Study design
The study was a descriptive analytical survey of bacterial isolates from infected chronic wounds at the surgical ward of MRRH from August 2020 to October 2020.
Study setting.
Participants were enrolled from the surgical ward of MRRH between August 2020 and October 2020. MRRH is a public health facility with a bed Capacity of 300 beds and it is a Regional Referral Hospital in Western Uganda located in Mbarara Municipality, approximately 250 km from Kampala, the capital City of Uganda. Its catchment population is approximately 10 million people. This Hospital also serves as a Teaching Hospital for MUST. According to the patient discharge register, the average number of patients admitted with a diagnosis of various infected wounds is 35 patients per month with an annual prevalence of 420 patients. The surgical ward is currently run by 10 nurses, 25 residents, 4 general surgeons, 1 plastic surgeon, 1 orthopedic surgeon, 1 pharmacy technician,1 Hospital Pharmacist and 1 neurosurgeon. The surgical ward is subdivided into the male and female sections with a total bed capacity of 55.
The microbiological procedures were carried out in the Microbiology Laboratory of MUST, Mbarara City, Uganda. The Microbiology Laboratory is managed by three highly experienced staff that is 2 Laboratory technologists and 1 senior laboratory technologist. The Laboratory is well equipped with the necessary equipment and materials including equipment such as electronic microscopes, florescent microscopes, biosafety cabins, incubators, autoclaves, analytical profile index analyzer and polymerase chain reaction (PCR) machine. Therefore, the Laboratory is able to offer a range of laboratory tests such as gram staining, microscopy, culture and sensitivity tests, Liver function tests and serological tests such as typhoid test, Brucella agglutination test and Human immunodeficiency test (HIV) serology).
In addition, this Microbiology Laboratory follows stringent Laboratory quality assurance measures from the Central public health Laboratory of Uganda that have been designed based on the recommendations of Clinical Laboratory standard Institute.
Study population:
The study population was patients with infected chronic wounds admitted at the Surgical Ward of MRRH in Uganda.
Selection criteria:
All inpatients admitted in the surgical ward with signs and symptoms of infected chronic wounds (increasing pain at the ulcer site, erythema, edema, heat, purulent exudate, serous exudate, delayed ulcer healing, discolored granulation tissue, friable granulation tissue, wound base pocketing, foul odor and wound breakdown) and consented to participate in the study were included in this study while patients without record of medication history and those who expressed voluntary withdrawal were excluded.
Sample size:
The following assumptions were made during sample size calculation;
- Research data was collected for 3 months and the expected population of patients with infected wounds was 105 patients in 3 months (approximately 35 patients per month). This assumption was based on a review of primary data from the patient discharge register in the surgical ward which had 420 patients with a diagnosis of various infected wounds in one year (2018).
- The prevalence of infected chronic wounds was estimated to be 22% (7).
No= Z2*P (1-P)/E2
No= Sample size.
Z= Confidence level.
P= Estimated proportion of infected chronic wounds in the population.
E= Desired level of precision.
Z = 1.96, P = 0.22(22%), E = 0.05
No = 1.962*0.22(1-0.22)/0.052, =3.842*0.22*0.78/0.0025.
=264 Patients.
Finite population correction (8): This was required because the expected average population of patients in three months of data collection was 105 patients based on the above record in the surgical ward.
n = No/ (No-1)/N+1,
n= Adjusted Sample size.
N = Population size (105 patients).
n = 264/ (264-1)/105+1, n = 264/3.5 = 75 patients.
Sampling Technique
Convenience sampling technique was used to select the study subjects who met the criteria for infected chronic wounds (9).
Study procedures:
For diagnosis of infected chronic wounds, a checklist containing symptoms and signs of chronic infected wounds was used by the Clinician to guide the clinical diagnosis of chronic infected wounds.
Sample Collection and Bacterial identification:
Two nurses working in the surgical ward were trained by an experienced laboratory technologist to empower them with skills of obtaining wound swabs for culture and sensitivity.
After obtaining an informed consent from the patients meeting the criteria, routine clinical samples were aseptically collected by a trained nurse from the patients’ wound base using sterile cotton swabs. The standard operating procedure developed by British Columbia Provincial Nursing Skin & Wound Committee were used to ensure an aseptic procedure (10).The samples were transported to the Microbiology Laboratory of MUST within 30 minutes. Only one swab was obtained from each patient after cleaning the wound base with sterile normal saline.
Laboratory procedures
- Primary cultures: On receipt, swab specimens were registered in the laboratory research register.
- Depending on the nature of samples, each specimen was inoculated on chocolate, blood, mannitol salt sugar, xylose lysine decarboxylated agar, and MacConkey Agar as follows; and incubated at
- Using inoculating loop, each sample was streaked onto the upper one fourth portion of an agar plate with parallel overlapping strokes. The plates were labeled.
- The loop was flamed and allowed to cool. The plate was turned at right angle. Overlapped the previous streak once or twice and repeated the streaking process on one-half of the remaining area.
- Procedure 4 was repeated.
- The plates were incubated overnight at 350C-370C in the incubator.
- After incubation for 16-20 hours, the plates were checked for bacterial growth.
