|
African Journal of Biotechnology
Academic Journals
ISSN: 1684-5315
Vol. 2, Num. 10, 2003, pp. 374-378
|
African Journal of Biotechnology Vol. 2, No. 10, October 2003,
pp. 374-378
Antibiotic resistant Staphylococcus
aureus in Abia State of Nigeria
CHIGBU, CHINWE .O.
AND EZERONYE, O.U.
Department of Biological Science, Michael Okpara University
of Agriculture, Umudike, Abia State, Nigeria.
*Corresponding author; E-mail: ezeronyeob@yahoo.com.
Accepted 26 September 2003
Code Number: jb03076
ABSTRACT
A total of 70 ear and nasal swab samples collected from
35 persons, 16-hospital population and 19 non-hospital population was examined
for presence of Staphylococcus aureus.
Eighty percent of the population studied were found to be carriers of S.
aureus. Of the 28 positive cases, 35.7% were carriers of S.
aureus in both the ear and nostrils, while 14.3% and 50.0% had it only
in their ear and nostrils, respectively. The S.
aureus isolates varied in their antibiotic susceptibility pattern when
tested for their sensitivity to 16 antibiotics. Eighty percent of the isolates
were resistant to more than one antimicrobial agent. All the isolates showed
resistance to nalidixic acid and 100% sensitivity to rifampicin.
Key words: Staphylococcus
aureus, antibiotic resistance, inhibition zone diameter.
INTRODUCTION
Staphylococcus aureus is
a Gram-positive, catalase positive, coagulase positive, non-motile coccus bacterium
that causes a variety of human infection in all age groups (Boyce, 1981).
It is the major causative agent in surgical wound infections and epidermal
skin diseases in newborn infants (Baldwin et al., 1957). S.
aureus infection may also be superimposed on superficial dermatological
diseases such as eczema, pediculosis and mycosis (Kloos and Bannerman, 1995).
They live as commensals in anterior naves of over half the population of humans
(Doig, 1981). The cocci are spread from these sites into
the environment by the hands, handkerchief, clothing and dust. S.
aureus is an opportunistic pathogen in the sense that it causes infection
most commonly in tissues and sites with lowered host resistance such as in
individuals with diabetes, old malnourished persons and other chronic cases
(Burnett et al., 1996).
S. aureus causes
folliculitis, boil, furnculosis, scalded skin syndrome, conjunctivitis, paronychia,
mastitis, and toxic shock syndrome for menstruating women who use tampons.
Staphylococcal pneumonia can occur if staphylococcal infection spreads to the
lungs (Klodkowska-Farner, et al., 1995).Hospital
acquired Staphylococcal infections are common in newborn babies, surgical patients
and hospital staff. Patients develop sepsis in operation wounds, which take
place in the theatre during operation, and others post-operations in the ward
(Tuo et al., 1995). Staphylococcal food
poisoning can also occur in which a toxin produced by the bacteria is ingested
with food. Food with a high salt or sugar content favours the growth of S.
aureus (Tuo et al., 1995). Many outbreaks of staphylococcal
food poisoning result from hand contacts (Bryant et al., 1998).
Attempts to control these diseases by chemotherapy through
the use of antimicrobial agents particularly antibiotics have resulted in increased
prevalence of resistance to these agents (Levy, 1998).
Several investigations have been conducted to study the antimicrobial resistance
pattern of S. aureus and it has been
shown that the organism is resistant to β-lactam
antibiotics, amino glycoside and macrolides (Atkinson and Lorian, 1984;
Maple et al., 1989). S. aureus strains carry a wide variety of multi-drug resistant genes
on plasmids, which can be exchanged and spread among different species of Staphylococci
(Neihart et al., 1988).
The multi-resistance determinants can be transferred to
new bacterial hosts. The situation is made more difficult in developing countries
such as Nigeria where antimicrobial drugs are readily available to consumers
across the counter with or without prescription from a medical practitioner.Such
a practice has led to misuse of antimicrobial drugs with the associated high
prevalence of drug resistance among the Staphylococci (Nnochiri, 1973;
Adekeye, 1979; Paul et al., 1982).
