Medical Microbiology Quiz

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Questions and Answers

Which part of the urinary tract is considered part of the lower urinary tract?

Ureters

Prostate (correct)

Kidneys

Bladder (correct)

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

Pseudomonas

Staphylococcus saprophyticus

Klebsiella

E.coli (correct)

Which of the following symptoms is typical for cystitis?

Fever

Dysuria with frequent urination (correct)

Pain in the kidneys

Bacteriuria

What type of UTI is characterized by dysuria, pyuria, and bacteriuria commonly found in young women?

Acute urethral syndrome Signup and view all the answers

Which route of infection refers to the spread of bacteria from the urethra to the bladder and kidneys?

Ascending route Signup and view all the answers

What is the purpose of Sodium Polyanethol Sulfonate in blood culture media?

To minimize its antibacterial effects Signup and view all the answers

Which media are most commonly used for cultures?

BAP and CHOC Signup and view all the answers

What is the recommended blood volume for cultures in children?

100-1000 organisms/mL Signup and view all the answers

Which organism is commonly associated with viral encephalitis?

Viruses Signup and view all the answers

What type of meningitis is characterized by a lack of growth from bacterial cultures?

Viral meningitis Signup and view all the answers

What is the sensitivity range of Gram stain smears?

75-90% Signup and view all the answers

Which test should be used to supplement smears and cultures for identification of specific pathogens?

Antigen detection tests Signup and view all the answers

What best describes gastritis?

Inflammation of the stomach Signup and view all the answers

What is a common cause of brain abscesses?

Anaerobic bacteria Signup and view all the answers

Which organisms are typically associated with inflammatory diarrhea?

Salmonella spp. and Shigella spp. Signup and view all the answers

What is a characteristic of non-inflammatory diarrhea?

Afebrile with watery, large-volume stool Signup and view all the answers

What is the function of normal flora in the gastrointestinal tract?

To prevent colonization of pathogens Signup and view all the answers

What is diarrhea defined as?

Abnormal increase in number of bowel movements Signup and view all the answers

What is the most common cause of nosocomial bacteremia?

Coagulase negative staphylococci Signup and view all the answers

Which method is preferred for blood collection during a venipuncture?

Syringe collection Signup and view all the answers

What should be done to disinfect specimen container tops before use?

Wipe with 70% alcohol or iodine Signup and view all the answers

What is the role of Sodium Polyanethol Sulfonate (SPS) in blood collection?

Prevents clotting Signup and view all the answers

Which collection method is not recommended due to contamination risks?

Indwelling intravascular catheters Signup and view all the answers

What should be used to clean the skin before blood collection to avoid contamination?

Alcohol and iodine Signup and view all the answers

What should be done immediately after collecting blood into a syringe?

Inoculate blood into culture bottles Signup and view all the answers

What anticoagulant is recommended for blood specimen collection?

Sodium polyanethol sulfonate (SPS) Signup and view all the answers

Which of the following is a common predisposing factor for urinary tract infections in men over 60 years?

Enlarged prostate Signup and view all the answers

What is the primary reason for using a clean-catch midstream urine specimen?

To avoid collecting the first urine passed Signup and view all the answers

What type of specimen is unsuitable for anaerobic culture?

Urine collected from catheter bags Signup and view all the answers

What is the significance of a positive leukocyte esterase test?

Indicates the presence of white blood cells Signup and view all the answers

What does a CFU count of 0-999 CFU/mL in urine indicate?

No growth Signup and view all the answers

Which of the following factors is essential in interpreting a urine culture?

The type of specimen and patient symptoms Signup and view all the answers

Which method is appropriate for collecting a specimen from the bladder directly?

Suprapubic aspiration Signup and view all the answers

What is the recommended storage condition for urine specimens if they cannot be cultured within 2 hours of collection?

Refrigerated to prolong viability Signup and view all the answers

Which result indicates significant bacteriuria in a urine culture?

1 organism > 100,000 CFU/mL Signup and view all the answers

What are the specific bacteria associated with intravascular bacteremia?

Viridans streptococci Signup and view all the answers

Which is NOT a characteristic of intermittent bacteremia?

Consistently present in bloodstream Signup and view all the answers

What is the function of boric acid in urine specimen transport?

Prolongs room temperature transport time Signup and view all the answers

Which type of culture media is primarily used for quantitative urine cultures?

Blood Agar Plate Signup and view all the answers

In a urine culture, what does it indicate if the count shows >104 CFU/mL with one or two organisms?

