viii
Illustrated Case Studies
Quick
Review
Case 1: Man with necrosis of the great toe
This 63-year-old man with a long history of diabetes mellitus
was seen in consultation because of an abrupt deterioration
in his clinical status. He was admitted to the hospital for
treatment of an ulcer, which had been present on his left
great toe for several months. Figure 34.1 shows a typical
example of perforating ulcer in a diabetic man.
Because of the inability of medical therapy (multiple courses
of oral antibiotics) to resolve the ulcer, he underwent ampu-
tation of his left leg below the knee. On the first postopera-
tive day he developed a temperature of 101
o
F, and on the
second postoperative day he became disoriented and his
temperature reached 105.2
o
F. His amputation stump was
mottled with many areas of purplish discoloration, and the
most distal areas were quite obviously necrotic (dead).
Crepitus (the sensation of displacing gas when an area is
pressed with the fingers) was palpable up to his patella. An
X-ray of the left lower extremity showed gas in the soft tis-
sues, extending beyond the knee to the area of the distal
femur. A Gram stain of a swab from the necrotic tissue is
shown in Figure 34.2.
Figure 34.1
Perforating ulcer of the great toe.
Figure 34.2
Gram stain of material swabbed from deep within
a crepitant area. There are numerous polymorpho-
nuclear leukocytes, and many large gram-positive
bacilli, as well as a few gram-negative bacilli and
cocci.
Grampositive
bacillus
Polymorphonuclear
leukocyte
Common characteristics
•
Linear, double-stranded DNA genome
•
Replicate in the nucleus
•
Envelope contains antigenic, species-specific glycoproteins
•
In the tegument between the envelope and capsid are a
number of virus-coded enzymes and transcription factors
essential for initiation of the infectious cycle
•
All herpesviruses can enter a latent state following primary
infection, to be reactivated at a later time
Herpesviridae
Epstein-Barr virus
Herpes simplex virus,Type 1
Herpes simplex virus,Type 2
Human cytomegalovirus
Human herpesvirus,Type 8
Varicella-zoster virus
Staphylococcus
species
Staphylococcus aureus
Staphylococcus epidermidis
Staphylococcus saprophyticus
1Most isolates resistant topenicillinG
2Used inmethicillin-resistant isolates
•
Catalase (+)
•
Nonmotile
•
Donot form spores
•
Round cocci tending tooccur
inbunches likegrapes
•
Facultativeanaerobic
organisms
•
Culturedon enrichedmedia
containingbroth and/or
blood
1
Oxacillin
1
Nafcillin
1
Oxacillin
1
Nafcillin
2
Vancomycin
2
•
Skin and soft
tissue infections
•
Osteomyelitis
•
Septicarthritis
•
Endocarditis
•
Septicemia
•
Necrotizingpneumonia
•
Toxicshocksyndrome
•
Foodpoisoning
(antibiotic therapy not
used)
•
Infectionsof catheters
andheartvalves
•
Cystitis inwomen
Staphylococcus aureus
cultured fromawound
infection
Staphylococcal scalded skin syndrome
Superficial impetigo
Furuncle caused by
Staphylococcus aureus
Folliculitis causedby
Staphylococcus aureus
Carbuncle caused by
Staphylococcus aureus
Staphylococcus
aureus on blood
agar surrounded by
zoneof
β
hemo-
lysis.
Figure 8.12
Summary of staphylococcal disease.
Colonies are yellow
1
Vancomycin
2
Teicoplanin
1
Vancomycin
1
Trimthoprim/
sulfmethoxazole
Quinupristin-
dalfopristin
2
1
Linezolid
1
Daptomycin
Gram (+) cocci
1
2
Indicates first-line drugs; indicates alternative drugs.
Methicillin susceptible
Methicillin resistant
(health-careassociated)
Methicillin resistant
(community-acquired;
mild-moderate infection)
Methicillin resistant
(community-acquired;
severe infection)
1
Doxycycline
Ciprofloxacin
Note:TreatmentofMRSAmayvaryby the typeand
locationof infection.
Staphylococcus saprophyticus
•
S. saprophyticus isa frequent causeof cystitis
inwomen,probably related to itsoccurrence as
part ofnormal vaginal flora. It is alsoan
importantagentof hospital-acquired infections
associatedwith the use of catheters.
•
S. saprophyticus isa coagulase-negative
staphylococcal species. It tends tobe sensitive
tomostantibiotics,evenpenicillinG. It canbe
distinguished frommostother
coagulase-negative staphylococci by itsnatural
resistance tonovobiocin.
0 10
60 70 80 90
50 40 30 20
Approximateprevalence (%)
Common causes of UTI
1
Staphylococcus saprophyticus
Staphylococcus saprophyticus
Escherichia coli
Escherichia coli
Proteus
Proteus
Pseudomonasaeruginosa
Pseudomonas aeruginosa
Klebsiella
Klebsiella
A
Classification of pathogens
B
URINARY TRACT INFECTIONS
Common
complaints
C
Escherichia coli
•
E. coli is themost common causeof urinary tract
infections (UTI), including cystitisand
pyelonephritis.Women are particularly at risk for
infection.Transmission is frequently from the
patient’s flora.
•
Uncomplicated cystitis (themost commonly
encounteredUTI) is caused by uropathogenic
strains ofE. coli, characterized byP fimbriae (an
adherence factor).ComplicatedUTI
(pyelonephritis)oftenoccurs in settingsof
obstructed urinary flow,andmay be causedby
nonuropathogenic strainsofE. coli.UTI require
treatmentwith antibiotics.
Pseudomonas aeruginosa
•
P.aeruginosa isa significantopportunistic
pathogen,andamajor causeofhospital-acquired
(nosocomial) infections suchasUTI,particularly
inpatientswhohavebeen subjected to
catheterization, instrumentation, surgery,or renal
transplantationor topriorantibiotic therapy.
•
P.aeruginosadisease beginswith attachment
and colonizationof host tissue.Pilion the
bacteriamediate adherence, and glycocalyx
capsule reduces the effectiveness of nor al
clearancemechanisms.Host tissue damage
facilitates adherence and colonization.Because
pseudomonas infections typically occur in
patientswith impaired defenses, aggressive
antimicrobial therapy is generally required.
Other enterobacteria
•
OthergeneraofEnterobacteriaceae, uch as
Klebsiella,Enterobacter,Proteus, andSerratia,
which canbe found as normal inhabitants of the
large intestine, includeorganisms that are
primarily opportunisticand often nosocomial
pathogens.Theyall frequently colonize
hospitalized patients,especially in association
withantibiotic treatment, indwelling catheters,
or invasiveprocedures, causing extra-intestinal
infections such as those of the urinary tract.
•
These organisms produce exotoxins.
Wide-spread antibiotic resistance among these
organismsnecessitates sensitivity testing to
determine theappropriate antibiotic treatment.
Disease summary of urinary tract infections.
1
Uncomplicated cystitis.
DYSURIA
LUMBARPAIN
Figure 33.4
(continued on the next page)
CHILLS
108
104
100
98
94
Normal
FEVER
Gram (–) rods
Gram (+)cocci
Double stranded
Enveloped
Summary of common diseases
Summaries of bacteria and their diseases
Unique Clinical Features
