American-Eurasian Journal of Scientific Research 5 (4): 230-233, 2010
ISSN 1818-6785
© IDOSI Publications, 2010
Antibiogram and Beta-Lactamase Production of Staphylococcus aureus Isolates from
Different Human Clinical Specimens in a Tertiary Health Institution in Ile-ife, Nigeria
1
A.A. Akindele, 3I.K. Adewuyi, 2O.A. Adefioye, 1S.A. Adedokun and 4A.O. Olaolu
Department of Community Medicine, College of Health Sciences,
Ladoke Akintola University of Technology, P.M.B. 4400, Osogbo, Nigeria
2
Department of Medical Microbiology and Parasitology, College of Health Sciences,
Ladoke Akintola University of Technology, P.M.B. 4400, Osogbo, Nigeria
3
Department of Medical Microbiology and Parasitology,
School of Medical Laboratory Science, OAUTHC, Ile Ife, Nigeria
4
Department of Biomedical Science, College of Health Sciences,
Ladoke Akintola University of Technology, P.M.B. 4400, Osogbo, Nigeria
1
Abstract: The prevalence of ß-lactamase producing Staphylococcus aureus infections and their antimicrobial
susceptibility pattern are reported in this study. Beta-lactamase production was detected using a standard starch paper
technique on all the isolates. And In - Vitro antimicrobial susceptibility study was conducted by agar disc diffusion
method. One hundred S.aureus isolates obtained from different clinical specimens were studied. Out of total 100 strains
of S. aureus, 80% were found to be ß-lactamase producer, which probably accounted for 100% and 96% resistant rate
obtained for penicillin and ampicillin respectively.Among the ß-Lactamase producing organisms, susceptibility to
antibiotics were: erythromycin (82.5%), Cephalexin (71%) Ceftriaxone (70%), Cloxacillin (66%), Others were
chloramphenicol, Gentamicin, tetracycline and streptomycin with 62.5%, 61%, 30% and 53.8% susceptible respectively.
This thus suggests that clinicians should enlighten patients on the consequences of indiscriminate use of Penicillin and
other antimicrobial agents.
Key words: Staphyloccus aureus
ß-lactamase
Antimicrobial resistance
INTRODUCTION
inductive. ß-lactamase (also known as penicillinase) is a
enzyme that cleaves the ß-lactam ring and inactivates
the antibiotic. Therefore, empiric therapy for suspected
staphylococcal infections should always include a
ß-lactamase stable antibiotic. To overcome bacterial
resistance, some drugs combine a ß-lactam antibiotic and
a ß-lactamase inhibitor, thus creating a stable, new
compound with good activity against Staphylococcus [5].
The characterization of S. aureus and monitoring of
antimicrobial susceptibility patterns are important for
clinicians in selecting empiric antimicrobial therapy
and providing useful information on the surveillance of
this pathogen. This study is designed to find out the
antimicrobial susceptibility patterns of ß-lactamase
producing S. aureus isolates obtained from various
clinical samples.
Staphylococcus aureus has emerged as one of the
most important human pathogens and has over the past
several decades, been a leading cause of hospital and
community- acquired infections [1]. It is associated with
a variety of clinical infections including septicemia,
pneumonia, wound sepsis, septic arthritis, osteomyelitis
and post-surgical toxic shock syndrome with substantial
rates of morbidity and mortality [2, 3]. One of the reasons
for the success of this human pathogen is its great
variability, occurring at different periods and places with
diverse clonal types and antibiotic resistance patterns
within regions and countries. Although infections caused
by antibiotic- resistant S. aureus bring about serious
problems in the general population, such infections can
be particularly devastating for the very young, the elderly
and the immunocompromised [4].
The best known mechanism of bacterial resistance is
resistance to ß-lactam, which may be chromosomally or
plasmid mediated and they may be constitutive or
MATERIALS AND METHODS
This study was carried out at department of Medical
Microbiology, Obafemi Awolowo University Teaching
Corresponding Author: A.A. Akindele, College of Health Sciences,
Ladoke Akintola University of Technology, P.M.B. 4400, Osogbo, Nigeria.
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Am-Euras. J. Sci. Res., 5 (4): 230-233, 2010
Hospital Complex, Ile-Ife, Nigeria. One hundred
Staphylococci isolates obtained from different clinical
specimens were studied for ß-lactamase production and
antimicrobial sensitivity pattern, identification of the
organism was based on growth in blood agar and
macConkey agar media, colonial morphology, Gram
stain and positive results for calalase and coagulase.
Coagulase positive Staphylococci were considered as
S. aureus. ß-lactamase production was assessed by
standard starch paper technique [6].
Antibiotic susceptibility testing was performed
using the disc diffusion method. The antibiotics included:
ampicillin (10µg), penicillin (1i.u), chloramphenicol (10µg),
cloxacillin (5µg), erythromycin (5µg), Gentamicin (10µg),
streptomycin (10µg)tetracycline (10µg), ceftriaxone (30µg)
and cephalexin (30µg).
Table 2: Antimicrobial
Antibiotic
of
ß-lactamase
Number of Isolates
Numberof Isolates
Sensitive (%)
Resistance (%)
Penicillin
0(0)
Ampicillin
3(3.8)
77 (96.3)
Cloxacillin
53 (66.3)
27 (33.8)
Ceftriazone
53 (70.0)
24 (30.0)
Cephalexin
57(71.0)
23 (28.8)
Erythromycin
66(82.5)
14 (17.5)
Gentamicin
49 (61.3)
31(38.5)
80 (100)
Streptomycin
43(53.8)
37 (46.3)
Tetracycline
24(30.0)
56 (70.0)
Chloramphenicol
50(62.5)
30(37.5)
Table 3: Antimicrobial Susceptibility
Patterns
of
non
ß-lactamase
Producing Stains
Antibiotic
The prevalence of ß-lactamase producing strains of
S. aureus studied was 80%.
Table 1 shows the result of overall antimicrobial
susceptibility patterns irrespective of ß-lactamase
production.