Hospital strains of S. aureus are
usually resistant to a variety of different antibiotics. Few strains are resistant
to all clinically useful antibiotics except vancomycin. Some workers have reported
however the presence of vancomycin resistant strains (Aubry-Damon et al., 1998;
Shakibaie et al., 2002). This work was undertaken
to determine the prevalence of antibiotic resistant S.
aureus in hospital and non-hospital populations in Abia State of Nigeria.
MATERIALS AND METHODS
Antibiotics and media
Antibiotic discs used and their concentrations were as follows:
penicillin (30 µg/disc), rifampicin (10 µg/disc), peflacine (10 µg/disc), streptomycin
(30 µg/disc), gentamycin ((10 µg/disc), lincomycin (30 µg/disc), ciprofloxacin
(10 µg/disc), nalidixic acid (30 µg/disc), chloramphenicol (25 µg/disc), septrin
(cotrimoxazole) (25 µg/disc), erythromycin ((25 µg/disc), tetracycline
(30 µg/disc), ampicillin (25 µg/disc), ampiclox (30 µg/disc), amoxil (Amoxycillin)
(10 µg/disc), cloxacillin (12.5 µg /disc). Mannitol salt agar and Nutrient
agar are the media used.
Sample collection
Ear and nasal swabs were collected from hospitalized patients
and staff of Priscilla Hospital and New Era Hospital in Umuahia (referred to
as Hospital population) and students of Michael Okpara University of Agriculture
Umudike, Abia State, Nigeria (referred to as non-hospital population) using
sterile swab sticks (EVEPON). All specimens were transported to the laboratory
and cultured within 3 to 4 hours of collection. A total of 70 samples (32 hospital
and 38 non-hospital population) were collected.
Isolation and characterization
of bacteria
The swab specimens were inoculated on mannitol salt agar
(Difco) and streaked with sterilized wire loop so as to obtain discrete colonies.
The plates were incubated at 37oC for 24 h under aerobic conditions.
After 24 h of incubation, the culture plates were examined recording the appearance,
size, colour, and morphology of the colonies. Gram stain reaction, catalase
test and coagulase test were carried out. Isolates that were gram-positive
cocci, catalase positive, and coagulated human plasma were considered S.
aureus in this study.
Susceptibility of
Isolates to various antibiotics
Antibiotic sensitivity test was carried out on all isolates
using paper disc diffusion technique. A total of 16 antibiotics shown above
were tested. A 0.2 ml of 12-h peptone water culture of the test organism was
used to inoculate on a dry sterile nutrient agar plate. This was spread over
the entire surface of the nutrient agar using a sterile glass spreader and
allowed to dry for about 15 to 30 min. The antibiotic discs were placed on
the agar using sterile forceps. Each disc was placed far from each other to
avoid their zones of inhibition from coalescing into the other. The plates
with the antibiotic discs were then incubated at 37°C for 24 h to observe
the zones of growth inhibition produced by the antibiotics.
RESULTS
Of 35 persons screened, 80.0% were positive for S.
aureus. Table 1 shows that out of 16 persons from the hospital population
(Hp) screened, only 2 did not harbour any S.
aureus and 14 (87,5%) were colonized either in the ear or nostril or
both. Out of nineteen persons from non-hospital population (NHp), 5 did
not harbor any S. aureus, while
14 (73.7%) were colonized. In both populations, 14 persons each were colonized
in ear and nostril (Table 2).
Table 1. Frequency of isolation
of S. aureus from hospital and non-hospital population.
|
Source
|
Number
sampled
|
S.
aureus positive (%)
|
|
Hospital
|
16
|
14
(87.5%)
|
|
Non-hospital
|
19
|
14
(73.7%)
|
|
Total
|
35
|
28
(80%)
|
Table 2. Frequency
of isolation of S. aureus from nostril and ear.
|
Source
|
Pattern
of S. aureus colonization (%)
|
|
Ear
and nostril
|
Ear
only
|
Nostril
only
|
|
Hospital
|
35.7
|
14.3
|
50
|
|
Non-hospital
|
35.7
|
14.3
|
50
|
The inhibition zone diameter (IZD) range of test antibiotics
against the different isolates of S.
aureus from hospital and non-hospital
sources are shown in Tables 3 and 4,
respectively. No isolate showed susceptibility to nalidixic acid (Na) whereas
rifampicin was active against all strains. The results are summarized as antibiotic
sensitivity (S) and resistance (R) pattern for both ear and nostril isolates.
No strain was sensitive to all 16 antibiotics; rather there was multiple drug
resistance ranging from resistance of 2 antibiotics to 14 antibiotics (87.5%).
Figure 1 represents a summary of the multiple drug resistance patterns among
hospital and non-hospital strains. About 5.26% of hospital strains and 10.53%
of non-hospital were resistance to 14 antibiotics.
Table 3. Inhibition zone diameter (IZD) of test antibiotics against
different isolates of S. aureus from non-hospital sources.
|
Code of Strains
|
Antibiogram
|
|
NA
|
CO
|
CP
|
TE
|
PF
|
ST
|
SP
|
LN
|
AP
|
PN
|
GN
|
ER
|
CL
|
RF
|
AX
|
AC
|
PR
|
|
NHP-1E
|
R
|
S+++
|
S+++
|
R
|
S++
|
S+
|
R
|
S+++
|
R
|
R
|
R
|
S++
|
R
|
S+++
|
R
|
S++
|
50
|
|
NHP-1N
|
R
|
R
|
R
|
R
|
R
|
S+
|
R
|
R
|
S++
|
R
|
R
|
R
|
R
|
R
|
R
|
R
|
87.5
|
|
NHP-2E
|
R
|
S++
|
S+++
|
R
|
S++
|
S+
|
S+
|
S++
|
R
|
S+
|
R
|
S++
|
R
|
S+++
|
R
|
S+
|
37.5
|
|
NHP-2N
|
R
|
R
|
S++
|
R
|
R
|
S+
|
R
|
S+
|
S+
|
S+
|
S+
|
R
|
S+
|
S+
|
R
|
S+
|
43.8
|
|
NHP-3E
|
R
|
S+++
|
S++
|
R
|
S++
|
S+
|
R
|
S++
|
R
|
S+
|
S+
|
S+
|
S+
|
S+
|
R
|
S+
|
31.3
|
|
NHP-4E
|
R
|
S+++
|
S++
|
S+
|
S++
|
R
|
R
|
S+
|
S+
|
S+
|
R
|
S++
|
R
|
S+
|
R
|
R
|
43.8
|
|
NHP-4N
|
R
|
S++
|
S++
|
S+
|
S++
|
R
|
S+
|
S+
|
R
|
S+
|
S++
|
S++
|
R
|
S++
|
R
|
S+
|
31.3
|
|
NHP-5E
|
R
|
S++
|
S+
|
R
|
S+
|
S++
|
S++
|
S++
|
R
|
R
|
S++
|
R
|
S+
|
S+
|
R
|
R
|
43.8
|
|
NHP-6N
|
R
|
S++
|
S+
|
R
|
R
|
S+
|
R
|
R
|
R
|
R
|
S++
|
S++
|
R
|
S+++
|
R
|
S++
|
56.3
|
|
NHP-7N
|
R
|
S+++
|
S+
|
S+
|
S++
|
S+
|
R
|
R
|
S+
|
S+
|
S+
|
S+
|
R
|
S+
|
R
|
S++
|
31.3
|
|
NHP-8N
|
R
|
S++
|
S+++
|
S++
|
S++
|
S++
|
S++
|
S+
|
R
|
R
|
S+
|
S++
|
S+
|
S++
|
R
|
S++
|
25
|
|
NHP-11N
|
R
|
S++
|
S++
|
R
|
S++
|
S+
|
R
|
S+
|
R
|
R
|
S++
|
S++
|
R
|
S+++
|
R
|
S+
|
43.8
|
|
NHP-12N
|
R
|
S++
|
S+
|
S+
|
R
|
S++
|
R
|
S++
|
R
|
R
|
S+
|
R
|
R
|
S++
|
R
|
R
|
56.3
|
|
NHP-15E
|
R
|
S++
|
S+++
|
R
|
S++
|
S++
|
R
|
S++
|
S++
|
S+
|
S++
|
S++
|
R
|
S++
|
R
|
S++
|
31.3
|
|
NHP-15N
|
R
|
S++
|
S+
|
S++
|
S++
|
S++
|
R
|
S+++
|
S+
|
R
|
S+++
|
S+
|
R
|
S++
|
R
|
R
|
37.5
|
|
NHP-16E
|
R
|
S++
|
S+
|
S+
|
S++
|
S++
|
R
|
R
|
S+
|
S++
|
R
|
R
|
R
|
S+
|
S+
|
R
|
43.8
|
|
NHP-16N
|
R
|
R
|
R
|
R
|
R
|
R
|
S+
|
R
|
R
|
R
|
R
|
R
|
R
|
S++
|
R
|
R
|
87.5
|
|
NHP-17N
NHP-18N
|
R
R
|
S++
R
|
S+
S++
|
R
R
|
R
S+++
|
S+
R
|
S++
S++
|
S++
R
|
S+
R
|
R
R
|
S++
S+
|
S+
S+
|
R
R
|
S+
S+
|
R
R
|
S++
R
|
37.5
62.5
|
NA, nalidixic
acid; CO, cloxacillin; CP, ciprofloxacin; TE, tetracycline; PF, peflacine;
SP, septrin; LN, lincomycin; AP, Ampicillin; PN, penicillin; GN, gentamycin;
ER, erythromycin; ST, streptomycin; CL, chloramphenical; RF, rifampicin; AX,
amoxil; AC, ampiclox; PR, percent resistance (%).
