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Egyptian Journal of Medical Microbiology Volume 24 / No. 3 / July 2015 95-102
ORIGINAL ARTICLE
Diabetic foot Infection: Microbiological Causes with Special
Reference to their Antibiotic Resistance Pattern
1
Reham Dwedar*, 2Dalia Kadry Ismail and 3Amr Abdulbaky
Lecturer of Medical Microbiology& Immunology Faculty of Medicine, Cairo University
Lecturer of Clinical and Chemical pathology Department, Faculty of Medicine, Cairo University
3
Associate Professor in General and Vascular Surgery Faculty of Medicine, Cairo University
1
2
ABSTRACT
Key words:
Diabetic foot infections,
Polymicrobial, ESB,
Carbapenemases
Producers, MRSA, MDR
Background: Foot infections are one of the major complications of diabetes mellitus and
are a significant risk factor for lower extremity amputation. Providing effective
antimicrobial therapy is an important component in treating these infections. Objectives:
This study investigates the microbial causes of diabetic foot infections and their
antibiotic susceptibility pattern. Methodology: A prospective study of 80 patients with
diabetic foot infections admitted to Cairo university hospitals was undertaken. Samples
were collected by using sterile swabs and they were processed. Detailed antimicrobial
susceptibility testing was performed according to CLSI guidelines 2014, including
testing for Methicillin Resistant Staphylococcus aureus (MRSA), ESBL and
carbapenemase production. Results: In the present study, a single organism was isolated
from 48.75% patients and mixed bacterial growths were seen in 51.15% patients. Gramnegative bacteria (56.08%), were more commonly isolated compared with Gram-positive
bacteria (27.7%), while gram-negative anaerobes accounted for (8.1%),and Candida
species (8.1%). The commonest isolate was Proteus mirabilis (16.8%) followed by
Escherichia coli (13.5%), Methicillin Sensitive Staphyloccus aureus (MSSA) (11.4%),
Pseudomonas spp (10.8%), and MRSA (10.1%). Among the gram-negative bacteria 49%
were ESBL producers and 3.6%were carbapenemases producerswhile46.8%
Staphylococcus aureus were methicillin resistant Staphylococcus aureus. Overall 42.5%
isolates were identified as MDR. Vancomycin was found to be the most effective against
Gram-positive bacteria, whereas imipenem, amikacin and colistin were most effective
against Gram-negative bacteria. Conclusion: This study showed a preponderance of
gram negative bacilli among the isolates from the diabetic foot ulcers. Knowledge on the
antibiotic sensitivity pattern of the isolates will be helpful in determining the drugs for
the empirical treatment of diabetic ulcers
INTRODUCTION
Diabetic foot is one of the most feared
complications of diabetes and is the leading cause of
hospitalisation in diabetic patients1,2. Diabetic patients
have a lifetime risk as high as 25% for developing foot
ulceration 3. Diabetic ulcers have 15 to 46 times higher
risk of limb amputation than foot ulcers due to other
causes 4. Every year more than a million diabetic
patients require limbamputation1. The impaired microvascular circulation in patients with diabetic foot limits
the access of phagocytes favouring development of
infection2,5.
* Corresponding Author:
Reham Ali Dwedar
Lecturer of Medical Microbiology& Immunology,
Faculty of medicine, Cairo University
E-mail: [email protected], Tel: 01222744624
Egyptian Journal of Medical Microbiology
Diabetic foot infections are oftenpolymicrobial.4,5
Escherichia coli, Proteus spp., Pseudomonas spp.,
Staphylococcus aureus and Enterococcus spp. are the
most frequent pathogens contributing to progressive and
widespread tissue destruction2,5.
The increasing association of multi-drug resistant
(MDR) pathogens with diabetic foot ulcers further
compounds the challenge faced by the physician or the
surgeon in treating diabetic ulcers without resorting to
amputation6. Infection with MDR pathogens is also
responsible for the increased duration of hospitalization
and cost of management.
