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Introduction of Specimenwsie Common Etiological Agents

The topic’ Specimenwsie Common Etiological Agents’ is a collection of human specimens or samples preferred in suspicious cases of infectious diseases and the probability of microbes responsible for those diseases.  e.g. in the case of urinary tract infection (UTI), the specimen is urine, and microbes responsible for UTI are E. coli, Klebsiella species, Enterococci, Staphylococcus saprophyticus, Candida albicans, etc.

Specimenwsie Common Etiological Agents

The list of common specimens/samples that are tested for isolation and identification of microbes are as follows-

• Urine
• Pus
• Sputum
• CSF
• Body fluid (Pleural, ascitic/peritoneal, synovial, and others)
• Blood Culture
• Stool Culture
• High Vaginal Swab (HVS), Endocervicalswab and Urethral Discharge
• Throat Swab
• Eye Swab
• Aural/ Ear Discharge or swab

Specimenwsie Common Etiological Agents

Urine Common Etiological Agents

Gram-negative

•  E. coli
• Proteus species
• Klebsiella species
• Pseudomonas aerugisosa
• Salmonella Typhi
• Salmonella Paratyphi
• Neisseria gonorrhoeae

Gram-positive

• Enterococci 
•  Haemolytic streptococci
• Staphylococcus saprophyticus 

Pus Common Etiological Agents

Gram-negative

• Escherichia coli
• Pseudomonas aeruginosa
• Proteus species
• Klebsiella species
• Haemophilus influenzae
• Pasteurella species

Gram-positive

• Staphylococcus aureus 
• Enterococci       

   Sputum Common Etiological Agents

• Gram-negative Haemophilus influenzae
• Klebsiella pneumoniae
•  Pseudomonas aeruginosa
• Proteus species
• Yersinia pestis

Gram-positive

• Streptococcus pneumoniae
• Streptococcus pyogenes
• Staphylococcus aureus             

Cerebrospinal fluid (CSF)  Common Etiological Agents

Neonate:  E. coli, S. agalactiae, Listeria monocytoges, Herpes Simplex Virus (HSV)-2

< months: E. coli, S. agalactiae, L. monocytogenes

<10 years: Haemophilus influenzae, Neisseria meningitidis, Streptococcus pneumoniae, viruses

Young adults: N. meningitidis, viruses

Adult: Streptococcus pneumoniae, Neisseria meningitidis

Elderly: Streptococcus pneumoniae, Listeria monocytogenes, Coagulase Negative Staphylococci (CoNS)

AIDS patients: Cryptococcus neoformans

Note: According test ordered, you can also do India ink preparation for Cryptococcus capsule observation. similarly Gram stain, fungal culture and sensitivity, antigens detection, CSF wet mount for protozoan parasites Acanthomeba, Naegleria, and so on.

Body fluid (Pleural, ascitic/peritoneal, synovial, and others) Common Etiological Agents

Gram-negative  

• Haemophilus influenzae     
• Neisseria meningitidis
• Pseudomonas aeruginosa 
• Salmonella species
• Other Gram-negative bacilli

Gram-positive

•   Streptococcus pneumoniae
• Staphylococcus aureus
• Streptococcus pneumoniae  
•  Streptococcus agalactiae                                                          

     Blood Culture Common Etiological Agents

Gram-negative

• Salmonella Typhi
• Salmonella Paratyphi A
• Other Salmonella 
•   E. coli          
• Klebsiella species 
• Pseudomonas aeruginosa 
•  Proteus species
• Shigella species
• Haemophilus influenzae 
• Neisseria meningitidis                         

Gram-positive

• Staphylococcus aureus
•  Streptococcus pneumoniae 
• Streptococcus pyogenes 
•  Varidans streptococci               

                                                                                                                                                                                                 Note: Bacillus and Micrococcus, Coagulase-negative staphylococci, and Acinetobacter species all are skin contaminants.

Staphylococcus: Plenty of Gram-positive cocci singly, pairs, and clusters.

Streptococcus: Gram-positive cocci in chains.

Streptococcus pneumoniae: Elongated Gram-positive diplococci (lancet-shaped).

Haemophilus influenzae: Small negative rods/bacilli, sometimes coccobacilli forms.

Neisseria gonorrheae: Intracellularly gram-negative diplococci from culture while in the specimen (urethral discharge) Gram-negative diplococci intracellular as well as extracellular.

Neisseria meningitides: Gram negative diplococci

Vibrio cholerae: Gram-negative usually curved rods.

Yeast Cells:  Gram-positive oval-shaped.

Stool/Feces Common Etiological Agents

Gram negative

•  Salmonella species
•  Shigella species
• Vibrio cholerae                                                        

High Vaginal Swab (HVS), Endocervicalswab and Urethral Discharge Common Etiological Agents

Gram-negative

• E. coli
• Klebsiella species
• Neisseria gonorrhoeae 
• Other Gram-negative Bacilli                                                                                                   

     Gram-positive

•  Hemolytic streptococci
• Staphylococcus aureus
• Yeast cells                                                           

Throat Swab Common Etiological Agents

Group A streptococci (Streptococcus pyogenes)

Eye Swab Common Etiological Agents

Gram-negative

• Neisseria gonorrhoeae 
•  Haemophilus influenzae        
• Pseudomonas aeruginosa 
• Enterobacteriaceae         

Gram-positive

• Staphylococcus aureus
• Streptococcus pneumoniae
• Streptococcus agalactiae
• Streptococcus pyogenes                         
• Other hemolytic streptococci

Aural/Ear Discharge swab Common Etiological Agents

Gram- negative          

•   Pseudomonas aeruginosa     
• Haemophilus influenzae
• Proteus species
• E. coli  and other coliforms

Gram-positive

• Staphylococcus aureus
• Streptococcus pyogenes
• Streptococcus pneumoniae 
• Other  B- hemolytic streptococci               

Specimenwsie Common Etiological Agents

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