Occurrence of extended-spectrum and AmpC β-lactamases in multiple drug resistant Salmonella isolates from clinical samples in Lagos, Nigeria

Figures & data

Table 1 ESBL, AmpC production and AmpC fox gene detection and coexistence of two enzymes among the Salmonella isolates

Salmonella spp. (number screened)	Cefoxitin resistance test, +ve (%)	ESBL, +ve (%)	Plasmid-mediated AmpC β-lactamase production (%)	AmpC fox gene (%)	ESBL + AmpC (%)	ESBL + AmpC fox gene (%)
Salmonella typhi (13)	12 (92.3)	6 (46.2)	4 (30.8)	7 (53.8)	2 (15.4)	2 (15.4)
Salmonella typhimurium (10)	8 (80.0)	3 (30.0)	2 (20.0)	4 (40.0)	0 (0.0)	0 (0.0)
Salmonella enteritidis (8)	8 (100)	4 (50.0)	3 (37.5)	3 (37.5)	1 (12.5)	1 (12.5)
Salmonella paratyphi (4)	2 (50.0)	1 (25.0)	1 (25.0)	0 (0.0)	0 (0.0)	0 (0.0)
Salmonella choleraesuis (5)	2 (40.0)	2 (40.0)	0 (0.0)	2 (40.0)	0 (0.0)	0 ().0)
Total (40)	32 (80.0)	16 (40.0)	10 (25.0)	16 (40.0)	3 (7.5)	3 (7.5)

Abbreviation: ESBL, extended-spectrum β-lactamase.

Figure 1 Distribution of Salmonella isolates in the clinical samples studied.

Figure 2 Extended-spectrum β-lactamase production by Salmonella enteritidis and Salmonella typhi in plates (A) and (B), respectively.

Figure 3 Detection of 380 bp AmpC fox gene by PCR among the Salmonella isolates.

Notes: Lane M = 100 bp ladder; lanes 1–3 = Salmonella typhimurium; lanes 4–7 = Salmonella typhi; lanes 8 and 9 = Salmonella enteritidis; lane 10 = Salmonella choleraesuis; lane 11 = Salmonella paratyphi.

Abbreviation: PCR, polymerase chain reaction.

Table 2 Comparison of AmpC-producing and nonproducing Salmonella enterica serovars in relation to antibiotic resistance

Antibiotics	AmpC-producing and nonproducing Salmonella enterica serovars for antibiotic resistance
	fox AmpC (+ve, n=16, %)	fox AmpC (−ve, n=24, %)	χ^2	P-value
AMP	16 (100)	22 (91.7)	0.19	>0.05
COT	16 (100)	21 (87.5)	0.74	>0.05
NIT	9 (56.3)	2 (8.3)	8.7	<0.01
GEN	13 (81.3)	20 (83.3)	0.06	>0.05
NAL	16 (100)	13 (54.2)	7.9	<0.05
OFL	0 (0)	0 (0)	ND	ND
AUG	16 (100)	16 (66.7)	4.8	<0.05
TET	16 (0)	24 (100)	ND	ND
IMP	2 (12.5)	0 (0)	1.07	>0.05

Notes: Data are number (%) with disparity in % antibiotic resistance between fox AmpC (+ve) and fox AmpC (−ve) analyzed by chi-square (χ²) or Fischer’s exact test. P<0.05 was considered to be significant.

Abbreviations: AMP, ampicillin; AUG, augmentin; COT, cotrimoxazole; GEN, gentamicin; IMP, imipenem; NAL, nalidixic acid; ND, not determined; NIT, nitrofurantoin; OFL, ofloxacin; TET, tetracycline.

Table 3 MIC of antibiotics against fox AmpC and ESBL-producing isolates

Antibiotics	AmpC	AmpC + ESBL	AmpC	AmpC + ESBL	P-value	AmpC	AmpC + ESBL	AmpC	AmpC + ESBL	P-value
	Salmonella choleraesuis		Salmonella enteritidis			Salmonella typhimurium		Salmonella typhi
LAEV	0.19 (0.12–0.25)	ND	0.19 (0.12–0.5)	0.2 (0.12–0.25)	>0.05	0.47 (0.12–1.0)	ND	0.77 (0.12–2.0)	1.07 (0.5–2.0)	>0.05
IMP	0.18 (0.25–0.5)	ND	0.42 (0.25–0.5)	0.42 (0.25–0.5)	>0.05	0.56 (0.25–1.0)	ND	0.71 (0.25–2.0)	1.07 (0.5–2.0)	>0.05
COT	8.5 (4–16)	ND	8 (4–16)	13.3 (8–16)	>0.05	10 (4–16)	ND	9.7 (4–16)	11.4 (4–16)	>0.05
GEN	1.5 (1–2)	ND	2.3 (1–4)	3.3 (2–4)	>0.05	2.75 (1–4)	ND	3 (1–4)	3.4 (1–4)	>0.05
CAZ	6 (4–8)	ND	5.3 (4–8)	13.3 (8–16)	<0.05	4.5 (2–8)	ND	7.1 (2–16)	19.4 (8–32)	<0.05

Notes: MIC, mean (range), μg/mL. Difference in mean MIC values between AmpC + ESBL versus AmpC alone was analyzed by Student’s t-test. P<0.05 was considered to be significant.

Abbreviations: CAZ, ceftazidime; COT, cotrimoxazole; ESBL, extended-spectrum β-lactamase; GEN, gentamicin; IMP, imipenem; LAEV, levofloxacin; MIC, minimum inhibitory concentration; ND, not determined.