Characterization of rifampin-resistant Staphylococcus aureus nasal carriage in patients receiving rifampin-containing regimens for tuberculosis

Figures & data

Figure 1 Study algorithm for nasal swab cultures of patients who received rifampin (RIF)-containing regimens against tuberculosis (TB) and their colonization status for methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA).

Abbreviation: FEMH, Far Eastern Memorial Hospital.

Table 1 Demographic data and clinical features of 200 enrolled patients stratified by status of nasal colonization of Staphylococcus aureus at enrollment

Characteristics	No. (%) of patients at enrollment			P-value
	All(n=200)	Without evidence of colonization (n=190)	With evidence of colonization (n=10)
Age (mean ± SD)	53.0± 18.5	53.4± 18.2	45.9±23.1	0.259
Antibiotic usage within previous month^a	92 (46.0%)	89 (46.8%)	3 (30%)	0.347
Concurrent antibiotic usage at entry^b	78 (39.0%)	76 (40%)	2 (20%)	0.321
Sex (male/female)	121/79	114/76	7/3	0.743
Diabetes mellitus	42 (21%)	41 (21.6%)	1 (10%)	0.691
Liver cirrhosis	1 (0.5%)	1 (0.5%)	0 (0%)	1
CRI and ESRD	6 (3.0%)	6 (3.2%)	0 (0%)	1

Notes: ^aTwenty-one patients received first-generation cephalosporins, eight received third-generation cephalosporins, one received carbapenem, one received oxacillin, seven received amoxicillin, 67 received ß-lactam/ß-lactamase inhibitors, 17 received fluoroquinolones, and 13 received macrolides within one month prior to entry.

b At entry, eight patients received first-generation cephalosporins, six received third-generation cephalosporins, two received amoxicillin, 46 received ß-lactam/ß-lactamase inhibitors, 13 received fluoroquinolones, and seven received macrolides.

Abbreviations: CRI, chronic renal insufficiency; ESRD, end-stage renal disease.

Table 2 Susceptibilities of the 23 methicillin-susceptible Staphylococcus aureus isolates to ten antimicrobial agents as determined by the Phoenix automation system and the Etest (for rifampin only)

Agents	MIC (mg/L)			No. (%) of susceptible isolates
	Range	50%	90%
Clindamycin	≤0.5	≤0.5	≤0.5	23 (100)
Tetracycline	≤0.5->8	8	>8	10 (43.5)
Gentamicin	≤2->8	≤2	≤2	21 (91.3)
Erythromycin	≤0.25->4	≤0.25	>4	21 (91.3)
Trimethoprim/sulfamethoxazole	≤0.5/9.5->2/38	≤0.5/9.5	≤0.5/9.5	22 (95.7)
Ciprofloxacin	≤0.5	≤0.5	≤0.5	23 (100)
Vancomycin	≤1	≤1	≤1	23 (100)
Fusidic acid	≤1-4	≤1	≤1	21 (9l.3)^a
Linezolid	≤1-2	2	2	23 (100)
Rifampin	≤0.5->2	≤0.5	>2	l9 (82.6)
Rifampin (by the Etest)	0.004->32	0.006	>32	l9 (82.6)

Notes: ^aMIC interpretive breakpoints are not available in the current version of CLSI.¹⁰ Clinical breakpoint (susceptible, MIC ≤1 mg/L) recommended by the EUCAST was applied.¹¹

Abbreviations: MIC, minimum inhibitory concentration; CLSI, Clinical and Laboratory Standards Institute; EUCAST, European Committee on Antimicrobial Susceptibility Testing.

Table 3 Antimicrobial susceptibilities and molecular typing of seven isolates of methicillin-resistant Staphylococcus aureus (MRSA) recovered from the four patients with nasal colonialization of MRSA

Patient	MICs (mg/L) determined by				MRSA typing			Mutations in rpoB, nucleotide change (amino acid change)^a
	Phoenix system			Etest	ST	spa	SCCmec
	RIF	LZD	FA	RIF
2	≤0.5	2	≤1	0.004	59	t2365	V	None
4	≤0.5	≤1	≤1	0.004	59	t437	V	None
7	>2	≤1	8	>32	45	t026	V	TTA→TCA (L466S), GAC→AAC (D471N),
	>2	2	8	>32	45	t026	V	AAC→AAT (474 silent mutation), GCT→GAT (A477D), GCG→GCT
	>2	2	8	>32	45	t026	V	(498 silent mutation)
	>2	2	8	>32	45	t026	V
13	>2	≤1	≤1	>32	45	t6508	V	TTA→TCA (L466S), GAC→AAC (D471N) AAC→AAT (474 silent mutation), GCT→GAT (A477D), GCG→GCT (498 silent mutation)

Notes: ^aMutation sites of rpoB and the corresponding amino acid changes are identical among the five isolates from Patient 7 and 13. “V” refers to the type of SCCmec strain.

Abbreviations: MICs, minimum inhibitory concentrations; ST, sequence type; FA, fusidic acid, LZD, linezolid, RIF, rifampicin.