AIM OF THE WORK
The present study was carried out to determine the
relative frequency of different microbial isolates
cultured from community-acquired diabetic foot
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Dwedar et al. / Diabetic foot Infection: Microbiological Causes with Special Reference, Volume 24 / No. 3 / July 2015 95-102
infections and to determine their in-vitro susceptibility
to the commonly used antibiotics.
METHODOLOGY
The current study is an observational prospective
study that was carried out at the Department of General
Surgery, Kasr Alainy Hospitals, Cairo University.
80 diabetic patients with foot ulcers were included
in this study, which was conducted from July 2014 to
December 2014.The demographics of the participants
with regards to age, sex, the duration of diabetes,
complications of diabetes, the type of treatment which
was received and the presence of other systemic
illnesses were recorded. The patients were also assessed
clinically and the ulcers were graded according to
Wagner’s grade7.
Wagner’s Classification of Diabetic Foot Ulcers
Grade 0: no ulcer in a high-risk foot.
 Grade 1: superficial ulcer involving the full skin
thickness but not underlying tissues.
 Grade 2: deep ulcer, penetrating down to ligaments
and muscles, but no bone involvement or abscess
formation.
 Grade 3: deep ulcer with cellulitis or abscess
formation often with osteomyelitis.
 Grade 4: localized gangrene.
 Grade 5: extensive gangrene involving the whole
foot.
Sample collection.
The samples were collected after obtaining
informed consents from the patients. Samples were
collected from the deeper portion of the ulcers by
asterileswab, which was dipped in sterile glucose broth.
The samples were collected by making a firm, rotatory
movement with the swabs. A direct Gram stained smear
of the specimen was examined. The specimens were
incubated aerobically on blood agar, Chocolate agar and
MacConkey’s agar and anaerobically on blood agar for
isolation of aerobic and anaerobic bacteria at 37oC, the
plates were examined for growth the next day for
facultative anaerobic bacteria and after 4-5 days for
anaerobic bacteria. Further processing was done
according to the nature of the isolate, as was determined
by Gram staining and the colony morphology and,
necessary biochemical tests were performed. Gram
negative organisms were identified using oxidase test,
citrate utilization, urea hydrolysis, triple sugar iron
(TSI), lysin decarboxylation, indole production and
API 20 E identification panel for Enterobacteriaceae
were performed for species level identification.
Staphylococcus spp. was identified on the basis of
positive catalase test, coagulase enzyme and growth on
mannitol salt agar. Streptococcus spp. was identified by
negative catalase test and esculin hydrolysis. Yeasts
were identified by Gram's staining and germ tube test
(GTT) 8 .
96
Antibiotic Susceptibility testing:
The antibiotic susceptibility testing was done by the
Kirby Bauer disc diffusion method, as per the CLSI
guidelines, 20149. The antimicrobial discs which were
used were those of Ampicillin (20μg), Aztreonam
(30μg), Gentamicin (10μg), Amikacin (30μg), Cefaclor
(30μg), Cefazolin (30μg), Cefoxitin (30μg), Cefotaxime
(30μg) Cefepime (30μg), AUG=Amoxicillin-Clavulenic
acid30 (20+10 μg), Piperacillin/tazobactam (100+10μg),
Imipenem (10μg), Meropenem (10 μg), Ciprofloxacin,
(5μg), Levofloxacin (5μg), Sulph-trimethoprim (1.25 +
23.75 μg) and Colistin (10μg) for the Gram negative
bacilli.
Ampicillin (20μg),AUG= Amoxicillin-Clavulenic
acid 30 (20+10 μg), Cefoxitin (30μg), Cefotaxime
(30μg), Imipenem (10μg) Clindamycin (2μg),
Erythromycin (15μg), Vancomycin (30μg), Gentamicin
(10μg), Amikacin (30μg), Ciprofloxacin (5μg),
Levofloxacin
(5μg),
Sulph-trimethoprim
(1.25+23.75μg), Fusidic (10 μg), and Rifampin (5μg),
were used to study the susceptibility patterns of the
Gram positive cocci.
