Clinical Microbiology Laboratory
Durham, North Carolina 27710
SUMMARY OF
ANTIMICROBIAL SUSCEPTIBILITY
TEST RESULTS
1999
HOURS OF
OPERATION:
24 hours per day 365 days per year.
TELEPHONE:
684-2089
A certified medical technologist is
on duty at all times.
CONSULTATIONS:
Page 970-8885
A physician (Medical Microbiology
Fellow or Resident) is on call at all times
with faculty backup.
TEACHING:
Teaching Rounds (Clinical correlations)
Monday-Friday 1:15-1:45 PM
2/2000
These data were obtained by broth microdilution or disk diffusion methods according to National Committee for Clinical Laboratory Standards (NCCLS)
guidelines. Data are based on microorganisms from both inpatients and outpatients. No attempt was made to differentiate nosocomial isolates.
TABLE 1. Percent Susceptiblea, Gram-positive Cocci
(MIC breakpoint, g per ml)
Beta-lactams
Other Antimicrobials
________________________
________________________________
Microorganism (No. tested)
AMP
NAF
CFZ
CLI
ERY
VAN
T/S
(8)
(2)
(8)
(0.5)
(0.5)
(4)
(2/38)
________________________________________________________________________________________________________________________
Enterococcusb (1084)
82
NT
NT
NT
NT
79
NT
Staphylococcus aureus (2017)
NT
49
49
54
37
100
77
Staphylococcus, coagulasenegative (341)
NT
26c
26
NT
NT
100
47
________________________________________________________________________________________________________________________
a Susceptible implies that an infection due to the microorganism may be appropriately treated with the dosage of antimicrobial agent recommended for
that type of infection and infecting species, unless otherwise contraindicated.
b For Enterococcus the designation "susceptible" implies the need for combined therapy (ampicillin or vancomycin plus an aminoglycoside) in
endocarditis or other serious invasive infections to achieve bactericidal action and an improved therapeutic response.
c Susceptible MIC breakpoint is <0.25 µg/ml for coagulase-negative Staphylococcus.
MIC (minimum inhibitory concentration) is the lowest concentration of a drug which will inhibit growth of a microorganism in vitro. For the drug to be
effective in vivo, a higher concentration than the MIC of the drug (at least 2 to 4 times higher) should be achieved at the site of infection. MIC
breakpoints are based on achievable serum levels in adults with normal renal function.
________________________________________________________________________________________________________________________
NT = Not tested.
$ = Relative daily acquisition cost for recommended doses of parenteral therapy.
AMK (amikacin) - $/$$)
AMP (ampicillin - $)
AMP/SUL (ampicillin/sulbactam - $$$$$)
CAZ (ceftazidime - $$$)
CFZ (cefazolin - $)
CIP (ciprofloxacin) (oral - $; IV - $$$$)
CLI (clindamycin - $)
CRO (ceftriaxone - $$$)
CTX (cefotaxime - $$$)
ERY (erythromycin - $)
GEN (gentamicin - $)
IMP (imipenem - $$$$$$)
NAF (nafcillin - $)
PEN (penicillin - $)
PIP (piperacillin - $$$$$)
TOB (tobramycin - $)
T/S (trimethoprim/sulfamethoxazole - $)
VAN (vancomycin - $$)
________________________________________________________________________________________________________________________
TABLE 2. Percent Susceptible, Gram-negative Bacilli
(MIC breakpoint, g per ml)
Other
Beta-lactams
Aminoglycosides
Antimicrobials
__________________________________________
___________________
______________
AMP/
Microorganism (No. tested)
AMP
SUL
CFZ
CAZ CROb IMP
PIP
GEN AMK TOB
CIP
T/S
(8)
(8/4)
(8)
(8)
(8)
(4)
(16)
(4)
(16) (4)
(1)
(2/38)
_______________________________________________________________________________________________________________________
Acinetobacter baumannii (71)
NT
NT
0
90
74
100
83
85
93
89
88
84
0
98
98
100
100
100
93
100
100
100
100
98
13
58
7
61
62
100
55
95
100
95
91
80
Enterobacter aerogenes (146)
0
0
0
76
77
99
74
97
98
97
90
94
Enterobacter cloacae (246)
0
0
0
67
65
100
64
95
100
96
93
89
Escherichia coli (2593)
59
73
91
99
99
100
63
97
100
98
97
82
Klebsiella oxytoca (76)
0
76
55
89
91
100
85
89
94
91
95
89
Klebsiella pneumoniae (764)
0
75
86
89
90
100
72
89
97
89
87
77
Morganella morganii (46)
0
0
0
84
95
97
82
92
97
92
93
91
Proteus mirabilis (306)
91
96
94
99
100
98
95
95
99
97
88
91
Pseudomonas aeruginosa (1105)
NT
NT
NT
80a
NT
79
82c
67
75
85
66
11
0
0
0
96
99
100
95
99
99
92
91
92
NT
NT
0
39
0
0
0
0
0
0
31
94
Citrobacter koserii (diversus) (56)
Citrobacter freundii (98)
Serratia marcescens (142)
Stenotrophomonas maltophilia (123)
_______________________________________________________________________________________________________________________
Numbers in boldface indicate >10% decrease in susceptibility from 1998 to 1999
a For P. aeruginosa, ceftazidime (CAZ) usually predicts susceptibility to aztreonam.
