Microbiology Diarrhea Quiz

Gastrointestinal Tract

The gastrointestinal tract includes the esophagus, stomach, small intestines (duodenum, jejunum, ileum), large intestines (cecum, colon, rectum), and anus.
Inflammation of the stomach is called gastritis.
Inflammation of the stomach and intestines is gastroenteritis.
Inflammation of the small and large intestines is enterocolitis.
Diarrhea is an abnormal increase in bowel movement, loose to liquid stool.
Dysentery is diarrhea with cramping abdominal pain.
Proctitis is inflammation of the rectal mucosa.
80% of the dry weight of feces is bacteria.
Normal flora prevents colonization of pathogens.
Common bacteria in normal flora include anaerobic bacilli (Bacteroides spp.), GN enteric bacilli, Enterococci, Streptococci, and S. aureus.
Yeast (Candida) is also present.
Non-inflammatory diarrhea is caused by bacterial toxins or enterotoxins.
Symptoms include watery, large-volume stool, and no blood, mucous, or PMNs.
Bacterial causes include Vibrio cholerae, Enterotoxigenic E. coli, and Bacteroides spp.
Viral causes include Giardia lamblia, Cyclospora, and Cryptosporidium.
Inflammatory diarrhea is caused by organisms that invade the intestinal mucosa and produce cytotoxins.
Symptoms include fever, loose, small-volume stool, and blood, mucous, and PMNs in fecal specimens.
Bacterial causes include Salmonella spp., Shigella spp., Y. enterocolitica, Campylobacter spp., Enteroinvasive E. coli, and Clostridium difficile.
Enterotoxin-mediated diarrhea is caused by ingestion of food containing toxins.
Rapid onset (<12 hours), and symptoms include watery stool.
Common causes include Enterotoxigenic E. coli, V. cholera, S. aureus, C. perfringens, and B. cereus.
Diarrheal diseases include salmonellosis, shigellosis, Y. enterocolitica, Campylobacter, Vibrio cholerae, and V. parahaemolyticus.
Additional diarrheal diseases include Edwardsiella tarda, Plesiomonas shigelloides, and Listeria monocytogenes.
Intestinal parasites that cause diarrhea include Giardia, Entamoeba, Cryptosporidium, Cyclospora, and Microsporidia.
Viral causes of diarrhea include Rotavirus, adenovirus, calicivirus, and astrovirus. Additional diseases like Gastritis, peptic and duodenal ulcers, antibiotic-associated diarrhea, pseudomembranous colitis, enterotoxin, and GI diseases are also common.

Specimen Collection

Collect 2-3 fecal specimens in clean, non-sterile, wide-mouth containers.
Avoid contamination with urine.
Use Cary-Blair transport medium.
Process specimens within 1-2 hours of collection.
Other specimens include duodenal, colostomy, ileostomy material, and diapers.
Also include food samples if foodborne illness is suspected.

Visual Examination

Macroscopic examination for blood, mucous, consistency (watery, formed, loose), and color.

Microscopic Examination

Fecal WBC (PMN) examination.
Use methylene blue and make a wet mount.
Look for motility of Campylobacter, Gram stain morphology.
Identify curved GNR (Vibrio) and GPR (Clostridium).

Stool WBC

Distinguish inflammatory from non-inflammatory diarrhea.

Culture

It's not practical to culture all isolates.
Look specifically for Salmonella, Shigella, Campylobacter, E. coli O157:H7, and Vibrio.
Rely on physician's request for special cultures based on patient history and symptoms.

Media Inoculation

Use non-sterile pipettes or swabs to inoculate media.
Streak plates for bacterial isolation.
Inoculate enrichment broth with swab or pipette containing a large amount of specimen.