MRSA, ESBL and carbapenemase production were
detected as per the CLSI guidelines 20149.
MRSA detection:
The phenotypic test for the detection of MRSA was
done by using a cefoxitin (30 μg) disc. A zone of
inhibition which was equal to or more than 22 mm was
considered as susceptible to Cefoxitin and the organism
was reported as Methicillin Sensitive Staphylococcus
aureus. Those isolates which produced a zone of
inhibition which was less than or equal to 21 mm were
considered as Methicillin Resistant Staphylococcus
aureus (MRSA).
ESBL production was confirmed by using discs of
Ceftazidime (30 μg) and Ceftazidime Clavulanic acid
(30/10μg) respectively. The test organism was
inoculated as a lawn on a Muellar Hinton agar plate and
the above mentioned discs were placed on the plate. The
plates were incubated at 370C overnight and they were
examined next day. An increase in the zone diameter,
which was equal to or more than 5 mm for the
antimicrobial agent which was tested in combination
with clavulanic acid, in comparison to the antimicrobial
which was tested alone, indicated that the strain was an
ESBL producer.
Carbapenemase production was detected by
using the Modified Hodge test. A 0.5 Mac Farland’s
suspension of ATCC Escherichia coli 25922, was
diluted 1 in 10 in sterile saline. This was inoculated on a
Muellar Hinton agar plate, as for the routine disc
diffusion testing. The plate was dried for 5 minutes and
a disc of Meropenem 10 μg was placed in the centre of
the agar plate. [3-5] colonies of the test organism were
picked and inoculated in a straight line, from the edge of
the disc, upto a distance of at least 20mm. The plates
were incubated at 370C overnight and they were
Egyptian Journal of Medical Microbiology
Dwedar et al. / Diabetic foot Infection: Microbiological Causes with Special Reference, Volume 24 / No. 3 / July 2015 95-102
examined next day. They were checked for an enhanced
growth around the test organism, at the intersection of
the streak and for a zone of inhibition. The presence of
an enhanced growth indicated Carbapenemase
production, and the absence of an enhanced growth
meant that the test isolate did not produce
carbapenemase.
RESULTS
A total of 80 diabetic patients, 48males (57%) and
32 females (43%), aged between 35 to 75 years and
duration of diabetes from 5 to 32 years were
investigated. The maximum number of patients (33%)
was in the age group of 60 to 65 years. The next most
prevalent age group was between 50 and 55 years
(27%). Out of 80 test samples, 36 Diabetic foot ulcer
cases were included in Wagner’s grade 1,40 were
included in Wagner’s grade 2, and 4 were included in
Wagner’s grade3.
Out of 80 lesions only 3 proved sterile, in the
remaining 77 patients a total of 148bacteria were
isolated resulting in an average of 1.92organisms per
lesion.
In this study, gram negative bacilli were isolated
more frequently than gram positive cocci with gramnegative aerobes accounting for 83 (56.08%), aerobic
gram-positive
cocci
41(27.7%),
gram-negative
anaerobes 12 (8.1%) and Candida species 12 (8.1%).
The commonest isolate was Proteus mirabilis(16.8%)
followed by Escherichia coli(13.5%), Methicillin
Sensitive Staphyloccus aureus (MSSA) (11.4%),
Pseudomonas spp (10.8%), and Methicillin Resistant
Staphylococcus aureus (MRSA) (10.1%).The other
organisms which were isolated were Proteus vulgaris,
Klebsiella oxytoca Streptococcus pyogenes, Klebsiella
pneumoniae, Enterococcus spp, Acinetobacter spp,
Citrobacter spp, CoNS and Enterobacter, gram-negative
aerobes and Candida species.
In the present study, single organisms were isolated
from 39(48.75%)patients and polymicrobial infections
were seen in 41 (51.15%) patients. The details of the
organisms which were isolated from the infected foot
lesions have been tabulated in [Table1]. Gram-positive
organisms were found as the only isolate in 14 (17.5%)
patients, while 25 (31.25 %) patients had only gramnegative organisms.