b For Enterobacteriaceae, ceftriaxone (CRO) usually predicts susceptibility to cefotaxime.
c For P. aeruginosa, susceptible MIC breakpoint for piperacillin (with or without tazobactam) is < 64 µg/ml which requires high doses.
TABLE 3. Percent Susceptible, Anaerobic Gram-negative Bacillia
MIC
Antimicrobial
Breakpoint
B. fragilis groupb
(cost per day)
(µg per ml)
(No. tested = 106)
_________________________________________________________________
Ampicillin/sulbactam ($$$$$)
8/4
86
Cefoxitin ($$$)
16
67
Clindamycin ($)
2
75
Imipenem (Meropenem) ($$$$$$)
4
100
Metronidazole ($ - $$)
4
100
Piperacillin/tazobactam ($$$$$)
32/4
100
__________________________________________________________________
a
B. melaninogenica group, Fusobacterium spp., and gram-positive anaerobic cocci and
bacilli are usually susceptible to -lactam antibiotics, clindamycin, and metronidazole.
b Includes B. fragilis, B. thetaiotaomicron, B. ovatus, B. distasonis, B. vulgatus,
B. uniformis, and B. caccae.
TABLE 4. Fastidious Microorganisms
1. Haemophilus influenzae (No. tested = 142). All isolates except one were non-type b.
89 (63%) were ß-lactamase negative and predictably susceptible to ampicillin
(amoxicillin); 53 (37%) were ß -lactamase positive and, therefore, resistant to
ampicillin (amoxicillin). H. influenzae is predictably susceptible to cefotaxime and
ceftriaxone and usually to cefuroxime.
2. Streptococcus pneumoniae. Rx NOTE: Breakpoints for pneumococci are based on
concentrations of penicillin and ceftriaxone (or cefotaxime) required to treat
meningitis. Infections in other sites usually respond to these drugs of choice for
pneumococcal infections despite in-vitro resistance based on meningitis breakpoints.
Consult Infectious Diseases if questions about individual patients.
(No. tested)
Penicillin
(121)
Ceftriaxone or
cefotaxime
(121)
Erythromycin (93)
MIC Breakpoint (µg/ml)
% Susceptible
% Intermediate
16 (0.1-1)
45 (<0.06)
24 (1)
64 (<0.5)
46
(<0.25)
----
% Resistant
39 (>2)
12 (>2)
----
TABLE 5. Yeast: Percent Susceptible
(No. tested)
Amphotericin B*
(MIC Breakpoint = <1 g/ml)
Fluconazole
(MIC Breakpoint = <8 g/ml)
Candida albicans
100 (35)
78 (51)
C. tropicalis
100 (14)
78 (41)
C. parapsilosis
100 (19)
91 (34)
C. krusei
l
m
C. glabrata
100 (14)
15 (20)

C. lusitaniae
l
Cryptococcus neoformans
l
88 (16)
l = usually susceptible  = often resistant m = inherently resistant
Testing is useful in serious or persistent infections due to organisms with unpredictable
susceptibility profiles, especially when standard regimens fail or are contraindicated.
* NCCLS M27-A (1997) Reference Method for Broth Dilution Antifungal Susceptibility Testing
of Yeasts (tentative breakpoint)