Quinolone Resistant Staphylococcus aureus in Okigwe, Imo State Nigeria

MATERIALS AND METHODS

Study area: This research was carried out in Okigwe Imo state, Nigeria between March and October 2006.

Antibiotics and media used: Antibiotic discs used and their concentrations were as follows: Tarivid (10 mg/disc), ceporex (30 mg/disc), peflacine (10 mg/disc), nalidixic acid (30 mg/disc) and ciprofloxacin (30 mg/disc). These discs were obtained commercially. Optun disc (Optun laboratories, Aba Nigeria) were used. The media used were Nutrient agar (Oxoid), Mannitol Salt agar (Difco), Bacto-peptone (Oxoid) and Mueller Hinton agar (Antec Diagnostics India) and were prepared according to manufacturers instructions.

Sample collection: Ear, vaginal, urethral, wound and carbuncle swabs were collected from patients attending General hospital Okigwe and Winners Hospital Okigwe using sterile swab sticks (Evepon). Urine, semen and stool samples were also collected from patients in the same hospitals using sterile specimen bottles. All specimens were transported to the Microbiology Laboratory of Abia State University and cultured within 3 h of collection. A total of 79 samples were isolated and characterized for presence of bacteria.

The specimens were inoculated on mannitol salt agar plates and Nutrient agar plates with sterilized wire loop to obtain discrete colonies. The plates were incubated at 37°C for 24 h under aerobic conditions. After 24 h of incubation, the culture plates were examined recording appearance, size, colour and morphology of colonies. Grams stain reaction, catalase test and coagulase tests were carried out on isolates. Isolates that were gram-positive cocci, catalase positive and coagulated human plasma were considered as Staphylococcus aureus (Chigbu and Ezeronye, 2003; Uaboi-Egbenni, 2003).

SUSCEPTIBILITY OF ISOLATES TO THE QUINOLONES

Antimicrobial sensitivity test was carried out on all isolates using the paper diffusion technique. A 0.2 mL of the 12 h peptone water culture of the test organism was used to inoculate on sterile Mueller Hinton agar plate. This was spread over the entire surface of the agar plate using a sterile glass spreader and allowed to dry for about 15 to 30 min. The antibiotic discs were then placed on the agar using sterile forceps. Each disc was placed far from each other so as to avoid their zones of inhibition from coalescing into the other. The set up was then incubated at 37°C for 24 h to observe the zones of growth inhibition. The Inhibition Zone Diameter (IZD) was measured in millimeters and interpreted by the standard of National Committee for Clinical Laboratory Standards (NCCLS) (Cheesbrough, 2002).

RESULTS

Out of 79 samples collected, Staphylococcus aureus was isolated from 50 representing 71.42%. Thirty one (62%) of the isolates were resistant to ceporex, 32(64%) and 37(74%) were resistant to ciprofloxacin and tarivid, respectively, 22(44%) and 44(88%) were resistant to peflacine and nalidixic acid, respectively (Table 1 and 2). Fifteen isolates from the different sites were uniformly

resistant to the quinolones (Table 3). The number of isolates from different sites and the percentage resistant to each antibiotic is summarized in Table 4.

Table 1:	Antibiogram of Staphylococcus aureus isolates from Okigwe to quinolones
R = Resistant, I = Intermediate, S = Sensitivity, <12 mm = Resistant, 12-15 = Intermediate >16 mm sensitive

Table 2:	Number and percentage of Staphylococcus aureus isolates that were resistant, sensitive or intermediate zone to the quinolones
N = 50, Numbers in bracket are in percentages

Table 3:	Profile of isolates (Staphylococcus aureus) uniformly resistant to the 5 quinolones

Table 4:	Number of isolates from different sources sensitive and resistant to quinolones
S = Sensitivity (> 12 mm), R = Resistant (< 6 mm)

DISCUSSION

The high rate of isolation of Staphylococcus aureus in this study (71.42%) is not surprising because S. aureus is a normal microbial flora of humans and can therefore easily gain entry and cause infections as opportunistic pathogen. This high rate of isolation agrees with the finding of Chigbu and Ezeronye (2003). The high rate of resistance of Staphylococcus aureus to nalidixic acid has been reported by other researchers (Chigbu and Ezeronye, 2003). Nalixidic acid is one of the first generation quinolones, which has been on the pharmaceutical shops counter without regulation. People abuse the drug, selecting nalixidate resistant S. aureus. More so, nalidixic acid is a drug used against gram-negative organisms where as S. aureus is gram positive.

The low rate of resistance to peflacine (44%) coupled with other quinolones used for this study could be due to the fact that peflacine has not been long on the Nigerian market unlike the other quinolones that have been in the Nigerian market for some time now. The resistant rate of 64% reported for Ciprofloxacin in this work is similar to that reported by Buck et al. (2005), who reported 65% Ciprofloxacin resistant in Staphylococcus aureus in Minnesota, USA. The work suggested that ciprofloxacin resistant in Minnesota was a result of the use of ciprofloxacin in the treatment of bacterial diseases of poultry. Fluoroquinolones resistance in Okigwe could likely be as a result of drug abuse. The regulation of antimicrobial agents administration is not effective in Nigeria especially with the limited health care facilities available and the high cost of health care delivery. Moreso in the rural communities drugs are easily procured across the counter.

Quinolones resistance by Gram negative and Gram positive cocci other than Staphylococcus has been reported in Taiwan and Alabama on Salmonella and Streptococcus pneumonia (Crystal et al., 2005; Yan et al., 2005) and was attributed to the use of quinolone related compounds in the manufacture of antiseptic soap but in developing countries, the major problem is drug abuse.

Staphylococcus aureus isolates used in this study were most susceptible to peflacine (88%). This suggests that Staphylococcus aureus isolates have not acquired resistance at the rate at which they acquire resistance to other quinolones. This finding agrees with that of Chigbu and Ezeronye (2003) who also reported low resistance to peflacine in S. aureus isolates from both hospital and non hospital subjects in Umuahia Abia State, Nigeria.

The higher prevalence of quinolone resistance S. aureus isolates in Okigwe could be due to widespread indiscriminate use of antimicrobial agents. Rational drug use is important and should be emphasized in the formulation and implementation of a national drug policy by the government. Public health enlightenment on the use of drugs and drug abuse is necessary.