Table 1: Monomicrobial and Polymicrobial isolates from the diabetic foot infections
No. of isolates
No. of isolates
Bacteria
(Mono microbial)
(Poly microbial)
39
109
Proteus mirabilis
6
19
Escherichia coli
5
15
MSSA
5
12
Pseudomonas spp
7
9
MRSA
7
8
12
Fungi
anaerobic gram-negative bacilli
12
Enterococcus spp
2
4
Proteus vulgaris
2
4
Klebsiella oxytoca
1
5
Klebsiella pneumonia
4
Acinetobacter spp
2
1
Streptococcus pyogenes
2
Citrobacter spp
2
CoNS
1
Enterobacter spp
1
Total No. of
isolates (%)
148
25 (16.89%)
20(13.5%)
17(11.48%)
16(10.8%)
15(10.1%)
12(8.1%)
12(8.1%)
6(4%)
6(4%)
6(4%)
4(2.7%)
3(2%)
2(1.35%)
2(1.35%)
1(0.67%)
1(0.67%)
The antibiotic susceptibility patterns of the isolates have been tabulated in [Table2] which displays the antibiotic
resistance patterns of the gram negative bacilli and [Table 3] displays the antibiotic resistance patterns of the gram
positive cocci.
Egyptian Journal of Medical Microbiology
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Dwedar et al. / Diabetic foot Infection: Microbiological Causes with Special Reference, Volume 24 / No. 3 / July 2015 95-102
Table 2: Antibiotic Resistance pattern of the Gram negative bacilli. (% of resistance)
Antimicrobial category
Antimicrobial
agent
Proteus
(n=31)
E.coli
(n=20)
Pencillins
AMP
100
Combined penicillins
AUG
TZP
CFZ
CEC
CTX
CPM
Non-extended spectrum
cephalosporins; 1st and
2nd generation
cephalosporins
Extended-spectrum
cephalosporins; 3rd and 4th
generation cephalosporins
Cephamycins
Monobactams
Carbapenem
Klebsiella
spp.
(n =10)
100
Acinetobacter
spp
(n=3)
…..
Citrobacter
spp
(n=2)
100
Enterobacter
(n=1)
100
Pseudomonas
aeruginosa
(n=16)
…….
6.5
13
100
77
25
25
100
65
25
100
75
100
30
100
60
66.6
33.3
100
100
50
0
100
50
0
0
100
100
58
48
60
50
68.7
68.7
50
50
66.6
66.6
50
0
100
100
100
FOX
32
10
31
20
33.3
50
0
ATM
58
60
75
60
66.6
50
100
IPM
0
0
6.25
10
33.3
0
0
MEM
0
0
33.3
Aminoglycosides
AK
12
10
21
20
0
0
0
GN
64.5
40
37.5
30
66.6
0
0
Quinolones
CIP
12
40
37.5
30
66.6
50
100
LEV
14
20
31
20
33.3
0
0
SulphTrimetoprims
SXT
80
40
…….
60
100
100
100
Polymyxins
CST
100
0
0
0
0
0
0
AMP= Ampicillin ,AUG= Amoxicillin-Clavulenic acid ,TZP=Piperacillin+Taobactam , CFZ=Cefazolin,, CEC=Cefaclor, CTX = Cefotaxime,
CPM= Cefepime , FOX=Cefoxitin, ATM=Aztreonam IPM=Imipenem ,MEM= Meropenem ,AK= Amikacin ,GN= Gentamicin ,CIP=
Ciprofloxacin ,LEV= Levofloxacin , ,SXT= Sulphameth-Trimeth ,TM= Trimethoprim, CST=Colistin
Table 3: Antibiotic Resistance pattern of the Gram positive cocci. (% of resistance)
Antimicrobial category
Antimicrobial
agent
MSSA
(n=17)
MRSA
(n =15)
Enterococcus spp
(n= 6)
Streptococcus
pyogen (n =2)
CoNS
(n= 1)
Anti-staphylococcal
b-lactams
Pencillins
FOX
0
100
……..
