Microbiology of Meningitis and UTIs

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Questions and Answers

What is the primary function of cerebrospinal fluid (CSF)?

To facilitate blood circulation in the brain

To protect the brain and spinal cord (correct)

To supply nutrients to the brain

To transmit nerve signals between neurons

Which type of meningitis involves pus in the meninges?

Purulent meningitis (correct)

Viral meningitis

Aseptic meningitis

Encephalitis

What are common symptoms of acute bacterial meningitis?

Weight gain and dizziness

Rash and itching

Flu-like symptoms and nuchal rigidity (correct)

Cough and sore throat

What is the most common route of infection leading to meningitis?

Hematogenous spread Signup and view all the answers

Which of the following organisms is a common causative agent of meningitis in neonates?

Escherichia coli Signup and view all the answers

Which procedure is primarily used for specimen collection in suspected meningitis cases?

Lumbar puncture Signup and view all the answers

What is the main difference between aseptic and purulent meningitis?

Aseptic meningitis is typically viral, while purulent is bacterial Signup and view all the answers

Which organism is most associated with causing meningitis in elderly patients?

Streptococcus pneumoniae Signup and view all the answers

What is the most common cause of urinary tract infections (UTIs)?

E. coli Signup and view all the answers

Which type of urinary tract infection primarily involves the bladder?

Cystitis Signup and view all the answers

What is bacteriuria?

Bacteria in urine Signup and view all the answers

Which statement describes the ascending route of urinary tract infections?

Infection originates from the urethra and spreads to the bladder Signup and view all the answers

Which of the following is NOT part of the normal flora present in the urinary tract?

Coagulase-positive staphylococci Signup and view all the answers

Which symptom is characteristic of Pyelonephritis?

Fever and flank pain Signup and view all the answers

What procedure is primarily used for collecting fluid specimens in various medical tests?

Amniocentesis Signup and view all the answers

Which bacteria is particularly associated with Acute urethral syndrome (AUS) in young women?

Staphylococcus saprophyticus Signup and view all the answers

What type of specimen is collected for microbiological analysis?

3 tubes for microbiology Signup and view all the answers

What is the recommended incubation temperature for cultures in a microbiology lab?

35-37 C Signup and view all the answers

Which of the following is a common media used for bacterial cultures?

BAP Signup and view all the answers

What type of meningitis can be diagnosed using PCR?

Viral meningitis Signup and view all the answers

Which type of cells are usually found in bacterial meningitis based on CSF findings?

Neutrophils Signup and view all the answers

Which organism is known to cause encephalitis?

Listeria monocytogenes Signup and view all the answers

In the context of brain abscesses, which condition is commonly associated with anaerobic bacteria?

Streptococcal infection Signup and view all the answers

What is the primary method to detect fungal meningitis?

Antigen detection test Signup and view all the answers

Which of the following fluids are considered sterile?

All of the above Signup and view all the answers

What is the most common pathogen associated with infectious arthritis?

Staphylococcus aureus Signup and view all the answers

What condition is specifically associated with excess fluid in the pleural cavity?

Empyema Signup and view all the answers

Which organism is commonly involved in primary peritonitis?

Enterobacteriaceae Signup and view all the answers

What complication is indicated by the presence of purulent pleural fluid?

Empyema Signup and view all the answers

Which statement regarding pericarditis is accurate?

It is primarily caused by viral infections. Signup and view all the answers

What is the purpose of introducing dialysate into the peritoneal cavity?

To remove metabolic waste Signup and view all the answers

What is the primary cause of amnionitis?

Group B streptococci Signup and view all the answers

What is the most common nosocomial infection in hospitals in the US?

Urinary Tract Infection Signup and view all the answers

Which of the following is NOT a predisposing factor for urinary tract infections?

Low fluid intake Signup and view all the answers

What is the appropriate method for collecting a clean-catch midstream urine specimen?

Collect after voiding starts Signup and view all the answers

What should be done if urine specimens are not cultured within 2 hours of collection?