Infection likely present requiring further identification Signup and view all the answers

Study Notes

Urinary Tract Infections (UTIs)

UTIs are very common, caused by microbial invasion of the urinary system.
The upper urinary tract includes the kidneys and ureters.
The lower urinary tract includes the bladder, urethra, and prostate.
Normal flora (NF) are present in the urethra, including coagulase-negative staph, Corynebacterium, Micrococcus, streptococci, Enterobacteriaceae, anaerobic bacteria, yeast, and Mycoplasma. The area above the urethra is typically sterile.
Types of UTIs:
- Cystitis (lower UTI): bladder infection, dysuria (painful urination), frequent urination.
- Pyelonephritis (upper UTI): kidney infection, fever, pain, dysuria, frequent urination.
- Acute urethral syndrome (AUS) is similar to UTI symptoms in young women, sometimes associated with bacteriuria (bacteria in urine) and pyuria (white blood cells in urine). Urethritis has the same symptoms as UTI but is considered sexually transmitted.
UTIs are often caused by endogenous flora, including E. coli (most common), other Enterobacteriaceae (Klebsiella), Staphylococcus saprophyticus (young women), S. aureus, enterococci, and Pseudomonas. AUS can be caused by S. saprophyticus, Enterobacteriaceae, N. gonorrhoeae, and C. trachomatis.
Routes of infection include ascending (from urethra to bladder/kidneys) and descending (carried by bloodstream to kidneys).
Predisposing factors for UTIs include urinary tract abnormalities, enlarged prostate, kidney stones, instrumentation (e.g., catheters), and underlying medical conditions such as diabetes.
UTIs in women are more common due to a shorter urethra, hormonal changes, sexual activity, and pregnancy. UTIs in men usually occur in individuals older than 60 and are associated with an enlarged prostate.
Common nosocomial (hospital-acquired) infections are UTIs, frequently preceded by catheter use or other instrumentation.
Key specimen collection and transport considerations for UTIs to avoid contamination:
- use only pre-sterilized, clean-catch midstream samples or samples collected using a sterile straight catheter, indwelling catheter, suprapubic aspirates, or cystoscopy. (Urine from catheter tips or pooled 24-hour specimens are not acceptable).
- specimens should be refrigerated if not cultured within 2 hours.
- avoid using specimen containers like bedpans or urinals.
Urine sediment examination is a standard part of urinalysis, often using a microscopic aliquot of centrifuged sediment.
Chemical methods like leukocyte esterase test (dipstick measure of WBCs) and nitrate test (detects nitrite from bacteria reduction of nitrate) help initial screen for UTI.
BAP, enteric agar (MAC, EMB), and CHOC agar are common culture media to identify bacteria.
Inoculation typically involves using loops for measured volumes of uncentrifuged urine, streaking over a plate to disperse, then spread for full surface coverage.
Cultures must be incubated overnight at 35°C, and CFU/mL is calculated.
Factors crucial to consider during workup include the type of specimen, patient history, and suspected pathogens. Different approaches are taken for counts under 10,000 CFU/mL, 10,000 - 100,000 CFU/mL, and over 100,000 CFU/mL.

Bacteremia and Sepsis

Bacteremia: bacteria in bloodstream.
Septicemia: bacteremia with clinical signs and symptoms (fever, chills, hypothermia, hyperventilation), possibly leading to septic shock and a mortality rate greater than 50%.
Types of bacteremia:
- Primary bacteremia: without other known infected sites.
- Secondary bacteremia: associated with an infected body site.
- Occult bacteremia: unknown cause, sometimes with or without symptoms, often in children.
- Pseudobacteremia: a false positive caused by contaminated materials in blood culture media.
Bacteremia patterns include transient (minutes to hours in bloodstream), intermittent (periodic release into bloodstream), and continuous (organically present constantly).
Sources of bacteremia: Intravascular (e.g., infected heart valves, catheters) and extravascular (e.g., infections of organs in the urinary system (kidney/bladder), wounds, or abscesses, which can extend to the blood).
Common causes of nosocomial bacteremia: coagulase-negative staphylococci, S. aureus, Enterococcus, Candida albicans, enteric bacteria, and non-fermenting Gram-negative rods (e.g., Pseudomonas and Acinetobacter baumannii).
Peripheral aseptic venipuncture is recommended for blood collection.
Standard methods for blood collection include syringe methods and tube methods with centrifugation.
Collection procedure should focus on specimen material preparation and site preparation with antiseptic methods like alcohol or iodine. Use sodium polyanethol sulfonate (SPS) as an anticoagulant.
Important considerations for blood cultures include obtaining blood volumes appropriate to the patient's age (larger volumes are generally needed in children). Recommended ratios of blood to blood culture broth are 1:5 to 1:10.
Ideal times for performing blood cultures are before any antimicrobial therapy begins.
Newer recommendations frequently suggest collecting three blood cultures simultaneously from separated sites to improve detection rates, then performing transport in room temperature or incubator if delayed.
Culture media commonly used include BHI, Brucella, Columbia, Thioglycollate, Trypticase Soy, SPS.
Incubation conditions vary based on target organism and should follow appropriate temperature (e.g. 35-37°C) and atmosphere (e.g., CO2) conditions.
Gram-stained smears are the first step in processing and identifying bacteria by cell morphology and gram stain reaction. Appropriate subcultures must be performed on specific media for identification and confirmation.

