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.

backgroundAlthough β-lactam antibiotics are heavily used in many developing countries, the diversity of β-lactamase genes (bla) is poorly understood. We screened for major β-lactamase phenotypes and diversity of bla genes among 912 E. coli strains isolated from clinical samples obtained between 1992 and 2010 from hospitalized and non-hospitalized patients.

resultsNone of the isolates was resistant to carbapenems but 30% of all isolates were susceptible to cefepime, cephamycins and piperacillin-tazobactam. Narrow spectrum β-lactamase (NSBL) phenotype was observed in 278 (30%) isolates that contained bla(TEM-1) (54%) or bla(SHV-1) (35%) or both (11%). Extended Spectrum β-lactamase (ESBL) phenotype was detected in 247 (27%) isolates which carried blaCTX-M-14 (29%), bla(CTX-M-15) (24%), bla(CTX-M-9) (2%), bla(CTX-M-8) (4%), bla(CTX-M-3) (11%), bla(CTX-M-1) (6%), blaSHV-5 (3%), bla(SHV-12) (5%), and bla(TEM-52) (16%). Complex Mutant TEM-like (CMT) phenotype was detected in 220 (24%) isolates which carried bla(TEM-125) (29%), while bla(TEM-50), bla(TEM-78), bla(TEM-109), bla(TEM -152) and bla(TEM-158) were detected in lower frequencies of between 7% and 11%. Majority of isolates producing a combination of CTX-M-15 + OXA-1 + TEM-1 exhibited resistance phenotypes barely indistinguishable from those of CMT-producers. Although 73 (8%) isolates exhibited Inhibitor Resistant TEM-like (IRT) phenotype, bla(TEM-103) was the only true IRT-encoding gene identified in 18 (25%) of strains with this phenotype while the rest produced a combination of TEM-1 + OXA-1. The pAmpCs-like phenotype was observed in 94 (10%) isolates of which 77 (82%) carried bla(CMY-2) while 18% contained blaCMY-1.Isolates from urine accounted for 53%, 53%, 74% and 72% of strains exhibiting complex phenotypes such as IRT, ESBL, CMT or pAmpC respectively. On the contrary, 55% isolates from stool exhibited the relatively more susceptible NSBL-like phenotype. All the phenotypes, and majority of the bla genes, were detected both in isolates from hospitalized and non-hospitalized patients but complex phenotypes were particularly common among strains obtained between 2000 and 2010 from urine of hospitalized patients.

conclusionsThe phenotypes and diversity of bla genes in E. coli strains implicated in clinical infections in non-hospitalized and hospitalized patients in Kenya is worryingly high. In order to preserve the efficacy of β-lactam antibiotics, culture and susceptibility data should guide therapy and surveillance studies for β-lactamase-producers in developing countries should be launched.