.

Possible agents:
● Many different Gram-negative organisms colonize urinary catheters, often becoming invasive infections.
●The most commonly isolated pathogens are Escherichia coli and Enterococcus spp.E.coli uses fimbriae to adhere to the urinary epithelium, thereby reducing the risk of being washed away.
● Infections caused by Proteus spp. are more likely in patients who have stones as Proteus spp. have urease activity that raises urinary pH, thus encouraging stone formation.
● Staphylococcus saprophyticus is a common isolate from sexually active females.
● Other intestinal bacteria, including Klebsiella pneumoniae (K.pneumoniae), Proteus mirabilis (P.mirabilis) , and Citrobacter.
●Others include Pseudomonas aeruginosa (P.aeruginosa), Enterobacter, and Serratia species, gram-positive organisms, including Enterococcus species, and S. saprophyticus .

Most possible diagnosis: Staphylococcus saprophyticus, Klebsiella pneumoniae, Proteus mirabilis and Enterococcus
UTI in this patient should be due to the presence of the catheter in the urethra. Hence these microbes might the possible reason.

Case Study 4
Patient: Male /68 years old
Signs and symptoms: fever, chills, excessive phlegm, breathing problems Suspected Diagnosis: Bronchitis
Specimen collected: Sputum

Information on Bronchitis

Inflammation of the mucous membrane in the lungs' bronchial passages
Narrowed bronchial passages shuts off the tiny airways in the lungs
Results in coughing spells, thick phlegm and breathlessness
Two forms: acute (lasts less than 6 weeks) and chronic (more than two years)

Acute bronchitis
●responsible for the hacking cough and phlegm production that sometimes accompany an upper respiratory infection
● In most cases the infection is viral in origin, but sometimes it's caused by bacteria
● very common among both children and adults

Chronic bronchitis
● a serious long-term disorder that often requires regular medical treatment

Possible agents
1) Adenovirus
● Non-enveloped double-stranded linear DNA
● Icosahedral nucleocapsid with a fiber protruding from each of the 12 vertices
●Causes bronchitis when it affects the lower respiratory tract

2) Bordetella
●Small, coccobacillary, encapsulated gram negative rod
● Restricted to the respiratory tract (negative blood culture)
●Isolated and grown on Border-Gengou agar

3)Parainfluenza virus
●Single stranded RNA negative-strand viruses

4) Streptococcus pneumoniae
● Gram positive lancet-shaped cocci
● Arranged in pairs or short chains
●Higher mortality in persons aged 65 and above

5) Chlamydia pneumoniae
●Obligate intracellular bacteria
●Require host cells for growth
● Causes upper and lower respiratory tract infections

Most possible microbes:
These microbes expressed similar symptoms as the patient in this case study. Hence, they are the most likely microbes to be causing this illness.

Case Study 5
Patient: Male /37 years old
Signs and symptoms: fever, Swelling around operation wound
Suspected Diagnosis: Wound Infection
Specimen collected: wound swab

Wound Infection caused by bacteria
● This is because swelling is one of the hallmarks of inflammation due to infection by either endogenous factors like tissue necrosis or exogenous factors like microorganism infections.
● Fever, on the other hand, is a common manifestation of infection and inflammation that is caused by many bacterial products eg endogenous or exogenous pyrogens.
● Most wound infections are caused by normal flora found on the skin/body.

Pathogens related to different surgical procedures/operations:

Pathogens Commonly Associated with Wound Infections and Frequency of Occurrence are as follows:
● Staphylococcus aureus (20%)
● Coagulase-negative staphylococci (14%)
● Enterococci (12%)
● Escherichia coli (8%)
● Pseudomonas aeruginosa (8%)
● Enterobacter species (7%)
● Proteus mirabilis (3%)
● Klebsiella pneumoniae (3%)
● Other streptococci (3%)
● Candida albicans (3%)
● Group D streptococci (2%)
● Other gram-positive aerobes (2%)Bacteroides fragilis (2%)

Most possible microbes:
However, out of all the organisms, the most common bacteria involved in wound infection due to operation was found to be Staphylococcus aureus, which accounts for 17-20% of the cases reported. Out of these cases, 40-50% are due to MRSA (
Methicillin-resistant Staphylococcus aureus).

Case Study 6
Patient: Female/37 years old
Signs and symptoms: Fever, pain during urination and virginal discharge
Suspected Diagnosis: Urinary tract infection
Specimen collected: Vaginal discharge

Possible agents:
1) Trichomoniasis
A sexually transmitted disease caused by the anaerobic, flagellated protozoa Trichomonas vaginalis.
Symptoms of Trichomoniasis include painful urination, fever, discharge greenish-yellow vaginal fluid, lower abdominal pain and discomfort during sexual intercourse.

2) Bacterial Vaginosis
It is caused by imbalance of bacteria flora in vagina. Usually, it is characteristic by the overgrowth of Gardnerella vaginalis and Gardneralla mobiluncus,.
Gardnerella bacteria is facultative anaerobic and gram-negative, while Mycoplasma hominis
It symptoms includes gray vaginal discharge and painful urination.

3) Vaginal Candidiasis
An infection caused by yeast, Candida albicans.
Its morphology appearance is normally single-celled.
Symptoms includes discomfort during urination and produce cottage cheese-like vaginal discharge or irritation in genital area

Another sexually transmitted disease caused by Neisseria gonorrhoeae, which is a gram-negative, cocci and aerobic bacteria.
Which produces symptoms like fever, yellowish discharge and urethritis.

A sexually transmitted disease caused by gram-negative cocci and aerobic bacteria Chlamydia trachomatis.
Chlamydia trachomatis required a host organism to survive.
Patients with Chlamydia will experience symptoms like fever, abnormal discharge and painful urination.

Most possible microbes:
Since Gonorrhea, Trichomoniasis and Chlamydia expressed similar symptoms as the patient in this case study, they are the most likely microbes to be causing this illness.


No comments: