Overview Of Escherichia Coli Biology Essay


Escherichia coli is a important nosocomial and community acquired pathogen  and one of the commensals of the human intestinal tract[1]. Pathogenic strains of Escherichia coli have long been recognized as agents of foodborne diarrhea [2]. It is not always appreciated that E. coli is an important cause of extraintestinal diseases-diseases that occur in bodily sites outside the gastrointestinal tract [3]. These include the urinary tract, central nervous system, circulatory system, and respiratory system [4]. The ability of E. coli to cause extra intestinal infections depends largely on several virulence factors, which help in the survival of E. coli under adverse conditions present in those sites. E.coli strains that induce extraintestinal diseases are termed extraintestinal pathogenic E. coli (ExPEC) [5]. In terms of morbidity and mortality, ExPEC has a great impact on public health, with an economic cost of several billion dollars annually[4].

Pathogenic isolates of E.coli have relatively high potentials for developing resistance[6]. Therefore, the treatment of E. coli infections is increasingly becoming difficult.Extended spectrum β -lactamase (ESBL) producing organisms pose a major problem for clinical therapeutics [7]. The knowledge of drug resistance pattern in a geographical area and the formulation of an appropriate hospital antibiotic policy will go a long way in the control of these infections. Therefore, it is necessary to know the antibiotic susceptibility pattern of pathogenic E. coli to select the correct antibiotic(s) for proper treatment of infections caused by it [8].The objectives of the present study were to demonstrate the spectrum of infections caused by ExPEC and the its drug resistance pattern.

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A total of 379 isolates of E. coli from extraintestinal infections obtained from January 2009 to December 2010 were included in the study. The study population included hospitalised patients of all age groups in a tertiary care referral hospital attached to a medical college. Due permission has been obtained from the institutional head to conduct this study. Specimens received by the Department of Microbiology were pus, exudates, clean catch midstream urine, sputum and blood from patients suffering from wound infections, intra-abdominal infections, urinary tract infections, respiratory infections and blood stream infections. The samples were processed immediately and identified using standard techniques[9].

Antibiotic susceptibility was tested with the Kirby-Bauer disc diffusion method, according to the CLSI guidelines [10]. The antibiotic disks (Hi Media, Mumbai) used were ampicillin (10 μg), amikacin (30 μg), co-trimoxazole (25 μg), cefotaxime (30 μg), ciprofloxacin (5 μg), gentamicin (30 μg), netlimicin (30 μg) and imipenam(10µg). After 18 hours of incubation at 37 °C, the inner diameter of the zone of inhibition was measured using a millimetre scale around each antimicrobial disk on the undersurface of the plate. The zone size around each antimicrobial disk was interpreted as sensitive, intermediate or resistant according to CLSI guidelines 2009[10].


Of the 7864 samples received by our department, 2428(30.9%) were from suspected UTI, 1858(23.6%) were from respiratory tract infections, 2473(31.4%) were from skin and soft tissue infections/ear infections/intra-abdominal infections and 1105(14.0%) were from blood stream infections.

Out of 2428 urine samples received 943(38.8%) were culture positive for E.coli and 538(29.0%) out of 1858 sputum samples, 1534(62.0%) out of 2473 pus/exudates and 166(15.0%) out of 1105 blood samples were culture positive for E.coli respectively.

Of the 943 culture positive urine samples 253(26.8%) were due to E.coli, so also 23(4.3%) out of 538 culture positive sputum samples, 101(6.5%) out of 1534 culture positive pus/exudate samples out of which 65(4.2%) were from skin/soft tissue infections, 26(1.7%) were from ear infection and 10(0.7%) were from intra-abdominal infections. 2(1.2%) out of 166 blood samples were positive for E.coli.

