Pakistan Journal of Medical Sciences


ISSN 1681-715X





Volume 24

April - June 2008 (Part-I)

Number  2


PDF of this Article

Antibiotic sensitivity pattern of
staphylococcus aureus
in Abakaliki, Nigeria

Ikeagwu IJ1, Amadi ES2, Iroha IR3


Objective: To investigate the sensitivity pattern of Staphylococcus aureus isolates obtained from clinical specimens including urine, wound, high vaginal swab and semen to commonly used antibiotics.

Methodology: The susceptibility patterns of these isolates were determined using the disc diffusion and agar well diffusion methods.

Results: Out of 174 samples, 51 (29.2%) yielded S. aureus with the highest isolation from semen (66.7%) and the least from urine (15.6%). Following the disc diffusion, the highest sensitivity was recorded for Ofloxacin (65%) while the least was for Co-trimoxazole (6%). Amoxicillin, Ampicillin, Tetracycline and Cloxacillin recorded 37%, 19%, 8% and 11% respectively. Also, following the agar well diffusion method, the highest sensitivity was recorded for Ofloxacin (65%) and the least for Co-trimoxazole (8%). The other drugs recorded the following readings; Amoxycillin (37%), Ampicillin (21%), Tetracycline (23%) and Cloxacillin (13%).

Conclusions: The study recommends the use of Ofloxacin in the treatment of S. aureus infections in the study area. It also underscores the need for sensitivity testing before the administration of antibiotics for the treatment of Staphylococcal infections.

KEY WORDS: Antibiotics, Abakaliki, Sensitivity, Resistance, Staphylococcus Aureus.

Pak J Med Sci    April - June 2008 (Part-I)    Vol. 24 No. 2    231-235

1. Ikeagwu IJ, PGD
Department of Medical Microbiology,
Federal Medical Centre,
Abakaliki, Ebonyi State,
2. Amadi ES, Ph.D
3. Iroha IR, Ph.D
2-3: Department of Applied Microbiology,
Faculty of Applied and Natural Sciences,
Ebonyi State University,
PMB 053 Abakaliki, Ebonyi State, Nigeria.


Dr. Amadi ES,
Department of Applied Microbiology,
Faculty of Applied and Natural Sciences,
Ebonyi State University,
PMB 053 Abakaliki, Ebonyi State, Nigeria.

* Received for Publication: October 6, 2007
* Accepted for Publication: February 8, 2008


Staphylococcus aureus is a Gram positive, non-motile, catalase positive, coagulase positive, facultative anaerobe, involved in causing a number of diseases including, boils, pustules, impetigo, osteomyelitis, mastitis, septicemia, meningitis, pneumonia and toxic shock syndrome.1,2 Nosocomial infections of which S. aureus is a typical example, are known to account for morbidity and mortality of millions of patients annually worldwide.3 S. aureus is considered the most resistant of all non-spore forming pathogens, with well developed capacities to withstand high salt (7.5-10%), extremes in pH and high temperatures (up to 60oC for 60 minutes). It also remains viable after months of air-drying and resists the effects of many disinfectants and antibiotics.2

S. aureus is known to be notorious in their acquisition of resistance to new drugs and continues to defy attempts at medical control.2 Many strains of S. aureus carry a wide variety of multi-drug resistant genes on plasmids. The resistance of S. aureus isolates from different parts of the world to commonly used antibiotics has been widely reported.4-8 This study aimed at determining the sensitivity of different isolates of S. aureus from Abakaliki, Ebonyi State in Nigeria to commonly used antibiotics.


Collection and Processing of Samples: Wound swabs and high vaginal swab (HVS) samples were collected from wound infection and pelvic inflammatory disease patients respectively, using sterile swab sticks. Mid stream urine and semen samples were collected from patients suspected to be suffering from urinary tract infection and infertility problems respectively. A total of 174 samples were collected from these patients attending the Federal Medical Center Abakaliki between April and June 2006.

The samples were cultured aerobically in blood agar and cystine lactose electrolyte deficient (CLED) agar. The plates were incubated at 37oC overnight. Streak plate technique was used to obtain pure culture of each isolate prio to identification.

Identification of Isolates: The isolates were identified using motility test, colony morphology, Gram staining and Biochemical tests including catalase and coagulase tests as described by Cheesbrough.1

Sensitivity testing using disc diffusion Technique: The discs were made from Whattman’s No. 1 filter papers and prepared as described by Isu and Onyeagba9 to obtain the following concentrations of antibiotics per disc; Ofloxacin 10mg, Amoxycillin 30mg, Co-trimoxazole 25mg, Ampicillin 30mg, Cloxacillin 5mg and Tetracycline 25mg.

Overnight cultures of each isolate were adjusted to McFarland turbidity standard (0.5), and the disc sensitivity screening conducted as described by Cheesbrough.1 Sterile swabs were used to inoculate the test organism onto the sensitivity agar (Mueller Hinton). Sterile forceps were used to carefully distribute the antibiotic discs evenly on the inoculated plates. After allowing for about 30 minutes on the bench for proper diffusion, the plates were inverted and incubated aerobically at 35oC for 18 hours. The inhibition zone diameters were measured in millimeters using meter rule.