Media

BAP: detects S. aureus and yeast overgrowth.
MAC or EMB: differential and selective.
NLF: identifies Salmonella, Shigella, Y. enterocolitica, E. tarda, Plesiomonas, Aeromonas, and Vibrio.
XLD or HE, SS: differential and selective, for salmonella and shigella, colourless colonies, +/- black center.
Campy-BAP: Campylobacter selective media, isolates C. jejuni and C. coli.
Enrichment broth: GN: Salmonella, Shigella
Selenite F: Salmonella, some Shigella
CIN agar: Y. enterocolitica, incubated aerobically.
SS agar: Salmonella Shigella, Shigella can be inhibited.
Sorbitol MAC: Differentiates E. coli O157:H7.
TCBS: Vibrio.
CCFA: Clostridium difficile, anaerobic.

Incubation Conditions

Incubate BAP, MAC, EMB, XLD, HE, SS, TCBS at 35°C in ambient air.
Campy-BAP: microaerobic at 42°C.
Enrichment media: incubated for a few hours and subcultured onto agar media.

Work-Up

Examine plates for suspicious organisms and test to determine if they are enteric pathogens.
Use biochemical tests for screening before performing complete identification.

Reporting Results

Report identification and susceptibility panel.
Notify public health officials for Salmonella and Shigella.
Report overgrowth of S. aureus, yeast, or Pseudomonas aeruginosa.
Negative results are reported as no Salmonella, Shigella, Vibrio, E. coli O157:H7, or Campylobacter isolates.

Respiratory Tract

URT infections involve the oral cavity, neck (nose, mouth, throat, epiglottis, larynx), and contains normal flora.
LRT involves the trachea, bronchi, bronchioles, lung alveoli, and is normally sterile below the larynx.
Normal flora in the URT includes staphylococci, streptococci, diphtheroids, neisseria, haemophilus, anaerobes, and spirochetes.
URT infections include thrush, laryngitis, epiglottitis, pharyngitis, tonsillitis, sinusitis, otitis media, and diphtheria.
URT pathogens include respiratory viruses (influenza, parainfluenza, RSV, adenovirus, rhinovirus, coronavirus, coxsackie A, EBV, CMV), S. pyogenes, B-hemolytic strep group C, F, G, and Arcanobacterium haemolyticum, H. influenzae, N. gonorrhoeae, Corynebacterium diphtheriae, Bordetella pertussis and parapertussis, and yeast.
LRT infections include bronchitis, influenzae, pneumonia, empyema, and purulent fluid in pleural space, and Tuberculosis.
LRT pathogens include respiratory viruses (including influenza A and B), S. pneumoniae, H. influenzae, M. catarrhalis, M. pneumoniae, and Chlamydia spp., as well as GNR, S. aureus, Legionella spp., Anaerobes, Mycobacteria, and Fungi.
Community-acquired pneumonia (CAP) agents include S. pneumoniae (most common), Mycoplasma pneumoniae, H. influenzae, M. catarrhalis.
Hospital-acquired pneumonia (HAP) agents include contaminated ventilators, Enterobacteriaceae, K. pneumoniae, S. marcescens, S. aureus, NFGNR, P. aeruginosa, Burkholderia cepacia, CF, nosocomial S. pneumoniae, and anaerobic bacteria.
Miscellaneous agents include Mycobacteria (MTB), Legionella, Chlamydia (C. trachomatis in neonates and C. pneumoniae in young adults).
Emerging viral infections include avian influenza-H5N1, H1N1 influenza A, and SARS coronavirus.
Bioterrorism agents include B. anthracis (anthrax), Y. pestis (plague), Coxiella burnetii (Q fever), and F. tularensis (tularemia).

Specimen Transport and Processing

Sterile screw-cap tubes for specimens.
Bronchial brushes in sterile saline.
Cultures must be performed within 2 hours.
Processing includes gram stain.
Routine cultures for sputum, tracheal aspirates, bronchial washings, brushings, and biopsies use BAP, CHOC, and MAC media, incubated at 35°C with CO2.
Cystic fibrosis patients may require special media.
Anaerobic cultures for lung aspirates (pleural fluid) and open lung biopsies are performed.

Gram Stain Analysis of Sputum

Low power field (LPF) examination of 10x initially to count epithelial and PMN cells.
10, <25 or >25 count indicates specimen quality.
If >25 epithelial cells/LPF, reject the specimen. Under oil immersion, record quantity and type of bacteria.