Central Nervous System (CNS) Infections

The CNS comprises the brain, spinal cord, and meninges (protective membranes). CSF bathes the brain and spinal cord.
Meningitis is the inflammation of meninges; purulent meningitis is a type of pyogenic meningitis, characterized by pus in the meninges, and is usually of bacterial origin.
Aseptic meningitis is non-pyogenic, usually caused by a virus. Encephalitis is inflammation of the brain, often cause by a virus. Meningoencephalitis is inflammation of both brain and meninges.
Routes of infection include hematogenous (most common—spread from another infected site through bloodstream), contiguous spread (spread from an adjacent infected site), and trauma/surgery (breaching CNS protective barriers).
Symptoms of acute bacterial meningitis include flu-like symptoms, headache, fever, nausea, vomiting, nuchal rigidity (stiff neck), and mental status changes.
Common causative agents include E. coli, other Gram-negative rods (e.g., Klebsiella, Enterobacter), S. agalactiae (group B streptococci in neonates), Listeria monoctyogenes, Haemophilus influenzae, N. meningitidis (meningococci), S. pneumo nieae (pneumococci) in older children and adults.
Specimen collection primarily relies on lumbar puncture (spinal needle insertion to extract cerebrospinal fluid)
- Processing should occur STAT within 15 minutes. - Three-four tubes are collected: tube one–chemistry (proteins and glucose), tube two– microbiology (gram stain, culture), and tube three–hematology (cell count).
- Processing must be done immediately using centrifuge or sedimentation for smear and culture preparation.
Gram-stained smears and thick smears are necessary for preliminary screening of the bacterial species.
- Media like BAP, CHOC, MAC/EMB (for GNR), are used for culture preparation.
Antigen detection tests supplement smears and cultures.
Special cultures may be necessary for certain pathogens.
Treatment involves initial empiric antimicrobial therapy, then adjusting to narrow spectrum based on identification and susceptibility testing.

Gastrointestinal Tract Infections

The GI tract consists of the esophagus, stomach, small intestines (duodenum, jejunum, ileum), large intestines (cecum, colon, rectum), and anus.
Common GI infections: Gastritis (stomach inflammation), Gastroenteritis (inflammation of stomach and intestines), Enterocolitis (inflammation of small and large intestines), Diarrhea (abnormal increase in loose or liquid stool), Dysentery (diarrhea with abdominal cramping), and Proctitis (inflammation of rectal mucosa).
Normal flora (NF) comprises predominantly anaerobic bacilli (Bacteroides spp), GN enteric bacilli, enterococci, streptococci, S. aureus, and yeast (Candida) and prevents pathogens' colonization.
Non-inflammatory diarrhea:
- results from toxins (ie, bacterial enterotoxins) leading to increased fluid and electrolyte release.
- Symptoms include watery stool, absence of PMN, blood, or mucus.
- Commonly caused by V. cholerae, enterotoxigenic E. coli, Bacteroides, viruses (Giardia lamblia, Cyclospora species, and Cryptosporidium species).
Inflammatory diarrhea:
- results from organisms invading intestinal mucosa and cell destruction.
- Symptoms include PMNs, blood, and mucus.
- Commonly caused by Salmonella spp., Shigella spp., Y. enterocolitica, Campylobacter spp., Enteroinvasive E.coli, and C. diff.
Enterotoxin-mediated diarrhea is characterized by rapid onset (often within 12 hours) and is caused by specific bacterial toxins present in foods, such as those produced by V. cholera, S. aureus, C. perfringens, and B. cereus.
Common diarrheal diseases include infections with Salmonella, Shigella, Y. enterocolitica, Campylobacter jejuni, and E. coli (enterohemorrhagic, enterotoxigenic, enteropathogenic, enteroaggregative). Other uncommon GI pathogens include Edwardsiella tarda, Vibrio cholera, V. parahaemolyticus, Plesiomonas shigelloides, and L. monocytogenes.
Common pathogenic organisms associated with GI tract illness also include parasites (Giardia, Entamoeba, Cryptosporidium, Cyclospora, Microsporidia), viruses (rotavirus, adenovirus, calcivirus, and astrovirus), H. pylori (chronic gastritis, ulcers), C. difficile (antibiotic-associated diarrhea, pseudomembranous colitis), C. perfringens, and M. avium.
Fecal specimens are typically collected in non-sterile containers with transport media (eg, Cary-Blair medium).
Samples are processed/examined for macroscopic appearance (blood, mucus, consistency, color).
Microscopic examination involves looking for the presence of WBCs, using methylene blue and other staining methods to identify and observe specific organism characteristics (ie., motility, appearance)
Several media types are used for culture, depending on the suspected pathogen, for isolation and identification (including BAP, MAC/EMB. HE, SS, TCBS, Campy-BAP, enrichment broths)
- Plates are tested to determine if enteric pathogens are present.
Physicians are usually consulted to make specific culture requests, which may differ based on location of infection, symptoms, patient demographics, specific organisms to look-out for.