- Representative bacterial colonies were selected based on the difference in shape, size and color. Selected colonies from each plate were sub-cultured and incubated overnight.
- Bacterial identification: This was performed based on morphological, cultural characteristics such as hemolysis on blood agar, swarming (positive for proteus spp), changes in physical appearance on differential agar (pink appearance of lactose-fermenting bacterial colonies on macConkey agar), motility test was positive for enterobacter agglomerans and providencia spp. In addition, the following biochemical tests were performed to confirm the identity of bacterial pathogens;
Table 1: Biochemical tests for Identification of bacterial pathogens.
Isolate
|
Biochemical test
|
Results
|
Staphylococcus aureus
|
Catalase
|
Positive
|
Coagulase
|
Positive
|
Mannitol fermentation
|
Positive
|
Dnase
|
Positive
|
Klebsiella spp
|
Citrate
|
Positive
|
Urea
|
Positive
|
Indole
|
Negative
|
Proteus spp
|
Hydrogen sulphide
|
Positive
|
Urea
|
Positive
|
Citrate
|
Positive
|
Oxidation
|
Positive
|
Enterobacter agglomerans
|
Hydrogen sulphide
|
Negative
|
Urea
|
Negative
|
Indole
|
Negative
|
Providential spp
|
Indole, methyl red, citrate, nitrate reductase and catalase
|
postive
|
Antibacterial susceptibility Testing:
The minimum inhibitory concentrations and antibacterial susceptibility testing were performed using broth microdilution technique as described by CLSI and the review in the general principle and practices of antimicrobial susceptibility testing (11). The Procedure for Broth microdilution involved the following steps;
- Preparation of stock solutions: Stock solutions were prepared based on the manufacturer’s instruction for reconstitution. All the 5 antibiotic brands did not have potency information and the weight for antibiotics were calculated based on the highest plasma concentrations derived from the following pharmacokinetic studies because of the correlation that exist between MIC and pharmacokinetic parameters (12).
Table 2: Weight of powder for stock solutions.
S/no.
|
Antibiotic.
|
Maximum plasma concentration (desired concentration).
|
Reference.
|
Weight of powder(g)
(desired concentration) X volume of diluent(1000ml) divide by 1000000
|
1
|
Ceftriaxone 1g (Epicephin®)
|
168µg/ml
|
(13).
|
0.168g
|
2
|
Cefoperazone+ Sulbactam 2g (Sulcef®)
|
159µg/ml
|
(Rosenfeld et al., 1983).
|
0.159g
|
3
|
Cefotaxime 1g (Omnatax®)
|
41.1µg/ml
|
(14).
|
0.0411g
|
4
|
Cefpodoxime 200mg (Ximeprox®)
|
2.7µg/ml
|
(15)
|
0.0027g
|
5
|
Cefixime 400mg (gramocef-o 400®).
|
2.47µg/ml
|
(16)
|
0.00247g
|
The antibiotic solutions were kept in the refrigerator at a temperature of 40 C.
- Using a pipette, 100µl of sterile brain heart infusion were dispensed into the wells of microtitre plates, each row labeled to corresponding antibiotic.
- 100µl of the antibiotic stock solution were also dispensed into the well in column 1. Using the pipette set at 100µl, mix the antibiotics into the wells in column 1 by sucking up and down 6 times.
- 100µl of this were withdrawn from column1 and added to column 2, making column 2 a two-fold dilution of column 1.
- 100µl of column 2 were transferred to column 3. This was repeated down to column 9.
- 5µl of isolates suspended in sterile water and adjusted to McFarland turbidity (104x105CFU/ml) were dispensed into the wells except wells in column 11 for sterility control. Wells in column 10 were used for growth control and contained 100µl of brain heart infusion and 5µl of isolates.
- Microtitre plates were then covered with sterile aluminum foil to prevent evaporation during incubation.
- After 24 hour incubation at 370C, the microtitre plates were observed using a reading mirror for visible bacterial growth as indicated by turbidity. The smallest concentrations of antibiotics that inhibited growth were recorded as the MIC.
Quality control:
To ensure consistent and high quality research outputs, the researcher implemented quality control measures throughout the entire research process. Antibiotics for the third generation cephalosporins, culture media and staining reagents were procured from premises licensed by the National Drug Authority of Uganda to avoid the risk of counterfeit products which could affect the quality of research results. In- addition, the procured antibiotics, culture media and staining reagents were strictly stored at conditions specified by the manufacturers to avoid product deterioration during the research process.
Data processing and Analysis Plan:
The study data was entered into Microsoft Excel and exported to STATA version 15.0 for statistical analysis. Frequencies, and mean (SD; standard deviation) were computed to summarize the data.
- Objective 1: The prevalence of pathogens was first summarized as proportions and to determine the existence of any association between age group, gender of study participants and prevalence of specific pathogens, a Chi-Square/Fisher’s Exact test was computed. Results were presented in a bar graph and table.
- Objective 2: The MIC values were summarized as mean± SD and analyzed using one-way ANOVA (Analysis of Variance) to determine if there were significant differences between the mean MICs for the isolates with respect to the different groups of antibiotics studied and the final results were presented in a table. The level of significance was preset at 5% and p-values less than 0.05 were considered statistically significant in each of the above statistical tests.