0
0
AMP
58.8
100
0
100
Combined penicillins
Extended-spectrum cephalosporins; 3rd
Cephalosporins
Carbapenim
AUG
CTX
0
0
100
100
0
0
0
0
……….
0
100
33.3
0
0
IPM
CLI
23.5
33
………..
0
0
E
29
46.6
50
50
100
FUS
0
20
33.3
0
VA
0
0
0
0
0
CIP
11.7
33
50
0
LEV
0
26.6
66.6
0
Aminoglycosides
AK
0
20
33.3
0
GN
0
33
66.6
0
SulphTrimethoprims
SXT
29
66.6(10
……
100
Ansamycins
RIF
0
6.66(1
0
0
0
FOX=Cefoxitin ,AMP= Ampicillin ,AUG= Amoxicillin-Clavulenic acid, CTX = Cefotaxime, IPM= Imipenem , CLI=Clindamycin ,E=
Erythromycin, FUS=Fusidic acid, VA= Vancomycin, , CIP= Ciprofloxacin, LEV= Levofloxacin, AK= Amikacin ,GN= Gentamicin ,SXT= Sulphtrimethoprim , RIF=Rifampin.
Cefoxitin represents all other b-lactams (and cephamycins) and resistance to either of these predicts non-susceptibility to all categories of b-lactam
antimicrobials
Lincosamides
Macrolides
Fucidanes
Glycopeptides
quinolones
Among the 83 isolates belonging to Enterobacteriaceae and the non-fermenting gram-negative bacteria 41(49%)
were ESBL producers and 3(3.6%) were carbapenemases producers as shown in [ Fig-1] while 15 out of the 32
(46.8%) Staphylococcus aureuswere resistant to cefoxitin and were therefore considered as methicillin resistant
Staphylococcus aureus (MRSA).
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Egyptian Journal of Medical Microbiology
Dwedar et al. / Diabetic foot Infection: Microbiological Causes with Special Reference, Volume 24 / No. 3 / July 2015 95-102
Fig. 1: Percentage of ESBL and carbapenamases producers within the Gram Negative bacilli.
Overall 63 out of the 148 (42.5%) isolates were
identified as MDR by being resistant to three or more
antimicrobial classes and none were described as
extensively drug-resistant (XDR) by being nonsusceptible to at least one agent in all but two or fewer
antimicrobial categories.
DISCUSSION
Diabetic patients often have chronic non-healing
foot ulcers due to several underlying factors such as
neuropathy, high plantar pressures and peripheral
arterial disease; such chronic long-standing ulcers are
more prone for infection which further delays the
wound healing process. A wide range of bacteria can
cause infection in these patients.10
In cases of chronic and deep foot ulcers with tissue
necrosis and gangrene or in patients with recent
antibiotic treatment has failed, infection usually occurs
with 3-5 different species of bacteria2,11,12. In the present
study, single organisms was isolated from 39 (48.75%)
patients and mixed bacterial growths were seen in 41
(51.15%) patients The findings of this study correlate
with Shanmugam et al13and Renina et al.14in which
single bacterial isolate was seen in 50% and 41.1% of
the samples respectively and mixed bacterial growth
was seen in 50 % and 58.9% of the samples
respectively. However our finding was not matching
with Zubair et al.,15, Anandi et al., 2, Ramakant et al. 16,
Pappu et al.17 and Citron et al.18whoreported 56.6%,
19%, 23 %, 92% and 16.2 % of their isolates
respectively were monomicrobial infections and 33%,
Egyptian Journal of Medical Microbiology
67%, 66%, 7.7% and 83 % respectively were
polymicrobial infections .