0 to 5 mm Resistance (R)
5 to 15 mm Sensitive (S+)
15
to 25 mm Sensitive (S++)
25 to 35 mm Sensitive (S+++)
Table 4. Inhibition zone diameter (IZD) of test antibiotics against
different isolates of S. aureus from hospital sources.
|
Code of Strains
|
Antibiogram
|
|
NA
|
CO
|
CP
|
TE
|
PF
|
ST
|
SP
|
LN
|
AP
|
PN
|
GN
|
ER
|
CL
|
RF
|
AX
|
AC
|
PR
|
|
HP-1E
|
R
|
S++
|
S++
|
S+
|
S+++
|
S+
|
S++
|
S+
|
R
|
R
|
R
|
S+++
|
R
|
S+++
|
R
|
S++
|
37.5
|
|
HP-1N
|
R
|
S+++
|
S+++
|
S+
|
S++
|
S++
|
S++
|
S+
|
S++
|
R
|
S++
|
S++
|
S+
|
S+++
|
R
|
S++
|
18.8
|
|
HP-2N
|
R
|
S+++
|
S+++
|
S+
|
S+++
|
S++
|
S+
|
S++
|
S+
|
R
|
S+++
|
S++
|
S+
|
S+++
|
S++
|
S++
|
12.5
|
|
HP-3N
|
R
|
S+
|
R
|
R
|
R
|
S+
|
R
|
R
|
R
|
S++
|
S++
|
R
|
S+
|
S+
|
R
|
S+
|
56.3
|
|
HP-4N
|
R
|
R
|
R
|
R
|
S+
|
R
|
R
|
S+
|
R
|
R
|
S++
|
R
|
S+
|
S+++
|
R
|
R
|
68.8
|
|
HP-5E
|
R
|
S++
|
S++
|
S+
|
S++
|
S+
|
S++
|
S+
|
R
|
S+
|
S+
|
R
|
R
|
S++
|
S++
|
S++
|
25
|
|
HP-5N
|
R
|
R
|
R
|
R
|
S++
|
S++
|
R
|
S++
|
S+
|
S+
|
R
|
R
|
R
|
S++
|
R
|
R
|
62.5
|
|
HP-7E
|
R
|
R
|
S+
|
R
|
R
|
S+
|
R
|
R
|
R
|
R
|
R
|
R
|
R
|
S+
|
R
|
R
|
81.3
|
|
HP-7N
|
R
|
S+
|
R
|
R
|
S+
|
R
|
R
|
R
|
S+
|
R
|
S++
|
R
|
S+
|
S+
|
R
|
R
|
62.5
|
|
HP-8N
|
R
|
S+
|
R
|
R
|
S+
|
R
|
R
|
S+
|
R
|
R
|
S+
|
S++
|
R
|
S++
|
R
|
R
|
62.5
|
|
HP-9N
|
R
|
R
|
R
|
R
|
S++
|
R
|
R
|
R
|
R
|
R
|
R
|
R
|
R
|
S+++
|
R
|
R
|
87.5
|
|
HP-11E
|
R
|
S++
|
S++
|
S+
|
S++
|
S++
|
R
|
S++
|
S++
|
S++
|
S++
|
S+
|
R
|
S+++
|
R
|
S+++
|
25
|
|
HP-11N
|
R
|
R
|
S++
|
R
|
S++
|
R
|
R
|
S++
|
R
|
R
|
S+
|
R
|
R
|
S++
|
R
|
S+
|
62.5
|
|
HP-12N
|
R
|
R
|
R
|
R
|
S+
|
R
|
R
|
S++
|
R
|
R
|
R
|
R
|
R
|
S++
|
R
|
R
|
81.3
|
|
HP-13E
|
R
|
S+
|
S++
|
S+
|
S+
|
S+
|
S+
|
R
|
R
|
R
|
S++
|
S+++
|
S++
|
S+++
|
R
|
S+
|
31.3
|
|
HP-13N
|
R
|
R
|
S+
|
R
|
R
|
R
|
R
|
S+++
|
R
|
R
|
S+
|
S+
|
R
|
S+++
|
R
|
R
|
68.8
|
|
HP-14E
|
R
|
S+++
|
S+
|
S++
|
S+++
|
R
|
S++
|
R
|
S+
|
S+
|
S++
|
S+
|
R
|
S++
|
R
|
R
|
37.5
|
|
HP-15N
HP-16E |
R
R
|
S++
S++
|
S+
S+
|
S++
S+
|
S++
S++
|
S++
S++
|
R
R
|
S+++
R
|
S+
S+
|
R
S++
|
S+++
R
|
S+
R
|
R
R
|
S++
S+
|
R
S+
|
R
R
|
37.5
43.7
|
NA, nalidixic
acid; CO, cloxacillin; CP, ciprofloxacin; TE, tetracycline; PF, peflacine;
SP, septrin; LN, lincomycin; AP, Ampicillin; PN, penicillin; GN, gentamycin;
ER, erythromycin; ST, streptomycin; CL, chloramphenical; RF, rifampicin; AX,
amoxil; AC, ampiclox; PR, percent resistance (%).
0 to 5 mm Resistance (R)
5 to 15 mm Sensitive (S+)
15 to 25 mm Sensitive (S++)
25 to 35 mm Sensitive (S+++)
