Table 2. Results of MALDI-TOF and extended-spectrum β-lactamase NDP testing of 245 blood cultures positive for gram-negative bacilli and definitive identification and antibiotic resistance phenotype obtained with cultured bacteria* .

30 min				24–48 h
MALDI-TOF identification	No.	ESBL NDP test		Definitive identification	β-Lactam resistance phenotype a
Enterobacteriaceae
Escherichia coli	38	–		E. coli	Wild-type
	47	–		E. coli	Penicillinase
	1	–		E. coli	IRT
	1	–		E. coli	Low-level cephalosporinase
	1	–		E. coli	Overexpressed cephalosporinase
	30	+		E. coli	ESBL
Proteus mirabilis	3	–		P. mirabilis	Penicillinase
Salmonella spp.	1	–		Salmonella Typhimurium	Wild-type
	1	–		Salmonella Enteritidis	Wild-type
	1	–		Salmonella Paratyphi A	Wild-type
	1	–		Salmonella Typhi	Wild-type
	1	–		Salmonella Kentucky	Penicillinase
Klebsiella pneumoniae	23	–		K. pneumoniae	Wild-type
	1	–		K. pneumoniae	Acquired cephalosporinase
	13	+		K. pneumoniae	ESBL
K. oxytoca	5	–		K. oxytoca	Wild-type
Citrobacter koseri	2	–		C. koseri	Wild-type
Enterobacter cloacae	12	–		E. cloacae	Wild-type
	5	–		E. cloacae	Overexpressed cephalosporinase
	3	+		E. cloacae	ESBL
Enterobacter aerogenes	5	–		E. aerogenes	Wild-type
Citrobacter braaki	1	–		C. braaki	Wild-type
C. freundii	1	+		C. freundii	ESBL
Morganella morganii	4	–		M. morganii	Wild-type
Providencia rettgeri	2	–		P. rettgeri	Wild-type
Proteus vulgaris	1	–		P. vulgaris	Wild-type
Serratia marcescens	4	–		S. marcescens	Wild-type
None	1	–		E. coli + Proteus mirabilis	Penicillinase + Penicillinase
	2	–		K. pneumoniae + S. marcescens	Wild-type + Penicillinase
Nonfermenting bacilli
Pseudomonas aeruginosa	24	–		Pseudomonas aeruginosa	Ceftazidime S
Acinetobacter baumannii	2	–		A. baumannii	Ceftazidime S
A. junii	1	–		A. junii	Ceftazidime S
Stenotrophomonas maltophilia	2	–		Stenotrophomonas maltophilia	Ceftazidime S
Roseomonas gilardii	1	–		Roseomonas gilardii	Ceftazidime S
Sphingobacterium multivorum	1	–		Sphingobacterium multivorum	Ceftazidime S
Anaerobic gram-negative bacilli
Bacteroides fragilis	1	–		B. fragilis	Wild-type
	1	–		B. fragilis	Cefotaxime R
B. vulgatus	1	–		B. vulgatus	Cefotaxime R
*MALDI-TOF, matrix-assisted laser desorption/ionization time-of-flight; NDP, Nordmann/Dortet/Poirel test; ESBL, extended spectrum β-lactamase; –, negative test result; IRT, inhibitor-resistant TEM β-lactamase; +, positive test result.