The analysis of drug resistance pattern shows that among 379 isolates of E.coli maximum number i.e 357(94.2%) were resistant to ampicillin and the resistance was lowest in carbapenams 0(0%) followed by netilmicin 59(15.6%)

Among the isolates from urine maximum resistance was observed for ampicillin 238(94.1%) followed by cotrimaxazole 171(67.6%), Gentamicin 120 (47.4%), cefotaxime 81(32.0%), Amikacin 60(23.7%), Ciprofloxacin 48(19%) and Netillin 30(11.8%) as shown in Table.3

In isolates from pus and exudates maximum resistance was observed for Ampicillin 97(96.0%) followed by cotrimaxazole 84(83.2 %), Ciprofloxacin 69(68.3%), Gentamicin 68(67.3%), Amikacin 45(44.6%), Cefotaxime 44(43.6%), and Netilmicin 23(22.8%), as shown in Table.4

Among sputum isolates maximum resistance was observed for Ampicillin 22(95.6%), followed by Cotrimoxazole 16(69.5%), Ciprofloxacin 15(65.2 %), Gentamicin 12(52.2%), Amikacin 9(39.1%), Cefotaxime 7(30.4%), and Netilmicin 6(26.1%), as shown in Table.5

E.coli isolated from blood were sensitive to all the antibiotics.

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None of the E.coli isolated from the various samples were resistant to carbapenams.


E. coli has widely been implicated in various clinical infections as hospital acquired and community infections as reported by Shah et al[11]. Extraintestinal pathogenic Escherichia coli (ExPEC) possesses virulence traits that allow it to invade, colonize, and induce disease in bodily sites outside of the gastrointestinal tract[2] by overcoming the host defence mechanisms. The virulence of individual strains in a given infection is determined by the presence and actual expression of the virulence genes present in them, and also by the environmental conditions in the host [3]. E. coli is therefore able to cause a variety of infections such as urinary tract infection(UTI), soft tissue infections, bacteraemia, respiratory tract infections etc as seen in our study with UTI being the predominant infection. This is similar to a study done by Olowe et al[12].

Drug resistance is on the rise among E. coli strains that cause human infections. Studies in other developing countries have shown that the trend in enteric pathogens is toward increasing antibiotic resistance[13].

In our study, antibiotic susceptibility pattern was studied for all isolates of E. coli. Resistance was observed to commonly used antibiotics such as ampicillin, ciprofloxacin, co-trimoxazole, cefotaxime, gentamicin, amikacin and netillin. The greater prevalence of resistance to common antibiotics has also been reported by other workers[14,15]. The presence of multidrug resistance may be related to the dissemination of antibiotic resistance among hospital isolates of E. coli. Such multi drug resistance has serious implications for the empiric therapy of infections caused by E. coli and for the possible co-selection of antimicrobial resistance mediated by multi drug resistance plasmids[16]. Among aminoglycosides, netilmicin was found to have an edge over gentamicin and amikacin. Similar observations have been made by a previous group of workers[14]. Maximum number of isolates (76.9%) were resistant to ampicillin and the lowest (42.8%) to netillin. These results are consistent with the previous studies on drug resistance in E. coli[17,18].

On the specific subject of uropathogens, a number of alarming papers concerning rising resistance rates have been published[19,20,21]and a recent case-control study by Hillier et al[22] provides evidence that exposure to antibiotics is a strong risk factor for a resistant E. coli UTI.Our study is similar in having high degree of resistance to Ampicillin, Cotrimoxazole and Gentamicin.

Though carbapenam resistance has been reported from other studies [23], we have not encountered any such resistance among E.coli in our centre. Hence, judicious use of this group of antibiotics still holds a ray of hope for patients infected with multi-drug organisms.

Therefore, the correct detection of drug resistant E.coli is important. Judicious use of antibiotics and good antibiotic policy are needed to limit the emergence and spread of antibiotic resistance in bacteria. When selecting empirical therapy, in vitro susceptibility patterns must be considered along with other factors, such as expected efficacy, adverse effects, cost, cost-effectiveness, and selection of resistant strains [24].


The continued development of antimicrobial resistance among E.coli isolates is disturbing and requires both further surveillance and new approaches to slow the emergence of resistance. Trends seen with E. coli may also occur with other pathogenic organisms. Proper selection of antibiotics for treatment depends on the results of antibiotic sensitivity test. Since antimicrobial resistant patterns are constantly evolving, and it is a present global public health problem, there is the necessity for constant antimicrobial sensitivity surveillance. This will help clinicians provide safe and effective empiric therapies.