A Few Bacteria to Know: Difference between revisions

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When identifying a bacterium, the first step is Gram stain, which can tell us whether it has a Gram-positive or Gram-negative cell wall, and can give us information about the size and shape (bacilli or cocci, usually). Everyone needs to know how to interpret a Gram-stain report, since it is still one of the first pieces of information we get about a bacterial infection.
When identifying a bacterium, the first step is Gram stain, which can tell us whether it has a Gram-positive or Gram-negative cell wall, and can give us information about the size and shape (bacilli or cocci, usually). Everyone needs to know how to interpret a Gram-stain report, since it is still one of the first pieces of information we get about a bacterial infection.


== Gram-positive Bacteria ==
==Gram-positive Bacteria==
=== Cocci ===
===Cocci===
==== Clusters or Groups ====
====Clusters or Groups====
{| class="wikitable"
{| class="wikitable"
! Species
!Species
! Clinical Syndromes
!Clinical Syndromes
|-
|-
| ''Staphylococcus aureus''
|''Staphylococcus aureus''
| Purulent skin and soft tissue infections, abscesses, endocarditis, HAP/VAP, food poisoning
|Purulent skin and soft tissue infections, abscesses, endocarditis, HAP/VAP, food poisoning
|-
|-
| Coagulase-negative Staphylococci
|Coagulase-negative Staphylococci
| Line infections, UTIs (''S. saprophyticus'')
|Line infections, UTIs (''S. saprophyticus'')
|}
|}


==== Pairs or Chains ====
====Pairs or Chains====
{| class="wikitable"
{| class="wikitable"
! Species
!Species
! Clinical Syndromes
!Clinical Syndromes
|-
|-
| ''Streptococcus pyogenes''/GAS
|''Streptococcus pyogenes''/Group A ''Streptococcus''
|Cellulitis, necrotizing fasciitis, toxic shock syndrome
| Cellulitis
|-
|-
| Other Lancefield-group Streptococci
|Other Lancefield-group streptococci
| Cellulitis, UTIs, endocarditis
|Cellulitis, UTIs, endocarditis
|-
|-
| ''Streptococcus pneumoniae''
|''Streptococcus pneumoniae''
| Pneumonia, meningitis
|Pneumonia, meningitis
|-
|-
| ''Enterococcus'' spp.
|''Enterococcus'' species
| UTIs, line infections, endocarditis
|UTIs, line infections, endocarditis
|}
|}


=== Bacilli ===
===Bacilli===
{| class="wikitable"
{| class="wikitable"
! Species
!Species
! Clinical Syndromes
!Clinical Syndromes
|-
|-
| ''Clostridium difficile/tetani/botulinum/perfringens''
|''Clostridium difficile/tetani/botulinum/perfringens''
| Diarrhea/tetanus/botulism/nec. fasc.
|Diarrhea/tetanus/botulism/nec. fasc.
|-
|-
| ''Bacillus cereus''
|''Bacillus cereus''
| Food poisoning
|Food poisoning; often contaminant
|-
|-
| Other ''Bacillus'' species
|Other ''Bacillus'' species
|Often contaminant
| Contaminant
|-
|-
| ''Listeria monocytogenes''
|''Listeria monocytogenes''
| Meningitis
|Meningitis
|}
|}


== Gram-negative Bacteria ==
==Gram-negative Bacteria==
=== Bacilli ===
===Bacilli===
==== Enterobacteraceae (Poop!) ====
====Enterobacterales (Poop!)====
{| class="wikitable"
{| class="wikitable"
! Species
!Species
! Clinical Syndromes
!Clinical Syndromes
|-
|-
| ''Yersinia''/''Shigella''/''Salmonella''/''E.coli'' O157:H7/''Campylobacter''
|''Yersinia''/''Shigella''/''Salmonella''/''E.coli'' O157:H7/''Campylobacter''
| Infectious diarrhea/dysentery
|Infectious diarrhea/dysentery
|-
|-
| ''Escherichia coli''
|''Escherichia coli''
| Intraabdominal infections, UTIs, HAP/VAP
|Intraabdominal infections, UTIs, HAP/VAP
|-
|-
| ''Klebsiella'' spp.
|''Klebsiella'' spp.
| Intraabdominal infections, UTIs, HAP/VAP
|Intraabdominal infections, UTIs, HAP/VAP
|-
|-
| ''Proteus'' spp.
|''Proteus'' spp.
| Intraabdominal infections, UTIs, HAP/VAP
|Intraabdominal infections, UTIs, HAP/VAP
|-
|-
| SPICE bugs
|SPICE bugs
| Very resistant, generally use carbapenems empirically
|Very resistant, generally use carbapenems empirically
|}
|}


==== Others ====
====Others====
{| class="wikitable"
{| class="wikitable"
! Species
!Species
! Clinical Syndromes
!Clinical Syndromes
|-
|-
| ''Pseudomonas aeruginosa''
|''Pseudomonas aeruginosa''
| Otitis externa, hot-tub folliculitis, UTIs, pneumonias... very resistant to antibiotics
|Otitis externa, hot-tub folliculitis, UTIs, pneumonias... very resistant to antibiotics
|}
|}