Genital Tract and STDs

STD: Sexually Transmitted Disease.
Urethritis: inflammation of urethra; can be caused by infections like gonorrhea (N. gonorrhoeae) or Chlamydia (C. trachomatis), or other infections. UTIs have similar symptoms.
Female genital tract consists of ovaries, fallopian tubes, uterus, cervix, vagina, and vulva. Indigenous microbiota varies with age and hormone levels.
Common vaginal infections (vaginitis): -Candida albicans (yeast infection) -Trichomonas vaginalis -Enterobacteriaceae. -N. gonorrhoeae -C. trachomatis -S. aureus -Actinomyces.
Bacterial vaginosis: due to reduced Lactobacillus numbers. Key diagnostics include wet prep (clue cells, with tiny gram variable bacteria) and Whiff test (amine or fishy smell using KOH).
Cervicitis: inflammation of cervix, frequently caused by N. gonorrhoeae or C. trachomatis.
Bartholinitis: acute inflammation of Bartholin's gland, caused by sexually transmitted organisms (e.g. N. gonorrhoeae, C. trachomatis).
Group B Streptococcal infection is common cause of neonatal meningitis. Screening is common during pregnancy.
PID: Pelvic Inflammatory Disease includes inflammation of fallopian tubes, uterus and ovaries. It is usually related to other STI infections or may appear post childbirth or IUD usage.
Male genital tract consists of urethra, prostate, epididymis, and testicles.
Urogenital swabs are typically made of cotton or rayon treated with charcoal.
Specific recommendations vary based on the specimen type (e.g. urethra—patient avoids urination for 1–2 hours before; for cervix, a speculum is used and swabs are inserted and extracted with care).
Microbiological tests may vary depending on the suspected pathogen, and incubation conditions may also have to be adapted.

Body Fluids

Body fluids, like pleural, peritoneal, pericardial, synovial, and amniotic fluids, are typically sterile. Pathogens may arise through infection of underlying organs/structures.
Pleural fluid – thoracentesis, infection from lungs into pleural cavity, usually causes pneumonia-like pathogens.
Peritoneal fluid – paracentesis
- Primary peritonitis: spontaneous bacterial peritonitis, bacteria spreading from an unidentified site).
- Secondary peritonitis: known site of infection (e.g., ruptured appendix or perforated bowel), often caused by Enterobacteriaceae, enterococci, Bacteroides, and other anaerobes.
Peritoneal dialysis fluid (CAPD): introduce into peritoneal cavity for metabolic waste removal by dialysis. It is commonly caused by skin flora if sterile technique is not followed (e.g. Staph, strep, GNR, Corynebacterium).
Pericardial fluid- pericardiocentesis: infection in the pericardial space around the heart.
Synovial fluid- arthrocentesis; infectious/septic arthritis, often caused by S. aureus, streptococci, N. gonorrhoeae, H. influenzae, and Bacteroides.
Amniotic fluid - amniocentesis: infection of amniotic membrane (amnionitis). Often caused by, but not limited to, Group B Streptococci, anaerobes, E. coli, Gardnerella vaginalis, Ureaplasma urealyticum arising from rupture of membranes.
Specimens are collected using percutaneous aspirations with needles and syringes.
Fluid specimens are processed urgently (STAT). Usually done with gram staining and culture preparation to identify bacteria present.

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Test your knowledge on the basics of medical microbiology, including urinary tract infections, blood culture media, and meningitis. This quiz covers various pathogens, their associated infections, and diagnostic methods. Perfect for students in healthcare fields or anyone interested in infectious diseases.