Refrigerate the urine Signup and view all the answers

Which urine specimen type is suitable for anaerobic culture?

Suprapubic aspirate Signup and view all the answers

What indicates a positive leukocyte esterase test?

Presence of white blood cells Signup and view all the answers

What should urine specimens be cultured on for quantitative analysis?

Blood Agar Plate Signup and view all the answers

Which factor could lead to a false positive nitrite test result?

Contamination from nitrate-reducing organisms Signup and view all the answers

What is the correct calculation for colony-forming units (CFU/mL) using a 0.01 mL loop?

Number of colonies x 100 Signup and view all the answers

What is indicated by a colony count of 100,000 CFU/mL?

Probable infection Signup and view all the answers

Which of these specimens is considered unacceptable for urine culture?

Unrefrigerated urine over 2 hours Signup and view all the answers

What does a negative culture report typically indicate?

0-999 CFU/mL detected Signup and view all the answers

What is recommended for transportation of urine specimens?

Transport at room temperature and culture within 2 hours Signup and view all the answers

Study Notes

Central Nervous System

The central nervous system (CNS) includes the brain and spinal cord.
The meninges are membranes that surround and protect the brain and spinal cord.
Cerebrospinal fluid (CSF) bathes the brain and spinal cord.
CSF is clear and colorless and is tested for culture, cell count, glucose, and protein levels.
Meningitis is an inflammation of the meninges.
Purulent meningitis, also known as pyogenic meningitis, involves pus in the meninges and is typically caused by bacteria.

Introduction to Body Fluids

Body fluids are sterile.
Pleural fluid covers the lungs, lining the chest cavity.
Peritoneal fluid is found in the abdominal cavity.
Pericardial fluid surrounds the heart.
Synovial fluid is joint fluid.
Amniotic fluid surrounds the fetus.

Routes of Infection

Hematogenous spread—bloodstream carrying organisms from infected site to meninges.
- N. meningitidis colonize the nasopharynx then enter the bloodstream causing meningitis.
Contiguous spread—organisms spreading from infected adjacent site (e.g., sinusitis).
Trauma – breach of the CNS protective barrier (e.g. skull fracture).
Surgery—microbial contamination.
Shunts—placed to remove fluid, become a portal of entry.

Acute Bacterial Meningitis Symptoms

Flu-like symptoms
Headache
Fever
Nausea
Vomiting
Nuchal rigidity (stiff neck)
Photophobia
Mental status changes

Causative Agents

Neonates

E. coli
Other gram-negative rods (GNR) such as Klebsiella and Enterobacter
Streptococcus agalactiae
Listeria monocytogenes

Young Children (6 months–5 years)

Haemophilus influenzae type b
Neisseria meningitidis (meningococci)
Streptococcus pneumoniae (pneumococci)

Older Children and Adults

Neisseria meningitidis (meningococci)
Streptococcus pneumoniae (pneumococci)
Gram-negative rods (GNRs)
Listeria monocytogenes
Immunocompromised patients–bacteria like Listeria monocytogenes, encapsulated bacteria.
Shunt patients– staphylococci and S. aureus

Specimen Collection

Lumbar puncture – spinal needle is inserted between the third and fourth lumbar vertebrae.
CSF is transported at room temperature (<15 min.)
If the transport time extends beyond 15 minutes, CSF should be refrigerated.

Specimen Collection (Additional)

Three to four tubes are collected.
Tube #1 contains CSF for chemistry tests (protein, glucose).
Tube #2 contains CSF for microbiology tests (gram stain, culture).
Tube #3 contains CSF for hematology tests (cell count, differential).

Microbiology Processing

If more than 1 ml of CSF is collected, it is centrifuged
Sediment is used for smear and culture.
Gram stain smears have a sensitivity of 75-90%.
Thick smears are also performed.