=== Cocci ===
===Cocci===
{| class="wikitable"
{| class="wikitable"
! Species
!Species
! Clinical Syndromes
!Clinical Syndromes
|-
|-
| ''Neisseria meningitidis''
|''Neisseria meningitidis''
| Meningitis
|Meningitis
|-
|-
| ''Neisseria gonorrhoeae''
|''Neisseria gonorrhoeae''
| Urethritis, PID, disemminated gonococcal infection
|Urethritis, PID, disemminated gonococcal infection
|}
|}


== Miscellaneous Bacteria ==
==Miscellaneous Bacteria==
{| class="wikitable"
{| class="wikitable"
! Feature
!Feature
! Species
!Species
! Clinical Syndromes
!Clinical Syndromes
|-
|-
| Acid-fast bacilli
|Acid-fast bacilli
| ''Mycobacterium tuberculosis''
|''Mycobacterium tuberculosis''
| Pulmonary tuberculosis, extrapulmonary tuberculosis
|Pulmonary tuberculosis, extrapulmonary tuberculosis
|-
|-
| rowspan="2" |Spirochetes
| Spirochete
| ''Treponema pallidum''
|''Treponema pallidum''
| Syphilis (primary, secondary, tertiary)
|Syphilis (primary, secondary, tertiary)
|-
|-
⚫
|''Borrelia burgdorferi''
| Spirochete
⚫
|Lyme disease
⚫
| ''Borrelia burgdorferi''
⚫
| Lyme disease
|-
|-
| Intracellular
| rowspan="2" |Intracellular bacteria
| ''Chlamydia trachomatis''
|''Chlamydia trachomatis''
| Urethritis, PID
|Urethritis, PID
|-
|-
⚫
|''Chlamydia pneumophila''
| Intracellular
⚫
|Atypical pneumonia
⚫
| ''Chlamydia pneumophila''
⚫
| Atypical pneumonia
|-
|-
| No cell wall
|Bacteria without a cell wall
| ''Mycoplasma pneumoniae''
|''Mycoplasma pneumoniae''
| Atypical pneumonia
|Atypical pneumonia
|}
|}


Latest revision as of 13:51, 9 March 2021

When identifying a bacterium, the first step is Gram stain, which can tell us whether it has a Gram-positive or Gram-negative cell wall, and can give us information about the size and shape (bacilli or cocci, usually). Everyone needs to know how to interpret a Gram-stain report, since it is still one of the first pieces of information we get about a bacterial infection.

Gram-positive Bacteria

Cocci

Clusters or Groups

Species Clinical Syndromes
Staphylococcus aureus Purulent skin and soft tissue infections, abscesses, endocarditis, HAP/VAP, food poisoning
Coagulase-negative Staphylococci Line infections, UTIs (S. saprophyticus)

Pairs or Chains

Species Clinical Syndromes
Streptococcus pyogenes/Group A Streptococcus Cellulitis, necrotizing fasciitis, toxic shock syndrome
Other Lancefield-group streptococci Cellulitis, UTIs, endocarditis
Streptococcus pneumoniae Pneumonia, meningitis
Enterococcus species UTIs, line infections, endocarditis

Bacilli

Species Clinical Syndromes
Clostridium difficile/tetani/botulinum/perfringens Diarrhea/tetanus/botulism/nec. fasc.
Bacillus cereus Food poisoning; often contaminant
Other Bacillus species Often contaminant
Listeria monocytogenes Meningitis

Gram-negative Bacteria

Bacilli

Enterobacterales (Poop!)

Species Clinical Syndromes
Yersinia/Shigella/Salmonella/E.coli O157:H7/Campylobacter Infectious diarrhea/dysentery
Escherichia coli Intraabdominal infections, UTIs, HAP/VAP
Klebsiella spp. Intraabdominal infections, UTIs, HAP/VAP
Proteus spp. Intraabdominal infections, UTIs, HAP/VAP
SPICE bugs Very resistant, generally use carbapenems empirically

Others

Species Clinical Syndromes
Pseudomonas aeruginosa Otitis externa, hot-tub folliculitis, UTIs, pneumonias... very resistant to antibiotics

Cocci

Species Clinical Syndromes
Neisseria meningitidis Meningitis
Neisseria gonorrhoeae Urethritis, PID, disemminated gonococcal infection

Miscellaneous Bacteria

Feature Species Clinical Syndromes
Acid-fast bacilli Mycobacterium tuberculosis Pulmonary tuberculosis, extrapulmonary tuberculosis
Spirochetes Treponema pallidum Syphilis (primary, secondary, tertiary)
Borrelia burgdorferi Lyme disease
Intracellular bacteria Chlamydia trachomatis Urethritis, PID
Chlamydia pneumophila Atypical pneumonia
Bacteria without a cell wall Mycoplasma pneumoniae Atypical pneumonia
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