The present study revealed that Gram-negative
bacteria were the predominant pathogens constituting 83
(56.08%) of the isolates, while aerobic gram-positive
cocci 41(27.7%), gram-negative anaerobes 12 (8.1%)
and Candida species 12 (8.1%). This difference could
be explained by different types of infections as most
mild infections are caused byaerobic gram-positive
cocci such as S.aureus, and Streptococci while deeper
limb threatening infections are usually polymicrobial
and caused by aerobic gram-positive cocci, gramnegative bacilli and anaerobes 19.
Similarly, in several recent studies, gram-negative
bacteria were the commonest agents as observed by
Benwan et al., 20 in Kuwait, Pappu et al.,17, Bansal et
al.21 Shankar et al.22, Gadepalli et al.5, Raja 23 and
Renina et al. 14who reported that gram negative bacilli
comprised 51.2%,76% 76 %, 57.6 %,, 51.4 %,52 % , 67
respectively of the total organisms which were isolated
in their studies. Our findings were not matching with
earlier studies by Citron et al., 18 and Abdulrazak et
al.24who reported gram-positive bacteria mainly
Staphyloccus aureus was the predominant pathogen,
which comprised 57.2% and73.6% of their isolates
respectively Therefore, there seems to be a changing
trend in the organisms causing diabetic foot infections,
with gram-negative bacteria replacing gram-positive
bacteria as commonest agents. Thus, it may be essential
to select antibiotics that are more effective against
Gram-negative bacteria in contrast to Gram-positive
organisms, which clinicians are inclined to prescribe on
observing deep tissue infection or infected gangrene.
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Dwedar et al. / Diabetic foot Infection: Microbiological Causes with Special Reference, Volume 24 / No. 3 / July 2015 95-102
The present study showed that Proteus mirabilis
was the commonest gram-negative aetiological agent,
followed by Escherichia coli, Pseudomonas spp, while
Staphylococcus aureus was the commonest grampositive bacteria. This was matching with a study by
Raja23 which showed that Proteus spp were the
commonest gram-negative aetiological agent also this
was in agreement with Ramakant et al.16 who studied
the changing microbiological profile of pathogenic
bacteria isolated from DFU in, Lucknow, India over a
period of 8 years; 1632 cultures were isolated from 434
patients with diabetic foot infections, showing that
Gram-negative bacterial infection was increasing from
50.6% to 66% and the most common isolates were P.
aeruginosa, E. coli and Proteus spp.
Anaerobic bacteria are almost always isolated with
aerobes from diabetic foot infections. Gram-negative
anaerobes were recoverd from 12 (8.1%) patients and in
mixed infections, this was in agreement with
Abdulrazak et al.24, Ako Nai et al.25, El-Tahawy19 and
Hayat 26in which anaerobes was recovered in 10.5%,
9.2% ,7%, 2% of their isolates respectively. But at a
lower rate than Benwan et al.,20in which anaerobes
accounted for15.3%.of their isolates.
Candida was recovered from 12 (8.1%) patients and
in mixed infections. This was consistent with
Abdulrazak et al.24, El-Tahawy19 andHayat26 in which
fungi were recovered in 7%., 5% and4% of their isolates
respectively.
The awareness about the antibiotic susceptibility
pattern of the isolates from diabetic foot infections is
crucial for appropriate treatment of cases. It was
observed
that
49%
of
the
members
of
Enterobacteriaceae and the non-fermenting gramnegative bacteria were ESBL producers and 3.6% were
carbepenemase producers. Similarly Gadepalli et
al.,5also have documented ESBL production in 44.7%
of bacterial isolates while Umadevi et al.27and, Akhi et
al28demonstrated that ESBLproduction was observed in
56% and 31.3%. of Enterobacteriaceae members
respectively. ESBL producers are resistant to all
extended-spectrumcephalosporins
and
aztreonam.
Imipenem and piperacillin-tazobactam and recently
polymixins are the drugs of choice for successful
control of such ESBL producers.