Culture Media

Blood agar plates (BAP), chocolate agar plates (CHOC) are most commonly used.
MacConkey agar (MAC) or eosin methylene blue agar (EMB) are used if gram-negative rods (GNRs) are seen in gram-stained smears.
Anaerobic blood agar plates (anaBAP) can be used if requested.
- Anaerobic bacteria are rarely isolated.
Plates are incubated at 35-37°C in 5% carbon dioxide.

Antigen Detection Tests

Antigen detection tests are available for group B streptococci, Haemophilus influenzae type b (Hib), Neisseria meningitidis, and Streptococcus pneumoniae.
These should supplement smears and cultures, not replace them.

Other Types of Meningitis

Spirochetes

Treponema pallidum and Borrelia burgdorferi

Viral

Aseptic meningitis is a viral infection with no bacterial growth in cultures.

Mycobacterial

Mycobacterium tuberculosis

Fungal and Parasitic

These infections are rare.

CSF Findings

Bacterial meningitis shows mainly neutrophils.
Fungal meningitis shows mainly lymph cells.
TB meningitis shows mainly lymph cells.
Syphilitic meningitis shows mainly lymph cells.
Viral meningitis shows mainly lymph cells.
Parasitic meningitis shows mainly lymph cells and eosinophils.

Brain Abscesses

Caused by non-fastidious organisms (NF) including anaerobic bacteria, staphylococci, viridans streptococci.
Aspirate and biopsy materials, transported in anaerobic conditions.
Examined microscopically and cultured aerobically and anaerobically.

Encephalitis/Meningoencephalitis

Viruses are the most common cause.
Bacteria like Listeria monocytogenes, Rickettsia, Mycoplasma, and Borrelia burgdorferi.
Parasites such as Naegleria and Acanthamoeba.

Reporting Results

Immediate notification of critical values.
Verbal communication and written report.

Urinary Tract

Introduction: The urinary tract. includes the kidneys, ureters, bladder, urethra and prostate.

Urinary Tract Normal Flora

Sterile above the urethra
Non-fastidious (NF) in urethra
- coagulase-negative staphylococci
- Corynebacterium
- Micrococcus
- Streptococci
- Enterobacteriaceae
- anaerobic bacteria
- Yeast
- Mycoplasma

Urinary Tract Infection (UTI)

Microbial invasion of the urinary system, very common.
Bacteriuria – bacteria in urine, Pyuria – WBCs in urine.

Four Types of UTIs

Cystitis (lower UTI): bladder infection, dysuria (painful urination) with frequent urination,
Pyelonephritis (upper UTI): kidney infection, fever, pain, dysuria, and frequent urination
Acute urethral syndrome (AUS): similar symptoms as UTI, but considered sexually transmitted, common in young women
Urethritis: inflammation of urethra.

UTI Causative Agents

E. coli (most common)
Staphylococcus saprophyticus (young women)
S. aureus
Enterobacteriaceae (e.g., Klebsiella)
Enterococci
Pseudomonas
Other NF organisms

Routes of UTI Infection

Ascending route: from urethra to bladder and kidneys.
Descending route: carried by the bloodstream to the kidneys.

Predisposing Factors for UTIs

Urinary tract abnormalities
Enlarged prostate
Kidney stones
Instrumentation (e.g., catheterization)
Underlying medical conditions (e.g., diabetes mellitus)

Epidemiology of UTIs

Women

Short female urethra; hormonal changes; sexual activity; pregnancy.

Men

60 years with enlarged prostate

Nosocomial Infections

UTIs are the most common nosocomial infections in hospitals.
Onset is often preceded by catheterization and other instrumentation.

Specimen Collection & Transportation

Urine is sterile above the urethra.
Contamination during collection: from urethral, vaginal, skin, and fecal organisms.
Periurethral area is cleaned with mild soap and rinsed.
Specimens are collected in sterile containers.
Bedpans and urinals should not be used.

Timing of UrineCollection

Urine should remain in the bladder as long as possible.
Urine is a good growth medium.
The number of colony-forming units (CFU)/mL increases with incubation.
The specimen of choice is the first morning specimen.

