Analysis of β-lactamase phenotypes and carriage of selected β-lactamase genes among Escherichia coli strains obtained from Kenyan patients during an 18-year period

Table 1 β-lactamase phenotypes encountered among the 912 strains analyzed

Antibiotics to which isolates were resistant
Penicillins, 1st & 2nd generation cephalosporins	3rd Generation cephalosporins & Monobactams	4th Generation cephalosporins	inhibitors	Cephamycins	Most probable Phenotype^a	Total (%)n = 912
AMP, KF, AMX	−	−	−	−	NSBL	103 (11)
AMP, AMX, KF OXA	−	−	−	−	NSBL	175 (19)
AMP, AMX, KF OXA	−	−	AMC, AMS	−	IRT	65 (7)
AMP, KF, AMX,	−	−	AMC, AMS	−	IRT	8 (1)
AMP, AMX, KF, CXM	CTX^b, AZT^b	−	−	−	ESBL	105 (12)
AMP, AMX , KF, CXM	CTX, CAZ^*, AZT	−	−	−	ESBL	75 (8)
AMP, AMX, OXA KF, CXM	CTX^b, CAZ^b, AZT	FEP	AMS	−	ESBL	67 (7)
AMP, AMX, OXA KF, CXM	CTX, CAZ^*, AZT	FEP	AMC, AMS	−	CMT	40 (4)
AMP, AMX, OXA, KF, CXM	CTX, CAZ, AZT	FEP	AMC, AMS, TZP	−	CMT	180 (20)
AMP, AMX, OXA KF, CXM	CTX, CAZ, AZT	FEP	AMC, AMS, TZP	FOX	pAmpC	94 (10)

Resistance phenotypes of the 912 isolates investigated.
a: β-lactamase phenotypes observed in different isolates were defined as follow:- Narrow spectrum β-lactamases (NSBLs) were resistant to penicillins but were susceptible to other classes of β-lactam antibiotics. Isolates exhibiting the inhibitor resistant TEM phenotype (IRT) were those capable of degrading penicillins, were not inhibited by β-lactamase inhibitors but were susceptible to other classes of β-lactam antibiotics. The ESBL-producers were resistant to penicillins, 2^nd and most 3^rd generation cephalosporins, and exhibited intermediate resistance to 4^th generation cephalosporins and were fully susceptible to cephamycins, carbapenems and β-lactamase inhibitors. The complex mutant TEMs (CMTs) were resistant to most β-lactams and β-lactamase inhibitors including TZP but were susceptible to cephamycins and carbapenems. Isolates with the pAmpC phenotypes were resistant to all generations of β-lactam antibiotics, were susceptible to carbapenems and were either susceptible or exhibited intermediate resistance to 4^th generation cephalosporins.
^b: appearance of zones of synergy between a given cephalosporin or monobactam and amoxicillin-clavulanic acid (AMC).
(−) isolate with a given phenotype were susceptible to a given set of antibiotics.

ISSN: 1471-2180