DISCUSSION
The carrier rate of S.
aureus in this study was 35.7% and 14.3% for ear and nostril, respectively.
There were more colonization in nostrils alone (50.0%) followed by both
ear and nostril (37.5%) and then ear alone (14.3%). The nasal carrier rate
in this study was higher than what earlier
workers reported in normal population (Osuide et al., 1996).
This may be attributed to its function as the air passage, making it more
prone to dust carrying S. aureus. Individuals also touch their nose more frequently thereby
transferring bacteria from the hand and skin to nostril. The ear is colonized
by S. aureus less because of
constant cleaning of the ear with cotton buds, soap and water thereby reducing
the microbial load. Individuals also touch their ear less often than their
nose. The carrier rate in the male and female were comparable (data not
shown) indicating that sex is not a notable factor in carriage and there
is no activity or behavior of any of the sexes which predisposes them to S.
aureus infection.
All the isolates of Staph
aureus from both hospital and non-hospital populations were found to
be resistant to nalidixic acid. Nalidixic acid is an antibiotic specifically
use for gram-negative organisms and all strains tested were gram-positive,
which explains why there seems to be a high resistance in all the isolates
tested. Rifampicin recorded the highest inhibition zone diameter and all
the isolates were sensitive to it. This high rate of sensitivity may be
because rifampicin is not in common use and is normally used in the treatment
of tuberculosis caused by Mycobacterium
tuberculosis. Cloxacillin, ciprofloxacin, peflacine and lincomycin
also recorded high sensitivity. This may be because they are relatively
new and not in common use by the population as compared to penicillin,
chloramphenicol, ampicillin, ampiclox and septrin.
In this study, the isolates from hospital population
showed resistance to many antibiotics than isolates from non-hospital population,
which is similar to previous reports (Osuide et al., 1996;
Shakibaie et al., 2002). The higher prevalence of resistance
to anti-microbial agents in this environment could be due to widespread, indiscriminate
use of antibiotics. The formulation and implementation of a national drug policy
by governments are fundamental to ensure rational drug use. Proper use of drugs
has to be promoted by providing objective information and training.
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