Acceptable Urine Specimens

Clean-catch midstream
Straight catheter
Indwelling catheter
Suprapubic aspirates
Cystoscopy specimens

Clean-Catch Midstream Procedure

Periurethral area is cleaned.
Patient begins to void.
Collects midstream urine; first urine passed is not collected.
Avoid non-fastidious organisms from urethra.

Straight Catheter Procedure

In/out catheterized urine
Periurethral cleaned.
Catheter inserted into bladder.
Collects midstream specimen from bladder.

Indwelling Catheter Procedure

Clean catheter collection port with alcohol.
Aspirate specimen with needle and syringe.
Avoid collecting specimen from catheter bag.

Suprapubic Aspirates

Needle inserted through abdominal wall into the full bladder.
Suitable for the collection of anaerobic bacteria.

Cystoscopy Specimens

Collected using a cystoscope.
Urine is collected from the bladder and/or ureters.

Urine Transportation

Transport at room temperature (RT)
Culture within 2 hours of collection
If not, refrigerate; preservatives prolong RT transport time to 24 hours.
Boric acid maintains original colony counts.

Specimens to Avoid

Urine catheter tips (Foley catheters)
Pooled 24-hour urine
Unrefrigerated or unpreserved urine (older than 2 hours)
Urine other than suprapubic aspirates for anaerobic culture.

Urine Sediment Examination

Urinalysis includes a microscopic aliquot centrifuged.
Wet mount of the sediment is examined for WBC and bacteria, indicative of UTI.
The analysis helps to check for infections.

Chemical Methods

Chemical tests such as leukocyte esterase and nitrite tests are included with a urinalysis.
These tests help to screen for UTIs.

Leukocyte Esterase Test

WBCs in urine; detects leukocyte esterase enzyme, positive results for pyuria.

Nitrite Test

Presence of nitrite = significant bacteriuria; some organisms are not nitrite reducers.

Culture Media (for Urine)

Blood agar plates (BAP)
Enteric agar (MAC, EMB)
Chocolate agar (CHOC) for Haemophilus

Inoculation

Quantitative culture on BAP agar.
CFU/mL is important diagnostic tool.
Calibrated loops deliver 0.001 or 0.01 mL of urine.
Loops are dipped into well-mixed uncentrifuged urine.
Streaked down the center of plates with subsequent spreading.

Streaking and Incubation Methods

Streaking methods on the plates to create isolated colonies.
Incubated overnight at 35°C.

Colony Count Calculations

CFU/mL is calculated if 0.01 mL loop used: # colonies x 100 = CFU/mL
CFU/mL is calculated if 0.001 mL loop used: # colonies x 1000 = CFU/mL

Colony Count Techniques

Inoculate 0.001 mL of specimen evenly dispersed across a plate.
Incubate, then count all types of colonies.

Urine Culture

Process urine cultures.

Workup Factors

Specimen type (voided vs. catheterized)
Patient history and symptoms
Voided specimens may be contaminated with non-fastidious organisms (NF), requiring colony count and determination of predominant organisms.

General Guidelines

1 or 2 organisms, >104 CFU/mL: ID and sensitivity.
1 organism, >103 CFU/mL, symptomatic: ID and sensitivity.
≥3 organisms, no predominant: contaminated specimen, reject; request new specimen.

Specific Guidelines (Suprapubic Aspirates)

ID and sensitivity as appropriate; special request—non-routine.

Specific Guidelines for Catheterized Specimens

ID and sensitivity for any count: special request, may be non-routine.

No Growth

0-999 CFU/mL: Report no growth at xx hours.

Possible Pathogens (1 Type)

Possible contamination: No work-up
10,000 – 100,000 CFU/ml: Possible infection—ID and sensitivity.
100,000 CFU/ml: Probable infection—ID and sensitivity.