Sensitivity testing using agar well diffusion Technique: The antibiotics were prepared for administration into wells bored with sterile cork borer using sterile distilled water to obtain the following concentrations per drop (a drop equivalent to 0.01ml); Ofloxacin (10mg), Amoxycillin (30mg), Co-trimoxazole (25mg), Ampicillin (30mg), Cloxacillin (5mg) and Tetracycline (25mg).9

Overnight cultures of each isolate were adjusted as in the case of disc diffusion and subjected to agar-well diffusion screening as described by Perez et al.10 The sensitivity agar were inoculated as described for the disc diffusion method and a drop, each, of the prepared antibiotic concentrations were introduced into respective wells. They were left on the bench for 30 minutes and incubated aerobically as stated for the disc diffusion method. The inhibition zones were also recorded as previously stated.


Isolation of Staphylococcus aureus from different clinical specimens: Of the 174 clinical samples examined, 51 (29.2%) were positive for Staphylococcus aureus. The highest isolation of S. aureus was from semen (66.7%) while the least was from urine (15.6%). (Table-I).

Sensitivity pattern of S. aureus isolates using the disc diffusion Technique: The degree of sensitivity of S. aureus isolates following the disc diffusion method was analysed according to Chigbu and Ezeronye.6 Inhibition zone diameter (IZD) 0-5mm was regarded as resistance (R), 5-15mm sensitive (S1), 15-25mm, sensitive (S11) and 25-35mm, sensitive (S111).

The highest sensitivity was recorded for Ofloxacin (65%) while the least was for Co-trimoxazole (6%). The inhibition zone diameters obtained ranged from 0 to 35mm (Table-III).

Sensitivity pattern of S. aureus isolates using the agar well diffusion Technique: The degree of sensitivity of S. aureus isolates was also analysed as in the case of disc diffusion. The highest sensitivity was recorded for Ofloxacin (65%) and the lowest for Co-trimoxazole (8%). (Table-II) The inhibition zone diameters obtained also ranged from 0 to 35mm (Table-IV).


In this study, out of the 174 samples analysed, 51 (29.2%) were positive for Staphylococcus aureus with 66.7% occurrence in semen, seconded by wound specimen (56.3%) and the least from urine samples (15.6%). This is in line with previous reports in which S. aureus was the most common organism isolated from semen11,12 and wound samples.13 This picture was however different in Jos, Nigeria, where Oguachuba14 found Proteus species to be the most common isolate with occurrence rate of 41.9%, followed by S. aureus with 25.6%. The reason for this variation is not yet ascertained.

The result of this study indicated that Ofloxacin had the highest sensitivity (65%) to the S. aureus isolates following both the disc diffusion and agar well diffusion techniques. This apparently high level of sensitivity to Ofloxacin appears to suggest that Ofloxacin could be a drug of choice for treating infections caused by S. aureus in the study area, especially at the present time, when S. aureus strains resistant to other commonly used antibiotics has been reported.15 This finding is consistent with previous reports. For instance, 100% sensitivity of S. aureus isolates to Ofloxacin has been reported.16 In addition, high sensitivity of Ofloxacin against S. aureus isolates was also highlighted by Chalita et al.17 Low sensitivity however was reported among most strains of methicillin resistant Staphylococcus aureus (MRSA) isolated from patients with ocular infections.18

Although low sensitivities of S. aureus isolates to ampicillin (37%) and cloxacillin (13%) were recorded in this study, enhanced susceptibility had been reported by previous workers. Uwaezuoke and Aririatu8 reported 85.4% sensitivity of cloxacillin to S. aureus strains isolated from Owerri, Nigeria. Similarly, Farzana et al.,7 recorded 74% sensitivity of S. aureus isolates to ampicillin in Mullan city, Pakistan. The reason for the variation could most likely be attributable to strain differentiation. On the other hand, a number of prio investigations had reported high level of resistance of S. aureus to cloxacillin and ampicillin in line with the result of this study.6,19,20

The 63% resistance of amoxycillin to S. aureus isolates as recorded in this work is in conformity with the findings of Astal et al.,5 in which 73.6% amoxycillin resistant strains of S. aureus was reported. 100% resistance of S. aureus isolates to amoxycillin has also been reported.4

Low sensitivities of S. aureus to tetracycline and co-trimoxazole as observed in this study is consistent with earlier studies. 98% and 69.6% resistance of S aureus isolates to tetracycline were reported by Obi et al.,16 and Olayinka et al.,21 respectively. Also 87.5% and 68% resistance of S. aureus isolates to tetracyclines were also respectively reported by Uwaezuoke and Aririatu8 and Oyagade and Oguntoyinbo.19 Further, prio researchers including Farzana et al.,7 and Astal et al.,5 reported 81.8% and 66.1% resistance of S. aureus isolates to co-trimoxazole respectively. It is therefore less likely that tetracycline and co-trimoxazole will be desirable, as drugs of choice for the management of S. aureus infections in Abakaliki, area in Nigeria.

There was a slight variation in the zone of inhibition obtained from disc diffusion and agar well diffusion methods respectively (Tables-III, IV). This was apparent with ampicillin, tetracycline, cloxacillin and co-trimoxazole. The reason for the apparently enhanced inhibition zone diameters recorded for agar well diffusion could be attributed to the possibility of losing some fractions of the antibiotics on the paper disc or its inability to express all absorbed drugs to the agar media. Nevertheless, the slight difference probably suggests that both techniques are appropriate for the determination of sensitivity of antibiotics to microbial agents.

This study therefore underscores the need for antibiotic sensitivity screening before the administration of any antibiotic for treatment of Staphylococcal infections in Abakaliki, Ebonyi State, Nigeria.


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