Sixty patients were recruited in the study. Thirty-five (58.33%) were males. Total number of isolates was 62. The most prevalent isolates were E. coli 15/62(24.2%) followed by Pseudomonas aeruginosa 14/62(22.6%) Proteus spp 12/62(19.4%) and then Staphylococcus spp 9/62(14.52%). Other isolates occurred in small numbers such as Acinetobactor spp 1/62(1.61%), Citrobacter spp 1/62(1.61%), Klebsiella pneumonia 4/62(6.45%), Streptococcus spp 4/62(6.45%), Morganella morgani 1/62(1.61%) and non-fermenting gram negative bacilli 1/62(1.61%) whose prevalence was collectively 12/62(19.3%). Our results are similar to a study in India where the most common gram-positive cocci in order of frequency were Staphylococcus aureus (17%), Streptococcus spp, (6%) and Enterococci spp., (5.0%). Escherichia coli (20%) was the predominant isolate followed by Pseudomonas spp., (18%), Klebsiella spp., (10%), Proteus spp., (6.0%) and Acinetobacter spp., (3%) in gram negative bacilli. However, the Indian study had Coagulase Negative Staphylococcus (CONS) prevalence of 12% which is double our prevalence. This discrepancy may be due to the fact that the Indian study had 148 isolates which is more than twice the number of our isolates . The source of infection, use of antibiotic drug for treatment, sample collection method, and different types of infection can influence pathogen diversity in DFI .
From 60 patients with infected DFU in this study, a single bacterial isolate was isolated from 47(78.33%) patients, 6(10.00%) had two isolates, 1(1.67%) had three isolates and 6(13.04%) had no bacterial growth. Although we did not perform regression analyses on the association between multiple isolates and treatment outcome due to low numbers, our data indicates adverse outcome with multiple isolates. For instance, of all patients with multiple isolates 4/7 (57.14 %) ended up with some form of major limb amputation. This poor prognosis may be explained by the fact that diabetes is an immune suppressive disease and multiple bacterial infection indicates poor glycemic control. We observed a similar finding in Egypt where a study showed predominance of single bacterial isolate in 52% of the cultures, 40% with mixed infections and 8% with sterile growth. . However, a Nigerian study showed a different observation where there was a predominance of multiple bacterial infections of approximately 71.2%, which is higher than our findings. There are, however, situations where single and multiple isolates occur in the same proportions. This was the case in India where the proportion of multiple isolates was 48/108(44.4%), single isolates was 48/108(44.4%), and no growth in 12/108(11.1%).
Majority of the bacterial isolates were gram negative and were multi-resistant. Of the 49/62(79.3%) gram negative isolates, 8(16.33%) were monoresistant, 30(61.22%) were multi-resistant, and 11(22.45%) were susceptible. Of the multi-resistant isolates, Escherichia coli 12/15(80.00%), and Pseudomonas aeruginosa 7/14(50.00%) were predominant. Of the 13/62(20.97%) Gram positive isolates, 2(15.38%) were monoresistant, 3(23.08%) were multi resistant, and 8/13(61.54%) were susceptible. Studies have identified factors responsible for multi-resistance to be frequent hospitalization, recent use of broad‑spectrum antibiotics, inadequate surgical source reduction, chronic wounds, irrational use of antibiotics, and the transfer of resistance genes by transport means. A high level of multi drug resistance could be due to the fact that in a tertiary care hospital there is a widespread usage of broadspectrum antibiotics leading to selective survival advantage of pathogens, a phenomenon called antibiotic selection pressure.
In this study, more than a half of the isolates 17/25 (68%) were resistant to ceftriaxone. This is unarguably a high resistance level to a third-generation cephalosporin class of antibiotics. Ceftriaxone has been, over time, excessively and inappropriately prescribed in hospital settings in Tanzanian hospitals. It is the non-chalant use of this important class of antibiotics that has resulted to such a high level of bacterial resistance against ceftriaxone. Our data have shown, however, that the next higher level of antibiotic use, carbapenems, are still very useful where the bacterial resistance against carbapenems were very low. Imipenem resistance was 1/21(4.76%) and meropenem 1/15(6.67%). Carbapenem use in Tanzania is still low currently. However, with such increasing trend of ceftriaxone resistance, carbapenem use is likely to occur. In the face of lack of new molecules from pharmaceutical companies in the last three decades, we risk reverting to a pre-antibiotic era after running out of therapeutic options[4, 29]. To reverse this trend, we need to practice a judicial use of antibiotics by promoting hospital antimicrobial stewardship programs[30–32]. Hospital antimicrobial stewardship programs cannot be over emphasized to mitigate escalation of antimicrobial resistance. A similar observation was done in Mwanza, Tanzania where isolates showed high resistance to commonly used antibiotics (such as ampicillin, augmentin, cotrimoxazole, tetracycline, penicillin, gentamicin, erythromycin, oxacillin) except for meropenem and imipenem, which were both 100% sensitive. The low resistance to carbapenems is similarly observed in India where sensitivity to imipenem, meropenem were high; imipenem (89%) and meropenem (84%). An important decision is not to switch to carbapenems but make a judicial use of antimicrobials, through antimicrobial stewardship programs, to mitigate escalation of antimicrobial resistance.
With special reference to Pseudomonas aeruginosa, in this study, 14/62(22.58%) were isolated and of the tested isolates 7/14(50.00%) were multi-resistant to the tested antibiotics and 2/14(14.29%) were monoresistant. As high as 11/14(78.57%) of patients from whom Pseudomonas aeruginosa were isolated ended up having a major limb amputation. Two Indian studies show that pseudomonal control requires “reserve” antibiotics that are not routinely available in hospital settings in Tanzania as essential drug list. One study showed that 15 (83.3%) Pseudomonas aeruginosa strains were susceptible to cefotaxime with a resistance rate of (16.6%) . Another showed that Pseudomonas culture isolates were sensitive to amikacin (90%), imipenem (72%), meropenem (70%), and piperacillin‑tazobactam combination (74%).
With regard to some form of major limb amputation or surgical removal of body parts, Pseudomonas aeruginosa had the highest number of isolates 11/14(78.57%) followed by Escherichia coli 7/15(46.67%). A major problem in Pseudomonas aeruginosa infection may be that this pathogen exhibits a high degree of resistance to a broad spectrum of antibiotics because of its ability (intrinsic) to produce β-lactamases, efflux pumps, outer membrane modification, and biofilm lifestyle thus making it a dangerous and dreaded pathogen. Most infections with Pseudomonas spp occur in compromised hosts. The high rate of amputations among patients from whom Pseudomonas aeruginosa was isolated might be due to its ability to cause severe tissue damage in diabetics, its inherent resistance mechanism, referred to as intrinsic resistance and its multiplicity in resistance mechanisms. Our data indicate how difficult it is to treat a diabetic patient with an ulcer infected by Pseudomonas. Being nosocomially acquired, hospital infection prevention and control (IPC) is a mandatory component of mitigation of antimicrobial resistance. This study commands some strengths in showing an adequate description of the microbiological isolates with reference to treatment outcome. It describes a clinical picture of the different spectrum of bacterial infection complications in relation to the type of organism isolated from a diabetic foot ulcer.