Among
the
83
isolates
belonging
to
Enterobacteriaceae and the non-fermenting gramnegative bacteria, only3 (3.6%) were carbepenemase
producers which is not matching with Shanmugam et
al13, who demonstrated that carbapenamase production
was observed in 31% of their gram negative isolates.
46.8% of the Staphylococcus aureus were
considered as MRSA. Staphylococcus aureus isolates in
our study were found to be uniformly susceptible to
vancomycin, Umadevi et al., 27 demonstrated that 65.5%
of S aureus were MRSA positive while other studies on
diabetic foot infections which have reported only 10 –
100
44% MRSA5,22,29,30. A British study 31 compared the
prevalence of pathogenic organisms isolated from foot
ulcer in diabetic patients at a diabetic foot clinic. MRSA
was isolated in 30.2% of the patient in 2001 almost
double the proportion carrying this organisms in 1998.
Enterococci are considered commensals with low
virulence except in compromised patients, such as
diabetics, in whom they can act as opportunistic
pathogens. All the Enterococcus spp. Were susceptible
to vancomycin, though they showed varying
susceptibility to other antibiotics. Similarly, in another
study all enterococcal isolates were noted to be
uniformly susceptible to vancomycin5. Hence,
vancomycin can be considered as an important drug in
the empirical regimen for treatment of diabetic foot
infections especially in settings with high resistance to
other antibiotics.
Overall 63 of the 148 (42.5%) isolates were
identified as MDR by being resistant to three or more
antimicrobial classes. In our study, infection with
microorganisms resistant to multiple drugs was
associated with history of recent antibiotic therapy. A
similar result was obtained by kandrmir et al.32Earlier
studies on diabetic foot infections reported 20 - 40% of
the isolates to bemulti-drug-resistant22. However
higher rates were observed by Gadepalli et al5in which
72% of the patients with diabetic ulcers were found to
be infected with MDR organisms .It is known that the
group of multi-resistant bacteria usually causes more
damage to the infected patients when compared to those
outcomes of patients afflicted by susceptible strains
from the same species. This data can be seen in
infections caused by bacteria such as Klebsiella
pneumoniae, Acinetobacter baumannii, Pseudomonas
aeruginosa, Enterobacter, and others. The reason for
such unsatisfactory results is not necessarily linked to
the virulence profile of the strain, but to the
antimicrobial empiric treatment that was given to these
patients in the beginning of the infection33.
All isolated Gram-positive bacteria sensitive to
vancomycin, while imipenem and amikacin had
acceptable sensitivity against Gram-negative bacteria.
This is compatible with results of other studies 20,22,23,27.
This may be due to the decrease in the use of amikacin
in diabetic patients because of its nephrotoxic effect.
In our study all aerobic gram-negative strains were
fully susceptible to Colistin. Parenteral use of
polymyxins was abandoned ~20 years ago in most
countries, except for treatment of patients with cystic
fibrosis, because of reports of common and serious
nephrotoxicity and neurotoxicity. Recent studies of
patients who received intravenous polymyxins for the
treatment of serious P. aeruginosa and Acinetobacter
baumannii infections of various types, including
pneumonia, bacteremia, and urinary tract infections,
have led to the conclusion that these antibiotics have
Egyptian Journal of Medical Microbiology
Dwedar et al. / Diabetic foot Infection: Microbiological Causes with Special Reference, Volume 24 / No. 3 / July 2015 95-102
acceptable effectiveness and considerably less toxicity
than was reported in old studies34.
A combination regimen consisting of amikacin,
piperacillin-tazobactam or imipenem and vancomycin
seems to be the most prudent empirical treatment of
diabetic foot infection. This empirical therapy can be
later modified appropriately based on the antibiogram of
the isolates from the individual patients.
CONCLUSION
This study showed a preponderance of gram
negative bacilli among the isolates from the diabetic
foot ulcers. Knowledge of the antibiotic susceptibility
pattern of the isolates from diabetic foot infections is
crucial for planning the appropriate treatment of these
cases prior to getting the susceptibility reports from the
laboratory.
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