Possible Pathogens (2 Types)

Each >10,000 CFU/mL: Possible infection—ID and sensitivity for both.
One >10,000 and the other <10,000: Possible infection based on predominant organism; ID and sensitivity for the first one; count and describe the other.
Both <10,000 CFU/mL: Probable contamination; State colony count and description; No work-up.

Possible Pathogens (3 or More Types)

If one organism is predominant (>100,000 CFU/mL): ID and sensitivity on that one; Describe other organisms.
If all organisms have similar counts: Contamination; No work-up.

Genital Tract and STDs

Sexually transmitted disease (STD).
Urethritis – inflammation of the urethra. Common pathogens include N. gonorrhoeae and C. trachomatis.
Genital Ulcer Disease—Haemophilus ducreyi (chancroid), Treponema pallidum (syphilis), Herpes simplex virus-2 (genital herpes), Klebsiella granulomatis (Donovanosis), Chlamydia trachomatis (LGV).
Genital Ulcer Infections: include others like HPV(human papillomavirus).

Female Genital Tract

Ovaries, fallopian tubes, uterus, cervix, vagina, and vulva.
Indigenous microbes: Include Lactobacillus, Staphylococcus, Streptococcus, Enterobacteriaceae, Corynebacterium, Gardnerella vaginalis, Mycoplasma, and Ureaplasma, which vary with age and pH levels.

Female Genital Diseases

Lower genital tract infections include infections of the vulva, vagina, and cervix.
Upper genital tract infections affect the uterus, fallopian tube, ovaries, and abdominal cavity and are often exogenous; some are rare endogenous infections.
Vaginitis: Candida albicans; Trichomonas vaginalis; Enterobacteriaceae; N. gonorrhoeae; C. trachomatis; S. aureus; Actinomyces.
Bacterial vaginosis: Due to reduced numbers of Lactobacilli; presence of clue cells; wet prep for confirmation; whiff test for odor (KOH).
Cervicitis: caused by N. gonorrhoeae or C. trachomatis.
Bartholinitis: Caused by N. gonorrhoeae or C. trachomatis; gland ducts obstructed leading to abscess formation with aerobic and anaerobic NF.

Male Genital Tract

Includes urethra, prostate, epididymis, and testicles.
Upper tract infections in males include epididymitis, prostatitis, and orchitis; symptoms similar to lower UTI; similar organisms as UTIs cause these infections.

Specimen Collection for Gental Tract

Urogenital swabs—made of cotton or rayon treated with charcoal.
Avoid cotton swabs or wooden shafts; routine culture specimens are transported and stored at RT.
Specific recommendations: Urethra—not urinate 1-2 hours before collection; insert swab into urethra or discharge.

Specific Recommendations

Use a speculum in vagina, cervix, and endometrium; sterile swab to collect material deep within. Collect specimens from Barthollin gland, fallopian tubes, & epididymis. Get biopsy & tissue specimens when necessary. These specimens are stored at room temperature (RT).

Microscopic Examination

Diagnostics for bacterial vaginosis: Clue cells and amine odor.
Diagnostics for gonorrhea (GC) in men: Intracellular Gram-negative diplococci, suggestive of other organisms such as Haemophilus ducreyi.

Culture

Not all organisms can be tested.
Physician request for screening of gonorrhea (GC), mycoplasma, and group B streptococci.
Anaerobic cultures (anaBAP).

Incubation

Vary with culture medium and organism sought. Incubate aerobically, aerobically with 5% CO2, anaerobically at 35˚C, and in high humidity and CO2.

Workup Protocol (Dependent on Specimen)

Type of specimen; specimen quality; type of culture.
Group B streptococci; Listeria monocytogenes; Chlamydia; GC, currently done by PCR, amplification, and detection.

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This quiz tests your knowledge on the microbiological aspects of meningitis and urinary tract infections (UTIs). Questions cover the causes, symptoms, diagnosis, and differences between various types of meningitis and UTIs. Ideal for medical students or anyone interested in infectious diseases.