Results of antimicrobial susceptibility patterns of ßlactamase producing strains are shown in Table 2, while
Table 3 shows antimicrobial susceptibility patterns
of n on ß-lactamase producing strains. Among the
ß-lactamase producing S. aureus, all (100%) isolates were
resistant to penicillin. The isolates were also highly
resistant to penicillin (96%). Resistance to tetracycline
was also widespread; 70% of isolates tested were
resistant, 46% of isolates were resistant to streptomycin
and 39% resistant to gentamicin. The prevalence of
Isolates to Different Antibiotics (n = 100)
Number of Isolates
Numberof Isolates
Sensitive (%)
Resistance (%)
Ampicillin (10µg)
10(10%)
90 (90%)
Penicillin (1 i.u)
4(4%)
96(965)
70(70%)
Cloxacillin (5µg)
30(30%)
Cephalexin (30µg)
75(75%)
25(25%)
Ceftriaxone (30µg)
74(74%)
16(16%)
Gentamicin (10µg)
61(61%)
39(39%)
Erythromycin (5µg)
70(70%)
30(30%)
Streptomycin (10µg)
52(52%)
48(48%)
Tetracycline (10µg)
29(29%)
71(71%)
Chloramphenicol (10µg)
66(66%)
34(34%)
Number of Isolates
Numberof Isolates
Sensitive (%)
Resistance (%)
Penicillin
4 (20)
16 (80.0)
Ampicillin
7 (35)
13 (65.0)
Cloxacilin
14 (70)
6 (30.0)
Ceftriazone
19(95)
1(5.0)
Cephalexin
19 (95)
1(5.0)
Erythromycin
16 (80)
4(20.0)
Gentamicin
16 (80)
4(20.0)
Streptomycin
12 (60)
8 (40.0)
Tetracycline
7(35)
13(65.0)
Chloramphenicol
15 (75)
5(25.0)
resistance to chloramphenicol was 37.5% and only 34%
of isolates were resistant to cloxacillin. Resistance to
ceftriazone and cephalexin were 30% and 29%
respectively. The isolates (ß-lactamase producing strains)
had the least percentage resistance to erythromycin.
Average Susceptibility Patterns of All Staphyloccus Aureus
Antibiotic
Patterns
Producing Stains
RESULTS
Table 1:
Susceptibility
DISCUSSION AND CONCLUSION
Staphylococcal infections are prevalent in various
communities and healthcare institutions both in
developed and developing countries [7]. Staphylococci
are know to have a remarkable genetic versatility which
allows for adaptation to the presence of antibiotics, such
that many strains can be multiresistant to several classes
of drugs [8]. This study was designed to highlight the
current antimicrobial susceptibility pattern of
Staphylococcus with respect to ß-lactamse production in
order to guide clinician as to the choice of antimicrobial
agents.
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Am-Euras. J. Sci. Res., 5 (4): 230-233, 2010
An overall prevalence of 80% of ß-lactamase
producers was recorded for S. aureus strains out of one
hundred isolates studied. This value is in line with
the previously reported prevalence of 70.8% by
Rotimi et al. [9], 83.7% by Odugbemi et al. [10] and
86.2% by Kesah et al. at LUTH, Lagos,Nigeria [11].
Beta-lactamase production by staphylococci is the
recognized mechanism of resistance to ß-lactamase
antibiotics, such as penicillin G and ampicillin, as such the
high prevalence of ß-lactamase production by S. aureus
isolated explains the high resistance to penicillin and
ampicillin obtained in this study.
It is believed that 70 -80% of staphylococci world
wide are penicillinase producers and as a result are
resistant to penicillin G, V and the amino-caboxy and
acylureido penicillins [8]. High rate resistance seen in non
ß-lactamase producing isolates to penicillins may be due
to lack of penicillin receptors (PBPs) or inaccessibility of
receptors because of permeability barriers of autolytic
enzymes in the cell wall, which can result in inhibition
without killing bacteria may also contribute to high
resistance rate seen in non ß-lactamase producers [12].
In this study, the resistance rate of ß-lactamase
producing isolates to the two cephalosprins (ceftriazone
and cephalexin) were 30% and 29% respectively. But the
resistance rate was greatly reduced in non ß-lactamase
producing strains. The organism had 5% resistance to
both ceftriazone and cephalosporin. This agrees with the
work of Takashi et al. [5]. Which reported that S. aureus
develops resistance to cloxacillin (ß-lactamase stable )was
34% by the ß-lactamase producing stains. This shows
that susceptibility should not be assumed for cloxacillin,
in vitro efficacy is needed to validate therapeutic usage.
According to the findings of this investigation,
ß-lactamase producing S. aureus was found to have
highest percentage susceptibility to erythromycin
(82.5%). But the percentage susceptibility of
non ß-lacctamase producing strains to erythromycin was
80%. This results is in consonance with the study of
kesah et al. [11].
In has to be noted that erythromycin was found to be
the best antistaphylococal drug in this study. However,
Kesah et al. [11] and Brooks et al. [12] recommended
vacomycin for empiric therapy in life threatening
staphylococcal infection. Nevertheless, inability to get
vancomycin in this work to confirm their report is
regretted.
In light of these findings, diagnostic medical
microbiology laboratories should perform antibiotic
susceptibility tests in addition to tests for the B-lactamase
production. This will help in monitoring the sensitivity
patterns of isolates in the environment as a barometer for
antibiotic policy formulation.
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